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History of the Planet_ How Mountains Grow and Continents Change · Night Science Stories

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  Speaker 1: Good evening. Welcome to Night Science Stories. Tonight we will
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  Speaker 1: take a slow walk through the deep time of our planet,
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  Speaker 1: settle in and let your breath find an easy rhythm.
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  Speaker 1: I will speak softly as we follow the patient forces
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  Speaker 1: that move continents and lift mountains. If you drift into
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  Speaker 1: sleep while listening, the story will keep flowing beneath you
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  Speaker 1: like a quiet current. Far below our feet, the interior
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  Speaker 1: of Earth is not a hollow fire. It is rock
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  Speaker 1: that is mostly solid, yet it can flow when time
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  Speaker 1: is measured in millions of years. Imagine a landscape made
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  Speaker 1: of crystals of olivine and pyroxene, warm and pressurized, moving
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  Speaker 1: as if it were very stiff honey. Heat from the
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  Speaker 1: core and from the slow decay of natural radioactivity rises upward.
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  Speaker 1: Where that heat wells up, the surrounding mantle expands a little,
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  Speaker 1: becomes slightly less dense, and begins to rise. Where material
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  Speaker 1: cools near the surface, it becomes a little heavier and
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  Speaker 1: tends to sink. These motions are faint and grand at
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  Speaker 1: the same time. The cycle is convection. and it is
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  Speaker 1: the planet's quiet heartbeat. We cannot see this motion directly
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  Speaker 1: with our eyes, but we have many ways to listen
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  Speaker 1: to it. Earthquakes send waves through the planet, and those
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  Speaker 1: waves speed up in cooler, stiffer regions and slow down
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  Speaker 1: in warmer, softer ones. By recording thousands of earthquakes, scientists
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  Speaker 1: build maps of the deep, as if they were doing
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  Speaker 1: a medical scan of a living body. The pictures reveal
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  Speaker 1: long tongues that sink toward the core. These are the
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  Speaker 1: shadows of old ocean floors that have slid down along
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  Speaker 1: great faults at the edges of oceans. They also reveal
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  Speaker 1: warm columns that rise from deep below in a few places,
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  Speaker 1: feeding volcanic islands that line up like strings of beads.
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  Speaker 1: The interior is not still. It is a slow river
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  Speaker 1: of stone. Where this motion reaches the surface, the thin
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  Speaker 1: shell of earth cannot stay whole. It breaks into large rafts,
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  Speaker 1: the plates of the outer shell, which move because the
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  Speaker 1: underlying mantle keeps sliding. The plates carry continents as passengers.
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  Speaker 1: They also carry the floors of the oceans. Where plates
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  Speaker 1: move away from each other, new ocean floor appears. Where
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  Speaker 1: they meet, one can slide beneath the other and sink.
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  Speaker 1: The journey is slow. A plate can creep at a
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  Speaker 1: speed that you could match with your fingernails, yet over
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  Speaker 1: a few tens of millions of years, those tiny steps
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  Speaker 1: add up to journeys that span an ocean. Picture now
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  Speaker 1: a long scar that runs down the centre of many
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  Speaker 1: oceans like a seam on an old leather ball. This
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  Speaker 1: is a mid-ocean ridge. Here hot mantle material rises and
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  Speaker 1: partially melts as pressure eases. The melt gathers in small
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  Speaker 1: chambers and feeds cracks at the surface. Basaltic lava flows out,
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  Speaker 1: often under water, and as it meets the cold sea,
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  Speaker 1: it forms smooth, rounded shapes that look like stacks of pillows.
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  Speaker 1: A new strip of oceanic crust is born. The ridge
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  Speaker 1: itself is not a single peak but a ragged chain
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  Speaker 1: of mountains that stretches around the world, a wound that
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  Speaker 1: is always healing and always opening. The space above these
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  Speaker 1: ridges is a world of chemistry and life. Seawater percolates
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  Speaker 1: down through cracks until it meets hot rock. It heats,
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  Speaker 1: reacts and rushes back out at vents as a dark,
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  Speaker 1: mineral-rich fluid. The fluid looks like smoke, but is water
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  Speaker 1: loaded with fine particles of metal sulphides that form as
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  Speaker 1: the hot liquid meets cold seawater. Around these vents are
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  Speaker 1: communities of creatures that do not rely on sunlight. Bacteria
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  Speaker 1: use chemical energy from the vents to build sugars, and
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  Speaker 1: larger organisms including tube worms and clams host these bacteria
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  Speaker 1: in their tissues. In the darkness, a food web thrives
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  Speaker 1: powered by reactions that begin in rock and water. When
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  Speaker 1: we watch the vents, we are seeing a conversation between
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  Speaker 1: mantle heat, seawater and life. If we could glide over
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  Speaker 1: the ocean floor from a ridge toward a distant continent,
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  Speaker 1: we would cross a pattern that looks like a barcode.
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  Speaker 1: Long stripes of rock on one side of the ridge
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  Speaker 1: mirror similar stripes on the other side. The stripes are
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  Speaker 1: made not by colour but by tiny magnets inside the basalt.
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  Speaker 1: When lava cools, crystals of magnetite lock in a record
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  Speaker 1: of the direction of Earth's magnetic field at that moment.
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  Speaker 1: The magnetic field is not fixed forever. From time to
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  Speaker 1: time it flips so that a compass that once pointed
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  Speaker 1: north would point south. These flips do not follow a
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  Speaker 1: simple schedule, but when they happen, new lava cools with
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  Speaker 1: the reversed direction. As the sea floor spreads away from
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  Speaker 1: the ridge, it carries the magnetic memory with it. The
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  Speaker 1: ridge writes a symmetric diary of Earth's field into the
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  Speaker 1: ocean floor. When this diary was first read, it gave
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  Speaker 1: the world simple proof that the surface of the planet
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  Speaker 1: moves outward from ridges. The stripes are the patient handwriting
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  Speaker 1: of the sea. there is another quiet measurement that makes
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  Speaker 1: this motion feel real and immediate. Many places around the
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  Speaker 1: world carry small radio receivers that listen to signals from satellites.
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  Speaker 1: These receivers measure their positions with astonishing precision. When we
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  Speaker 1: compare positions month After month and year after year, we
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  Speaker 1: see cities move by a few millimetres, sometimes a few centimetres.
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  Speaker 1: The Pacific Northwest inches toward Alaska. Parts of Australia slide north.
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  Speaker 1: The Atlantic grows a little wider as North America and
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  Speaker 1: Europe drift apart. The numbers are small but unsleeping. In
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  Speaker 1: one human lifetime, a plate can travel a distance that
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  Speaker 1: a person could walk in an afternoon, and in that
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  Speaker 1: time mountains rise a little and fault lines breathe. Where
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  Speaker 1: plates meet, the encounter can take several forms. In many
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  Speaker 1: places where the ocean floor meets another plate, the denser
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  Speaker 1: oceanic crust and its upper mantle begin to slide downward
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  Speaker 1: into the mantle beneath. This is subduction. The place where
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  Speaker 1: the descent begins is marked at the surface by a
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  Speaker 1: deep trench in the ocean. The angle of the sliding
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  Speaker 1: slab varies with place and time. Water goes down with
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  Speaker 1: the sinking crust, locked in minerals that formed on the
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  Speaker 1: sea floor. As the slab plunges to greater pressure and temperature,
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  Speaker 1: those hydrated minerals break down and release water into the
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  Speaker 1: overlying hot mantle. The water makes that mantle melt more easily.
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  Speaker 1: The melt rises to feed volcanoes that line up in
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  Speaker 1: an arc above the sliding slab. Farther landward, the crust
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  Speaker 1: is bowed down by the pull of the slab and
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  Speaker 1: by the weight of sediments and volcanic rocks. Outboard, near
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  Speaker 1: the trench, sediment scraped from the sinking plate jumbles into
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  Speaker 1: a wedge that grows by accretion. The whole system operates
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  Speaker 1: as a giant slow conveyor that recycles ocean crust into
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  Speaker 1: the interior and builds new crust at volcanoes near the surface.
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  Speaker 1: These volcanic chains form graceful arcs because they trace the
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  Speaker 1: contour above the sinking slab at a fairly constant distance
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  Speaker 1: from the trench. The chemistry of their rocks often shows
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  Speaker 1: a signature of water-rich melts. Andesite and dacite are common,
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  Speaker 1: richer in silica than the basalts of the ocean floor.
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  Speaker 1: The landscape wears cones and calderas, snow and ice on
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  Speaker 1: the higher peaks, forests on the lower flanks. The air
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  Speaker 1: around these ranges is full of tiny crystals of volcanic
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  Speaker 1: glass when eruptions occur, but most days it is quiet.
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  Speaker 1: with thin steam rising from vents and warm springs curing
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  Speaker 1: the chill of mountain valleys. The word arc is not
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  Speaker 1: only a shape, it is a rhythm. These volcanoes are
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  Speaker 1: young and watchful. They grow grain by grain over thousands
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  Speaker 1: of years, and from time to time they reset their
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  Speaker 1: profiles with an eruption, then return to the slow business
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  Speaker 1: of building. There is another kind of mountain that rises
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  Speaker 1: when two continents meet. Neither continent is dense enough to
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  Speaker 1: sink easily. When they collide, they crumple and thicken. The
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  Speaker 1: crust piles up and the deep roots of the mountain
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  Speaker 1: thicken as well. Imagine the meeting of India and Eurasia.
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  Speaker 1: Between them once lay an ocean floor that was consumed
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  Speaker 1: by subduction. As the gap closed, fragments of that old
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  Speaker 1: ocean floor were sometimes thrust up and welded onto the
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  Speaker 1: edge of the continent. These fragments are called ophiolites. They
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  Speaker 1: are souvenirs of a vanished ocean preserved on land. When
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  Speaker 1: the last piece of oceanic crust vanished, the continents pressed
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  Speaker 1: together and a broad plateau began to rise. Rocks that
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  Speaker 1: once lay many kilometres down became exposed at the surface.
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  Speaker 1: Fossils that formed in shallow, warm seas now rest near
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  Speaker 1: the feet of glaciated summits. The mountains speak of travel
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  Speaker 1: long completed. Even mountains that pierce the sky are not
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  Speaker 1: free to grow without limit. The crust floats on the
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  Speaker 1: softer mantle below it, much like an iceberg floats in water.
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  Speaker 1: This state of balance is called isostasy. If the crust
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  Speaker 1: becomes thicker in one area, it sinks a little deeper
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  Speaker 1: until the buoyant forces match the weight. If material is
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  Speaker 1: removed from the top by erosion, the root rises a little.
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  Speaker 1: The balance is dynamic. Picture a wooden raft loaded with stones.
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  Speaker 1: As you remove stones from the top, the raft rides higher.
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  Speaker 1: In the crust, The timing is measured in thousands to
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  Speaker 1: millions of years, but the principle is as simple as
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  Speaker 1: a child's hand in a lake. The roots of great
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  Speaker 1: mountain ranges reach far below what we can see. In
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  Speaker 1: some ranges, the crust can be twice as thick as
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  Speaker 1: average continental crust. The thickening creates a root that swims
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  Speaker 1: in the warmer mantle like the lower block of an iceberg.
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  Speaker 1: We can sense these roots through seismic waves that travel
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  Speaker 1: more slowly through thick, warm crust than through thin, cooler crust.
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  Speaker 1: Gravity measurements also reveal their presence. Over time, the roots
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  Speaker 1: themselves can change. Parts may become dense due to changes
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  Speaker 1: in their minerals at depth. Those dense parts can detach
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  Speaker 1: and sink, like a stone breaking free from a raft.
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  Speaker 1: allowing the overlying mountains to rise or the surface to relax.
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  Speaker 1: The mountain we see is only part of a deeper
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  Speaker 1: structure that finds its equilibrium again and again. While these
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  Speaker 1: balances play out, the surface of a mountain range is
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  Speaker 1: being carved. Erosion is the patient sculptor. It uses sunlight, water, ice,
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  Speaker 1: wind and even life to move grains of rock from
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  Speaker 1: high places to low. Chemical reactions loosen minerals and turn
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  Speaker 1: some rocks into clays and iron-rich soils. Frost wedges rocks
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  Speaker 1: apart when water seeps into cracks and freezes. Glaciers grind
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  Speaker 1: and polish valleys and carry fine flour of rock many kilometres.
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  Speaker 1: Rivers cut channels and wander, lifting stones in floods and
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  Speaker 1: laying them down as bars when the energy wanes. Plants
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  Speaker 1: and microbes pry apart grains with roots and acids, then
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  Speaker 1: hold the soil as it moves. None of this is hurried.
