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Banded Iron Formations - BIFs · PlanetGeo: The Geology Podcast

• 0:02
  SPEAKER_01: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
• 0:13
  SPEAKER_01: Chris, your game left you a little while ago.
• 0:16
  SPEAKER_01: One episode re-recorded.
• 0:18
  SPEAKER_01: You were not on your game.
• 0:19
  SPEAKER_01: You could not, you know, put two words together that made sense.
• 0:23
  SPEAKER_01: What was it?
• 0:24
  SPEAKER_01: What was going on?
• 0:24
  SPEAKER_01: I don't know.
• 0:25
  SPEAKER_01: Your game left you.
• 0:26
  SPEAKER_01: You know, it's like Space Jam.
• 0:27
  SPEAKER_01: You ever seen the movie Space Jam, Chris?
• 0:29
  SPEAKER_01: No, I've not seen the movie Space Jam.
• 0:30
  SPEAKER_01: The monstars came and took your game from you.
• 0:34
  SPEAKER_01: Stole your game.
• 0:35
  SPEAKER_00: Well, that is such a rare uh occurrence that I um I don't remember.
• 0:43
  SPEAKER_00: You know who you're like, Chris?
• 0:44
  SPEAKER_01: You're now that I'm thinking about this, you're a lot like Charles Barkley, the round mound of rebound.
• 0:48
  SPEAKER_01: You're a lot like Charles Barclay in Monstar.
• 0:52
  SPEAKER_00: Oh, look at you.
• 0:53
  SPEAKER_00: I you know, it's been a long time since you've been dropping basketball analogies, you know.
• 0:58
  SPEAKER_01: I thought that part of your life was gone.
• 1:00
  SPEAKER_01: Uh, it's been on my mind again recently because I'm not that I'm not very good anymore.
• 1:05
  SPEAKER_01: So anyway.
• 1:07
  SPEAKER_01: Huh.
• 1:08
  SPEAKER_01: All right.
• 1:08
  SPEAKER_01: Hey, shall we uh get into it here?
• 1:12
  SPEAKER_01: I think we should, yeah.
• 1:13
  SPEAKER_01: So, Chris Bullheis, what are we talking about today?
• 1:17
  SPEAKER_00: Uh, yes, we're gonna talk finally.
• 1:19
  SPEAKER_00: This has been on the books for a long time.
• 1:22
  SPEAKER_00: It has.
• 1:23
  SPEAKER_00: Uh, we're gonna talk about banded iron formations, otherwise known as biffs.
• 1:28
  SPEAKER_00: These are just I don't know, there's some debate swirling around this.
• 1:31
  SPEAKER_00: I think it was just why we decided to hold off on it for so long.
• 1:34
  SPEAKER_01: We scripted this out a long time ago.
• 1:36
  SPEAKER_01: This was early on, like I mean, episode five, I think you wanted to do banded iron formations.
• 1:41
  SPEAKER_01: I was like, uh, I'm not really comfortable.
• 1:43
  SPEAKER_01: There's like all this debate, so it's a kind of a controversial topic, which I tend to be a little bit more scared of, perhaps, in a podcast space or something.
• 1:52
  SPEAKER_01: But uh, we finally getting around to it.
• 1:54
  SPEAKER_01: It's a one of the prettier rocks out there, I think.
• 1:57
  SPEAKER_01: Banded iron formation.
• 1:59
  SPEAKER_01: If you've ever been to a rock museum, I almost guarantee there's a slab of banded iron formation in it.
• 2:05
  SPEAKER_01: It's like one of the must-haves that museums you know are always pursuing, I think.
• 2:09
  SPEAKER_00: That's right.
• 2:09
  SPEAKER_00: That's right.
• 2:10
  SPEAKER_00: It is an absolutely beautiful rock because it's gonna be just the banded iron formation that I've seen, the biff that I've seen a lot of, is you know, it alternates between like silver and red or black and red, and it's intricately banded, and it is just gorgeous.
• 2:28
  SPEAKER_00: I have tons of this stuff, actually, um of clever.
• 2:32
  SPEAKER_01: So much of it.
• 2:33
  SPEAKER_01: And Chris, actually, the field trip, was it in the geology class?
• 2:37
  SPEAKER_01: I think the field trip that goes up to the upper peninsula of Michigan, where actually Biff was discovered or named, I think it probably been discovered before that, but actually sort of named and identified as unique rock in 1844, was up in northern Michigan in a place called Jasper Knob and the region around their big iron mining country in northern Michigan.
• 2:56
  SPEAKER_01: But you took me there when I was a student of yours on field trip, and we went uh we've been a couple times, and there's a strip of well, we don't want to give away good rock collecting spots, but there's a little strip of of land up there that uh has a bunch of riprap, you know, the constructing the road, and there's amazing banded iron pieces in this like riprap section that's right, that's tossed up alongside the shoreline there um almost as waste.
• 3:23
  SPEAKER_00: Yeah.
