Latest / Daniel and Kelly’s Extraordinary Universe / Can supernovas cause ice ages?

Transcript

Can supernovas cause ice ages? · Daniel and Kelly’s Extraordinary Universe

• 0:07
  Speaker 1: Hey, Jorge, been enjoying their recent run of rainy days.
• 0:10
  Speaker 2: Yeah, I like a rainy day. It's kind of cozy.
• 0:13
  Speaker 1: Well, I guess that's what we get for living in
• 0:15
  Speaker 1: ice age rainy days. Even in southern California.
• 0:18
  Speaker 2: Where we're in an ice age, I don't see any
• 0:20
  Speaker 2: wooly mammoths around.
• 0:23
  Speaker 1: Yeah, the wooly mammoths disappeared, and not just because the temperature.
• 0:27
  Speaker 2: What happened They moved to a warmer planet.
• 0:30
  Speaker 1: No, I think our ancestors turned them all into soup
• 0:33
  Speaker 1: and blankets so they could be cozy on rainy days.
• 0:36
  Speaker 2: Wait, that's not what I saw in the movie Ice Age.
• 0:39
  Speaker 1: Not a documentary.
• 0:40
  Speaker 2: It's also not TG I guess. I am Hore Makertoona
• 0:59
  Speaker 2: and the author of Oliver's Great Big Universe.
• 1:01
  Speaker 1: Hi, I'm Daniel. I'm a particle physicist and a professor
• 1:04
  Speaker 1: at UC Irvine, and I live for the sunshine.
• 1:07
  Speaker 2: Well, we all live because of the sunshine too.
• 1:10
  Speaker 1: Right, Yeah, that's right. Almost all energy used by life
• 1:13
  Speaker 1: on Earth comes initially from the sun.
• 1:16
  Speaker 2: It grows vegetables and food, and that's how we can
• 1:19
  Speaker 2: all stay alive and warm.
• 1:20
  Speaker 1: Also, that's right, when you burn a piece of wood
• 1:22
  Speaker 1: and you feel that glow. It's like it's released that
• 1:25
  Speaker 1: original solar energy trees are basically solar energy batteries.
• 1:30
  Speaker 2: Yeah, whenever I see a big green field that I
• 1:31
  Speaker 2: always thinking, well, that's an awesome natural solar panel.
• 1:37
  Speaker 1: I know, it is incredible that evolution has devised this
• 1:40
  Speaker 1: way to eat photons and turn it right into chemical energy.
• 1:44
  Speaker 1: Pretty amazing.
• 1:45
  Speaker 2: Yeah. Yeah, although in between there's you know, a nice salad,
• 1:50
  Speaker 2: and maybe more in between is a nice a piece
• 1:53
  Speaker 2: of fried chicken.
• 1:55
  Speaker 1: I like to think of all the photons in my.
• 1:57
  Speaker 2: Salad, although it is a little heavy. It's not very
• 1:59
  Speaker 2: light to have a fried chicken salad. But anyways, welcome
• 2:05
  Speaker 2: to our podcast Daniel and Jorge Explain the Universe, a
• 2:08
  Speaker 2: production of iHeartRadio.
• 2:09
  Speaker 1: In which we try to shine a light on all
• 2:11
  Speaker 1: the heavy questions of the universe. How does it all work?
• 2:15
  Speaker 1: What are the smallest little bits? How do those come
• 2:17
  Speaker 1: together to make grass and chicken and people and planets
• 2:21
  Speaker 1: and stars and black holes and everything else that we
• 2:24
  Speaker 1: see out there in the universe. It's an incredible, dizzying
• 2:28
  Speaker 1: array of complexity, but we think it's possible to simplify it,
• 2:31
  Speaker 1: to boil it all down into a few basic ideas
• 2:34
  Speaker 1: that could be understood by you.
• 2:36
  Speaker 2: That's right. We try to serve up a nice, tantalizing
• 2:38
  Speaker 2: buffet of amazing facts about the universe, amazing discoveries, and
• 2:43
  Speaker 2: also incredible mysteries that we are still trying to figure
• 2:46
  Speaker 2: out in a way that is hopefully not a word
• 2:48
  Speaker 2: salad in your head.
• 2:51
  Speaker 1: A crucial goal of doing physics is understanding the nature
• 2:54
  Speaker 1: of the universe so that we can get a better
• 2:56
  Speaker 1: sense for our context. Every time we learn something about
• 2:59
  Speaker 1: where we are in the cosmos and how it works,
• 3:01
  Speaker 1: it changes the way we relate to it, how we
• 3:03
  Speaker 1: live our lives, what we think about it. And of course,
• 3:06
  Speaker 1: at the center of our local cosmic neighborhood is the Sun,
• 3:09
  Speaker 1: which is a source of all energy for life on
• 3:11
  Speaker 1: Earth and could eventually fry everything on Earth.
• 3:14
  Speaker 2: Yeah, because I guess it's easy sometimes to forget that
• 3:17
  Speaker 2: we are just sitting atop a little tiny rock, flying
• 3:21
  Speaker 2: around a big burning ball of gas in the middle
• 3:24
  Speaker 2: of a gigantic space full of things that might at
• 3:27
  Speaker 2: any moment kill us.
• 3:29
  Speaker 1: It seems like sort of a precarious and fragile situation,
• 3:32
  Speaker 1: Like if we didn't live it, and you read about
• 3:34
  Speaker 1: it in a science fiction novel, you'd be like, hmm,
• 3:36
  Speaker 1: that sounds kind of implausible.
• 3:38
  Speaker 2: You mean, the idea that we were just like perched
• 3:40
  Speaker 2: in the middle of a giant void where that might
• 3:44
  Speaker 2: kill us at anytime.
• 3:45
  Speaker 1: Yeah, that we're the perfect place between a huge freezing
• 3:48
  Speaker 1: void and an enormous ball of fire that could kill us,
• 3:51
  Speaker 1: and we're in the Goldilocks zone right in between them.
• 3:54
  Speaker 2: Yeah, and an orbit that is sort of miraculously stable, right,
• 3:58
  Speaker 2: that just keeps going around the over and over again
• 4:01
  Speaker 2: in a very stable way.
• 4:02
  Speaker 1: It is sort of amazing that it's worked for this long,
• 4:06
  Speaker 1: and we are grateful for it.
• 4:08
  Speaker 2: It's amazing that the Sun arises every day because it
• 4:13
  Speaker 2: could not, right.
• 4:14
  Speaker 1: It could just stay in bed like your local cartoonists.
• 4:16
  Speaker 2: Yeah, yeah, that's right, thankfully.
• 4:21
  Speaker 1: But the Sun and other stars out there are not
• 4:23
  Speaker 1: eternal fixtures which will be pumping out energy to support
• 4:27
  Speaker 1: life on Earth and alien planets forever. Sometimes they go boom.
• 4:31
  Speaker 1: Sometimes they explode in enormous supernova which can fry their
• 4:35
  Speaker 1: local region of space.
• 4:37
  Speaker 2: Yeah. I think we're used to the stars being out
• 4:39
  Speaker 2: their way out there and not really affecting our everyday
• 4:42
  Speaker 2: lives other than making for nice night sky view here
• 4:46
  Speaker 2: on Earth. But it is possible for those stars out
• 4:49
  Speaker 2: there to actually affect us and maybe change the way
• 4:51
  Speaker 2: that we live.
• 4:52
  Speaker 1: That's right. It's not so crazy to imagine that our
• 4:54
  Speaker 1: sun's variations as it gets brighter or colder as we
• 4:58
  Speaker 1: move closer further away, could affect temperature on Earth and
• 5:01
  Speaker 1: even potentially cause ice ages or global heating. But what
• 5:04
  Speaker 1: about other stars out there in the universe. How susceptible
• 5:07
  Speaker 1: are we to their.
• 5:09
  Speaker 2: Quirks or their big explosive quirks for that matter. So
• 5:14
  Speaker 2: to the podcast, we'll be asking the question, can super
• 5:22
  Speaker 2: nova's cause ice ages? Well, I feel like that's two
• 5:26
  Speaker 2: movie names and one title here, super novas, And I.
• 5:31
  Speaker 1: Know, I know it means we're in danger of jumping
• 5:33
  Speaker 1: the Shark, because now we're doing like bizarre mashups, you know,
• 5:36
  Speaker 1: like Shark Tornado.
• 5:40
  Speaker 2: I think we jumped to Shark a few hundred episodes ago,
• 5:43
  Speaker 2: didn't we? And we're still here. We're still writing the Shark.
• 5:46
  Speaker 1: I promise I didn't come up with this episode by
• 5:48
  Speaker 1: randomly throwing darts at the wall with topic names.
• 5:52
  Speaker 2: Maybe we should do an episode on the physics of sharks.
• 5:54
  Speaker 1: Jumping, the physics of sharknados.
• 5:58
  Speaker 2: You know, there's a lot of questions there. How do
• 6:00
  Speaker 2: you launch the shark? What are the aerodynamics of the
• 6:03
  Speaker 2: shark in air?
• 6:04
  Speaker 1: Yeah, we have a crossover episode with Katie, she probably
• 6:07
  Speaker 1: knows all about it.
• 6:08
  Speaker 2: There you go, and then you could have maybe Henry
• 6:10
  Speaker 2: Winkler the Fawns as a guest star, just to wrap
• 6:14
  Speaker 2: it all up.