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  Speaker 1: A cliff that feels solid under your hand today is
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  Speaker 1: a story in progress, written line by line by rain
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  Speaker 1: and thaw and the growth of a lichen. As erosion
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  Speaker 1: removes mass from a range, isostasy responds. The crust that
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  Speaker 1: was pressed down by the weight of tall peaks begins
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  Speaker 1: to rise a little. This rebound can keep the highest
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  Speaker 1: parts of a range near the sky, even as their
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  Speaker 1: rocks are removed and carried away. In some places, the
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  Speaker 1: rebound after the melting of a great ice sheet is
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  Speaker 1: still lifting the land today. Quietly, some northern shorelines are
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  Speaker 1: rising by the thickness of a finger each year. Old
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  Speaker 1: ports are now stranded above the tide. Lakes tilt slightly
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  Speaker 1: and their waters find new paths. The ground remembers the
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  Speaker 1: weight of ice and the relief of its departure. Every
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  Speaker 1: grain that leaves a mountain must go somewhere. Rivers are
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  Speaker 1: the movers. They carry sand, silt and clay, as well
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  Speaker 1: as dissolved minerals, toward basins that lie at lower elevation.
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  Speaker 1: When the river slows, it drops part of its load.
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  Speaker 1: On the plains, it spreads out in wide sheets during
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  Speaker 1: floods and leaves new soil that makes fields fertile. At
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  Speaker 1: the foot of slopes, it may pour out of a
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  Speaker 1: canyon and spread into a fan. Where a river meets
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  Speaker 1: the sea, it builds a delta that crawls outward over
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  Speaker 1: centuries like a many-fingered hand. For a time, the weight
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  Speaker 1: of this new pile of sediment bends the crust downward
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  Speaker 1: like a wooden board sagging under a bag of grain.
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  Speaker 1: The bend makes more room for sediment. Layer builds on layer,
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  Speaker 1: each telling a story of a season or a storm,
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  Speaker 1: a sand drought or a muddy flood. In time, some
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  Speaker 1: of these layers may be carried back toward the place
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  Speaker 1: where mountains grow at subduction zones. There, the sediments can
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  Speaker 1: be compressed, heated and lifted, and the cycle runs again.
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  Speaker 1: This exchange between high and low is a quiet partnership
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  Speaker 1: rather than a battle. Mountains rise because the crust is
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  Speaker 1: thickened by the meeting of plates and by the flow
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  Speaker 1: of the mantle below. Mountains also rise in response to
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  Speaker 1: the removal of mass from their shoulders. Planes grow because
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  Speaker 1: rivers feed them with the gifts of distant heights. Planes
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  Speaker 1: in turn load the edges of continents with sediments that
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  Speaker 1: become the raw material of future rock. In this way,
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  Speaker 1: the planet writes a long poem where the themes return
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  Speaker 1: with variations. Ocean becomes mountain. Mountain becomes plane. Plane becomes
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  Speaker 1: a future mountain as plates carry the story into another age.
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  Speaker 1: If you listen closely, there are small and rare facts
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  Speaker 1: tucked inside these grand motions. Basalt made at mid-ocean ridges
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  Speaker 1: often carries a trace of helium that is older than
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  Speaker 1: the continents, a whisper from the young Earth that escaped
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  Speaker 1: into the bubbles of lava. Sand found in a desert
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  Speaker 1: dune can contain grains of zircon that formed before any
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  Speaker 1: animals walked on land, grains that have survived many cycles
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  Speaker 1: of erosion and burial and uplift. A limestone taken from
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  Speaker 1: a high plateau may hold the shells of tiny sea
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  Speaker 1: creatures that settled in warm, shallow water millions of years
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  Speaker 1: before their home was raised toward the sky. These details
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  Speaker 1: are like notes in a lullaby. They do not surprise
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  Speaker 1: the song. They give it texture. You can feel the
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  Speaker 1: patience of these processes, even in an ordinary landscape. Stand
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  Speaker 1: on a low hill and watch a river bend. The
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  Speaker 1: outer bank erodes. The inner bank receives. Grass clings to
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  Speaker 1: the top of the outer bank until undercutting takes it
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  Speaker 1: down in a quiet slump. A tree near the bend
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  Speaker 1: leans a little more each year and then lies in
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  Speaker 1: the water where fish hide in its branches. Far away,
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  Speaker 1: a ridge casts a blue edge against the afternoon. The
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  Speaker 1: air carries the scent of soil after a last shower.
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  Speaker 1: Nothing is still and nothing is in a hurry. Imagine
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  Speaker 1: now following one grain of quartz. It rests in a
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  Speaker 1: hard vein inside granite, deep below an ancient range. Uplift
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  Speaker 1: brings it nearer the surface, and frost one winter loosens
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  Speaker 1: the rock and frees the grain. A stream picks it
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  Speaker 1: up and rolls it down a slope where it settles
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  Speaker 1: for a season behind a log, then moves again in
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  Speaker 1: a spring flood. The grain travels by many short steps
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  Speaker 1: toward a plain. It becomes part of a sandbar, then
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  Speaker 1: part of a dune, then part of a delta. It
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  Speaker 1: is buried and slowly pressed. After many lifetimes, it turns
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  Speaker 1: to sandstone. The plate under the sandstone moves, and part
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  Speaker 1: of the rock is carried down in a subduction zone.
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  Speaker 1: Some of its material melts and rises into a new
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  Speaker 1: chain of volcanoes. In time, that chain is uplifted into mountains.
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  Speaker 1: One day a block of the new rock reaches the
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  Speaker 1: surface and breaks, and our grain is freed once more.
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  Speaker 1: The planet has a patience that is kind. The drifting
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  Speaker 1: of continents is often told with maps that show shapes
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  Speaker 1: sliding around like pieces on a calm sea. The reality
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  Speaker 1: includes memory and feedback. As a continent moves, it changes
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  Speaker 1: wind and rain patterns that sweep across it. If a
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  Speaker 1: plateau rises It can cast a rain shadow that turns
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  Speaker 1: a region downwind into steppe and desert. If a mountain
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  Speaker 1: belt lowers, a coast can become greener. In the tropics,
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  Speaker 1: the growth of great ranges can even strengthen the cycle
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  Speaker 1: of monsoon winds that bring seasonal rains from the ocean.
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  Speaker 1: The landscape and the air are partners. What rises on
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  Speaker 1: the ground can alter what falls from the sky. These
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  Speaker 1: changes are never a single cause with a single effect.
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  Speaker 1: They are woven effects that slowly reshape a planet that
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  Speaker 1: remains familiar. Rivers still cut meanders. Grass still bends under wind.
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  Speaker 1: The ocean still brings smell and salt to the shore.
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  Speaker 1: The slow movements beneath the crust simply tilt the stage
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  Speaker 1: on which these daily actors perform. A ridge tens of
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  Speaker 1: kilometres below a mountain valley can cause a spring to
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  Speaker 1: emerge where someone will one day drink and rest. A
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  Speaker 1: fault that slips a few millimetres each year can create
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  Speaker 1: a gentle scarp that forces a small stream to braid
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  Speaker 1: and wander. A trench thousands of kilometres long can be
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  Speaker 1: the reason an arc of islands has rich soil for
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  Speaker 1: forests and farms. The deep and the near are connected.
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  Speaker 1: If you are still awake, picture the world map as
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  Speaker 1: a living thing. The Atlantic is widening a little each year.
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  Speaker 1: Not enough to notice from a boat, yet enough to
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  Speaker 1: matter in a million years. The Pacific is closing. Somewhere
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  Speaker 1: on the floor of that ocean basalt that cooled last night,
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  Speaker 1: has already begun its journey toward a trench. Somewhere at
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  Speaker 1: the edge of a continent, a few grains of sand
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  Speaker 1: joined a growing delta. Somewhere in a mountain, a tiny
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  Speaker 1: crystal of garnet grew inside a rock that is slowly
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  Speaker 1: traveling upward. The planet that carries us is not racing.
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  Speaker 1: It is drifting with confidence. We have walked together from
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  Speaker 1: the soft motion of the mantle to the place where
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  Speaker 1: oceans are born, down the barcode of the magnetic sea floor,
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  Speaker 1: across the measuring lines of satellites, into the shadows of
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  Speaker 1: trenches and the glow of arcs, up the sutures of
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  Speaker 1: colliding continents, into the floating roots of ranges, through the
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  Speaker 1: art of erosion. and out onto the plains where rivers
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  Speaker 1: deliver gifts. The lesson is one of comfort. Change can
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  Speaker 1: be gentle and sure. A restless mind can borrow that
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  Speaker 1: pace and let go. Far to the north and far
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  Speaker 1: to the south, a quiet weight presses on the crust.
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  Speaker 1: It is the weight of ice laid down by many winters.
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  Speaker 1: When ice collects into a sheet that is kilometers thick,
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  Speaker 1: it bows the crust down. flows very slowly beneath it,
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  Speaker 1: making a basin where the ice sits. Around the edge
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  Speaker 1: a raised rim forms where pushed rock has gathered. When
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  Speaker 1: a warm time arrives and the ice melts away, the
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  Speaker 1: weight is removed and the crust begins to rise. It
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  Speaker 1: does not spring back in a single season. It rises
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  Speaker 1: like a slow breath taken by stone. Shorelines tilt, rivers
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  Speaker 1: find new paths. Ancient harbours are left high above the tide.
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  Speaker 1: People still walk across beaches in parts of the north
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  Speaker 1: where waves once washed. and they stand among old anchors
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  Speaker 1: that now lie in grass. The land is returning to balance,
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  Speaker 1: and that balance is called isostatic rebound. The memory of
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  Speaker 1: ice reaches even into gravity. When satellites map the strength
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  Speaker 1: of gravity over the planet, they find a gentle low
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  Speaker 1: in the region of a great inland sea. The crust
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  Speaker 1: there is still rising, and the mass of rock is
• 24:32
  Speaker 1: still rearranging itself after ice departed thousands of years ago.
• 24:38
  Speaker 1: Some lakes nearby have shorelines that look like the lines
• 24:42
  Speaker 1: on a bathtub, each one a record of a time
• 24:45
  Speaker 1: when the water found a different level because the land
• 24:49
  Speaker 1: was lifted unevenly. In one region, stones that were once
• 24:54
  Speaker 1: on the sea floor are now stranded far above the waves,
• 24:58
  Speaker 1: carried there on plates of ice that melted and left
• 25:02
  Speaker 1: them like messages on a hill. All of these scenes
• 25:06
  Speaker 1: whisper the same idea. Ice has weight. Rock flows. The
• 25:12
  Speaker 1: crust breathes in response. Rebound. is not the only change
• 25:18
  Speaker 1: that ice brings. As the weight lifts and the crust rises,
• 25:22
  Speaker 1: faults wake and adjust by small amounts. Earthquakes occur in
• 25:27
  Speaker 1: places that are usually quiet. The heart of a continent
• 25:31
  Speaker 1: feels a series of slow aches that release long-stored strain.
• 25:37
  Speaker 1: In coastal places, rebound can lift land faster than the
• 25:41
  Speaker 1: sea rises, and new birch and spruce colonize marshes that
• 25:46
  Speaker 1: were recently under salt water. The opposite can happen near
• 25:50
  Speaker 1: the outer rim that was once raised by the ice.
• 25:54
  Speaker 1: That rim may sink a little as the centre rebounds,
• 25:58
  Speaker 1: and marshes there may flood. In these gentle shifts, we
• 26:02
  Speaker 1: see how water in its many forms shapes the skin
• 26:06
  Speaker 1: of the planet. From ice and isostasy, let us drift
• 26:11
  Speaker 1: to a different source of motion. In a few places,
• 26:14
  Speaker 1: hot columns of mantle rise from deep levels and feed
• 26:18
  Speaker 1: long-lived centres of volcanism. These upwellings are called plumes by
• 26:24
  Speaker 1: many geologists, and the places where they pierce the surface
• 26:29
  Speaker 1: are called hotspots. Picture a belt of oceanic crust moving
• 26:34
  Speaker 1: slowly over a fixed source of heat. Where the belt
• 26:38
  Speaker 1: passes above the source, volcanoes grow from the sea floor
• 26:42
  Speaker 1: and sometimes break the surface to form islands. As the
• 26:46
  Speaker 1: plate continues to move, the volcano that once had a
• 26:50
  Speaker 1: steady supply of melt is carried away and it goes quiet.