• 3:23
  SPEAKER_00: Um, you're right, because because that place I took you when you were a student, Jasper Knob, the mountain does not want to let go of it.
• 3:33
  SPEAKER_00: It is very, very difficult.
• 3:35
  SPEAKER_00: And I'm glad for that.
• 3:36
  SPEAKER_01: Collecting like it's hard to collect rocks.
• 3:38
  SPEAKER_01: You you can't collect rocks.
• 3:39
  SPEAKER_01: This rock is super hard, and we're gonna get into why it's super hard.
• 3:42
  SPEAKER_01: It's super hard and super heavy, super dense.
• 3:45
  SPEAKER_00: And and were I collect, I never would collect on the on the top of Jasper Knob.
• 3:49
  SPEAKER_00: It's just too pretty up there, and I don't want to disrupt that.
• 3:52
  SPEAKER_01: So let's just quickly paint a picture for anybody who hasn't seen a banded iron formation of what this is.
• 3:57
  SPEAKER_01: You described it as this you know really beautiful, layered, kind of laminated.
• 4:01
  SPEAKER_01: Sometimes people use the word laminated rock, and the one in Jasper Knob is red and silver.
• 4:08
  SPEAKER_01: And banded iron formation is the name here, and we have iron layers, and those are the silver ones in in uh Jasper Knob, and we have silica-rich layers, and they're not pure, it's not pure iron and pure silica.
• 4:23
  SPEAKER_01: There are iron-rich mineral layers and silica-rich mineral layers, and there's some mixing between them.
• 4:29
  SPEAKER_01: So you can get really beautiful color variations here.
• 4:32
  SPEAKER_01: You can get oranges and kind of pinkish colors, and silver and black, and really white or translucent.
• 4:39
  SPEAKER_01: Sometimes those silica-rich layers are nearly pure chert, and they can be different colors depending on what trace minerals are in there as well.
• 4:47
  SPEAKER_01: So the layers are pretty small, like millimeter to sort of maybe a centimeter at most, I think.
• 4:52
  SPEAKER_01: And so you get these really fine layers in them.
• 4:55
  SPEAKER_00: That's right.
• 4:56
  SPEAKER_00: The silver or really dark colored layers, the you said they're iron-rich, they typically are the minerals hematite or magnetite.
• 5:05
  SPEAKER_00: And to me, I prefer the hematite rich ones just because I am like hematite is one of my favorite minerals of all time.
• 5:11
  SPEAKER_00: I I love that stuff.
• 5:12
  SPEAKER_00: I just I have tons of that also.
• 5:14
  SPEAKER_00: But the magnetite is also really beautiful, but it's it's like almost black and then interbedded with this vibrant red, and then black, and then red, and so on.
• 5:24
  SPEAKER_00: So it's either the stuff that we're familiar with is hematite and magnetite, and then the reddish layers, at least up in the upper peninsula, are a mineral called jasper.
• 5:36
  SPEAKER_00: It's a form of of chalcedony, which chalcedony is almost always mispronounced by by Chalcedony, Chalcudney.
• 5:46
  SPEAKER_01: Yeah.
• 5:47
  SPEAKER_01: Well, I mean, it's basically it's the same formula as quartz.
• 5:50
  SPEAKER_01: It's SiO2.
• 5:51
  SPEAKER_01: And you can get different color variations.
• 5:53
  SPEAKER_01: I've seen ones up in the the northern Canada where I work that are a little bit more yellow and they have this black hematite background.
• 6:00
  SPEAKER_01: So you can get a variety of different minerals, greenolite, ciderite, anchorite, you know, in smaller proportions, but it's mostly SiO2 layers and iron oxide layers.
• 6:10
  SPEAKER_01: And the iron oxide can be in different forms depending on the oxidation state of how these things form.
• 6:15
  SPEAKER_01: So different proportions there between hematite and magnetite.
• 6:19
  SPEAKER_00: So when did these things form, Jesse?
• 6:21
  SPEAKER_00: Let's move into that.
• 6:22
  SPEAKER_00: Like when did they form and kind of where they formed?
• 6:26
  SPEAKER_01: Yeah.
• 6:26
  SPEAKER_01: And I think, Chris, let's not bury the lead here and let's like sort of give away the thing.
• 6:30
  SPEAKER_01: They're beautiful rocks, they're super pretty rocks, and so they're they're stunning to look at.
• 6:34
  SPEAKER_01: It's amazing that rocks can look this cool, I think.
• 6:38
  SPEAKER_01: But more importantly than that, when you're looking at this amazing rock, it is representation that the ancient earth was very different than the modern earth.
• 6:48
  SPEAKER_01: It shows us that the climate and the ocean chemistry on the ancient earth was really different.
• 6:53
  SPEAKER_01: And so these rocks are often quite old.
• 6:55
  SPEAKER_01: Like very few biffs are younger than about 1.9 billion years old, and most of them are about 2.7.
• 7:01
  SPEAKER_01: There's a there's a pulse of biff formation 2.7 billion years ago.