• 6:15
  Speaker 1: And then we'll take a field trip and literally jump
• 6:17
  Speaker 1: over a shark, just to hammer that point home. If
• 6:21
  Speaker 1: people weren't getting it already, right.
• 6:23
  Speaker 2: Right, I think that might be illegal, uh, and feel advised,
• 6:26
  Speaker 2: but hey, if you want to go for it, I'll
• 6:28
  Speaker 2: be unsure taking pictures.
• 6:30
  Speaker 1: But this is not just a rim collection words mashed
• 6:33
  Speaker 1: together for a new idea for an episode. This is
• 6:36
  Speaker 1: actually something on the cutting edge of science.
• 6:38
  Speaker 2: Yeah, the idea that maybe a supernova out there in
• 6:41
  Speaker 2: space could have, maybe or can cause an ice age
• 6:45
  Speaker 2: here on Earth. And so, as usual, we were wondering
• 6:47
  Speaker 2: how many people out there had thought about this question
• 6:49
  Speaker 2: or maybe even linked those two ideas together. I guess
• 6:53
  Speaker 2: if it was close enough, we could do a lot
• 6:55
  Speaker 2: of damage.
• 6:56
  Speaker 3: One way or the other supernova was sent out heavy
• 7:00
  Speaker 3: Adams and on a planet, if they pile up around
• 7:03
  Speaker 3: the planet, they can block the other sunlight that's closer
• 7:07
  Speaker 3: to the body and then calls ICAG just.
• 7:09
  Speaker 4: Indeed, hopefully that doesn't mean the Sun, because I'm not
• 7:12
  Speaker 4: sure if the Sun were to go super nova it
• 7:14
  Speaker 4: would be cold enough for an ice age. But if
• 7:17
  Speaker 4: it were like a close star, maybe some of the
• 7:20
  Speaker 4: matter coming off of that star would shield us from
• 7:24
  Speaker 4: the Sun and the temperatures were cool.
• 7:26
  Speaker 2: I don't know.
• 7:27
  Speaker 4: Seems far fetched, but I can't think of it any
• 7:29
  Speaker 4: other way.
• 7:30
  Speaker 5: This is a real if a butterfly flaps its wings
• 7:32
  Speaker 5: on the other side of the world kind of question. Sure,
• 7:35
  Speaker 5: a supernova would admit charged particles that would mess with
• 7:38
  Speaker 5: a magnetic field and potentially strippinozone layer, so that would
• 7:41
  Speaker 5: affect the climate dramatically. So yes, supernovas could cause ice ages.
• 7:47
  Speaker 1: Thanks very much to everybody who participates. I love hearing
• 7:50
  Speaker 1: your voices on the topics of the day. If you'd
• 7:53
  Speaker 1: like to lend your thoughts to this segment of the podcast,
• 7:56
  Speaker 1: please don't be shy wright to me. Two questions at
• 7:58
  Speaker 1: Daniel and Jorge dot com. I'm pretty sure nobody ever
• 8:01
  Speaker 1: regretted it.
• 8:02
  Speaker 2: Would they tell you though.
• 8:05
  Speaker 1: You know, people on the Internet are not shy to
• 8:07
  Speaker 1: share their opinions, so I'm pretty sure I would get
• 8:10
  Speaker 1: a grumpy email. If somebody's really grumpy about it.
• 8:13
  Speaker 2: Well, I think if they regretted it, they wouldn't reply
• 8:15
  Speaker 2: back again. So think about all the emails you're not getting.
• 8:20
  Speaker 1: If you participate in this segment of the podcast and
• 8:22
  Speaker 1: you deeply, deeply regret it, please write to me share
• 8:25
  Speaker 1: your pain.
• 8:30
  Speaker 2: Just havn't fill out a survey after every interaction with
• 8:32
  Speaker 2: ten you have you enjoyed my talking with me? Please
• 8:35
  Speaker 2: wanting to fill out the survey?
• 8:36
  Speaker 1: No, then they're going to regret it because everybody regrets
• 8:38
  Speaker 1: getting those surveys.
• 8:41
  Speaker 2: Well, maybe you haven't fill out a survey about being
• 8:44
  Speaker 2: asked to fill out.
• 8:44
  Speaker 1: A survey, and then they recursively begin to hate me.
• 8:49
  Speaker 2: Yeah, there you go, And as time goes to infinity,
• 8:52
  Speaker 2: the universe will filled with it all approach to having
• 8:55
  Speaker 2: gained zero.
• 8:56
  Speaker 1: Knowledge and the band with the Internet will be surveys.
• 9:01
  Speaker 2: But anyways, these are great answers from people. It seems
• 9:04
  Speaker 2: like people think that maybe there could be a connection
• 9:07
  Speaker 2: there in the same way that maybe a butterfly can
• 9:10
  Speaker 2: flap its wing and I could get fried chicken the
• 9:12
  Speaker 2: next morning because of that.
• 9:14
  Speaker 1: Yeah, it's sort of a cosmic butterfly effect. Imagine a
• 9:17
  Speaker 1: butterfly and alien planet triggering a supernova in that solar system,
• 9:21
  Speaker 1: which then somehow makes ice ages in hours. Amazing power
• 9:25
  Speaker 1: of butterflies.
• 9:26
  Speaker 2: Yeah, and fried chicken as well. But this is an
• 9:29
  Speaker 2: interesting question. Could a supernova out there in space somehow
• 9:32
  Speaker 2: affect the climate here on Earth to the extent that
• 9:36
  Speaker 2: maybe we actually get an ice age?
• 9:38
  Speaker 1: Hmm amazing.
• 9:40
  Speaker 2: So maybe let's start with the basics here that Daniel,
• 9:42
  Speaker 2: what is the supernova and could one happen near us?
• 9:46
  Speaker 1: A supernova is a really exciting and dramatic possible endpoint
• 9:50
  Speaker 1: to a star. Not every star ends the same way.
• 9:53
  Speaker 1: The fate of a star depends almost entirely on its
• 9:57
  Speaker 1: initial mass. These stars are formed from huge clouds of
• 10:00
  Speaker 1: gas and dust where something has triggered a gravitational runaway effect.
• 10:04
  Speaker 1: So klump of stuff pulls together, and if it's too
• 10:07
  Speaker 1: small it makes something like a brown dwarf. But if
• 10:10
  Speaker 1: you get enough stuff in there, you can think of
• 10:11
  Speaker 1: nice fusion and you can get a star and it
• 10:13
  Speaker 1: can be burning. A lot of stars are kind of small.
• 10:16
  Speaker 1: They're called like red dwarf stars, and those stars are
• 10:19
  Speaker 1: just going to burn for a long long time and
• 10:21
  Speaker 1: then eventually become like white dwarfs. Larger stars, though, when
• 10:24
  Speaker 1: they run out of fuel that fuels what's preventing them
• 10:27
  Speaker 1: from collapsing further gravitationally by providing pressure from the fusion
• 10:32
  Speaker 1: inside of them. Larger stars, when that fuel runs out,
• 10:35
  Speaker 1: they have so much gravity that they collapse, which then
• 10:38
  Speaker 1: triggers an explosion at the heart of the star, which
• 10:41
  Speaker 1: we call a supernova.
• 10:42
  Speaker 2: But I guess a couple of questions there. First of all,
• 10:46
  Speaker 2: do smaller stars ever run out of fuel? Don't they
• 10:48
  Speaker 2: run out of fuel too? And what happens to them
• 10:50
  Speaker 2: when they run out of fuel?
• 10:51
  Speaker 1: Yeah, smaller stars definitely run out of fuel because they're smaller,
• 10:55
  Speaker 1: their core is not as high temperature or as high pressure,
• 10:58
  Speaker 1: so they go through their fuel more. So they can
• 11:01
  Speaker 1: last for like billions and billions of years, but they
• 11:03
  Speaker 1: eventually will run out of fuel and they'll just form
• 11:06
  Speaker 1: white dwarfs. White dwarfs are just like their remnant of fusion.
• 11:09
  Speaker 1: But it's no longer fusing. Like if you produce a
• 11:12
  Speaker 1: bunch of carbon, but you're not hot enough to fuse carbon,
• 11:15
  Speaker 1: then you just turn into a hot lump of carbon,
• 11:17
  Speaker 1: and that white dwarf sits around for maybe trillions of years,
• 11:21
  Speaker 1: glowing in space without fusing, until cools enough to become
• 11:24
  Speaker 1: a black dwarf.
• 11:26
  Speaker 2: But somehow there's a difference between that and a larger
• 11:29
  Speaker 2: star because the larger stars collapse. The smaller stars don't collapse.
• 11:33
  Speaker 1: Yeah, the larger stars have born gravity and so they
• 11:36
  Speaker 1: can overcome the structural strength of the fusion remnants. Like
• 11:40
  Speaker 1: the reason that white dwarf doesn't collapse further is that
• 11:43
  Speaker 1: the structure of that big blob of carbon or nickel
• 11:45
  Speaker 1: or whatever it's turned out to be is stronger than
• 11:48
  Speaker 1: the gravitational forces. But if you have enough mass, you
• 11:51
  Speaker 1: can overcome that and you can trigger another collapse, and
• 11:54
  Speaker 1: that creates intense pressure and temperature at the core. So
• 11:57
  Speaker 1: now you can fuse stuff you couldn't fuse before, and
• 12:00
  Speaker 1: that creates very very fast, burning, very short lived reaction
• 12:03
  Speaker 1: which causes an explosion again, which blows out a huge
• 12:07
  Speaker 1: amount of material, and that's the supernova.