• 26:55
  Speaker 1: A new volcano forms nearer to the source and takes
• 26:59
  Speaker 1: its place. Over millions of years, this process makes a
• 27:05
  Speaker 1: chain of islands and seamounts that trace the path of
• 27:10
  Speaker 1: the plate across the deep engine below one notable chain
• 27:15
  Speaker 1: bears a graceful elbow the older underwater peaks point in
• 27:21
  Speaker 1: one direction and the younger islands point in another the
• 27:25
  Speaker 1: bend marks a change in the direction of plate motion
• 27:29
  Speaker 1: that happened long ago The islands themselves share families of
• 27:35
  Speaker 1: lavas that reveal the chemistry of the source and the
• 27:39
  Speaker 1: degree of melting that fed each stage of growth. Some
• 27:43
  Speaker 1: of the rocks are full of gas bubbles that later
• 27:47
  Speaker 1: filled with crystals of green olivine and pale zeolite. Some
• 27:52
  Speaker 1: hold rare fragments of deep mantle lifted to the surface
• 27:56
  Speaker 1: as if carried in a glass elevator. The islands also
• 28:01
  Speaker 1: tell the story of erosion and subsidence. As a volcano
• 28:05
  Speaker 1: ages and is carried into cooler water, the crust beneath
• 28:09
  Speaker 1: it cools and sinks. Waves and weather plane the summit
• 28:14
  Speaker 1: down so that a once bold island becomes a low
• 28:18
  Speaker 1: coral ring after the summit slips below the waves. The
• 28:22
  Speaker 1: ocean holds many such rings, silent blue circles that mark
• 28:27
  Speaker 1: the former heights. Hotspots can occur under continents as well.
• 28:32
  Speaker 1: In some lands, odd clusters of small volcanoes rise across
• 28:37
  Speaker 1: broad plains. They erupt unusual magmas that move quickly through
• 28:43
  Speaker 1: the crust and occasionally carry diamonds from deep sources. The
• 28:48
  Speaker 1: diamonds arrive embedded in pipes of dark rock that solidified
• 28:53
  Speaker 1: from very fast moving melts. Miners find these pipes by
• 28:58
  Speaker 1: careful mapping of subtle clues at the surface, and each
• 29:03
  Speaker 1: pipe is a diary of a rapid journey from high-pressure
• 29:06
  Speaker 1: realms to a quiet field. In other regions, huge outpourings
• 29:11
  Speaker 1: of lava occurred in ancient times, covering areas the size
• 29:16
  Speaker 1: of countries in stacked sheets. These events were rare and dramatic.
• 29:22
  Speaker 1: compared with the steady breathing of normal ridges and arcs.
• 29:26
  Speaker 1: They changed air and climate and left behind plateaus of
• 29:30
  Speaker 1: basalt with step-like cliffs that shine in evening light. The
• 29:35
  Speaker 1: patient motion of plates sets a rhythm. Hotspots and mantel
• 29:40
  Speaker 1: floods add rare symbols to the score. The stage on
• 29:44
  Speaker 1: which all this occurs changes through a long cycle that
• 29:49
  Speaker 1: joins oceans and continents in a repeating pattern. It begins
• 29:53
  Speaker 1: with a rift that opens in a continent. The crust
• 29:57
  Speaker 1: thins and the land splits along a line of faults.
• 30:01
  Speaker 1: Volcanic activity accompanies the stretching as mantle melt rises along
• 30:07
  Speaker 1: the cracks. Gradually, a narrow sea forms, and then an
• 30:12
  Speaker 1: ocean with a newborn ridge at its centre. For many
• 30:15
  Speaker 1: tens of millions of years, the ocean widens, and its
• 30:19
  Speaker 1: floor grows outward from the ridge. But plates are never
• 30:24
  Speaker 1: content to move in only one pattern. At some point,
• 30:29
  Speaker 1: new zones of subduction form along the edges, and the
• 30:32
  Speaker 1: ocean begins to be consumed. Island arcs grow. continents move closer.
• 30:39
  Speaker 1: In the end, two continents may meet and stitch together.
• 30:43
  Speaker 1: Mountains rise along the seam. The joined mass rests for
• 30:47
  Speaker 1: a time as a supercontinent. Heat builds under its broad blanket,
• 30:52
  Speaker 1: and eventually new rifts crack it apart, and the cycle
• 30:56
  Speaker 1: begins again. This long story is called the Wilson Cycle.
• 31:04
  Speaker 1: Evidence for this cycle is written in belts of metamorphic
• 31:08
  Speaker 1: rock that mark ancient sutures where continents joined. It is
• 31:13
  Speaker 1: written in fossil patterns that show creatures wandering across lands
• 31:18
  Speaker 1: that were once neighbours but are now far apart. It
• 31:22
  Speaker 1: is written in the ages of ocean floor rocks which
• 31:26
  Speaker 1: are all younger than a quarter of a billion years,
• 31:29
  Speaker 1: while continental crust holds terrains billions of years old. Oceans
• 31:35
  Speaker 1: are temporary theatres. Continents are long-lived actors who change costumes
• 31:41
  Speaker 1: again and again. Supercontinents have gathered and parted several times.
• 31:48
  Speaker 1: The most recent Grand Assembly is the one often shown
• 31:52
  Speaker 1: on classroom maps when the land was gathered into a
• 31:56
  Speaker 1: single mass that we call Pangea. Before that time, there
• 32:00
  Speaker 1: were older unions with different shapes and names. One of
• 32:05
  Speaker 1: them gathered most of the continents around the equator and
• 32:09
  Speaker 1: has the lyrical name Rodinia. The pieces of that one
• 32:13
  Speaker 1: later drifted apart and recombined in new arrangements long before
• 32:19
  Speaker 1: the first trees appeared on land. We hold fragments of
• 32:23
  Speaker 1: these stories in the paleomagnetic directions recorded in old rocks.
• 32:29
  Speaker 1: When a rock cooled, it kept a memory of which
• 32:32
  Speaker 1: way north lay at that time. By measuring many such memories,
• 32:37
  Speaker 1: geologists can turn the pieces like tiles until the directions match.
• 32:43
  Speaker 1: The shapes of matching coastlines and the positions of ancient
• 32:47
  Speaker 1: mountain belts confirm the fit. In the basement of some continents,
• 32:52
  Speaker 1: you can stand on rocks that were once neighbours to stones,
• 32:57
  Speaker 1: now a world away. The planet remembers its families even
• 33:02
  Speaker 1: after they scatter. There are lesser-known souvenirs that attach our
• 33:07
  Speaker 1: thoughts to deep time. A small crystal of zircon found
• 33:11
  Speaker 1: in a sandstone from a dry region has been dated
• 33:15
  Speaker 1: to nearly the dawn of the planet's history. It survived
• 33:19
  Speaker 1: cycles of weathering and burial and metamorphism, and still carries
• 33:25
  Speaker 1: within it a clear signal of age and even a
• 33:29
  Speaker 1: hint of the water-rich conditions under which it first grew.
• 33:33
  Speaker 1: A pebble polished by waves on a beach in a
• 33:37
  Speaker 1: landlocked desert shows that a shallow sea lapped there for
• 33:42
  Speaker 1: a time when continents were joined in a way no
• 33:45
  Speaker 1: human saw. Under the high grasses of a plain, a
• 33:49
  Speaker 1: belt of dark rock marks the trace of an ancient
• 33:53
  Speaker 1: rift where a supercontinent began to part. These are quiet
• 33:59
  Speaker 1: footnotes in The Book of Supercontinents, enough to carry a
• 34:04
  Speaker 1: mind into the long evening. while the body settles into rest.
• 34:11
  Speaker 1: To watch motion today, we do not have to guess.
• 34:15
  Speaker 1: We can measure directly. Small receivers on bedrock and on
• 34:20
  Speaker 1: buildings listen to signals from satellites that circle the planet.
• 34:25
  Speaker 1: The stations are tied into a stable frame based on
• 34:29
  Speaker 1: distant quasars that sit far beyond our galaxy. Using this
• 34:35
  Speaker 1: steady background, the stations can report their position to the
• 34:39
  Speaker 1: thickness of a coin. After months and years of quiet recording,
• 34:44
  Speaker 1: the results show movement that is both small and relentless.
• 34:50
  Speaker 1: A town in the south of a large continent glides
• 34:53
  Speaker 1: north by a few centimetres each year. Islands in an
• 34:58
  Speaker 1: arc draw closer together. Points on either side of a
• 35:02
  Speaker 1: fault creep past one another with steady grace, saving a
• 35:06
  Speaker 1: little motion for the day when strain will be released
• 35:09
  Speaker 1: by an earthquake. On the far side of the ocean,
• 35:13
  Speaker 1: another chain of measurements shows drift in a different direction.
• 35:18
  Speaker 1: The map becomes a slow movie. People like to say
• 35:22
  Speaker 1: that continents wander. With these instruments, we see that they
• 35:26
  Speaker 1: do so with the patience of stone. Satellites also measure
• 35:31
  Speaker 1: how the surface rises and falls. When a big fault slips,
• 35:37
  Speaker 1: or when a volcano swells with magma, they send radar
• 35:41
  Speaker 1: that bounces from the ground and returns with tiny changes
• 35:45
  Speaker 1: in distance. By comparing images taken on different days, scientists
• 35:50
  Speaker 1: can map a bulge on the flank of a volcano
• 35:54
  Speaker 1: that is smaller than your height. They can also watch
• 35:57
  Speaker 1: the ground around a city and see where it sinks
• 36:00
  Speaker 1: or lifts due to water use or the rebound of
• 36:04
  Speaker 1: old ice. In these images, the planet looks like a
• 36:09
  Speaker 1: sleeping chest that rises and falls almost imperceptibly with the
• 36:14
  Speaker 1: quiet breath of stress and release. Even without an eruption
• 36:19
  Speaker 1: or an earthquake, the daily background shows slow changes that
• 36:24
  Speaker 1: speak of mantle flow and of crust that bends under
• 36:29
  Speaker 1: loads and recovers when the load changes. Not all pieces
• 36:34
  Speaker 1: of continents travel as single blocks. Along many edges, small
• 36:39
  Speaker 1: bits arrive as passengers and are welded to the margin.
• 36:43
  Speaker 1: These fragments are called terrains. Some are the cores of
• 36:48
  Speaker 1: islands that lived alone for a long time. Some are
• 36:52
  Speaker 1: slivers of ocean floor that were scraped off and piled
• 36:57
  Speaker 1: onto the continent when a plate slid beneath it. Some
• 37:01
  Speaker 1: are microcontinents that rifted away from a larger mass, floated
• 37:06
  Speaker 1: for a while, and then found a new home on
• 37:09
  Speaker 1: the side of a different land. In some mountain belts,
• 37:13
  Speaker 1: you can walk along a valley and cross from rock
• 37:16
  Speaker 1: types that formed near the equator to rocks that formed
• 37:20
  Speaker 1: near the pole, each one carrying fossils that speak of
• 37:24
  Speaker 1: a very different climate. The only way this makes sense
• 37:29
  Speaker 1: is to picture these fragments travelling long distances before joining
• 37:33
  Speaker 1: the range. Terrains can bring mineral riches. They can also
• 37:39
  Speaker 1: bring their own peculiar structures, so that a traveller crosses
• 37:45
  Speaker 1: many crustal worlds in a single day's walk. The pattern
• 37:50
  Speaker 1: resembles a quilt with patches from many wardrobes sewn together
• 37:54
  Speaker 1: into a cloak that keeps the continent warm. At the
• 37:59
  Speaker 1: scale of human life, the edges of continents often look quiet.
• 38:04
  Speaker 1: At the scale of deep time, they are busy docks
• 38:07
  Speaker 1: where ships of stone unload their cargo. While mountains and
• 38:13
  Speaker 1: terrains capture the eye, there is another form of slow
• 38:17
  Speaker 1: change that acts on the interior of continents. It is
• 38:21
  Speaker 1: not the result of collision. It is a broad lift
• 38:25
  Speaker 1: or gentle subsidence of large regions that do not break
• 38:29
  Speaker 1: or fold. The word used for this is epirogeny. The
• 38:34
  Speaker 1: causes can include flexure under the load of sediments, thermal
• 38:39
  Speaker 1: changes in the lithosphere, or the push and pull of
• 38:42
  Speaker 1: currents in the mantle that flow on scales of many
• 38:46
  Speaker 1: hundreds of kilometres. If warm material rises beneath a region,
• 38:52
  Speaker 1: it can lift a plane by a few hundred metres
• 38:55
  Speaker 1: over millions of years. If cool, dense material gathers beneath,
• 39:00
  Speaker 1: the land can sink and a wide, shallow sea can return,
• 39:05
  Speaker 1: ancient shorelines mark such visitors in the rock record. Dinosaurs
• 39:10
  Speaker 1: once walked on beaches that are now thousands of kilometres
• 39:14
  Speaker 1: from the nearest tide because the interior of the continent
• 39:17
  Speaker 1: rose after those seas drained away. Modern instruments hint at
• 39:23
  Speaker 1: these gentle movements. Rivers that once flowed across featureless plains
• 39:29
  Speaker 1: now show a steady increase in relief along their courses.