• 7:05
  SPEAKER_01: There's a little bit of a pulse 2.4 and then 1.9.
• 7:09
  SPEAKER_01: And then there's some formed in the more recent past, like around 1.1 GA or about 800 MA, but not very many at all.
• 7:17
  SPEAKER_01: They're really a small proportion.
• 7:19
  SPEAKER_00: And I want to add to what you said too, in terms of the lead-in, that it's also an extremely important ore rock.
• 7:27
  SPEAKER_00: I mean, this is where the world gets the majority of our iron from BIFS.
• 7:34
  SPEAKER_00: So they're really very important.
• 7:36
  SPEAKER_01: There's a mine, one of the big ones, which is actually has some really interesting scientific studies coming out of this deposit.
• 7:42
  SPEAKER_01: But the Hammersley Basin in Australia is a massive, massive iron mine.
• 7:47
  SPEAKER_01: A hundred million tons of iron ore are removed every year from this place.
• 7:52
  SPEAKER_01: Because iron is so concentrated.
• 7:54
  SPEAKER_01: Like, and if you pick up a biff, or actually you could just look at it in a museum and you can tell this thing is dense.
• 8:00
  SPEAKER_01: Like if you're looking at a big slab of Bended Iron Form, look at the mounting brackets that the museum had to use to stand that up.
• 8:08
  SPEAKER_01: They're usually bolted into the wall.
• 8:10
  SPEAKER_01: I mean, this is a heavy, heavy, heavy rock because of all of that iron in it.
• 8:14
  SPEAKER_01: It's super dense.
• 8:16
  SPEAKER_01: And so the iron is kind of pre-concentrated by nature here.
• 8:19
  SPEAKER_00: Yeah, I'm getting too old to collect biff because um I I need I need young people around me to to like, hey, go help me.
• 8:27
  SPEAKER_00: Go get me that.
• 8:28
  SPEAKER_00: And hey, can you carry that to my truck, please?
• 8:32
  SPEAKER_01: I would phrase it differently, Chris.
• 8:33
  SPEAKER_01: You're becoming esteemed where you need, you know, field hands that carry rocks for you.
• 8:37
  SPEAKER_01: Oh, I like that a lot better than the way I said it.
• 8:40
  SPEAKER_01: That is true.
• 8:41
  SPEAKER_01: I'm I'm good.
• 8:42
  SPEAKER_01: My PhD supervisor is uh was famous for in a joking way.
• 8:46
  SPEAKER_01: He said, Well, he kind of likes graduate students who are quite big because then they can carry all the rocks and he doesn't have to carry as heavy of a load hiking around the tundra.
• 8:54
  SPEAKER_00: That's a very good point.
• 8:55
  SPEAKER_00: I'm I'm taking that with me.
• 8:57
  SPEAKER_00: Um, all right.
• 8:58
  SPEAKER_00: I think it's also important to understand then that we know that these were sedimentary rocks.
• 9:02
  SPEAKER_00: Okay, they were deposited in the way that you know sandstones and shales and and some of the chemical sedimentary rocks were deposited, like limestone, dolestone as well.
• 9:13
  SPEAKER_00: Now, they are very old rocks, though, as you already pointed out, and so some of them have been altered later.
• 9:20
  SPEAKER_00: They've been you know heated in pressure and and now they're metamorphic, but they were originally sedimentary rocks.
• 9:25
  SPEAKER_01: That's a great point.
• 9:26
  SPEAKER_01: I do this all the time.
• 9:28
  SPEAKER_01: You know, I look at old igneous rocks that are not igneous rocks, they're metamorphic rocks now.
• 9:33
  SPEAKER_01: And so when I usually refer to the age of igneous rocks, I'm talking about the primary crystallization age, like when it crystallized from a magma, and then it experienced metamorphism time and time again.
• 9:45
  SPEAKER_01: And I just did the exact same thing with Bandiron formations.
• 9:48
  SPEAKER_01: When I said 2.7 billion years and 1.9 billion years and 2.4 billion years, that was the depositional age of the rock, not the metamorphic age of the rock.
• 9:57
  SPEAKER_01: And the metamorphism has happened much younger or much later than that.
• 10:01
  SPEAKER_01: So if you wanted to probably be strict about the age of the rock, it's a metamorphic rock that was metamorphosed you know more recently than 1.9 billion years ago.
• 10:12
  SPEAKER_01: And that's a really interesting point, Chris, because when you look at these rocks, you have these really fine-scale laminations, but they kind of bend and twist and curve all over the place.
• 10:21
  SPEAKER_01: And a little bit of that is probably primary depositional layering.
• 10:25
  SPEAKER_01: Think of these minerals precipitating out of an ocean.
• 10:28
  SPEAKER_01: They can kind of slump.
• 10:29
  SPEAKER_01: It's like mud, basically.
• 10:30
  SPEAKER_01: You'd have this mud and it can kind of move around and get deformed.
• 10:33
  SPEAKER_01: But a lot of it is metamorphic as well.