• 12:11
  Speaker 2: Well, the other question I had was does the fate
• 12:13
  Speaker 2: of a star also depend on what it's made out of,
• 12:16
  Speaker 2: not just its mass, Like does a star with its
• 12:18
  Speaker 2: pure hydrogen have a different fate than one that's more
• 12:22
  Speaker 2: mixed in with other elements?
• 12:24
  Speaker 1: Yeah. Absolutely, the amount of metal that a star starts
• 12:27
  Speaker 1: with can really change the star's behavior. The more metal
• 12:30
  Speaker 1: there is in a star, the more opaque it is
• 12:32
  Speaker 1: to its own radiation, so the more it absorbs those
• 12:35
  Speaker 1: photons rather than emitting it, So that can really change
• 12:38
  Speaker 1: the temperature in the star, which changes the rate of fusion.
• 12:42
  Speaker 1: And so the question of like how much metal each
• 12:44
  Speaker 1: star starts with is really important one and one we're
• 12:47
  Speaker 1: still trying to understand. We had a whole episode recently
• 12:50
  Speaker 1: about how metal is our sun, and we know that
• 12:53
  Speaker 1: it's like a couple percent metal, by which we mean
• 12:56
  Speaker 1: things heavier than helium and hydrogen. But it is an
• 12:59
  Speaker 1: important contribution, and so it's mostly determined by the mass
• 13:03
  Speaker 1: of the star, but also other things like the composition,
• 13:05
  Speaker 1: and it's not totally understood, like which star will go
• 13:08
  Speaker 1: supernova is not something we can actually predict.
• 13:12
  Speaker 2: Now, does this star having more metal make it more
• 13:16
  Speaker 2: explosive or less explosive? Like it's being more metal, more radical.
• 13:23
  Speaker 1: More metallic stars are more likely to undergo supernova and
• 13:27
  Speaker 1: turn into neutron stars, whereas low metallicity stars are more
• 13:32
  Speaker 1: likely to collapse directly into a black hole and might
• 13:34
  Speaker 1: not even give you a supernova.
• 13:37
  Speaker 2: Interesting. Yeah, I guess I would go straight into a
• 13:39
  Speaker 2: black hole. Then there's nothing to explode out because nothing
• 13:41
  Speaker 2: can get out.
• 13:42
  Speaker 1: Yeah, exactly, But that's from like really massive stars above
• 13:46
  Speaker 1: like forty times the mass of our star. In the
• 13:49
  Speaker 1: intermediate region, like between ten and forty times the mass
• 13:52
  Speaker 1: of our star. A lot of these will go supernova,
• 13:55
  Speaker 1: but again it's hard to predict. It's a very chaotic event.
• 13:58
  Speaker 1: In the moment at which a star is going to
• 13:59
  Speaker 1: go supernova is not easy to tell. Like people have
• 14:02
  Speaker 1: been watching Beetlejuice recently because it's brightness has become quite
• 14:06
  Speaker 1: variable and they're wondering, like, is it about to go supernova?
• 14:09
  Speaker 1: But nobody can tell when a star is about to
• 14:11
  Speaker 1: go supernova. We don't understand the process, even in simulation.
• 14:15
  Speaker 1: It's not something we know how to explain.
• 14:18
  Speaker 2: Yeah, that's something that you said that also made me curious,
• 14:22
  Speaker 2: was this idea we don't really understand this process very well.
• 14:25
  Speaker 2: And I guess it's interesting that we haven't really studied
• 14:29
  Speaker 2: supernova's very much, right, Like, we haven't been present when
• 14:32
  Speaker 2: we see one. We haven't been up close to another
• 14:34
  Speaker 2: star when supernova goes up, thankfully, maybe, But it's all
• 14:40
  Speaker 2: sort of done through simulations and models of what we
• 14:43
  Speaker 2: think is happening inside of a star from what we
• 14:46
  Speaker 2: can gather from the kind of these pinpoints in the sky. Right.
• 14:50
  Speaker 1: Yeah, we certainly have studied supernova, and you're right, a
• 14:52
  Speaker 1: lot of the work is done in models. The reason
• 14:55
  Speaker 1: we haven't studied more supernova is because supernova are really rare.
• 14:59
  Speaker 1: It's not something that has depends all the time, sort
• 15:01
  Speaker 1: of thankfully, otherwise we might have been fried out of existence.
• 15:04
  Speaker 2: You know.
• 15:04
  Speaker 1: In the Milky Way, for example, we expect there to
• 15:06
  Speaker 1: be like two supernova's out of the hundreds of billions
• 15:09
  Speaker 1: of stars every hundred years, and so it's not something
• 15:13
  Speaker 1: that happens very often. And weirdly, we haven't seen a
• 15:16
  Speaker 1: supernova in the Milky Way for a few hundred years.
• 15:19
  Speaker 1: So that's another mystery we did a whole podcast episode about.
• 15:22
  Speaker 1: But it's not something that happens often enough for us
• 15:25
  Speaker 1: to get a lot of data. It's like spontaneous human combustion.
• 15:28
  Speaker 1: You know, you hear about it happening occasionally. It's really
• 15:31
  Speaker 1: hard to predict and so you have like sort of
• 15:33
  Speaker 1: sparse data to work with to understand, you know, what
• 15:36
  Speaker 1: might cause it.
• 15:37
  Speaker 2: M I guess what makes it hard to predict, Like,
• 15:41
  Speaker 2: isn't under signs that the sun goes through or the
• 15:44
  Speaker 2: star goes through right before it blows up, Like doesn't
• 15:46
  Speaker 2: it maybe ramp up in brightness or something.
• 15:48
  Speaker 1: We'd love to know that. And it's really tricky because
• 15:51
  Speaker 1: we can't monitor every single star until one of them
• 15:54
  Speaker 1: goes supernova. They're just so many stars. So typically what
• 15:57
  Speaker 1: happens is we see a star go supernova, then we
• 16:00
  Speaker 1: start taking a lot of detailed data on it, but
• 16:02
  Speaker 1: that's all post supernova. It we'd be very lucky to
• 16:05
  Speaker 1: have been watching in great detail star just before it
• 16:08
  Speaker 1: goes supernova, and that's one reason why we can't tell
• 16:11
  Speaker 1: it stars go supernova. And from the theoretical side, it's
• 16:14
  Speaker 1: very tricky because it's very intense physics. The stuff is
• 16:17
  Speaker 1: moving close to the speed of light. It's very high density,
• 16:20
  Speaker 1: it's very high intensity. There's a huge number of particles.
• 16:23
  Speaker 1: The kind of calculations are very difficult to do correctly
• 16:26
  Speaker 1: because not only are all the particles important, but it's
• 16:29
  Speaker 1: very chaotic, like a small change in the structure of
• 16:32
  Speaker 1: the star can lead to a large change in how
• 16:35
  Speaker 1: that collapse happens and the shock waves. It's very complicated.
• 16:38
  Speaker 1: I'm actually working with some folks at Berkeley who are
• 16:40
  Speaker 1: doing supernova simulations, and each one of them requires running
• 16:44
  Speaker 1: the supercomputer for millions and millions of hours, so we
• 16:47
  Speaker 1: don't even have a lot of examples of supernova in simulation.
• 16:51
  Speaker 2: Well, yeah, and I guess if you, you know, try
• 16:55
  Speaker 2: to look for supernova and by looking at this guy
• 16:58
  Speaker 2: all the time, you'd still be waiting, right, he said,
• 17:00
  Speaker 2: we haven't had one in a long time. When was
• 17:02
  Speaker 2: the last supernova that we've seen.
• 17:03
  Speaker 1: In our galaxy? The last supernova was seen I think
• 17:06
  Speaker 1: by Kepler, so four hundred years ago.
• 17:09
  Speaker 2: Four hundred years ago, is it possible that one happened?
• 17:12
  Speaker 2: What we didn't see it?
• 17:13
  Speaker 1: Those are just supernova's in the Milky Way, And it's
• 17:15
  Speaker 1: possible there have been supernova's in the Milky Way we
• 17:17
  Speaker 1: haven't seen because we can't see through all the cosmic
• 17:20
  Speaker 1: dust at the center of the galaxy. And weirdly, a
• 17:23
  Speaker 1: lot of the supernovas we have seen in the Milky
• 17:25
  Speaker 1: Way are far away from where most of the stars are.
• 17:28
  Speaker 1: That's a whole funny, amazing mystery. But because supernova are
• 17:32
  Speaker 1: so bright, we can also see them from other galaxies.
• 17:35
  Speaker 1: In fact, when a supernova goes sometimes they're like a
• 17:38
  Speaker 1: million or billion, or even a trillion times brighter than
• 17:42
  Speaker 1: the Sun. They can outshine the rest of the galaxy.
• 17:45
  Speaker 2: Yeah, they're super bright. But I guess any given time,
• 17:48
  Speaker 2: isn't it true that we can only look at half
• 17:50
  Speaker 2: of the sky, like the daylight side. We can't really
• 17:52
  Speaker 2: see any stars, right can we?
• 17:54
  Speaker 1: Yeah, that's right, we can only see half of the sky.