• 39:34
  Speaker 1: Waterfalls retreat upstream in landscapes that are slowly lifting. Some
• 39:40
  Speaker 1: lakes tilt so quietly that only a long line of
• 39:44
  Speaker 1: old piers shows the change. This dynamic topography, driven by
• 39:49
  Speaker 1: flow in the deep mantle, writes its story with a
• 39:53
  Speaker 1: very light hand. Under the right evening light, you might
• 39:57
  Speaker 1: see it in the way a horizon line sits ever
• 40:00
  Speaker 1: so slightly higher than an old surveyor's Across oceans, another
• 40:06
  Speaker 1: kind of boundary moves differently. Two plates can slide past
• 40:11
  Speaker 1: one another rather than collide or spread. The boundary between
• 40:15
  Speaker 1: them is a transform fault. Motion along these faults takes
• 40:19
  Speaker 1: place in small steps over long time. Pieces of crust
• 40:25
  Speaker 1: that were once neighbours can be separated by hundreds of
• 40:28
  Speaker 1: kilometres while remaining aligned. In the deep sea, Transform faults
• 40:34
  Speaker 1: offset segments of mid-ocean ridges and create valleys with ridges
• 40:39
  Speaker 1: on either side. A long continent's transforms can make long
• 40:45
  Speaker 1: linear valleys and ranges that run beside them. People living
• 40:50
  Speaker 1: near such a fault can feel sudden releases of the
• 40:53
  Speaker 1: stored motion as earthquakes when a locked patch finally yields.
• 40:59
  Speaker 1: But even when no quake occurs, the plates continue their
• 41:03
  Speaker 1: patient glide, and the landscape records it with streams that
• 41:08
  Speaker 1: change course and rocks that ride past each other with
• 41:11
  Speaker 1: matching layers now separated. The quiet part of transform motion
• 41:17
  Speaker 1: is not only the slow creep, it is the way
• 41:21
  Speaker 1: landscapes adapt. A river that met the sea at a
• 41:25
  Speaker 1: certain point can be shifted along the fault over time
• 41:29
  Speaker 1: so that it finds a new outlet. A ridge that
• 41:33
  Speaker 1: crossed the fault is broken and displaced so that its
• 41:37
  Speaker 1: halves no longer line up. Geologists trace these offsets like
• 41:42
  Speaker 1: detectives following clues across scrub and grass. Some of the
• 41:47
  Speaker 1: most famous offsets show rocks of the same age and type,
• 41:53
  Speaker 1: sitting on opposite sides of a valley separated by the
• 41:56
  Speaker 1: work of centuries and millennia of slip. The evidence sits
• 42:01
  Speaker 1: in sun and rain with no sign of hurry. Beneath
• 42:06
  Speaker 1: all of these motions is the rock cycle, a quiet
• 42:10
  Speaker 1: circle of change that turns igneous rock into sediment, sediment
• 42:15
  Speaker 1: into metamorphic rock, and all of them back again. When
• 42:19
  Speaker 1: a rock is buried and heated, its minerals begin to rearrange.
• 42:25
  Speaker 1: At first they may become slightly larger and more orderly.
• 42:29
  Speaker 1: Then New minerals may grow that are stable at higher
• 42:33
  Speaker 1: pressure and temperature. In some metamorphic rocks, minerals grow into long,
• 42:40
  Speaker 1: thin crystals that align under pressure and give the rock
• 42:43
  Speaker 1: a sheen that catches the light. Garnet can appear as
• 42:47
  Speaker 1: small red crystals in a shimmering matrix, each crystal a
• 42:51
  Speaker 1: tiny clock that records the conditions of its growth. Fluids
• 42:56
  Speaker 1: move through these rocks. and carry elements that can form
• 42:59
  Speaker 1: new veins when conditions change. The result is a deep
• 43:04
  Speaker 1: art of chemistry and texture. Under yet greater heat, rocks
• 43:09
  Speaker 1: may begin to melt. The melt rises and cools to
• 43:13
  Speaker 1: form granite deep underground. If uplift removes the cover, that
• 43:18
  Speaker 1: granite appears at the surface as rounded domes or as
• 43:22
  Speaker 1: cliffs that glow warm at sunset. At the same time,
• 43:27
  Speaker 1: Other rocks are exposed to wind and water, fall to grains,
• 43:32
  Speaker 1: and are carried away to basins where they become layers
• 43:36
  Speaker 1: of sand and mud. These layers may later be folded
• 43:40
  Speaker 1: and pushed into a mountain belt, where heat and pressure
• 43:44
  Speaker 1: transform them again. Some cycles close quickly in geologic terms.
• 43:51
  Speaker 1: Others take so long that continents change partners while the
• 43:55
  Speaker 1: story unfolds. Through it all, a single grain of mineral
• 44:00
  Speaker 1: may see many worlds within the same planet. At this
• 44:04
  Speaker 1: quiet hour, it is natural to wonder what comes next
• 44:08
  Speaker 1: for mountains and oceans. If the long rhythm of the
• 44:12
  Speaker 1: Wilson cycle continues, the present map is a moment within
• 44:17
  Speaker 1: an ongoing dance. In the far future, a new ocean
• 44:21
  Speaker 1: may open within a continent where rifting begins today. A
• 44:25
  Speaker 1: different ocean may be closing under a belt of island
• 44:30
  Speaker 1: arcs that will one day be part of a mountain
• 44:33
  Speaker 1: chain on a large landmass. The wash of shores along
• 44:37
  Speaker 1: one coast will look out on a smaller sea bounded
• 44:41
  Speaker 1: by rising ranges. Another coast will feel the long swell
• 44:46
  Speaker 1: of a growing ocean and see new basalt being born
• 44:51
  Speaker 1: along a ridge far away. Some scientists explore scenarios where
• 44:56
  Speaker 1: the present continents gather again. They draw maps with a
• 45:01
  Speaker 1: single landmass straddling old poles or hugging the equator. The
• 45:06
  Speaker 1: details differ, but the theme remains that continents are travellers
• 45:11
  Speaker 1: who sometimes camp together for a long season before parting.
• 45:16
  Speaker 1: In those maps, new deserts appear where winds are blocked
• 45:20
  Speaker 1: by high plateaus, and new forests appear where warm currents
• 45:25
  Speaker 1: and mountain shadows invite rain. Rivers redraw themselves across the
• 45:32
  Speaker 1: new heights and drop their load into seas that never
• 45:35
  Speaker 1: existed before. Creatures adapt. The sky writes new routes for storms.
• 45:42
  Speaker 1: The planet remains itself. What will happen to a particular
• 45:47
  Speaker 1: mountain range can be told in hints. If a range
• 45:51
  Speaker 1: sits above a thriving subduction zone, it will likely continue
• 45:55
  Speaker 1: to rise as long as ocean floor feeds the melting
• 46:00
  Speaker 1: mantle below. If a range was born from a collision
• 46:03
  Speaker 1: of continents, it will grow for a while. then settle
• 46:07
  Speaker 1: into a long age of erosion and isostatic adjustment. The
• 46:12
  Speaker 1: highest peaks will soften, the streams will carve deeper. In
• 46:16
  Speaker 1: a distant age, the old suture may be an unassuming
• 46:21
  Speaker 1: valley where a traveller walks among fossils that formed when
• 46:25
  Speaker 1: the sea returned for a time. Nothing in this is rushed.
• 46:30
  Speaker 1: A valley that looks new to us could be millions
• 46:33
  Speaker 1: of years old. A ridge that looks eternal is a
• 46:37
  Speaker 1: page that will turn. Even the deep structure changes. A
• 46:42
  Speaker 1: thick mountain root may become denser and drop away in
• 46:46
  Speaker 1: a drape-like fall called delamination. When that happens, the buoyant
• 46:51
  Speaker 1: crust above can rise a little and the surface may
• 46:55
  Speaker 1: lift in a broad swell. Later, the area may settle
• 47:00
  Speaker 1: as the lower crust cools. Over very long spans, the
• 47:04
  Speaker 1: mantle flows in patterns that lift some regions and lower
• 47:08
  Speaker 1: others for reasons that have nothing to do with local
• 47:12
  Speaker 1: faults or folds. Where warm material rises, plains can become
• 47:19
  Speaker 1: high plateaus with rivers that have more energy to cut.
• 47:23
  Speaker 1: Where cool material sinks, A shallow sea can flood a
• 47:27
  Speaker 1: land and leave chalk and limestone to mark its visit.
• 47:31
  Speaker 1: Tonight we have followed a slow procession. Ice sheets press
• 47:36
  Speaker 1: and let go, and the crust sighs with relief. Plumes
• 47:40
  Speaker 1: rise and leave trails of islands that bend with time.
• 47:45
  Speaker 1: Oceans open and close and stitch continents into grand quilts.
• 47:50
  Speaker 1: Then cut the stitches and begin anew. Memory lives in
• 47:55
  Speaker 1: tiny crystals that predate forests and in magnetic stripes that
• 48:00
  Speaker 1: run for thousands of kilometers under green water. Receivers on
• 48:05
  Speaker 1: quiet hills watch the planet move by the breath of
• 48:09
  Speaker 1: a fingernail each year. Small fragments arrive at continental docks
• 48:13
  Speaker 1: to be sewn into ranges. Planes lift and sink under
• 48:18
  Speaker 1: forces that come from far below. plates slide past with
• 48:23
  Speaker 1: the patience of old friends who do not hurry. Rocks
• 48:27
  Speaker 1: change clothes in heat and pressure and become something new.
• 48:32
  Speaker 1: The map of tomorrow grows from these actions without noise.
• 48:37
  Speaker 1: If you are still Imagine the globe slowly turning in space.
• 48:43
  Speaker 1: Night slips over one ocean while day brightens another. Under
• 48:48
  Speaker 1: the thin crust, the mantle continues its slow dance. A
• 48:52
  Speaker 1: new strip of basalt cools along a ridge. A set
• 48:56
  Speaker 1: of light earthquakes marks the place where a plate dives
• 49:00
  Speaker 1: under another. A glacier carves a small berg into a
• 49:04
  Speaker 1: cold sea. A river picks up a grain of sand
• 49:08
  Speaker 1: and carries it one bend closer to a distant delta.
• 49:12
  Speaker 1: Somewhere a mountain lifts by a fraction of a millimetre
• 49:15
  Speaker 1: because a thick root warmed and expanded. Somewhere else a
• 49:19
  Speaker 1: plain settles by the same small amount as the mantle
• 49:23
  Speaker 1: breathed outward. No trumpet announces these changes. They collect into futures.
• 49:30
  Speaker 1: Rest now inside that patience. The planet will keep its
• 49:35
  Speaker 1: slow schedule while you sleep. In the morning, the world
• 49:39
  Speaker 1: outside your window will seem exactly the same. Yet the
• 49:44
  Speaker 1: continents will have moved by a small kindness of distance.
• 49:49
  Speaker 1: Mountains will have gained or lost the thickness of a hair.
• 49:54
  Speaker 1: The deep will have traded a little heat with the shallow.
• 49:58
  Speaker 1: Everything will still be here. Everything will be on its way.
• 50:03
  Speaker 1: Along some continents, the edge of the land meets the
• 50:07
  Speaker 1: ocean with a sense of ease. These are passive margins.
• 50:11
  Speaker 1: They are not ruled by the loud meetings of plates,
• 50:15
  Speaker 1: but by slow cooling and steady sinking. Long ago, these
• 50:19
  Speaker 1: shores began as rifts that opened and filled with a
• 50:23
  Speaker 1: new ocean. As the young oceanic crust drifted away and cooled,
• 50:29
  Speaker 1: it became denser and heavier, and the edge of the
• 50:32
  Speaker 1: continent gently subsided beside it. With that gradual lowering came
• 50:38
  Speaker 1: wide shelves and smooth slopes, places where rivers could deliver
• 50:43
  Speaker 1: their loads, sand and mud spread outward in sheets and
• 50:48
  Speaker 1: tongues stacked by storms, tides and currents into a quiet
• 50:53
  Speaker 1: archive that thickens through millions of years. If you could
• 50:58
  Speaker 1: walk on the sea floor along one of these shelves,
• 51:02
  Speaker 1: you would see ridges made by waves that passed seasons
• 51:06
  Speaker 1: ago and furrows carved by storms that came once in
• 51:11
  Speaker 1: a decade. You might cross the head of a submarine
• 51:14
  Speaker 1: canyon that begins near the shelf edge. During rare floods,
• 51:19
  Speaker 1: dense flows race down these canyons, carrying sand from a
• 51:24
  Speaker 1: river mouth into the deeper sea. The flows settle into
• 51:28
  Speaker 1: layers on the slope and beyond, making beds that start
• 51:32
  Speaker 1: with coarse grains and grade into fine ones, each bed
• 51:37
  Speaker 1: a memory of a single event. Farther out lies a
• 51:41
  Speaker 1: vast rise built of many such beds, a gentle ramp
• 51:46
  Speaker 1: at the foot of the continent. Here and there warm
• 51:49
  Speaker 1: shallow banks grow reefs or carbonate plains, where tiny creatures
• 51:54
  Speaker 1: assemble chalk and limestone from dissolved shells. Barrier islands migrate slowly,
• 52:01
  Speaker 1: marshes thicken like quilts, and the shoreline inches forward or
• 52:06
  Speaker 1: back as rivers and waves negotiate a truce. It is
• 52:11
  Speaker 1: a coast that moves in the language of patience. To
• 52:15
  Speaker 1: understand how such peaceful edges begin, turn inland to places
• 52:22
  Speaker 1: where continents are stretching. The crust pulls apart, and as
• 52:26
  Speaker 1: it thins, it breaks along normal faults. Long blocks drop
• 52:31
  Speaker 1: down to form grabenes, and the blocks that remain high
• 52:34
  Speaker 1: become horsts. In these sunken valleys, lakes gather. They can
• 52:39
  Speaker 1: be narrow and deep and very old, with quiet waters
• 52:44
  Speaker 1: that layer fine sediment year after year in delicate couplets.