• 10:35
  SPEAKER_01: These things are kind of folded and bent and twisted, and they're actually, even though they're really hard and dense, they're easy to twist and bend because there's so much silica in there that makes these rocks kind of soft under metamorphic conditions when it gets a little hot.
• 10:50
  SPEAKER_00: That's right.
• 10:50
  SPEAKER_00: That's a good point.
• 10:51
  SPEAKER_00: All right, Jesse, can we move into what I really want to get into then?
• 10:54
  SPEAKER_00: I w I I want to talk about I want to talk about the geology of this, right?
• 10:58
  SPEAKER_01: Is this a are we uh is this something that I don't know what we're gonna talk about next?
• 11:02
  SPEAKER_01: You let into that, like I don't know where we're going.
• 11:04
  SPEAKER_01: You're gonna throw a ringer at me.
• 11:06
  SPEAKER_01: Okay.
• 11:06
  SPEAKER_00: No, I'm not I'm not throwing a ringer, I promise.
• 11:08
  SPEAKER_00: But I want to get into I always, you know, we gave a little bit of the background and so on, and why they're economically important, but how do they form, right?
• 11:18
  SPEAKER_00: I mean, these they're very, very important for or iron ore, but how geologically why are they all old, right?
• 11:27
  SPEAKER_00: And I think that's a that's a really important piece of the puzzle.
• 11:31
  SPEAKER_00: I mean, this is not going on anymore.
• 11:33
  SPEAKER_01: I agree, yeah.
• 11:34
  SPEAKER_01: And it is the more one of the more interesting parts.
• 11:37
  SPEAKER_01: And a lot of people have focused on studying these things because they're old and they're different, and they so they point to the fact that the early earth or the ancient earth was different than the modern, and so teasing apart why is it different, how is it different, are really important aspects.
• 11:50
  SPEAKER_00: Jesse, let me interrupt you a second because you're quick to point out that this is a very hotly debated thing in terms of the the formation of it, right?
• 11:59
  SPEAKER_00: There's a like a traditional view, and there's been some new research that's indicated some different processes.
• 12:06
  SPEAKER_00: I want to point out that when I look at these, I think that they're both at play.
• 12:12
  SPEAKER_00: The geology of banded iron formation is not necessarily this global explanation that it it the local geology plays in, and so there's no one correct, like summative geologic explanation for banded iron formation.
• 12:29
  SPEAKER_00: Would you you agree with that?
• 12:30
  SPEAKER_01: I would agree completely with that.
• 12:32
  SPEAKER_01: That's a great, great point.
• 12:33
  SPEAKER_01: And I think why don't we start out by Chris by saying what is shared, what is accepted here, and and what is accepted uh you know between all types of banded iron formation models or models for how banded iron formation is formed.
• 12:46
  SPEAKER_01: What's universally true is that ocean chemistry was very different.
• 12:51
  SPEAKER_01: We don't have silica precipitating out of the ocean chemically, or iron precipitating out of the ocean chemically much today on Earth in the same way that it does.
• 13:01
  SPEAKER_01: We don't have banded iron formations forming.
• 13:02
  SPEAKER_01: So it points to something different.
• 13:05
  SPEAKER_01: And the atmospheric composition did not have oxygen in it.
• 13:08
  SPEAKER_01: It had very, very, very little oxygen in it, and the ocean had very, very little oxygen in it as well, apart from the water.
• 13:16
  SPEAKER_00: That is a very important point that we all can agree on, because when you don't have oxygen present, then the iron that's in the water, that's getting to the water, can't precipitate out.
• 13:31
  SPEAKER_00: And so what happened then is over this time leading up to the formation of the biffs, it was just a lot of accumulation of iron.
• 13:40
  SPEAKER_00: So then something changes, right?
• 13:43
  SPEAKER_00: Uh oxygen is introduced into this equation, which then allows the precipitation of iron in massive amounts, right?
• 13:52
  SPEAKER_00: I mean, I think that's what we can agree on, right?
• 13:54
  SPEAKER_00: That in order to get them, you had to have iron accumulate in almost a super saturated kind of No, that's right.
• 14:02
  SPEAKER_01: You have to have iron accumulating in the ocean, and then it gets supersaturated, and then it's getting dumped out.
• 14:08
  SPEAKER_01: And the same with silica.
• 14:09
  SPEAKER_01: And so we have this layering, and the question has always sort of been what is the control of the layering?
• 14:15
  SPEAKER_01: Is it silica just precipitating in the background because the ancient oceans were silica saturated?
• 14:21
  SPEAKER_01: So they're just precipitating, crystallizing out jasper in the background or chert in the background, and then iron kind of turns on and off, on and off, on and off, on and off to get that layering.
• 14:32
  SPEAKER_01: Or is there a lot of iron precipitation in the background and quartz is turning on and off, on and off, on and off?
• 14:37
  SPEAKER_01: Or is there some feedback between the two that's driving this ocean chemistry?