• 17:56
  Speaker 1: And if you see a star in another galaxy go supernova,
• 18:00
  Speaker 1: you can tell something has gone supernova. But we can't
• 18:02
  Speaker 1: often pinpoint individual stars in other galaxies, so you can't
• 18:06
  Speaker 1: be like, oh, it was that one over there and
• 18:09
  Speaker 1: then go check your archival data to see what you
• 18:11
  Speaker 1: know about it. So if we had more telescopes constantly
• 18:14
  Speaker 1: studying the sky, then we could learn a lot more
• 18:16
  Speaker 1: about supernova because we could see them before they go,
• 18:20
  Speaker 1: which be really valuable.
• 18:21
  Speaker 2: But as we just said, basically, you'd be waiting for
• 18:23
  Speaker 2: four hundred years at this point, in which nobody wanted
• 18:26
  Speaker 2: to wait that long to get a PhD.
• 18:29
  Speaker 1: Yeah, exactly. And we have seen again in supernova more recently,
• 18:32
  Speaker 1: like there's a famous one in nineteen eighty seven, very bright.
• 18:35
  Speaker 1: You could almost even see it in the daytime from
• 18:37
  Speaker 1: another galaxy, of course, not in the Milky Way.
• 18:40
  Speaker 2: So they're sort of rare, but they do happen. And
• 18:43
  Speaker 2: of course the universe in our galaxies are billions of
• 18:46
  Speaker 2: years old, so many of them, probably a lot of
• 18:49
  Speaker 2: them have happened since. And so the idea is that
• 18:51
  Speaker 2: maybe the supernovas could somehow affect what life is like
• 18:55
  Speaker 2: here on Earth.
• 18:56
  Speaker 1: That's the question, yes, exactly, And so.
• 18:58
  Speaker 2: Let's get into that question of whether a super and
• 19:00
  Speaker 2: I can actually trigger an ice age here on this planet.
• 19:04
  Speaker 2: So let's dig into that, but first let's take a
• 19:06
  Speaker 2: quick break. All right, we're talking about supernovas and ice ages,
• 19:23
  Speaker 2: both great movies, different audience.
• 19:27
  Speaker 1: Though, what is the movie supernova? I haven't seen that one.
• 19:34
  Speaker 1: I think there must be a movie called Supernova. Yeah,
• 19:36
  Speaker 1: of course, you're right, there's a movie Supernova. Twenty twenty,
• 19:39
  Speaker 1: Sam and Tusker are traveling across England in their old
• 19:42
  Speaker 1: RV to visit friends. I'm not sure it's really about
• 19:45
  Speaker 1: the supernova, but yeah.
• 19:47
  Speaker 2: That doesn't sound like it's about astrophysics or space for
• 19:50
  Speaker 2: that matter. Isn't there an older movie called Supernova?
• 19:53
  Speaker 5: Oh?
• 19:53
  Speaker 1: Okay, here's one from two thousand. This is a science
• 19:57
  Speaker 1: fiction action film. Is it the one starting Killian Murphy?
• 20:00
  Speaker 1: It chronicles the search and rescue patrol of a medical
• 20:03
  Speaker 1: ship in deep space.
• 20:04
  Speaker 2: All right, well, obviously it was not very popular.
• 20:11
  Speaker 1: But everybody should go check it out. I mean, this
• 20:13
  Speaker 1: one from twenty has an eleven percent rating on Rotten Tomatoes.
• 20:16
  Speaker 2: So yeah, ja, I guess the movie didn't blow up.
• 20:21
  Speaker 1: Yeah, I don't think it an ignited passion in the audience.
• 20:24
  Speaker 2: Yeah, it just kind of collapsed under its own weight perhaps.
• 20:27
  Speaker 2: But anyways, we're talking about whether a supernova that happens
• 20:31
  Speaker 2: out there in space could somehow trigger an ice age
• 20:34
  Speaker 2: here on Earth, which is because sort of mind blowing
• 20:37
  Speaker 2: to think about that's something so far away that is
• 20:40
  Speaker 2: explosive and hot can somehow make us cooler. Yeah.
• 20:44
  Speaker 1: Yeah, it is amazing how interconnected everything is and how
• 20:47
  Speaker 1: delicate everything is.
• 20:50
  Speaker 2: Now we've talked about supernova's. Now let's talk about ice ages,
• 20:53
  Speaker 2: and so what do we know about ice ages here
• 20:55
  Speaker 2: on Earth?
• 20:56
  Speaker 1: So ice age is a generic term for basically a
• 20:59
  Speaker 1: period when Earth is cold, there's more glaciers, there's more
• 21:02
  Speaker 1: polar ice, and if you look back at the history
• 21:05
  Speaker 1: of life on Earth, you see these big variations in
• 21:08
  Speaker 1: the climate. So there are times when like all of
• 21:11
  Speaker 1: North America was under ice sheets, and then times when
• 21:14
  Speaker 1: there's almost no ice on Earth. So it oscillates between
• 21:17
  Speaker 1: like a greenhouse Earth and a snowball Earth.
• 21:21
  Speaker 2: So they're just periods in time where things were cold.
• 21:24
  Speaker 1: Yeah, exactly, And this is just what geologists have called
• 21:26
  Speaker 1: these historic periods when the average temperature was much lower.
• 21:30
  Speaker 1: But it's really fascinating because it tells us a lot
• 21:32
  Speaker 1: about how climate on Earth. Works. And there's not just
• 21:36
  Speaker 1: these big ice ages which lasts like millions of years,
• 21:39
  Speaker 1: but there's also cycles within those ice ages. So within
• 21:42
  Speaker 1: an ice age, there are glacial periods, which is when
• 21:45
  Speaker 1: it's colder, and interglacial periods when it's hotter. So like
• 21:49
  Speaker 1: currently we are in an ice age, but we're in
• 21:52
  Speaker 1: an interglacial period. Of that ice age, so like on
• 21:56
  Speaker 1: average it's colder than Earth has been in the past,
• 21:59
  Speaker 1: but we're in a warmer period of that ice age.
• 22:02
  Speaker 2: Well, yeah, I guess, first of all, it's kind of
• 22:04
  Speaker 2: a mind blown to think that, you know, the Earth
• 22:07
  Speaker 2: goes through these changes in these periods, like the Earth
• 22:10
  Speaker 2: hasn't always been the same.
• 22:12
  Speaker 1: It's sort of like a dynamic system. Yeah, it's definitely
• 22:15
  Speaker 1: a dynamic system. And these ice ages date back like
• 22:17
  Speaker 1: billions of years. One of the earliest ice ages we
• 22:20
  Speaker 1: know about started like almost two and a half billion
• 22:24
  Speaker 1: years ago, and then the more recent ones are all
• 22:27
  Speaker 1: in the last like five hundred million years. But the
• 22:30
  Speaker 1: Earth is definitely a dynamic and you know life on
• 22:32
  Speaker 1: Earth has responded to it and influenced it. You know,
• 22:35
  Speaker 1: early life, for example, couldn't tolerate the presence of oxygen,
• 22:38
  Speaker 1: and then when oxygen started to be produced by photosynthesis,
• 22:41
  Speaker 1: life then evolved to take advantage of that. And so
• 22:44
  Speaker 1: it's fascinating how it's all interconnected.
• 22:48
  Speaker 2: I guess the question is how do we know about
• 22:49
  Speaker 2: ice ages from billions of years ago? Like, wasn't the
• 22:53
  Speaker 2: Earth totally different? Do we still have evidence of those things?
• 22:55
  Speaker 1: We know a lot about the history of the Earth
• 22:58
  Speaker 1: from sort of three different categories of evidence. There's like
• 23:01
  Speaker 1: geological evidence, there's chemical evidence, and then there's evidence from life,
• 23:06
  Speaker 1: like paleontology. And so the geological evidence is like, let's
• 23:11
  Speaker 1: look at the shape of the surface of the Earth.
• 23:14
  Speaker 1: You know, about one hundred and fifty years ago or
• 23:16
  Speaker 1: in the mid eighteen hundreds, people were noticing weird things
• 23:18
  Speaker 1: they couldn't explain, like weirdly shaped valleys and like boulders
• 23:22
  Speaker 1: and the alps that looked like they came from much
• 23:24
  Speaker 1: further north in Europe, and like how did they get there.
• 23:27
  Speaker 1: There's then that people postulated this idea that like glaciers
• 23:30
  Speaker 1: move across the Earth and like create valleys and scrape
• 23:34
  Speaker 1: out regions of the earth and can carry boulders with
• 23:38
  Speaker 1: them for thousands of miles. So the geology of the
• 23:41
  Speaker 1: Earth tells us a lot about the sort of history of.
• 23:44
  Speaker 2: Glaciation, even though I guess rocks are constantly changing and
• 23:49
  Speaker 2: moving and churning with the core of the Earth.
• 23:52
  Speaker 1: Yeah, absolutely, there's a lot of things going on, but
• 23:54
  Speaker 1: this is one of the processes and an important one
• 23:56
  Speaker 1: for understanding sort of the shape of the surface of
• 23:59
  Speaker 1: the Earth.
• 24:00
  Speaker 2: Mm, so that's looking at rocks. How else can we know?
• 24:03
  Speaker 1: So we can also take samples of the Earth because
• 24:05
  Speaker 1: the different conditions on the surface are stored in the
• 24:08
  Speaker 1: history on Earth. So, for example, if you go to
• 24:11
  Speaker 1: the poles and you take ice cores, they do these
• 24:14
  Speaker 1: amazing drills where they're like drilled into the ice one
• 24:17
  Speaker 1: or two miles deep and then they pull it out.