• 52:49
  Speaker 1: Dark volcanic dikes slice upward, To feed small lava flows,
• 52:55
  Speaker 1: the mantle below rises a little to fill the space
• 52:58
  Speaker 1: left by thinning, and the warm rock reduces in pressure
• 53:02
  Speaker 1: enough to melt. The melts find fractures and take them
• 53:06
  Speaker 1: as paths to the surface. The pattern of faults sometimes
• 53:11
  Speaker 1: organizes into a three-armed junction, like a Y laid on
• 53:16
  Speaker 1: its side. Two arms can win the contest and open
• 53:20
  Speaker 1: into a young ocean while the third arm stalls and
• 53:24
  Speaker 1: becomes a valley that points like a fossil arrow. As
• 53:28
  Speaker 1: the rift matures, the land splits to let in seawater
• 53:32
  Speaker 1: and a narrow sea appears. Margins that were once active
• 53:37
  Speaker 1: with faults become quiet as the new ocean settles into
• 53:41
  Speaker 1: its life. The story of a calm shoreline is therefore
• 53:45
  Speaker 1: the echo of an old fracture, healed and breathing slowly.
• 53:51
  Speaker 1: Beyond volcanic arcs that guard the edges of many oceans,
• 53:56
  Speaker 1: another kind of basin can form. When an oceanic plate
• 53:59
  Speaker 1: sinks into the mantle, the slab can roll back towards
• 54:03
  Speaker 1: the sea. As it does, the area behind the volcanic
• 54:07
  Speaker 1: arc can stretch. That stretching opens a back-arc basin. In
• 54:13
  Speaker 1: the floor of such a basin, seafloor spreading can occur
• 54:17
  Speaker 1: on a small scale. There are ridges and vents, much
• 54:21
  Speaker 1: like those in the great mid-ocean belts, but here they
• 54:25
  Speaker 1: sit behind a line of volcanoes that are fed by
• 54:30
  Speaker 1: water released from the sinking slab. The crust in back-arc
• 54:36
  Speaker 1: regions is often thin, The basins can be temporary seas
• 54:42
  Speaker 1: whose outlines shift as the subducting slab changes angle and speed.
• 54:49
  Speaker 1: The chemistry of rocks in these basins tells of mixed influences.
• 54:54
  Speaker 1: Some lavas resemble mid-ocean basalt, others carry the flavour of
• 54:59
  Speaker 1: arc magmas that rose nearby. Hydrothermal vents here also host
• 55:05
  Speaker 1: life that thrives on chemical energy. The vents can enrich
• 55:09
  Speaker 1: the sea floor with unique mineral deposits that grow in
• 55:12
  Speaker 1: black chimneys where hot water meets cold ocean. The geography
• 55:17
  Speaker 1: of the basin is restless in a slow way. Spreading
• 55:21
  Speaker 1: may start and stop. Faults rise and die. Islands appear,
• 55:27
  Speaker 1: link and divide again. It is a world that records
• 55:32
  Speaker 1: both tension and compression. an inland echo of the greater
• 55:36
  Speaker 1: meeting of plates at the trench. Return now to the
• 55:40
  Speaker 1: very front of that meeting. At the trench where an
• 55:44
  Speaker 1: ocean plate descends, soft sediment on the sea floor is
• 55:48
  Speaker 1: not always pulled down smoothly. Much of it is scraped
• 55:53
  Speaker 1: off and piled into a wedge that leans landward. This
• 55:57
  Speaker 1: wedge is an accretionary prism. It grows by small additions,
• 56:03
  Speaker 1: layer after layer, as mud and sand are thrust upward
• 56:07
  Speaker 1: along gently dipping faults. Inside the prism, slices of old
• 56:12
  Speaker 1: seafloor and slumped sediment are folded and pressed together. Fluids
• 56:17
  Speaker 1: freed from the sinking crust rise through the wedge. They
• 56:21
  Speaker 1: reduce friction and help the layers glide. Now and then
• 56:25
  Speaker 1: the fluids reach the surface at cold seeps where communities
• 56:30
  Speaker 1: of clams and tubeworms gather to harvest chemical energy from
• 56:36
  Speaker 1: methane that leaks from the sediment. Mud volcanoes build gentle
• 56:42
  Speaker 1: cones where slurry oozes and dries, then oozes again. An
• 56:48
  Speaker 1: accretionary prism looks chaotic from the outside, but there is
• 56:53
  Speaker 1: an order in its growth. Each new slice pushes the
• 56:57
  Speaker 1: older ones upward and landward. The wedge finds an angle
• 57:01
  Speaker 1: that lets it barely resist sliding, and then keeps that
• 57:05
  Speaker 1: angle as it grows. It is like a pile of
• 57:08
  Speaker 1: damp sand at the foot of a board. Add a
• 57:12
  Speaker 1: little more and part of the pile slips, keeping the
• 57:15
  Speaker 1: slope nearly the same. The prism records earthquakes too. Some
• 57:20
  Speaker 1: faults inside it creep slowly, others lock and then slip
• 57:27
  Speaker 1: in a sudden shiver. The wedge rises grain by grain
• 57:32
  Speaker 1: over the ages, a slow construction project at the edge
• 57:37
  Speaker 1: of the world. On the other side of a rising
• 57:40
  Speaker 1: mountain belt, the weight of rock bends the crust downward
• 57:44
  Speaker 1: to make a long basin that hugs the range. This
• 57:49
  Speaker 1: is a foreland basin, a place where rivers carry the
• 57:52
  Speaker 1: gifts of the mountains and lay them down in thick packages.
• 57:58
  Speaker 1: Coarse fans of gravel spill from canyon mouths and grade
• 58:02
  Speaker 1: into broad plains of sand and silt. Farther out Lakes
• 58:07
  Speaker 1: and shallow seas come and go as the basin deepens
• 58:11
  Speaker 1: or fills. The load of new sediment makes the crust
• 58:14
  Speaker 1: sag a little more, which invites more sediment. The basin
• 58:19
  Speaker 1: migrates as the wedge of mountains grows and shifts. In
• 58:23
  Speaker 1: the rock record, the result can be a grand alternation. First,
• 58:28
  Speaker 1: deep water muds and sand, rich in marine fossils, lay
• 58:33
  Speaker 1: down while the basin was deep and quiet. Then, As
• 58:37
  Speaker 1: the mountains delivered more and more material, the basin shallowed
• 58:42
  Speaker 1: and was filled by river plains and deltas. The sequence
• 58:46
  Speaker 1: is a story of burden and response. These basins preserve
• 58:51
  Speaker 1: the blush of a mountain in youth. Pebbles show which
• 58:55
  Speaker 1: valleys were active. Sand grains record the kinds of rocks
• 58:59
  Speaker 1: being eroded. Paleosols mark pauses when the landscape breathed and
• 59:05
  Speaker 1: plants covered a floodplain. Coal seams tell of swamps. that
• 59:10
  Speaker 1: were drowned and buried. When we read this book of layers,
• 59:14
  Speaker 1: we see the mountain not just as a peak but
• 59:18
  Speaker 1: as a source, a fountain in stone whose waters are
• 59:21
  Speaker 1: sands and clays that flow outward and settle in patience.
• 59:28
  Speaker 1: Not all subduction dips steeply. In some settings, the sinking
• 59:33
  Speaker 1: plate glides beneath the continent at a shallow angle for
• 59:37
  Speaker 1: a long distance before it finally sinks deeper. This is
• 59:41
  Speaker 1: flat slab subduction. The shallow geometry increases the contact between
• 59:47
  Speaker 1: the plates and transfers compression far inland. Volcanism that would
• 59:52
  Speaker 1: normally mark a neat arc can be muted or shifted
• 59:56
  Speaker 1: far from the trench. The surface response can include broad
• 1:00:00
  Speaker 1: uplifts and the rise of ranges in places that might
• 1:00:04
  Speaker 1: otherwise have remained quiet. Rivers that crossed a plain may
• 1:00:09
  Speaker 1: now meet low ridges set athwart their path. The entire
• 1:00:14
  Speaker 1: region takes on the air of gentle pressure applied by
• 1:00:18
  Speaker 1: an unseen hand. Flat slabs may carry topographic features of
• 1:00:24
  Speaker 1: the ocean floor with them. If a buoyant plateau or
• 1:00:28
  Speaker 1: a chain of seamounts approaches the trench, it can resist
• 1:00:32
  Speaker 1: sinking and help hold the slab flat for a time.
• 1:00:36
  Speaker 1: Where such features pass under the continent, they can crumple
• 1:00:40
  Speaker 1: the crust above. and change fluid pathways. After the buoyant
• 1:00:45
  Speaker 1: feature passes, the slab can steepen again, and the volcanic
• 1:00:50
  Speaker 1: arc may reawaken in a new position. The silence and
• 1:00:55
  Speaker 1: speech of volcanoes in these settings are part of a
• 1:00:59
  Speaker 1: careful dialogue between geometry, density, and water. Sometimes the subducting
• 1:01:06
  Speaker 1: plate tears. A spreading ridge can also run into the
• 1:01:10
  Speaker 1: trench and be pulled under, leaving behind a gap in
• 1:01:14
  Speaker 1: the sinking slab. This creates a window. Through such a window,
• 1:01:19
  Speaker 1: warm mantle can flow upward into places that were once
• 1:01:23
  Speaker 1: shaded by the cold slab. The change in heat and
• 1:01:28
  Speaker 1: flow can spark unusual volcanism on the overriding plate. Rocks
• 1:01:34
  Speaker 1: erupted above a slab window can look different from typical
• 1:01:38
  Speaker 1: arc lavas. They can include magmas more like those at
• 1:01:42
  Speaker 1: mid-ocean ridges, mixed with melts of continental crust. Heat flow
• 1:01:48
  Speaker 1: at the surface may rise. Springs may change their chemistry.
• 1:01:53
  Speaker 1: In some regions, the track of a subducted ridge is
• 1:01:57
  Speaker 1: marked by a band of volcanic centres that do not
• 1:02:01
  Speaker 1: fit the usual arc pattern. Their position and age march
• 1:02:06
  Speaker 1: along in step with the imagined path of the window.
• 1:02:11
  Speaker 1: Geologists trace these hidden architectural changes with many clues. Seismic
• 1:02:17
  Speaker 1: waves show where the slab is present and where it fades.
• 1:02:22
  Speaker 1: The age of volcanic rocks traces the migration of heat sources.
• 1:02:27
  Speaker 1: Gravity and magnetics reveal buried ridges and plateaus that once
• 1:02:33
  Speaker 1: rode the plate into darkness. It is a reminder that
• 1:02:37
  Speaker 1: the surface is a calm room built on a shifting framework.
• 1:02:41
  Speaker 1: A missing wall in that framework lets a different breeze
• 1:02:45
  Speaker 1: move through. Mountains do more than tower. They change the
• 1:02:50
  Speaker 1: air and the long, slow cycle of carbon. Fresh rock
• 1:02:54
  Speaker 1: lifted to the sky is exposed to rainwater and to
• 1:02:58
  Speaker 1: the weak acids made by carbon dioxide dissolved in that
• 1:03:02
  Speaker 1: water and by the breath of soils. Silicate minerals react
• 1:03:07
  Speaker 1: and yield ions that rivers carry to the sea. There,
• 1:03:12
  Speaker 1: the ions help build shells and skeletons of marine organisms.
• 1:03:17
  Speaker 1: When those shells settle and become limestone or other carbonate rock,
• 1:03:22
  Speaker 1: a tiny portion of carbon is removed from the air
• 1:03:26
  Speaker 1: and tucked into stone. Over millions of years, this process
• 1:03:31
  Speaker 1: acts like a thermostat. When climates warm and rain falls more,
• 1:03:36
  Speaker 1: weathering can speed up and draw carbon down. When climates
• 1:03:41
  Speaker 1: cool and weathering slows, volcanoes that continue to bring carbon
• 1:03:46
  Speaker 1: from the interior can slowly rebuild the supply in the air.
• 1:03:51
  Speaker 1: The details depend on rock type, temperature, vegetation and the
• 1:03:56
  Speaker 1: way mountains channel clouds. Basalt weathers more quickly than granite.