• 14:41
  SPEAKER_00: Well, there's one explanation for how you can get this kind of interbetting between iron and the silica-rich jasper in this case.
• 14:49
  SPEAKER_00: It's related to bacteria, and these are photosynthetic organisms in the ocean.
• 14:54
  SPEAKER_00: So, really, this could be tied to the evolution of life in the oceans.
• 14:59
  SPEAKER_00: These organisms they kind of proliferate, they become more and more abundant, they're producing oxygen, and then the oxygen combines with the Fe3 plus, the one of the iron ions, and it precipitates out as magnetite or hematite.
• 15:13
  SPEAKER_00: But then these organisms they kind of suffocate in their own waste and they die out, which then silica gets precipitated.
• 15:22
  SPEAKER_00: But then these organisms rebound and they rebound and they become more abundant, and therefore another layer of iron gets precipitated and the cycle repeats itself just again and again and again.
• 15:34
  SPEAKER_00: That's one explanation for how we think bifs can form.
• 15:40
  SPEAKER_01: Yeah, that's right.
• 15:41
  SPEAKER_01: And I think it's important again to kind of come back to a point you you just made, Chris, earlier was that this is a local phenomenon.
• 15:46
  SPEAKER_01: So you can imagine this is not the entire ocean all at once having big bacterial blooms turning on and off.
• 15:53
  SPEAKER_01: This is happening in more restricted regional basins.
• 15:56
  SPEAKER_01: So you can have different biffs forming in different ways.
• 15:59
  SPEAKER_01: And you you pointed out earlier that there's hematite biffs, there's magnetite biffs.
• 16:03
  SPEAKER_01: So the chemistry is not the same all the time here, and we can have different processes turning these things on and off.
• 16:09
  SPEAKER_01: But that uh is definitely sort of one of the leading models for this.
• 16:13
  SPEAKER_01: There's another variation on that, I think, that links the banding to climate changes.
• 16:22
  SPEAKER_01: And there are some people that argue this is seasonal, like varves that occur in modern lake beds.
• 16:27
  SPEAKER_01: You can see seasonal variations in the city.
• 16:30
  SPEAKER_01: Oh, okay.
• 16:30
  SPEAKER_00: Let's define varves it real quick, Jesse, because I think there's kind of funny.
• 16:36
  SPEAKER_00: Well, oftentimes we get varves deposited in lakes, for instance, where you get these seasonal layers where you have a lot of organic material deposited in the clay-like sediment at the bottom of the lake, and that's indicative of spring and summer, and then you get the very organic poor layers deposited on top of that that indicates late fall and and winter where you don't have a lot of organic matter, and then the cycle just repeats itself.
• 17:01
  SPEAKER_00: And so that cycle of organic rich and organic poor layers is one varv.
• 17:08
  SPEAKER_01: Yes.
• 17:09
  SPEAKER_01: And so, model two that sort of is out there, I think, is that there's climatic variations.
• 17:14
  SPEAKER_01: So maybe it's seasonal, on, off, on, off.
• 17:17
  SPEAKER_01: There is also some similarities to Milankovic cycles, and this is a really cool one that is a relatively new discovery that some actually some friends of mine were affiliated with or did the geochronology of this.
• 17:29
  SPEAKER_00: But let me ask you about that a minute.
• 17:31
  SPEAKER_00: Uh, these friends, are they from what part of your life?
• 17:34
  SPEAKER_00: Are they from Alberta?
• 17:35
  SPEAKER_00: Are they from grad school?
• 17:37
  SPEAKER_00: Grad school.
• 17:37
  SPEAKER_01: Cool.
• 17:37
  SPEAKER_01: Yeah, we did our PhDs together, and um uh uh one colleague, Josh Davies, is a geochronologist now, uh professor geochronologist, and basically what they did is they went to this huge basin.
• 17:47
  SPEAKER_01: We talked about this Hammersley basin in Australia.
• 17:50
  SPEAKER_01: This is one of the ones they went to, but you can look and you just see kilometers of banded iron formation in all this layering.
• 17:55
  SPEAKER_01: And actually, interbedded in there, there are tufts or asphalt deposits.
• 18:00
  SPEAKER_01: And so if we have this big sediment layer, we can't really date the sediments very well.
• 18:06
  SPEAKER_01: But ash fall, those are volcanic eruptions, they contain zircons, which you can get really precise dates out of.
• 18:12
  SPEAKER_01: So if there's an asphall plume that fell in the ocean where this biff was being deposited, that ashfall plume will be preserved in the sediment record.
• 18:20
  SPEAKER_01: That gives you a point in time.
• 18:22
  SPEAKER_01: And so if you have a bunch of those asphalt deposits in this basin, you can date each one and you can then plot a line through the depositional history of this sedimentary basin.
• 18:31
  SPEAKER_00: And wait a minute, hold on, hold on, I'm gonna interrupt you here.
• 18:35
  SPEAKER_00: That's awesome, it's very cool.
• 18:37
  SPEAKER_00: But couldn't the zircons have been coughed up material from the throat of the volcano and therefore give you a date that is not indicative of the volcanic eruption?