• 24:19
  Speaker 1: You can see layers from all the different winters on Earth.
• 24:22
  Speaker 1: And in those layers you can measure like, first of all,
• 24:25
  Speaker 1: the thickness of the layer, like what was the average snowfall?
• 24:28
  Speaker 1: And there are trapped air bubbles in there which give
• 24:31
  Speaker 1: you samples of the atmosphere from hundreds of thousands of
• 24:34
  Speaker 1: years ago. And if you look at those samples of atmosphere,
• 24:38
  Speaker 1: you can do clever tricks to figure out like how
• 24:40
  Speaker 1: cold it.
• 24:40
  Speaker 2: Was back then, yeah, and what it smelled like. Right,
• 24:43
  Speaker 2: Basically you can smell the air from millions of years ago.
• 24:47
  Speaker 1: Yeah, that's right. We might have some mammoth farts saved
• 24:50
  Speaker 1: in the North Pole.
• 24:53
  Speaker 2: Well, Takende, we we're all smelling mammoths farts right now
• 24:57
  Speaker 2: because the same air molecules where around back then.
• 25:01
  Speaker 1: Yeah, I guess that's true. And so the ice cores
• 25:04
  Speaker 1: give us samples of the atmosphere up to like hundreds
• 25:06
  Speaker 1: of thousands of years ago. And we can go even
• 25:09
  Speaker 1: deeper into the path by looking at ocean sediment, like
• 25:12
  Speaker 1: stuff that falls into the ocean and then settles to
• 25:15
  Speaker 1: the bottom of the ocean. If you take cores of
• 25:17
  Speaker 1: the ocean floor, you can again drill down really really
• 25:20
  Speaker 1: far you find this sedimentation, and there's a lot of
• 25:24
  Speaker 1: details about the chemistry of that sedimentation and what's deposited
• 25:27
  Speaker 1: in the thickness of those layers that give you important
• 25:29
  Speaker 1: clues about what was going on in the Earth's atmosphere,
• 25:33
  Speaker 1: and that can take you back millions and millions of years.
• 25:36
  Speaker 2: Well, you can tell how cold and hot it was.
• 25:38
  Speaker 4: Yeah.
• 25:38
  Speaker 1: Most of these clues about the temperature from the ice
• 25:41
  Speaker 1: cores and the ocean sediment come from isotope ratios, because
• 25:46
  Speaker 1: different isotopes of water, for example, have different chemistry and
• 25:50
  Speaker 1: so like more of it will evaporate, for example, when
• 25:52
  Speaker 1: it's hotter, and so the ratio of these isotopes you
• 25:55
  Speaker 1: can back that out and figure out something about the
• 25:58
  Speaker 1: temperature of the air, which is pretty yeah.
• 26:01
  Speaker 2: Wow, it's sort of like carbon dating but water dating
• 26:04
  Speaker 2: kind of.
• 26:04
  Speaker 1: Yeah, exactly, and it's not trivial, right, there's lots of
• 26:07
  Speaker 1: reasons why stuff on the ocean floor or in the
• 26:09
  Speaker 1: ice cores can get confused, but it's an important part
• 26:12
  Speaker 1: of this evidence. There's a really impressive scientific body of
• 26:15
  Speaker 1: work here figuring out how to deduce this from these
• 26:18
  Speaker 1: weird clues.
• 26:19
  Speaker 2: Yeah, it's pretty amazing. And so we can also look
• 26:22
  Speaker 2: at fossils.
• 26:23
  Speaker 1: Right, Yeah, we can look to see where animals were,
• 26:25
  Speaker 1: and we can look to see, like from fossils, where
• 26:27
  Speaker 1: they lived and what the pattern and the climate might
• 26:30
  Speaker 1: have been. You know, if you know that one kind
• 26:33
  Speaker 1: of creature needs warmth and you see it in warm areas,
• 26:35
  Speaker 1: you can also see where else you find fossils and
• 26:38
  Speaker 1: that can give you a clue as to what the temperature.
• 26:40
  Speaker 1: But the climate might have been like when they were around.
• 26:43
  Speaker 2: So can you tell if there were sweating or if
• 26:44
  Speaker 2: they were shivering.
• 26:47
  Speaker 1: You can tell if their kids liked their dinners or
• 26:49
  Speaker 1: didn't like their dinners by the amount of complaining and whining.
• 26:52
  Speaker 1: That also changes the isotopes in the atmosphere. No, I'm
• 26:57
  Speaker 1: totally making that up, but you know, you can tell
• 26:59
  Speaker 1: what other organisms survive unchanged for millions of years, would
• 27:03
  Speaker 1: tell you that the climate was likely stable for millions
• 27:06
  Speaker 1: of years. So you can back out a lot of
• 27:08
  Speaker 1: interesting information from these fossils. And for me, this is
• 27:11
  Speaker 1: an example of the most impressive thing that science can do,
• 27:14
  Speaker 1: which is like reconstruct a detailed story from all these
• 27:18
  Speaker 1: incomplete threads, from little clues left here and there. We
• 27:22
  Speaker 1: can really figure out what life was like on Earth,
• 27:24
  Speaker 1: or understand what's inside the Earth or inside the Sun.
• 27:28
  Speaker 1: From all this incomplete knowledge. It's like the whole universe
• 27:30
  Speaker 1: is a huge mystery novel and we have just a
• 27:33
  Speaker 1: few traces of clues. But sometimes those clues come together
• 27:36
  Speaker 1: and tell you a coherent story, so you can become
• 27:39
  Speaker 1: convinced that you actually know something which you might have
• 27:41
  Speaker 1: thought would be impossible to figure out.
• 27:43
  Speaker 2: Yeah, it's amazing. We can look back in time. Basically,
• 27:45
  Speaker 2: it's like having a time machine.
• 27:47
  Speaker 1: Yeah, exactly.
• 27:49
  Speaker 2: And so what we've seen is that the temperature, the
• 27:51
  Speaker 2: climate on Earth has been changing a lot, and it
• 27:55
  Speaker 2: goes through ways and within those waves there are many waves.
• 27:58
  Speaker 2: I guess a big question now is what causes all
• 28:00
  Speaker 2: of these changes? Right? Like mm because the orbit around
• 28:04
  Speaker 2: the Sun hasn't changed that much for billions of years,
• 28:08
  Speaker 2: has it.
• 28:08
  Speaker 1: Yeah, Well, there's a lot of factors of play, but
• 28:10
  Speaker 1: one of them is the Earth's orbit. And this is
• 28:13
  Speaker 1: a very complex system and very chaotic because there's a
• 28:15
  Speaker 1: lot of feedback loops and we're gonna do some simplifications
• 28:18
  Speaker 1: here and we're not gonna be able to really treat
• 28:20
  Speaker 1: it with its full justice. But we do know some
• 28:23
  Speaker 1: things about what can cause an ice age. You know.
• 28:25
  Speaker 1: Number one is the atmosphere. If life on Earth produces
• 28:29
  Speaker 1: a lot of CO two or a lot of methane,
• 28:31
  Speaker 1: that can change the temperature on Earth for sure, right,
• 28:34
  Speaker 1: And there's been times in Earth's history when life is
• 28:37
  Speaker 1: producing more or less methane or more or less CO two,
• 28:40
  Speaker 1: And so what's in the atmosphere can change, like how
• 28:43
  Speaker 1: much light is absorbed by the Earth, how much is
• 28:45
  Speaker 1: reflected back out into space, and because it's a sensitive system,
• 28:49
  Speaker 1: that kind of an impact and even cause or end
• 28:51
  Speaker 1: ice ages. But another big factor is the orbit of
• 28:54
  Speaker 1: the Earth. There are these Melankovitch cycles, so the Earth
• 28:58
  Speaker 1: orbits the Sun and it's you know, mostly stable, but
• 29:00
  Speaker 1: there are wobbles here. Things process, and so there are
• 29:03
  Speaker 1: periods when we work closer and further on average, and so
• 29:06
  Speaker 1: these things really do change a little bit, and people
• 29:09
  Speaker 1: think that this is a big effect of these glacial
• 29:11
  Speaker 1: versus interglacial periods within an ice age.
• 29:14
  Speaker 2: WHOA, what causes these wobbles in our orbit? Is it
• 29:17
  Speaker 2: other planets or something else?
• 29:21
  Speaker 1: Yeah, essentially, it's because it's not such a simple system.
• 29:24
  Speaker 1: It's not a single mass orbiting another single mass. There's
• 29:27
  Speaker 1: an excentricity, we have an axial tilt, we have a procession,
• 29:31
  Speaker 1: and all of these things are interacting with the other
• 29:33
  Speaker 1: gravitational objects in the Solar System, and so we get
• 29:36
  Speaker 1: like little tugs from Jupiter and little tugs from other
• 29:39
  Speaker 1: stuff in the Solar system, and these things change. So
• 29:41
  Speaker 1: it changes like how much axial tilt we have and
• 29:44
  Speaker 1: exactly the procession of our ellipse around the Sun. And
• 29:47
  Speaker 1: as a result, we get slightly further or slightly closer
• 29:50
  Speaker 1: to the Sun, and that changes how much energy we get.
• 29:53
  Speaker 1: And these little effects can really cause a change in
• 29:56
  Speaker 1: the climate.