• 1:04:02
  Speaker 1: Steep slopes deliver fragments faster to rivers. Glaciers grind rock
• 1:04:08
  Speaker 1: into flour that reacts quickly with water in faraway plains
• 1:04:12
  Speaker 1: and coastal seas. Plant roots and microbes release organic acids
• 1:04:18
  Speaker 1: that help break minerals apart and carry the products into streams.
• 1:04:23
  Speaker 1: In some mountain lands with heavy monsoon rains, rivers deliver
• 1:04:28
  Speaker 1: huge loads of dissolved material each season. The effect is
• 1:04:33
  Speaker 1: not a switch that flips year to year. It is
• 1:04:36
  Speaker 1: a balance that plays out over spans that hold many
• 1:04:40
  Speaker 1: ice ages and many summers. Mountains rise and invite reactions.
• 1:04:45
  Speaker 1: The air replies in a soft voice and after a
• 1:04:48
  Speaker 1: long conversation the planet finds another comfort level. Some of
• 1:04:53
  Speaker 1: the most remarkable conversations between water and rock happen deep below,
• 1:05:00
  Speaker 1: where ocean crust and mantle rocks meet sea water along
• 1:05:04
  Speaker 1: faults and fractures. In these places, cold water percolates down
• 1:05:10
  Speaker 1: and meets warm ultramathic rock rich in olivine and pyroxene.
• 1:05:16
  Speaker 1: The water reacts and becomes part of new minerals. The
• 1:05:19
  Speaker 1: rock changes into serpentine, a flaky green mineral that is
• 1:05:23
  Speaker 1: slippery and lower in density. Magnetite can form as iron,
• 1:05:28
  Speaker 1: is rearranged. The reactions release hydrogen and small organic molecules.
• 1:05:34
  Speaker 1: These gases feed microbes that live in the dark, creating
• 1:05:39
  Speaker 1: tiny ecosystems powered by chemistry alone. Serpentinization changes the strength
• 1:05:47
  Speaker 1: of the oceanic plate. It makes some layers softer and
• 1:05:51
  Speaker 1: easier to deform. It can lubricate faults and contribute to
• 1:05:56
  Speaker 1: slow slip events and tremor at the base of subduction zones.
• 1:06:01
  Speaker 1: In some lands where slabs were once thrust up onto
• 1:06:05
  Speaker 1: the continent, slices of old sea floor and mantle rest
• 1:06:10
  Speaker 1: in mountains as ophiolites. Streams that run from these rocks
• 1:06:15
  Speaker 1: can carry the signature of serpentinization. In carefully designed experiments,
• 1:06:21
  Speaker 1: crushed ultramafic rock reacts with water to trap carbon as
• 1:06:27
  Speaker 1: solid carbonates. Nature does this too, slowly, in veins that
• 1:06:32
  Speaker 1: crisscross the rocks with white ribbons. The process suggests a
• 1:06:36
  Speaker 1: patient path by which part of the carbon we release
• 1:06:41
  Speaker 1: might someday be tucked back into Earth, not as gas,
• 1:06:47
  Speaker 1: but as solid stone. There are rocks that tell of
• 1:06:51
  Speaker 1: journeys to depths not usually imagined for continental crust. In
• 1:06:56
  Speaker 1: some mountain belts, metamorphic rocks contain minerals that can only
• 1:07:01
  Speaker 1: form at pressures corresponding to very great depths. Coesite is
• 1:07:07
  Speaker 1: a dense form of quartz that forms when pressure is high.
• 1:07:12
  Speaker 1: Tiny diamonds appear in some rocks that were once part
• 1:07:16
  Speaker 1: of the crust that rode down on top of a
• 1:07:18
  Speaker 1: subducting slab. These are signals of ultra-high pressure metamorphism. To
• 1:07:25
  Speaker 1: see such minerals at the surface, the rocks must have
• 1:07:29
  Speaker 1: returned from depths where they spent only a short time
• 1:07:33
  Speaker 1: in geologic terms. The path Down and back is a riddle.
• 1:07:38
  Speaker 1: One story holds that slices of the crust were carried
• 1:07:42
  Speaker 1: down as part of the top of the slab, and
• 1:07:45
  Speaker 1: then were buoyant enough to return along channels that opened
• 1:07:49
  Speaker 1: as the wedge above them flowed. Another story holds that
• 1:07:54
  Speaker 1: parts of the lower crust detached and rose as the
• 1:07:58
  Speaker 1: surrounding rocks softened The textures in these rocks are like
• 1:08:03
  Speaker 1: hieroglyphs Garnet crystals can trap tiny inclusions of minerals that
• 1:08:09
  Speaker 1: reveal the pressure and temperature at the moment of growth
• 1:08:13
  Speaker 1: Some inclusions show that the rock passed through a stage
• 1:08:17
  Speaker 1: where it held both coesite and more ordinary quartz as
• 1:08:22
  Speaker 1: it rose. The grain boundaries can show how fluids moved,
• 1:08:27
  Speaker 1: healing cracks and making new veins as pressure dropped. The
• 1:08:32
  Speaker 1: ages of different minerals mark the timing of the plunge
• 1:08:36
  Speaker 1: and the return. When we hold such a rock, we
• 1:08:40
  Speaker 1: hold a message from a depth. where continents rarely go,
• 1:08:44
  Speaker 1: it came back slowly, slower than any elevator, yet fast
• 1:08:49
  Speaker 1: enough that its high-pressure forms survived the ascent. All of
• 1:08:54
  Speaker 1: these scenes belong to slow rooms within the same house,
• 1:08:59
  Speaker 1: the quiet shelf that gathers sand, the rift that yawns
• 1:09:03
  Speaker 1: and breathes, the basin behind a volcanic arc, the wedge
• 1:09:08
  Speaker 1: of sediment at the trench, the long trough that leans
• 1:09:12
  Speaker 1: against a range, the broad uplifts born of a hidden
• 1:09:16
  Speaker 1: shallow slab, the hot breeze through a window in a plate,
• 1:09:21
  Speaker 1: the subtle removal of carbon from the sky by water
• 1:09:25
  Speaker 1: and stone, the green alteration of mantle rock that feeds
• 1:09:29
  Speaker 1: life in darkness, and the bright crystals that tell of
• 1:09:33
  Speaker 1: a deep visit and a safe return. Each part moves
• 1:09:38
  Speaker 1: in its own time, Yet all are linked to the
• 1:09:41
  Speaker 1: deep convection that stirs the mantle and to the steady
• 1:09:45
  Speaker 1: pull of gravity that asks mountains to share their heights
• 1:09:50
  Speaker 1: with the sea. As you rest, imagine a shore in softness. twilight,
• 1:09:56
  Speaker 1: waves arrive with no hurry and leave the scent of
• 1:10:00
  Speaker 1: salt in the air. Beyond the horizon, currents glide over
• 1:10:05
  Speaker 1: a burying slope where sand settles beside the skeletons of
• 1:10:09
  Speaker 1: tiny drifting creatures. Inland, a valley deepens by a finger's
• 1:10:15
  Speaker 1: width in a century as a rift opens. Far away,
• 1:10:19
  Speaker 1: behind an arc of volcanoes, a small sea grows by
• 1:10:23
  Speaker 1: the breadth of the mantle. At the great front where
• 1:10:26
  Speaker 1: a plate descends, a wedge of mud takes one more
• 1:10:31
  Speaker 1: slice and slides a little higher. In the lee of
• 1:10:35
  Speaker 1: a rising belt, a plane waits to receive the next
• 1:10:39
  Speaker 1: season of gravel and silt. Under the continent, a slab
• 1:10:44
  Speaker 1: moves for a while as a flattened guest before plunging,
• 1:10:48
  Speaker 1: and a pause in the voice of volcanoes allows cool
• 1:10:51
  Speaker 1: mornings to settle on distant fields. Through a tear in
• 1:10:56
  Speaker 1: the slab, warmth finds a path and writes a new
• 1:11:00
  Speaker 1: line of vents across old hills. Clouds gather around a
• 1:11:04
  Speaker 1: range where fresh rock meets rain and returns a little
• 1:11:08
  Speaker 1: carbon to the sea. On a ridge in the ocean,
• 1:11:12
  Speaker 1: deep water meets peridotite and makes a green mineral and
• 1:11:17
  Speaker 1: a little hydrogen. In a valley of high mountains, a
• 1:11:21
  Speaker 1: rock with a tiny diamond sleeps near a path where
• 1:11:25
  Speaker 1: sheep walk in summer. Let your breath move as slowly
• 1:11:30
  Speaker 1: as these scenes. The planet will keep writing while you sleep.
• 1:11:35
  Speaker 1: Shelves will thicken. Rifts will widen. Wedges will grow. Planes
• 1:11:40
  Speaker 1: will deepen. Slabs will change their angle. Windows will open
• 1:11:45
  Speaker 1: and close. Rivers will wash fresh ions to the sea.
• 1:11:50
  Speaker 1: Serpentine will become a quilt in the deepest places, and
• 1:11:55
  Speaker 1: bright crystals that once formed in the dark will wait
• 1:11:59
  Speaker 1: in sunlight for gentle hands to find them. In the
• 1:12:03
  Speaker 1: morning nothing will look different, and everything will be a
• 1:12:06
  Speaker 1: little changed, carried forward by processes that do not rush
• 1:12:11
  Speaker 1: and never tire. Deep in the roots of some mountain belts,
• 1:12:15
  Speaker 1: there is a heavy secret that the peaks carry for
• 1:12:19
  Speaker 1: a while and then quietly let go. When crust is
• 1:12:23
  Speaker 1: thickened during collision, it pushes deep into the upper mantle
• 1:12:27
  Speaker 1: and forms a bulb of cold, dense rock. Over time,
• 1:12:33
  Speaker 1: that root can become denser still as minerals reorganise under
• 1:12:37
  Speaker 1: pressure and as the base cools. If it grows heavy
• 1:12:41
  Speaker 1: enough compared with the warmer material around it, the root
• 1:12:45
  Speaker 1: can begin to sag. It stretches and narrows, and then
• 1:12:50
  Speaker 1: drops away like a slow tear sliding from a ledge.
• 1:12:53
  Speaker 1: This is delamination. The falling piece sinks into the mantle,
• 1:12:58
  Speaker 1: and warm, buoyant material flows upward to fill the space
• 1:13:03
  Speaker 1: it leaves behind. At the surface, the mountains feel lighter.
• 1:13:08
  Speaker 1: Valleys deepen as rivers respond to new gradients. Springs grow
• 1:13:13
  Speaker 1: warmer in some places as heat finds new paths. Volcanism
• 1:13:19
  Speaker 1: may return in a different flavour because the source region
• 1:13:22
  Speaker 1: feeding melts has changed. In some ranges you can read
• 1:13:27
  Speaker 1: the story in a rise that comes long after collision
• 1:13:32
  Speaker 1: should have ended. and in young lavas that carry crystals
• 1:13:36
  Speaker 1: from deep sources that were once hidden by the heavy root.
• 1:13:41
  Speaker 1: Delamination can happen in drips or in sheets. A small
• 1:13:45
  Speaker 1: patch of dense rock can peel away and sink like
• 1:13:49
  Speaker 1: a slow raindrop falling from a ceiling. Other times, a
• 1:13:53
  Speaker 1: larger region detaches along a weak layer and slides downward
• 1:13:57
  Speaker 1: as a broad slab. The signs are subtle. Seismic waves
• 1:14:02
  Speaker 1: reveal where the lower crust has thinned and where a
• 1:14:06
  Speaker 1: cool tongue of high-velocity rock has vanished. Gravity maps show
• 1:14:11
  Speaker 1: where a buried load once pulled the surface downward. River
• 1:14:16
  Speaker 1: terraces climb like old steps on the sides of valleys
• 1:14:20
  Speaker 1: where uplift accelerated. Forests colonize new zones as snow lines
• 1:14:26
  Speaker 1: lift a little higher No one sees the root fall.
• 1:14:30
  Speaker 1: The story is inferred from the whispers the surface makes
• 1:14:34
  Speaker 1: as it adjusts, from the chemistry of young magmas, and
• 1:14:39
  Speaker 1: from the quiet arithmetic of incision rates that rise and
• 1:14:44
  Speaker 1: then relax as the landscape finds its new balance. Not
• 1:14:49
  Speaker 1: every mountain core is a solid block that simply rises
• 1:14:53
  Speaker 1: or falls. In some belts the middle crust behaves like
• 1:14:57
  Speaker 1: warm taffy sandwiched between a strong lid above and a
• 1:15:02
  Speaker 1: strong base below. The heat that builds during thickening softens
• 1:15:07
  Speaker 1: this mid-crust. Under the load of a plateau, the soft
• 1:15:12
  Speaker 1: layer can begin to flow sideways toward places where the
• 1:15:16
  Speaker 1: lid is thinner and the surface is lower. As it moves,
• 1:15:20
  Speaker 1: it carries with it rocks that were heated and pressed
• 1:15:24
  Speaker 1: into new forms deep below. These rocks rise along channels
• 1:15:29
  Speaker 1: that act like hidden rivers within the crust. The surface
• 1:15:33
  Speaker 1: above responds by stretching. Large low-angle faults can form that
• 1:15:40
  Speaker 1: let the hot middle rise while the cooler lid slides away.