• 18:48
  SPEAKER_01: Yes, that's that's absolutely true.
• 18:50
  SPEAKER_01: But those are gonna be very small scale.
• 18:52
  SPEAKER_01: The age variation of a zircon from the throat compared to the zircon from the actual magmatic eruption itself is gonna be quite small.
• 18:59
  SPEAKER_01: If you go to Mount St.
• 19:00
  SPEAKER_01: Helens today and you look at the throat of the volcano, it's gonna be maybe a couple thousand years older, maybe ten thousand years older than the volcanic eruption that happened in 1980, but it's not gonna be ten million years older.
• 19:15
  SPEAKER_01: And and here we're looking for millions of years variation of spending information.
• 19:20
  SPEAKER_01: Okay, sorry to interact with the same.
• 19:21
  SPEAKER_01: Great question.
• 19:22
  SPEAKER_01: No, it's a it's a great point.
• 19:23
  SPEAKER_01: So when you do this, you can get a uh uh basically age versus depth or depositional rate, basically.
• 19:31
  SPEAKER_01: So how much sediment is being accumulated in between these two asphalt deposits, and then in between asphalt deposit two and three, and three and four, and four and five, etc., you get a rate of deposition between here, and this suggested quite a bit slower rate than traditionally was thought.
• 19:47
  SPEAKER_01: So traditionally these were thought to be like 20 to 200 meters per million years, which is still fairly slow, but this was even slower.
• 19:55
  SPEAKER_01: The suggestion here is between five and ten meters per million years.
• 19:59
  SPEAKER_01: So, okay, that relates to the formation of banded iron formations in some way.
• 20:04
  SPEAKER_01: But the more interesting thing, I think, is that you can look at these variations in the iron and silica in the layers.
• 20:11
  SPEAKER_01: And if you look at those variations, they look very much like the modern sediments that contain Milankovic cycles or really climate variations that are due to changes in Earth's orbit or cycles in the changes in Earth's orbit.
• 20:26
  SPEAKER_01: So these kind of repetitive cycles in the changes in Earth's orbit.
• 20:29
  SPEAKER_01: And Chris, I I'm I was trying to remember this.
• 20:32
  SPEAKER_01: Have we talked about Milankovic cycles before?
• 20:33
  SPEAKER_01: I don't really remember.
• 20:34
  SPEAKER_00: No, I was just gonna interrupt you and say, well, let's talk a little bit about those Milankovich cycles.
• 20:40
  SPEAKER_01: Yeah, what real briefly, can you give us the like the one-minute rundown here?
• 20:44
  SPEAKER_01: I think we should have another whole episode or a couple on Milankovic cycles because it's a complicated idea.
• 20:49
  SPEAKER_00: But these are uh natural orbital variations.
• 20:53
  SPEAKER_00: And uh so the quick rundown of it is that our orbit around the sun is not circular, it's elliptical, which puts us closer and further from the sun on very regular time periods, predictable time periods.
• 21:07
  SPEAKER_00: And it also not only is the orbit very elliptical, or not it's not very elliptical, it's elliptical, but it also slides back and forth.
• 21:15
  SPEAKER_00: And so the combined effect of that it's a hundred thousand-year cycle where our orbit becomes more elliptical and slides over to circular and becoming more center again.
• 21:27
  SPEAKER_00: And and again, so it's a 100,000-year cycle from start to finish.
• 21:32
  SPEAKER_00: And uh that puts us again closer and further from the sun because that just naturally happens with the elliptical orbit.
• 21:40
  SPEAKER_00: And also then we have this precession, which is basically the Earth's axis wobbles on a on it's like a top spinning slightly off balance on like a 23 to 26,000 year cycle.
• 21:55
  SPEAKER_00: And uh in addition to that, there's one other natural orbital variation is the obliquity.
• 22:00
  SPEAKER_00: The tilt of our axis.
• 22:02
  SPEAKER_00: Our axis changes from uh like twenty-two degrees.
• 22:06
  SPEAKER_00: We're currently at twenty-three and a half degrees, and it changes down to twenty-four or twenty-four and a half, and then back again on a forty-one thousand-year cycle.
• 22:15
  SPEAKER_00: So these are natural orbital variations.
• 22:18
  SPEAKER_00: They're called Milankovic cycles, and they what they do is they bring upon predictable time periods where the poles get cold and bring upon this this kind of polar ice age, and then alternately they warm up and then cold again and so on.
• 22:34
  SPEAKER_01: Yeah.
• 22:35
  SPEAKER_01: So these are natural cycles, and they're they're they're like you said, predictable, but it's just basically over this 20,000 year cycle, let's say, there'll be 5,000 years where the the poles are getting a lot more solar radiation because they're tilted more to the sun, and or the seasons are more extreme, and then these are sort of on average over hundreds of years average climate conditions.
• 22:59
  SPEAKER_01: That's what we're kind of talking about.