• 29:57
  Speaker 2: On Earth cool well or hot. I guess what else
• 30:01
  Speaker 2: it can cause an ice age.
• 30:02
  Speaker 1: Well, the Sun itself is variable, right, The Sun has
• 30:05
  Speaker 1: an eleven year cycle when it gets brighter and looser,
• 30:08
  Speaker 1: and then the north and south magnetic poles of the
• 30:10
  Speaker 1: Sun flips. This is not something we understand very well.
• 30:13
  Speaker 1: We don't really have a great model for the inner
• 30:16
  Speaker 1: workings of the Sun. We know there are these weird
• 30:18
  Speaker 1: plasma tubes, but it's again very chaotic, and we can't
• 30:21
  Speaker 1: see inside the Sun. But the Sun itself grows in
• 30:24
  Speaker 1: brightness and then fades, so that is part of the calculation.
• 30:28
  Speaker 2: Like the Sun is pulsating.
• 30:30
  Speaker 1: Years, yeah, exactly, and the Sun is gradually getting brighter overall, right,
• 30:35
  Speaker 1: the Sun's brightness is increasing very gradually as it gets older.
• 30:39
  Speaker 1: That doesn't change a lot over the last few centuries,
• 30:41
  Speaker 1: but over the long term, you know, all these things
• 30:44
  Speaker 1: do contribute to changes in the Earth's situation and therefore
• 30:48
  Speaker 1: it's climate. And then you have things like volcanoes on Earth.
• 30:52
  Speaker 1: If a volcano spews an enormous amount of stuff, it
• 30:55
  Speaker 1: could create a cloud which shrouds the earth and cools
• 30:59
  Speaker 1: it significantly. Or if you have like a meteor that
• 31:02
  Speaker 1: comes and impacts and throws up ejecta into the atmosphere,
• 31:06
  Speaker 1: or huge amounts of water vapor can also cause a
• 31:08
  Speaker 1: lot of reflectivity.
• 31:09
  Speaker 2: I feel really exposed right now, Like any of these
• 31:13
  Speaker 2: things at any moment could throw us into deathly freezing
• 31:17
  Speaker 2: temperatures or super duper unbearably hot temperatures.
• 31:20
  Speaker 1: Yeah. And it's this incredible combination of slow changing effects
• 31:25
  Speaker 1: and fast sudden effects like volcanoes and meteors. The last
• 31:30
  Speaker 1: major component is tectonic motion, like as the plates move
• 31:34
  Speaker 1: and as the continents themselves get dragged around the Earth,
• 31:37
  Speaker 1: it changes how like water flows around the Earth and
• 31:40
  Speaker 1: how wind currents move, and that can change the temperature
• 31:43
  Speaker 1: all over the Earth, like are you getting more air
• 31:46
  Speaker 1: from the Arctic? Is it getting fully distributed or is
• 31:49
  Speaker 1: it more segmented. Can really change what it's like to
• 31:51
  Speaker 1: be at lower latitudes.
• 31:53
  Speaker 2: M Well. Also, something interesting you said was that we're
• 31:56
  Speaker 2: currently in an ice age, meaning that over the long
• 32:01
  Speaker 2: history of the Earth, the average Earth temperature is actually
• 32:04
  Speaker 2: hotter than it is right now.
• 32:06
  Speaker 1: I don't know the exact number about the average, but
• 32:08
  Speaker 1: there definitely have been hotter periods on Earth than we
• 32:11
  Speaker 1: have right now.
• 32:12
  Speaker 2: Mm. So when you say it's colder, you mean it's
• 32:16
  Speaker 2: just like colder than the hottest it can get.
• 32:19
  Speaker 1: Yeah, the Earth is now colder than the hottest it's
• 32:22
  Speaker 1: ever been. For sure, there are some very very hot
• 32:24
  Speaker 1: periods in the history of the Earth. Of course, we
• 32:26
  Speaker 1: know that the Earth's climate has changed a lot in
• 32:29
  Speaker 1: the last one hundred ish years or so because of
• 32:30
  Speaker 1: the Industrial revolution and human contribution to the atmosphere, and
• 32:34
  Speaker 1: so things are changing pretty rapidly. But in the bigger strokes,
• 32:38
  Speaker 1: we are still in an ice age, though in an
• 32:40
  Speaker 1: interglacial period, right right.
• 32:42
  Speaker 2: Well, I think, and maybe an important dimension of this
• 32:46
  Speaker 2: idea is the rate at which things are changing, right
• 32:49
  Speaker 2: mm hmm. Like maybe in the past things have changed,
• 32:51
  Speaker 2: but maybe gradually, with enough time for life to evolve
• 32:55
  Speaker 2: and to adapt to it. But it can also change rapidly,
• 32:58
  Speaker 2: like for example, if it will case it blows up,
• 33:00
  Speaker 2: or if a meteor hits the Earth, that can change
• 33:02
  Speaker 2: things very rapidly to the point where we can that
• 33:05
  Speaker 2: or if we keep you know, pumping greenhouse gases into
• 33:08
  Speaker 2: the atmosphere, that can also make things change too rapidly
• 33:12
  Speaker 2: for anyone to adjust.
• 33:14
  Speaker 1: Yeah, it's a sensitive system and there are a lot
• 33:16
  Speaker 1: of things that affected and those things all have different
• 33:18
  Speaker 1: time scales, and they combine to make a very chaotic
• 33:22
  Speaker 1: sort of structure of the Earth's climate, and you have
• 33:25
  Speaker 1: these things that are very slowly but inevitably, like the
• 33:28
  Speaker 1: sun increasing in its temperature or regularly, and then the
• 33:31
  Speaker 1: Melankovitch cycles, which are actually like several different cycles layered
• 33:34
  Speaker 1: on top of each other. So as a result, you
• 33:36
  Speaker 1: gets very complex behavior of the Earth's climate, and it
• 33:40
  Speaker 1: has affected life on Ear even very recently, like this
• 33:43
  Speaker 1: interglacial period that we're in only started like ten to
• 33:46
  Speaker 1: fifteen thousand years ago, and obviously there were lots of
• 33:49
  Speaker 1: humans on Earth back then, and that's back when there
• 33:52
  Speaker 1: were more wooly mammos and there were glaciers much further
• 33:55
  Speaker 1: down across North America, for example. And so this is
• 33:58
  Speaker 1: sort of like in the deep history, maybe even the
• 34:00
  Speaker 1: deep memory of our own civilization.
• 34:04
  Speaker 2: The humans have written out some of these waves, is
• 34:07
  Speaker 2: what you're saying.
• 34:08
  Speaker 1: And these waves have affected human migration, right, there's all
• 34:11
  Speaker 1: these theories about humans leaving Africa and populating Europe and
• 34:14
  Speaker 1: doing so in several waves between ice ages perhaps, so
• 34:18
  Speaker 1: it's really set the whole context for life on Earth
• 34:20
  Speaker 1: and the evolution of humanity and its migration. It's basically
• 34:24
  Speaker 1: the frame in which we exist whoa.
• 34:27
  Speaker 2: That is pretty cool, maybe even ice cool.
• 34:30
  Speaker 1: It's definitely cosmic.
• 34:31
  Speaker 2: All right, Well, we talked about different things that can
• 34:34
  Speaker 2: maybe trigger changes in the climate, But the question we're
• 34:37
  Speaker 2: asking today is can a supernova from a star blowing
• 34:40
  Speaker 2: up far away from here? Can that maybe affect the
• 34:43
  Speaker 2: temperature and climate here on Earth? So let's dig into
• 34:47
  Speaker 2: that idea. But first let's take another quick break. All right,
• 35:03
  Speaker 2: we're asking a question can of supernova cause an ice age?
• 35:06
  Speaker 2: Which is kind of a triggy question, right because supernovas
• 35:09
  Speaker 2: are big, explosive, hot, deadly impactful, But an ice age
• 35:14
  Speaker 2: here on Earth is sort of slow and cold and
• 35:19
  Speaker 2: you know, freezing. So how can something exploding far away
• 35:22
  Speaker 2: cause things to get cooler here on Earth?
• 35:25
  Speaker 1: So the connection is still kind of tenuous, but it's
• 35:27
  Speaker 1: sort of fascinating. The idea is that supernovas, they don't
• 35:32
  Speaker 1: just go boom and send out a bunch of light
• 35:34
  Speaker 1: in the sky. They also send out dust, like little
• 35:37
  Speaker 1: bits of those supernovas that get carried along by like
• 35:41
  Speaker 1: cosmic and galactic winds and can come here to Earth.
• 35:45
  Speaker 1: And when supernovas do go boom, they make sort of
• 35:47
  Speaker 1: unique materials. They make stuff that you can't otherwise make
• 35:51
  Speaker 1: in the universe because you just don't have the conditions.
• 35:54
  Speaker 1: Like stars, they confuse hydrogen into helium, and helium into carbon,
• 35:58
  Speaker 1: and carbon into heavier stuff all the way up to
• 36:00
  Speaker 1: about iron, but they can't make anything heavier than that
• 36:03
  Speaker 1: because above that it costs more energy to fuse than
• 36:06
  Speaker 1: fusion creates. So all the heavier elements in the universe
• 36:09
  Speaker 1: are made under much more special conditions, such as neutron
• 36:13
  Speaker 1: star mergers or during those moments of supernova fusion. The
• 36:17
  Speaker 1: explosion that creates the supernova also can create weird new
• 36:22
  Speaker 1: heavy isotopes of elements and also heavier elements, and some
• 36:26
  Speaker 1: of those bits can fly through the universe and even
• 36:29
  Speaker 1: land on Earth, potentially affecting the climate here on Earth.