• 1:15:45
  Speaker 1: Where these faults reach the surface, domes of shimmering metamorphic
• 1:15:50
  Speaker 1: rock appear, ringed by broken blocks of the old lid
• 1:15:54
  Speaker 1: that was peeled back. Geologists call such places metamorphic core complexes.
• 1:16:01
  Speaker 1: their windows into a level of the crust that usually
• 1:16:06
  Speaker 1: stays out of sight. The textures in these risen cores
• 1:16:10
  Speaker 1: are silky with aligned minerals that grew during flow. Mikas
• 1:16:15
  Speaker 1: glitter in planes that once slipped past each other, grain
• 1:16:19
  Speaker 1: by grain. Garnet porphyroblasts sit like berries in a cake,
• 1:16:25
  Speaker 1: holding tiny inclusions of quartz and feldspar, that mark the
• 1:16:30
  Speaker 1: path the rock took as it rose and cooled. Radiometric
• 1:16:35
  Speaker 1: clocks in different minerals record different moments on that journey.
• 1:16:40
  Speaker 1: One tells when the rock cooled through a temperature where
• 1:16:44
  Speaker 1: a certain element could no longer move between crystals. Another
• 1:16:50
  Speaker 1: tells when the last high-pressure mineral broke down into a
• 1:16:54
  Speaker 1: lower-pressure form during ascent. Put together, the clocks reveal a
• 1:17:00
  Speaker 1: rise that can be surprisingly quick in geologic time, measured
• 1:17:05
  Speaker 1: in a few million years, guided by the interplay of
• 1:17:09
  Speaker 1: erosion that removes weight at the surface and extension that
• 1:17:14
  Speaker 1: opens a path from below. The landscape that wraps these
• 1:17:18
  Speaker 1: domes often holds long low ridges and wide basins, as
• 1:17:24
  Speaker 1: if the crust sighed and stretched while the warm core
• 1:17:28
  Speaker 1: came up to breathe. When a mountain system grows so
• 1:17:32
  Speaker 1: broad that its interior is far from the edges where
• 1:17:36
  Speaker 1: compression acts, it can rise into a plateau that seems
• 1:17:40
  Speaker 1: to float near the sky. These are orogenic plateaus. They
• 1:17:44
  Speaker 1: are made first by crustal thickening as blocks are stacked
• 1:17:50
  Speaker 1: and burrowed one under another. Later, given enough heat, the
• 1:17:54
  Speaker 1: lower parts can flow sideways like slow cream under a skin.
• 1:17:59
  Speaker 1: The result is a great tableland with margins that are
• 1:18:03
  Speaker 1: still being built, and an interior that is flat in
• 1:18:07
  Speaker 1: the very large view, though it holds its own ranges
• 1:18:12
  Speaker 1: and basins. On such a plateau, the air is thin
• 1:18:16
  Speaker 1: and the sun is sharp. Lakes gather in closed basins
• 1:18:21
  Speaker 1: because rivers that start in the interior often do not
• 1:18:25
  Speaker 1: reach the sea. In the day, the shadows of clouds
• 1:18:29
  Speaker 1: slide over distances that take hours to cross on foot.
• 1:18:33
  Speaker 1: At night, the cold is close because the air holds
• 1:18:37
  Speaker 1: little water. The wind has a long reach. Plateaus influence
• 1:18:42
  Speaker 1: winds on a continental scale. A tall hot deck in
• 1:18:46
  Speaker 1: summer draws moist air inward from the surrounding seas. and
• 1:18:50
  Speaker 1: helps steer seasonal rains. In winter, the deck becomes a
• 1:18:55
  Speaker 1: cold roof that pushes air outward. The margins of a
• 1:18:59
  Speaker 1: plateau become bands where rains gather and release on one
• 1:19:03
  Speaker 1: side and dry shadows form on the other. The plateau
• 1:19:09
  Speaker 1: also bears the marks of gravity that never rests. Where
• 1:19:13
  Speaker 1: it grows too high, it spreads under its own weight
• 1:19:17
  Speaker 1: and makes extensional basins along its edges. Where the deep
• 1:19:21
  Speaker 1: root grows too dense, it may be removed by delamination
• 1:19:26
  Speaker 1: and the surface above rises in a broad swell. Volcanoes
• 1:19:31
  Speaker 1: can dot the margins where mantle flow and crustal flow
• 1:19:35
  Speaker 1: meet in complicated ways. The story is not one of
• 1:19:40
  Speaker 1: a rigid table, but of a living tablecloth that shifts
• 1:19:45
  Speaker 1: under the slow pressure of deep currents and the constant
• 1:19:48
  Speaker 1: shaving of wind and water. Rivers that drain landscapes like
• 1:19:53
  Speaker 1: these have their own agendas. A river cuts downward where
• 1:19:58
  Speaker 1: fall increases and it widens its valley where fall decreases.
• 1:20:03
  Speaker 1: Headward erosion lets a river extend its reach upstream into
• 1:20:08
  Speaker 1: the territory of another. When one river gains more energy,
• 1:20:12
  Speaker 1: perhaps because of uplift in its lower course or because
• 1:20:16
  Speaker 1: base level has fallen at the coast, It can gnaw
• 1:20:19
  Speaker 1: its way through a divide and steal the headwaters of
• 1:20:23
  Speaker 1: a neighbor. This is river capture. The result is a
• 1:20:28
  Speaker 1: sudden change in the map of drainage that leaves behind
• 1:20:32
  Speaker 1: curious features for those who move slowly enough to notice.
• 1:20:37
  Speaker 1: There may be a dry valley that once carried a
• 1:20:40
  Speaker 1: stream called a wind gap, now a gentle saddle crossed
• 1:20:46
  Speaker 1: by deer and hikers. There may be a sharp elbow
• 1:20:50
  Speaker 1: bend where a river left its old bed and found
• 1:20:54
  Speaker 1: a shorter path. There may be a small stream that
• 1:20:58
  Speaker 1: flows in the wrong direction given the tilt of the
• 1:21:01
  Speaker 1: land because it is a remnant of the old network.
• 1:21:07
  Speaker 1: Capture changes life along the banks. Fish that lived in
• 1:21:12
  Speaker 1: one system find themselves connected to another. Sediment that once
• 1:21:17
  Speaker 1: fed a delta now feeds a different reach. Terraces cut
• 1:21:21
  Speaker 1: by the old flow hang above the new one like
• 1:21:24
  Speaker 1: quiet viewing platforms. The reasons for capture are many. Tectonic
• 1:21:29
  Speaker 1: tilt can give one river an advantage. Differences in rock
• 1:21:34
  Speaker 1: type make one basin erode faster. A glacier can plug
• 1:21:38
  Speaker 1: a valley and force a river to spill over a divide,
• 1:21:42
  Speaker 1: rebound after ice, lifts one region and drops another. The
• 1:21:48
  Speaker 1: proof that capture occurred lies in the geometry of valleys
• 1:21:52
  Speaker 1: and the ages of surfaces, in cobbles that do not
• 1:21:56
  Speaker 1: match their host basin, and in low divides where a
• 1:22:00
  Speaker 1: small headwater has reached far into ground it did not
• 1:22:04
  Speaker 1: own a million years ago. It is the gentle theft
• 1:22:08
  Speaker 1: of water written on landscapes that sleep and wake by millimeters.
• 1:22:14
  Speaker 1: Where land meets sea, shore platforms cut by waves can
• 1:22:19
  Speaker 1: be lifted in small increments to become terraces. The sea
• 1:22:24
  Speaker 1: makes a broad flat at the foot of a cliff
• 1:22:27
  Speaker 1: when waves attack it again and again. As sea level
• 1:22:31
  Speaker 1: changes with the breathing of ice sheets, the active platform
• 1:22:36
  Speaker 1: moves up If the land is also rising because of
• 1:22:41
  Speaker 1: tectonic uplift or rebound after ice, each still stand in
• 1:22:46
  Speaker 1: sea level or each return to a similar level can
• 1:22:49
  Speaker 1: leave another step in the staircase. Seen from the air,
• 1:22:54
  Speaker 1: these terraces are graceful arcs that mirror the coast, each
• 1:22:59
  Speaker 1: one a quiet memory of a time when waves paused there.
• 1:23:04
  Speaker 1: Corals that grew on warm platforms can be dated with
• 1:23:08
  Speaker 1: uranium series methods to anchor the story in time. Cosmogenic
• 1:23:14
  Speaker 1: nuclides in surface rocks can reveal how long a terrace
• 1:23:18
  Speaker 1: has sat in the sun. The spacing between steps records
• 1:23:23
  Speaker 1: the pace of uplift against the rhythms of the sea.
• 1:23:26
  Speaker 1: The terraces do more than mark motion. They stabilize slopes
• 1:23:31
  Speaker 1: and give people places to live. and plant. They hold
• 1:23:35
  Speaker 1: soils that formed over long ages and that carry the
• 1:23:40
  Speaker 1: imprint of ancient climates. They preserve shells and pebbles from
• 1:23:45
  Speaker 1: beaches that no longer feel waves. Earthquakes can lift a
• 1:23:49
  Speaker 1: coastal reach by the height of a person in a
• 1:23:52
  Speaker 1: single event and leave an abrupt new step. Slow uplift
• 1:23:58
  Speaker 1: can raise a terrace by the thickness of a fingernail
• 1:24:01
  Speaker 1: each year. Put together across many cycles, a climb of
• 1:24:06
  Speaker 1: several hundred metres becomes a quiet staircase that looks down
• 1:24:12
  Speaker 1: on the present shore. To trace the line of old
• 1:24:15
  Speaker 1: wave notches under an evening sky is to walk with
• 1:24:19
  Speaker 1: the sea as it goes upstairs and downstairs through time.
• 1:24:26
  Speaker 1: Faults that carry plates do not always release their motion
• 1:24:31
  Speaker 1: with a sudden jolt. In some regions deep along the
• 1:24:34
  Speaker 1: plate boundary, a slow slip event will occur. The two
• 1:24:39
  Speaker 1: sides of the fault move by a few centimetres over
• 1:24:43
  Speaker 1: weeks or months without sending strong shaking to the surface.
• 1:24:48
  Speaker 1: This motion is often accompanied by a low, continuous tremor
• 1:24:53
  Speaker 1: that sounds to instruments like rain on a distant roof.
• 1:24:57
  Speaker 1: The event repeats at intervals that may be roughly regular.
• 1:25:02
  Speaker 1: Scientists have observed such cycles along subduction zones and watch
• 1:25:08
  Speaker 1: them to understand how strain accumulates and is released. The
• 1:25:13
  Speaker 1: slow slip does not remove all stress from the shallower,
• 1:25:17
  Speaker 1: locked portion of the fault It may load that patch
• 1:25:22
  Speaker 1: and affect the timing of the next earthquake there. The
• 1:25:27
  Speaker 1: system breathes quietly in the deep, then occasionally coughs near
• 1:25:33
  Speaker 1: the surface. On some continental strike, slip faults a different
• 1:25:39
  Speaker 1: quiet motion occurs. Parts of the fault never lock fully,
• 1:25:44
  Speaker 1: they creep. Over years, survey markers across such a fault
• 1:25:48
  Speaker 1: show steady offset. Curbs and walls crack and move like
• 1:25:53
  Speaker 1: slow chalk lines. The creep can be fastest on clay-rich
• 1:25:58
  Speaker 1: or serpentinized sections that are weak, even at low pressure.
• 1:26:03
  Speaker 1: Where a creeping segment meets a locked one, stress can change.
• 1:26:08
  Speaker 1: The locked part may be brought closer to failure by
• 1:26:11
  Speaker 1: the gentle push next door. In the laboratory, rocks under
• 1:26:16
  Speaker 1: controlled humidity and pressure sometimes slide in small leaps that
• 1:26:22
  Speaker 1: repeat like a heartbeat. In the field, networks of instruments
• 1:26:27
  Speaker 1: aim to catch these patterns to help understand how large
• 1:26:31
  Speaker 1: ruptures begin. The lesson for our evening is simply that
• 1:26:35
  Speaker 1: faults have many voices. Some are whispers in a constant murmur.
• 1:26:41
  Speaker 1: Some are soft songs that return each season. Some are
• 1:26:45
  Speaker 1: calls that come rarely and change a valley in a minute.