• 23:00
  SPEAKER_01: So it's not anything really to do with carbon cycle or climate change in that regard.
• 23:05
  SPEAKER_01: It these are slight oscillations in climate due to the amount of incoming solar radiation that's hitting any part of the earth.
• 23:11
  SPEAKER_01: And okay, great explanation, Chris, of Milankovic cycles.
• 23:15
  SPEAKER_01: The key here is that the Earth-Moon distance, the distance from the moon to the Earth, how far away from the the planet the moon is, is a key thing for eccentricity.
• 23:24
  SPEAKER_01: It kind of helps control the eccentricity of our orbit or helps set the eccentricity.
• 23:30
  SPEAKER_01: And so what they did then is okay, they've got Milankovich cycles in this bandit I information.
• 23:35
  SPEAKER_01: They've got this cyclicity that looks like Milankovich cycles, and they could tell how the rate of those cycles has changed.
• 23:43
  SPEAKER_01: So a hundred thousand years, was it a hundred thousand year eccentricity, or was it 80,000 years, or is it 120,000 years?
• 23:49
  SPEAKER_01: And then from that you can calculate the Earth-Moon distance.
• 23:51
  SPEAKER_01: And so they concluded that the Earth was a little bit closer than it is today, but it was not a lot closer.
• 23:56
  SPEAKER_01: And it turns out we don't really have much idea of when the Earth and Moon, like what the position of the moon was back in time.
• 24:02
  SPEAKER_01: So anyway, it's not really about banded eye informations, this thing, but it's a bit about banded iron informations, or it's real it's a you know new signal detected in banded eye informations, which is kind of that's right.
• 24:12
  SPEAKER_00: That's very interesting.
• 24:13
  SPEAKER_00: We should maybe have your friend uh as a guest on Planet G.
• 24:18
  SPEAKER_01: Yeah, that's a good point, actually.
• 24:19
  SPEAKER_01: I hadn't hadn't thought about that.
• 24:20
  SPEAKER_01: Definitely sure.
• 24:21
  SPEAKER_01: Um, and then Chris, one one last thing here about the different models for banded iron formations.
• 24:27
  SPEAKER_01: There's one that and this is particular to a certain type of banded iron formation, the sort of small ones, the the thinner ones that I've seen in northern Canada frequently.
• 24:37
  SPEAKER_01: Some people suggest that these are black smoker deposits.
• 24:39
  SPEAKER_01: So if you think of these black smokers coming out of a mid-ocean ridge, we've seen these on the modern earth, those are pumping iron into the ocean.
• 24:46
  SPEAKER_01: And so if the ocean chemistry is a bit different, you could get iron deposited sort of in this this type of system near the mid-ocean ridge or where there's hot water.
• 24:56
  SPEAKER_01: Yeah, very locally.
• 24:57
  SPEAKER_01: Exactly.
• 24:58
  SPEAKER_01: So it kind of explains why you might have this local, small, thin, banded iron formation deposit.
• 25:04
  SPEAKER_01: And that would suggest that you have silica in the background depositing and then iron pulses coming out of these black smokers, perhaps.
• 25:10
  SPEAKER_00: Yes, that makes sense.
• 25:11
  SPEAKER_00: Okay, cool.
• 25:12
  SPEAKER_00: Well, Jesse, let's wrap things up by just kind of reiterating why they matter, why they're important.
• 25:19
  SPEAKER_00: First of all, they're beautiful rocks, and beautiful rocks are always important just because they're beautiful.
• 25:27
  SPEAKER_01: And I think, you know, they're they I have this beautiful band information.
• 25:30
  SPEAKER_01: I think I got it, I think I found it when you and I were up to the side.
• 25:33
  SPEAKER_00: Wait a minute, don't you have one right behind you right now?
• 25:36
  SPEAKER_01: I do have one.
• 25:36
  SPEAKER_01: I do, yeah.
• 25:37
  SPEAKER_01: This is uh I'm looking right at it.
• 25:39
  SPEAKER_01: Actually, I forgot about that, right?
• 25:40
  SPEAKER_01: Right there.
• 25:41
  SPEAKER_01: Um I have this amazing one from up in northern Michigan that is a bit more has the yellows and the grays and the blacks in it.
• 25:49
  SPEAKER_01: Uh, but it has it's about uh, I don't know, you know, beach ball size piece, and on one side it's faulted.
• 25:57
  SPEAKER_01: So these layers are broken apart and jumbled and then re-smashed back together.
• 26:01
  SPEAKER_01: So we call it a fault breccia.
• 26:03
  SPEAKER_01: So you can see on one half most of the rock has this beautiful layering in it, and then one corner has this jumbled up layering, and you can clearly see that this was a bandad formation that was faulted, cracked in half, and then kind of re-annealed back together.
• 26:17
  SPEAKER_01: And I just always look at it sits out front of our house, and whenever I walk past it, I'm always just like, Man, I can't believe that rocks like that are so pretty.
• 26:25
  SPEAKER_01: That rocks can be so beautiful.