• 36:33
  Speaker 2: Right, Because I think as a start collapses and becomes
• 36:36
  Speaker 2: a supernova, it collapses, then it crunches together, and then
• 36:39
  Speaker 2: it bounces, and then everything just kind of blows out
• 36:42
  Speaker 2: in all directions, and that shock wave is where a
• 36:45
  Speaker 2: lot of the heavier elements get made. Because things are
• 36:47
  Speaker 2: being exploded out and compressed so much they become heavier elements.
• 36:51
  Speaker 2: And you're saying that stuff being flung out can actually
• 36:54
  Speaker 2: maybe reach us at some point.
• 36:55
  Speaker 1: We know that it has reached us, and we found
• 36:57
  Speaker 1: evidence of it here on Earth. This one particular kind
• 37:01
  Speaker 1: of element is called iron sixty, so it's a heavy
• 37:03
  Speaker 1: isotope of iron. This is something which can be made
• 37:07
  Speaker 1: under other normal circumstances. But it's interesting because that's a
• 37:10
  Speaker 1: fairly short half life, just like two and a half
• 37:12
  Speaker 1: million years. So if it was present on Earth when
• 37:16
  Speaker 1: Earth was formed, for example, all of that would have
• 37:18
  Speaker 1: decayed away into nickel. So if you find iron sixty
• 37:22
  Speaker 1: on Earth, that means it was made fairly recently, sometime
• 37:25
  Speaker 1: in the last five to ten million years. But there's
• 37:28
  Speaker 1: no process on Earth that can make iron sixty. The
• 37:31
  Speaker 1: only way we know that you can make iron sixty
• 37:33
  Speaker 1: is in the heart of a star, especially in a supernova.
• 37:36
  Speaker 1: And so if you find iron sixty on Earth, that's
• 37:39
  Speaker 1: very strong evidence that you found remnants of a supernova
• 37:43
  Speaker 1: here on Earth, like supernova dust has landed on Earth.
• 37:47
  Speaker 2: WHOA wait, how do you know it's not just really
• 37:49
  Speaker 2: old iron sixty from when the Earth was formed? Cann't
• 37:52
  Speaker 2: you just have a bunch of it and some of
• 37:54
  Speaker 2: it still survived, like we still have uranium on Earth.
• 37:57
  Speaker 1: We do still have uranium on Earth. Uranium is on
• 37:59
  Speaker 1: much longer half life than a couple of million years.
• 38:02
  Speaker 1: The Earth is four and a half billion years, which
• 38:04
  Speaker 1: is many, many lifetimes. This stuff has a lifetime of
• 38:07
  Speaker 1: two and a half million years. And if there was
• 38:10
  Speaker 1: original primordial iron sixty, you would be evenly distributed and
• 38:15
  Speaker 1: you'd see a sort of typical decay. Well, what we
• 38:17
  Speaker 1: find when we look for iron sixty is we see
• 38:20
  Speaker 1: depositions consistent with an increased amount of iron sixty like
• 38:24
  Speaker 1: tuish million years ago, and maybe like another deposition like
• 38:27
  Speaker 1: a million years ago. It really looks like we got
• 38:30
  Speaker 1: fresh doses of iron sixty a couple of times in
• 38:33
  Speaker 1: the recent past.
• 38:34
  Speaker 2: Well you mean like we've seen basically coatings of the
• 38:38
  Speaker 2: Earth with this iron. Yeah, isotope exactly, and there's several coatings.
• 38:43
  Speaker 1: There's several coatings, and if you just like dig down
• 38:46
  Speaker 1: into the earth, you don't find this stuff. But on
• 38:48
  Speaker 1: the ocean floor you do see it, and you can
• 38:51
  Speaker 1: see it in the sedimentary layers. You could see it
• 38:54
  Speaker 1: like layered at certain times and not other times. And
• 38:57
  Speaker 1: so it's really consistent with like the Earth blasted with
• 39:01
  Speaker 1: supernova iron sixty.
• 39:03
  Speaker 2: Well, I wonder if you would see it on one
• 39:05
  Speaker 2: side of the Earth, you know, or not the other,
• 39:07
  Speaker 2: or would you see it evenly coating the whole earth.
• 39:09
  Speaker 1: Yeah, that's a great question because we'd love to know
• 39:12
  Speaker 1: where these supernova were, right, which direction did they come from?
• 39:16
  Speaker 1: And if you saw, like where it landed on the Earth,
• 39:18
  Speaker 1: you might be able to like reconstruct that not just
• 39:20
  Speaker 1: from which side it's on, but like where is it
• 39:23
  Speaker 1: more dense? And Unfortunately on Earth, these things tend to
• 39:26
  Speaker 1: get swirled around a lot. Like on the ocean floor,
• 39:28
  Speaker 1: things get mixed around, and so you can tell it's there,
• 39:31
  Speaker 1: and you can tell what year it was deposited. But
• 39:34
  Speaker 1: you know, over millions of years, these things do get
• 39:36
  Speaker 1: swirled around and spread out. But if we went to
• 39:39
  Speaker 1: the Moon, the moon is a much better place to
• 39:41
  Speaker 1: keep these sort of ancient geological records because you know,
• 39:45
  Speaker 1: there's no weather on the Moon, there's no water, there's
• 39:47
  Speaker 1: no air, and so where things landed on the Moon
• 39:50
  Speaker 1: is pretty much where they still are. So the Moon
• 39:52
  Speaker 1: might have a great snapshot if you measure the iron
• 39:55
  Speaker 1: sixty on the surface of the Moon to figure out
• 39:57
  Speaker 1: which direction these things came from.
• 40:00
  Speaker 2: Well, we've been to the Moon and we've gotten samples
• 40:03
  Speaker 2: from there, and what do we find in terms of
• 40:06
  Speaker 2: this iron?
• 40:07
  Speaker 1: We didn't find very much, But the samples are not
• 40:09
  Speaker 1: really the kind you would need to answer this question.
• 40:12
  Speaker 1: You know, Apollo landed on the near side of the Moon,
• 40:15
  Speaker 1: and much more likely these things landed on the far
• 40:17
  Speaker 1: side of the Moon because it's facing out, and so
• 40:20
  Speaker 1: we'd need much broader sampling also to like reconstruct the direction.
• 40:25
  Speaker 1: And so if you wanted to answer this question from
• 40:28
  Speaker 1: samples on the Moon, you need to sample very differently
• 40:30
  Speaker 1: from the way Apollo did. So we don't really have
• 40:33
  Speaker 1: the data we would need to answer that question. One
• 40:35
  Speaker 1: more reason to go back to the moon.
• 40:38
  Speaker 2: So the Earth has gone in a few dustings of
• 40:40
  Speaker 2: this iron from potentially supernova's. What's the connection to an
• 40:43
  Speaker 2: ice age? Then, so there's a couple of things. One
• 40:46
  Speaker 2: is they can look at the timing of the supernova
• 40:49
  Speaker 2: and it looks like there was a string of supernovas
• 40:51
  Speaker 2: that went off in the last ten million years in
• 40:54
  Speaker 2: our galaxy. It's like a blob of deposition of iron
• 40:57
  Speaker 2: sixty from like one point seven to three point five
• 41:00
  Speaker 2: two million years ago. And then there's another deposition like
• 41:03
  Speaker 2: two and a half million years ago and another one
• 41:05
  Speaker 2: zero point eight million years ago that they think are
• 41:08
  Speaker 2: consistent with supernova's that went off like around three hundred
• 41:11
  Speaker 2: light years away from the Earth, And the time of
• 41:13
  Speaker 2: these things kind of lines up with the timing of
• 41:16
  Speaker 2: the ice ages. So if you look at the history
• 41:18
  Speaker 2: of the climate on the Earth and you look at
• 41:20
  Speaker 2: the history of these supernova, you can like kind of
• 41:22
  Speaker 2: line these things up. Now that's just correlational, but it's
• 41:26
  Speaker 2: intriguing and it makes people wonder like, hmm, could the
• 41:29
  Speaker 2: arrival of this iron sixty on Earth somehow trigger climate
• 41:32
  Speaker 2: effects which lead to ice ages? WHOA. But I guess
• 41:36
  Speaker 2: maybe one question people might have right now is these
• 41:38
  Speaker 2: supernova were super duper far away. Three hundred light years
• 41:42
  Speaker 2: is gazillions of kilometers away. Could there still be enough
• 41:46
  Speaker 2: iron in that explosion this far out? Wouldn't it be
• 41:49
  Speaker 2: super diluted and spread out, it would actually be a
• 41:52
  Speaker 2: significant amount that we could see.
• 41:53
  Speaker 1: It's a great question, and it highlights the incredible numbers
• 41:56
  Speaker 1: that are going on here. Like, first of all, when
• 41:58
  Speaker 1: you make a supernova, the mounts of material are vast
• 42:02
  Speaker 1: because supernova come from really big stars right, So you're
• 42:05
  Speaker 1: starting with an incredible number of atoms. But then, of course,
• 42:08
  Speaker 1: as you say, space is huge and we're far away
• 42:10
  Speaker 1: from these things, so how are we getting any of them?