• 1:26:50
  Speaker 1: Deep within sediments and fractured rocks, fluids move with their
• 1:26:55
  Speaker 1: own slow agency. Organic matter buried in basins turns into
• 1:27:00
  Speaker 1: oil and gas as it is heated and compressed. The
• 1:27:03
  Speaker 1: liquids and gases migrate along layers and up faults, gathering
• 1:27:09
  Speaker 1: in traps beneath seals of shale or evaporate. Over geologic
• 1:27:14
  Speaker 1: time they leak from those traps and are renewed as
• 1:27:18
  Speaker 1: new layers are buried and cooked. Where migration reaches the
• 1:27:22
  Speaker 1: sea floor without fiery heat, cold seeps form. Methane and
• 1:27:29
  Speaker 1: other gases bubble out of sediments rich in shells of
• 1:27:32
  Speaker 1: tiny creatures that were laid down in quiet water. Bacteria
• 1:27:37
  Speaker 1: in the seep environment use methane and sulfur to make food.
• 1:27:42
  Speaker 1: Larger animals host these microbes inside their tissues and farm them.
• 1:27:47
  Speaker 1: The community glows pale in the light of a submersible
• 1:27:51
  Speaker 1: white clams, tube worms, soft mats of bacteria covering the
• 1:27:57
  Speaker 1: sediment like frost. The chemistry of fluids builds rock here too.
• 1:28:02
  Speaker 1: Carbonate cements grow where methane is consumed, turning soft mud
• 1:28:08
  Speaker 1: into crusts and chimneys. The seeps wink on and off
• 1:28:13
  Speaker 1: as pressure and flow change in hidden layers below. On
• 1:28:18
  Speaker 1: continental slopes, gas hydrates are common. These are ice-like crystals
• 1:28:24
  Speaker 1: of water that cage molecules of methane. They are stable
• 1:28:28
  Speaker 1: in cold conditions under pressure. Hydrates store more carbon than
• 1:28:33
  Speaker 1: many forests. They line pores in sediments like delicate frost.
• 1:28:38
  Speaker 1: When water warms or pressure drops, hydrates can dissolve and
• 1:28:42
  Speaker 1: release gas that moves upward. Sometimes the rising gas makes
• 1:28:47
  Speaker 1: pockmarks on the sea floor where sediment was expelled. Mud
• 1:28:52
  Speaker 1: volcanoes can form where pressurized mixtures of water and sediment
• 1:28:57
  Speaker 1: find a path. Over very long timescales, these deep fluids
• 1:29:02
  Speaker 1: act as travellers who carry chemical stories from deep basins
• 1:29:07
  Speaker 1: to the ocean and back into rocks. They can grease
• 1:29:12
  Speaker 1: faults and help them slip slowly. They can also strengthen
• 1:29:17
  Speaker 1: rocks by cementing pores. It is a quiet commerce between
• 1:29:22
  Speaker 1: layers that never see the sun. In some basins, a
• 1:29:26
  Speaker 1: very different material shapes the subsurface and even the surface
• 1:29:32
  Speaker 1: over millions of years. Salt is strong grain by grain,
• 1:29:36
  Speaker 1: but in layers many hundreds of meters thick, it can
• 1:29:39
  Speaker 1: flow under pressure like a very slow liquid. As new
• 1:29:43
  Speaker 1: sediment pours in and pushes down unevenly, the salt moves
• 1:29:49
  Speaker 1: away from areas of greater load and rises where the
• 1:29:52
  Speaker 1: load is light. It begins to form pillars and walls
• 1:29:57
  Speaker 1: called diapirs. These climb through younger sediments and can reach
• 1:30:01
  Speaker 1: near the surface. Their crowns may push up ridges and
• 1:30:05
  Speaker 1: create a pattern of small basins and highs that control
• 1:30:09
  Speaker 1: where rivers wander and where deltas choose to deposit. On
• 1:30:14
  Speaker 1: images that show the subsurface, the salt looks like bright
• 1:30:18
  Speaker 1: streams of toothpaste, smooth, and coherent compared with the layered
• 1:30:24
  Speaker 1: sediments it invades. Where a diapir nears the surface, groundwater
• 1:30:29
  Speaker 1: reacts with the salt and forms a cap of gypsum
• 1:30:33
  Speaker 1: and anhydrite and limestone that protects the mass below. This
• 1:30:38
  Speaker 1: cap rock can host caves and springs. Over time, if
• 1:30:43
  Speaker 1: the cap is breached, dissolution can make sinkholes that appear
• 1:30:47
  Speaker 1: without warning in quiet fields. Offshore, salt forms long walls
• 1:30:53
  Speaker 1: that channel the pathways of migrating oil and gas. Traps
• 1:30:58
  Speaker 1: form where layers bend over the salt and where faults
• 1:31:02
  Speaker 1: cut and seal against it. Engineers and geologists read these
• 1:31:08
  Speaker 1: shapes to find resources, but under all of that, the
• 1:31:12
  Speaker 1: simple physics is soothing. A material that is less dense
• 1:31:17
  Speaker 1: and more mobile rises through a stack of heavier, stiffer
• 1:31:21
  Speaker 1: layers as the pile above changes weight. The surface shows
• 1:31:27
  Speaker 1: the ripples as gentle ridges and troughs on which forests
• 1:31:32
  Speaker 1: grow and herons hunt. Beneath such dynamics lie blocks of
• 1:31:37
  Speaker 1: crust that have changed little for billions of years. These
• 1:31:42
  Speaker 1: are cratons. Their exposed parts are shields that hold old
• 1:31:47
  Speaker 1: rocks like gneiss and granite and greenstone belts that record
• 1:31:51
  Speaker 1: volcanic arcs and oceanic crust from the Archean Aeon. The
• 1:31:58
  Speaker 1: deep roots of cratons extend far into the mantle. They
• 1:32:02
  Speaker 1: are made of mantle rock that has been depleted by
• 1:32:06
  Speaker 1: ancient melting. That depletion makes the rock lighter and stronger
• 1:32:10
  Speaker 1: than normal mantle. The result is a keel that stabilises
• 1:32:15
  Speaker 1: the crust above it. Diamonds ride to the surface in
• 1:32:19
  Speaker 1: rare fast magmas that come from these depths. They bring
• 1:32:24
  Speaker 1: tiny crystals of the deep mantle with them, gems and
• 1:32:28
  Speaker 1: grains that tell of pressures far beyond those in ordinary rocks.
• 1:32:35
  Speaker 1: Shields wear their age on the surface too. They hold
• 1:32:39
  Speaker 1: belts of banded iron that formed long before oxygen flooded
• 1:32:43
  Speaker 1: the oceans. They hold traces of old rivers that ran
• 1:32:48
  Speaker 1: across plains where mountains no longer exist. They hold stable
• 1:32:53
  Speaker 1: platforms where sedimentary rocks lie flat and quiet over the
• 1:32:59
  Speaker 1: old basement. In these lands, very old faults can be
• 1:33:03
  Speaker 1: traced for hundreds of kilometres, not because they move today,
• 1:33:08
  Speaker 1: but because they mark contrasts in the very skeleton of
• 1:33:12
  Speaker 1: the continent. The stability of cratons makes them the cores
• 1:33:17
  Speaker 1: around which supercontinents gather. When plates rearrange, the cratons usually survive.
• 1:33:24
  Speaker 1: They are the elders at the fire, while younger lands
• 1:33:28
  Speaker 1: come and go. Under all plates there is a boundary
• 1:33:32
  Speaker 1: that separates the cooler, strong lid from the warmer, softer
• 1:33:37
  Speaker 1: layer that convects. This is the boundary between lithosphere and asthenosphere.
• 1:33:43
  Speaker 1: It is not a sharp wall, but a zone where temperature,
• 1:33:47
  Speaker 1: water content and grain size change how rocks deform. In
• 1:33:52
  Speaker 1: oceanic regions, the thickness of the lithosphere grows with the
• 1:33:56
  Speaker 1: square root of age as the plate cools while it
• 1:34:00
  Speaker 1: moves away from the ridge where it was formed. Seismic
• 1:34:05
  Speaker 1: waves that pass at different angles and frequencies can sense
• 1:34:10
  Speaker 1: a zone of lower velocity that often lies just below
• 1:34:14
  Speaker 1: the plate. Electrical measurements detect a layer that conducts more
• 1:34:20
  Speaker 1: easily than the rocks above. Many lines of evidence suggest
• 1:34:25
  Speaker 1: that in this zone small amounts of melt or a
• 1:34:28
  Speaker 1: bit more water or simply warmer temperatures make the rock softer.
• 1:34:35
  Speaker 1: The plate can glide over this smooth layer as if
• 1:34:38
  Speaker 1: on a film of warm wax. Beneath continents the lithosphere
• 1:34:43
  Speaker 1: is thicker in some places and thinner in others. Under
• 1:34:47
  Speaker 1: cratons it is very thick and cool, perhaps two or
• 1:34:52
  Speaker 1: three times thicker than the oceanic lithosphere near ridges. Under
• 1:34:57
  Speaker 1: rifts and young belts it can be thinned and warmed,
• 1:35:01
  Speaker 1: and magmas can rise along the thinned zones. In some places,
• 1:35:06
  Speaker 1: the base of the lithosphere may drip downward, where it
• 1:35:10
  Speaker 1: grows dense, much like the delamination of crustal roots above.
• 1:35:15
  Speaker 1: The boundary breathes in geological time. When the base is warmed,
• 1:35:21
  Speaker 1: the surface rises a little. When it cools, the surface settles.
• 1:35:26
  Speaker 1: When water is removed by melting or added by fluids
• 1:35:30
  Speaker 1: from below, the strength of the base changes. To imagine
• 1:35:34
  Speaker 1: a plate is to imagine a raft with a slippery
• 1:35:38
  Speaker 1: bottom moving over a deep, slow river. The raft can
• 1:35:43
  Speaker 1: crack and bend and carry mountains, but its underside slides
• 1:35:47
  Speaker 1: because the layer below is warm and forgiving. Let these
• 1:35:51
  Speaker 1: scenes assemble now into one gentle panorama. A mountain sheds
• 1:35:57
  Speaker 1: its heavy roots and rises by a whisper as the
• 1:36:00
  Speaker 1: deep burden falls away. A warm middle layer flows and
• 1:36:05
  Speaker 1: carries crystals upward to make a dome that shimmers in
• 1:36:09
  Speaker 1: sun and rain. A broad plateau rests under a sky
• 1:36:15
  Speaker 1: that feels close and guides winds across seasons. A river
• 1:36:19
  Speaker 1: nibbles through a divide and steals a headwater, leaving a
• 1:36:23
  Speaker 1: quiet gap crossed by deer. Old beach platforms climb a
• 1:36:28
  Speaker 1: hill like a staircase that the sea once climbed and
• 1:36:31
  Speaker 1: now has left behind. A fault beneath a forest moves
• 1:36:36
  Speaker 1: without shaking for a month and then falls quiet. Bubbles
• 1:36:40
  Speaker 1: of gas rise from a dark seep and feed a
• 1:36:43
  Speaker 1: white garden where no sun reaches. A pillar of salt
• 1:36:48
  Speaker 1: pushes aside clay and sand and makes a subtle ridge
• 1:36:52
  Speaker 1: where oaks stand in a line. An old shield holds
• 1:36:56
  Speaker 1: stones that remember a time when life knew no leaves,
• 1:37:01
  Speaker 1: and under every scene a sliding base lets the plates
• 1:37:04
  Speaker 1: drift with calm purpose. If you have stayed with me
• 1:37:09
  Speaker 1: this far, let the last images be spare and restful.
• 1:37:14
  Speaker 1: Night lies on a range where the stars feel close.
• 1:37:18
  Speaker 1: In the dark, deep currents move stones no one will
• 1:37:21
  Speaker 1: ever see. A root sags and a mountain lifts the
• 1:37:26
  Speaker 1: thickness of a hair. Over a plateau, thin air carries
• 1:37:30
  Speaker 1: a long wave of cold. A river runs quiet and
• 1:37:34
  Speaker 1: then hisses as it falls over a ledge that it
• 1:37:37
  Speaker 1: made long ago. Far at sea, waves trace long lines
• 1:37:41
  Speaker 1: across a terrace that will be a step on a
• 1:37:44
  Speaker 1: future hill. A fault sighs in slow, slip-deep underground. Methane
• 1:37:50
  Speaker 1: beads rise like pearls from a small chimney and vanish.
• 1:37:55
  Speaker 1: A salt dome breathes as more sediment arrives from a
• 1:37:58
  Speaker 1: distant river. The old heart of a continent rests and
• 1:38:03
  Speaker 1: holds its memories. The base of a plate slides forward
• 1:38:08
  Speaker 1: by a distance shorter than your breath expands as you
• 1:38:12
  Speaker 1: fall asleep. Thank you for sharing this quiet journey. The
• 1:38:17
  Speaker 1: planet will keep its patient schedule while you rest. May
• 1:38:22
  Speaker 1: your thoughts settle like silt in a calm bay and
• 1:38:26
  Speaker 1: your sleep be as steady as the drift of continents
• 1:38:30
  Speaker 1: Good night.