• 26:27
  SPEAKER_01: They're they're really, really stunningly beautiful things.
• 26:30
  SPEAKER_01: It's amazing.
• 26:31
  SPEAKER_00: That's right.
• 26:32
  SPEAKER_00: They are, and some with sometimes I feel like we don't talk enough about the beauty of rocks.
• 26:36
  SPEAKER_00: Um I'm just struck with this idea.
• 26:39
  SPEAKER_00: Like I agree.
• 26:40
  SPEAKER_00: These they they are stunningly beautiful.
• 26:42
  SPEAKER_00: Look them up, you can do an image search on them.
• 26:44
  SPEAKER_00: They're just they are gorgeous.
• 26:46
  SPEAKER_00: And from my experience to collecting, I think you know, collecting needs to be done responsibly, where it's it's you know, not in beautiful areas.
• 26:55
  SPEAKER_00: I I would never want to collect a rock from a beautiful area because I wouldn't want to mar that for anybody else.
• 27:00
  SPEAKER_01: Um if you get permission, yeah, absolutely.
• 27:05
  SPEAKER_00: But when you do attempt to do this, you're gonna need a sledgehammer and a chisel.
• 27:09
  SPEAKER_00: A rock hammer will not work in this case.
• 27:12
  SPEAKER_01: The the mountain wants to keep its rocks, and um and uh if you're Chris, you might need a couple field assistants, young young field assistants to carry your samples back for you.
• 27:23
  SPEAKER_00: That is so true.
• 27:24
  SPEAKER_00: Uh all right, moving on.
• 27:25
  SPEAKER_00: So they're beautiful rocks, and they are unique varieties of sediments that accumulated in in this very unique setting.
• 27:32
  SPEAKER_00: Also, they again we said this earlier, but they may show the evolution of early life and changing then their role and changing the atmospheric composition.
• 27:43
  SPEAKER_01: It's really important.
• 27:44
  SPEAKER_01: When you think at this about this beautiful rock, it's something that I think most people who even graduate with a degree in geology or you know take some geology classes, a couple of them, it's not something we'd really talk about.
• 27:56
  SPEAKER_01: It's how the early earth was very, very different from the modern earth.
• 28:01
  SPEAKER_01: And so I think it's really important to not forget that.
• 28:04
  SPEAKER_01: And I I'm biased because I studied early earth, but but I do think it's true, like to understand that the earth has changed dramatically throughout its lifetime.
• 28:14
  SPEAKER_01: In looking at these rocks, any remote.
• 28:16
  SPEAKER_00: Any devoted listener to Planet Geo, I I think would have to agree that we've done a fair amount.
• 28:22
  SPEAKER_00: We've done our part with looking at early Earth and how different it was.
• 28:26
  SPEAKER_01: It's true.
• 28:27
  SPEAKER_01: And that's just a bias uh that I've imposing.
• 28:32
  SPEAKER_01: So, yes, completely fair enough.
• 28:34
  SPEAKER_01: Fair enough.
• 28:37
  SPEAKER_01: All right.
• 28:38
  SPEAKER_01: Hey, this was a good episode, Chris.
• 28:40
  SPEAKER_01: You can learn all the basics about geoscience in our online conversational textbook.
• 28:46
  SPEAKER_01: That's Camp Geo.
• 28:47
  SPEAKER_01: It's the first link in your show notes.
• 28:48
  SPEAKER_01: If you wanna, we don't really cover banded iron formations yet, at least we haven't talked about it yet or put a chapter together.
• 28:54
  SPEAKER_01: But if you want to learn the basics of sedimentary rocks and plate tectonics and what is a mid-ocean ridge, go to that.
• 29:00
  SPEAKER_01: You can see cool graphics that we've integrated with uh conversational audio that Chris and I have put together.
• 29:05
  SPEAKER_01: That's super awesome.
• 29:07
  SPEAKER_01: Chris, we're working on an office hours episode, so please send us your questions.
• 29:10
  SPEAKER_01: Planetgeocast at gmail.com is our email.
• 29:14
  SPEAKER_01: We've got a whole bunch of great questions, I think.
• 29:15
  SPEAKER_01: And so we're putting together an office hours episode right now.
• 29:18
  SPEAKER_01: Um to be honest with you.
• 29:21
  SPEAKER_01: Um Yeah, we're gonna be probably breaking it apart into a couple different episodes here.
• 29:25
  SPEAKER_01: That's right.
• 29:26
  SPEAKER_01: That's right.
• 29:26
  SPEAKER_01: Uh, but yeah, shoot us your questions, give us a rating and a review.
• 29:30
  SPEAKER_01: We really appreciate that.
• 29:31
  SPEAKER_01: It helps the algorithm and uh helps us explain how great the geosciences are to a broader swath of people.
• 29:37
  SPEAKER_00: That's right.
• 29:38
  SPEAKER_00: Thanks for listening.
• 29:38
  SPEAKER_00: Cheers.
• 29:39
  SPEAKER_00: Peace.