• 42:13
  Speaker 1: And the answer is that we're not getting many. The
• 42:15
  Speaker 1: number of iron sixty atoms, we've recovered numbers in the thousands.
• 42:20
  Speaker 1: So we've scoured the planet for these things, and people
• 42:23
  Speaker 1: have done these incredible missions to the bottom of the ocean.
• 42:25
  Speaker 1: We don't have a lot of examples. We have enough
• 42:28
  Speaker 1: to reconstruct the timing of these things to say something
• 42:30
  Speaker 1: about which direction maybe they were coming from, but we
• 42:34
  Speaker 1: don't have a large number of examples.
• 42:36
  Speaker 2: No, meaning, this is a very faint signal.
• 42:39
  Speaker 1: It's a pretty faint signal, but it started out so
• 42:41
  Speaker 1: bright and so intense that even this far away we
• 42:44
  Speaker 1: can't pick it up.
• 42:46
  Speaker 2: Now, then, how can this iron affect the climate here
• 42:50
  Speaker 2: on Earth?
• 42:50
  Speaker 1: So that's something people are more speculating about and trying
• 42:53
  Speaker 1: to understand. Is not a solid model here, but you
• 42:56
  Speaker 1: can imagine that the arrival of heavy metals in the
• 42:59
  Speaker 1: app sphere could change the way things circulate and the
• 43:02
  Speaker 1: way things nucleate and the atmosphere chemistry, which is very
• 43:05
  Speaker 1: complicated and so there isn't like a very clear argument
• 43:09
  Speaker 1: here yet. I mean, I was reading some papers that
• 43:10
  Speaker 1: were kind of hand wavy. But the general idea is
• 43:14
  Speaker 1: the atmosphere composition is an important component of understanding the climate,
• 43:18
  Speaker 1: and changes in the atmosphere can change the climate. We
• 43:21
  Speaker 1: know that's true. And so the question is can iron
• 43:25
  Speaker 1: sixty or how much iron sixty would have to arrive
• 43:28
  Speaker 1: to trigger a change in the climate that might give
• 43:30
  Speaker 1: you an ice age. That question is not answered, right.
• 43:33
  Speaker 2: It seems like you wouldn't get I mean, if we
• 43:35
  Speaker 2: were talking about thousands of atoms, that doesn't seem like
• 43:38
  Speaker 2: a lot enough to trigger and ice it. But maybe
• 43:41
  Speaker 2: the super wall that send other things besides iron, right, Like,
• 43:44
  Speaker 2: maybe it's send other elements, Absolutely a ton of other elements.
• 43:47
  Speaker 1: Yeah, And we have found thousands of atoms. Of course,
• 43:49
  Speaker 1: we have a tiny detection efficiency, which means there are many,
• 43:52
  Speaker 1: many more atoms actually arrived on Earth. And you're absolutely right,
• 43:55
  Speaker 1: the iron sixty is just like one of the easiest
• 43:58
  Speaker 1: things to identify. Along with it must have come all
• 44:01
  Speaker 1: sorts of other debris from the supernova. And when you
• 44:04
  Speaker 1: get unusual, weird cosmic dust from space that might trigger
• 44:08
  Speaker 1: changes in the atmosphere, but it's kind of speculative. I
• 44:11
  Speaker 1: think the most suggestive piece of evidence is the coincidence
• 44:15
  Speaker 1: between the timing of the ice ages and the timing
• 44:17
  Speaker 1: of these recent supernova although it's hard to tell if
• 44:20
  Speaker 1: that's a coincidence or not.
• 44:21
  Speaker 2: I see, they seem correlated, they seem to be happening
• 44:24
  Speaker 2: at the same time, but we don't know how yet
• 44:26
  Speaker 2: or how that's even possible exactly.
• 44:29
  Speaker 1: And you know, this is the process of science. You
• 44:30
  Speaker 1: see this weird effect, you wonder if they could be connected.
• 44:33
  Speaker 1: You look for a mechanism. Rather than just saying, oh, look,
• 44:36
  Speaker 1: it happened at the same time, therefore one cause the other.
• 44:38
  Speaker 1: You try to dig into it and understand, like, how
• 44:40
  Speaker 1: could that be? Is is there a way that could
• 44:42
  Speaker 1: really happen, and how could we check that? And so
• 44:45
  Speaker 1: some people are working on that right now, like trying
• 44:47
  Speaker 1: to understand what kind of supernova debris might trigger a
• 44:50
  Speaker 1: change in the atmosphere.
• 44:52
  Speaker 2: Interesting. It made me think that you know, the supernovas
• 44:56
  Speaker 2: happened really far away, right and they're huge, and which
• 45:01
  Speaker 2: maybe affect the entire Milky Way galaxy or a big
• 45:04
  Speaker 2: part of the Milky Way galaxy, in which case, like
• 45:06
  Speaker 2: one of these supernovas exploding could maybe trigger an ice
• 45:09
  Speaker 2: age in a whole bunch of planets around that start, right.
• 45:12
  Speaker 1: Yeah, absolutely, And when the supernova happens, it like sterilizes
• 45:16
  Speaker 1: the nearby planets. It's cool to think it could have
• 45:18
  Speaker 1: a more subtle effect on even further away planets, right,
• 45:22
  Speaker 1: it can change the climate of those planets, which could
• 45:25
  Speaker 1: really affect the evolution of life on those planets. Like
• 45:28
  Speaker 1: maybe life is more likely to become intelligent when there
• 45:30
  Speaker 1: are ice ages or when it's oscillating ice ages and
• 45:33
  Speaker 1: warm periods. Who knows, right, But supernovas definitely have a
• 45:37
  Speaker 1: rippling effect on the whole history of the galaxy, and
• 45:40
  Speaker 1: that changes the whole frame for life everywhere in the galaxy.
• 45:43
  Speaker 2: Yeah, it's definitely a cool effect. And like you said,
• 45:46
  Speaker 2: like maybe it's possible that the only reason we evolved
• 45:49
  Speaker 2: is because of a supernova. Like maybe even that supernova
• 45:52
  Speaker 2: hadn't happened and sent all this material here, we wouldn't
• 45:55
  Speaker 2: have evolved.
• 45:56
  Speaker 1: Yeah, or we could have evolved very differently, you know,
• 45:58
  Speaker 1: migrated differently, had different patterns and paths if the climate
• 46:01
  Speaker 1: were different, and so life on Earth could be vastly
• 46:04
  Speaker 1: different without that super Nivah.
• 46:06
  Speaker 2: Yeah, without that iron in which case it means Daniel,
• 46:09
  Speaker 2: I think that we're all ironmen. It's not just Tony Stark,
• 46:17
  Speaker 2: that's right.
• 46:17
  Speaker 1: Oh, you don't have to run a marathon and bike
• 46:21
  Speaker 1: fifty miles and swimed in miles all the same time
• 46:24
  Speaker 1: to be iron man. You just got to live here
• 46:26
  Speaker 1: on Earth and listen to podcast.
• 46:28
  Speaker 2: And or build an armor, yes, a robotic armor.
• 46:31
  Speaker 1: Awesome. Well, I'm looking forward to writing my own saber
• 46:34
  Speaker 1: tooth cat to work.
• 46:35
  Speaker 2: And then yeah, you're looking forward to jumping your own
• 46:38
  Speaker 2: prehistoric shark.
• 46:39
  Speaker 1: Right, that's right, exactly, sabertooth shark.
• 46:42
  Speaker 2: Yes, or maybe you should start a new meme or term, right,
• 46:45
  Speaker 2: jumping the saber tooth tiger. We're jumping the wooly mammoth.
• 46:49
  Speaker 2: Oh that sounds even better, you go, yeah, we really
• 46:52
  Speaker 2: that podcast was great, but then it jumped the wooly mammoth,
• 46:54
  Speaker 2: and you know, now it's even better.
• 46:58
  Speaker 1: Yeah, well, maybe we're entering the vast podcast ice age.
• 47:01
  Speaker 2: Yeah. Thanks are definitely cooling a little bit here, all right. Well,
• 47:04
  Speaker 2: another reminder of how carrious life here on Earth is
• 47:08
  Speaker 2: to all of these cosmic events that are happening all
• 47:10
  Speaker 2: around this and maybe hopefully make your appreciate the fact
• 47:14
  Speaker 2: that we are here talking about these things. And then
• 47:16
  Speaker 2: maybe that fact is only possible because of a certain
• 47:20
  Speaker 2: string of events that happened billions of years ago.
• 47:22
  Speaker 1: Our curiosity to understand the universe continues to burn hot,
• 47:26
  Speaker 1: even if the heat of those stars eventually causes an
• 47:29
  Speaker 1: ice age.
• 47:30
  Speaker 4: Right.
• 47:30
  Speaker 2: We hope you enjoyed that. Thanks for joining us, See
• 47:33
  Speaker 2: you next time.
• 47:39
  Speaker 1: For more science and curiosity, come find us on social
• 47:42
  Speaker 1: media where we answer questions and post videos. We're on Twitter, Discord, Instant,
• 47:47
  Speaker 1: and now TikTok. Thanks for listening, and remember that Daniel
• 47:50
  Speaker 1: and Jorge Explain the Universe is a production of iHeartRadio.
• 47:54
  Speaker 1: For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
• 48:00
  Speaker 1: or wherever you listen to your favorite shows.