41: The Oldest Seafloor

The year is 1991. The place: a small corner of a small, rocky island off the coast of the Arctic Greenland tundra. This little gray spit of land, the size of a large sports stadium, is crawling with geologists wearing thick jackets, big backpacks, and cool sunglasses. They’re taking photographs, laying out rulers, and hammering away small samples for later labwork. At the very tip of the peninsula, they find a special layer of rock with stripes like a tiger or a zebra. The geologists chip off a piece of the old block and label it G91-26.

Five years later, this rock will become one of the most controversial stones in geology.

Episode 41: The Oldest Seafloor

For the past few episodes, we’ve explored the coast of southwest Greenland. These rocks are the crown jewel of Season 2, which is why we’re spending a lot of time here. Here’s an overview: The rocks are 3.9 to 3.6 billion years old, mid-Feb to mid-March on the Earth Calendar. If you traveled back in time, you would see a waterworld: vast oceans peppered with barren volcanic islands. If you looked up to the sky, you would see a dimmer sun, a larger, speedier moon, and regular meteor showers.

Greenland’s rocks can give us an even more detailed glimpse into this ancient world, if you know where to look. Last episode, we zoomed in to just one location, that little modern island in the cold open. That island is called Akilia. The island is the center of not one, not two, but three different debates.

Debate #1: How old are these rocks? Last episode, we settled on Feb 25 on the Earth Calendar, but there is still a vocal opposition for March 15, three weeks later. In actual dates, that’s 3.87 vs 3.65 billion years old, a disagreement of 200 million years, a span longer than the age of dinosaurs.

By themselves, all these dates are basically trivia. Why do we care if Greenland’s rocks are February or March on the Calendar? If the old date is right, the oceans we’ll meet today could have formed during massive meteor showers, the leftovers from the early solar system. For a refresher on those meteors, check out Episode 34: Bombardment. Depending on how severe those showers were, life could have had a unique challenge in its’ early days. It’s an interesting idea, but it needs to be tested with rocks.

Today, we tackle Debate #2: What types of rocks are on Akilia? Specifically, what type of rock is G91-26 from the cold open? You might be openly laughing right now: the world’s top geologists have studied this rock for 30 years, and we still can’t agree what it is? We’ll see if an agreement is reached by the end, but here’s the point:

If one side is right, these rocks could hold the oldest fossils on Earth. If the other side is right, there’s no way that’s possible.

Part 1: Back to BIFs

Let’s start by just describing this rock, before we get to any interpretations. This is the basis of field geology. If you find a funny rock, start with what you see before guessing how it got that way. There’s a picture of this rock on our website: bedrockpodcast.com, but if you can’t check it out, here’s a mental image.

*G91-26, the start of many, many debates*

Imagine you’re standing on the shore of Akilia Island. Behind you is a stony, boulder-strewn shoreline, with the potent smells of seaweed and seabirds. Ahead of you are low rolling hills, mostly barren rock but some patches of lichen and scrub. At your feet is G91-26, the rock everyone is arguing over, which stretches for several yards along the shore. The first thing you’d notice are layers: some are thin as a hair, some are thicker than your arm, most are finger-width. The layers alternate between dark and light, but not perfectly: think of a random, slightly wiggly bar code instead of a neat pin-striped suit. Sometimes the dark layers are black, sometimes they rust out in a reddish color. Clearly there’s a bit of iron inside this rock.

We’ve met a rock like this before, way back in Episode 32: a stripey, iron rich stone on the Arctic shores of Quebec. That rock is called a banded iron formation, or as we call them in the business, a BIF. It’s been a little while, so let’s review what a BIF is, and why we care.

BIFs are the backbone of the iron industry. Two-thirds of the world’s iron ore comes from BIFs, and most of that iron goes into steel. Take a second to find something made of steel around you. I’d bet good money it was originally an ancient BIF. BIFs also tell incredibly important stories about the history of life and oxygen. There are a few ways to make BIFs, and most of them involve life. Sometimes life farts out oxygen, which merges with iron to make rust. Sometimes life skips the middleman and makes rust all by itself. In either case, BIFs can sometimes be considered an “indirect fossil”: no bodies remain, but they helped build the BIF, like an ancient highway of iron.

Whether BIFs were made by life or plain old chemistry, everyone agrees they form at the bottom of the sea as a sedimentary rock, in the same broad family as mudstone and sandstone. As iron settles down in water, it creates gray and red layers, forming distinct tiger-striped rocks. Which brings us back to Akilia Island.

The striped rocks on Akilia sure sound like BIFs: they have similar patterns of rusty, iron-rich layers. They were first described way back in 1977 by our old friend Vic McGregor, the New Zealander who helped open Greenland to the world of ancient geology. After Vic described a cool old BIF on Akilia, you would expect everyone to come running, looking for fossils or economic iron. But it took 20 years for Akilia to reach the spotlight. Greenland is a large, remote place, and folks were busy at other locations with cool stories. The BIFs could wait.

1996 was finally the year of Akilia, with two major papers. One paper was headed by Allen Nutman, an Australian researcher we met last episode. Nutman agreed with Vic McGregor that Akilia’s striped rocks were indeed BIFs and added that they were the oldest on Earth. But wait! There’s more. In the same year, a paper came out in the journal Nature, the highest place a geologist can go. This landmark paper was headed by another name from last episode: Stephen Mojzsis at the Scripps Institute in San Diego, California. Nutman was also a coauthor- the pair agree on some Akilia stories, but not all. This time, they’re together.

So what did Mojzsis, Nutman, and their team find on Akilia Island? Hold onto your butts. They claimed that the Akilia BIFs hold the oldest evidence for life on Earth. I’m not talking about an “indirect fossil”, I mean messy carbon directly left behind by living cells.

As you can imagine, such a major claim attracted a lot of interest, and a lot of criticism. Some critics focused on the fossils themselves, the scraps of carbon that might be life or might be nothing. That fossil debate deserves a whole episode to itself, next episode to be specific. Today’s episode focuses on a simpler question: are the Akilia rocks actually BIFs? If not, what the heck are they?

Part 2: Rebuttals

Here’s one thing everyone agrees on: Akilia has been through the wringer. I’ve said many times that “Greenland is the gem of Season 2” and it is, but many places like Akilia are still very metamorphosed. Akilia has been baked to at least 600 °C, hotter than a tandoori oven. This is as cooked a rock can get, and still have a chance of holding any fossils or primary structure. At a certain point, you can take completely different stones like mudstone or a lava rock, and squeeze them so hard, it’s difficult to tell the difference.

In 2002, a different team of researchers studied Akilia Island, and returned with a completely different story than Nutman or Mojzsis. This study claimed that the rusty, striped Akilia rocks were not banded iron formations, but were instead volcanic rocks that had been stretched and warped by metamorphism. In other words, the rocks were not seafloor sediments, but were once boiling lava flows. Not a great place to make a fossil.

How do you take a lava rock and make it look like a banded iron formation? Two things need to happen: 1: you need to make thin layers, and 2: you need to concentrate iron in those layers.

Let’s start with the layers themselves. This part is actually fairly easy, we’ve seen it on the show before. When you squeeze a rock hard enough, randomly oriented minerals will align into layers. You can try this yourself at home. Throw a handful of coins or dried noodles in random directions on a table. Now, place your hands on either side of the pile and bring them together, like a trash compactor. The coins or noodles will orient themselves parallel to your hands as you squeeze them together.

The same thing happens during metamorphism: any rock can be pressed into tight layers like an accordion. In contrast, the layers in a banded iron formation, or a sandstone or mudstone can only form when sediment settles down to the seafloor. If you want to try that process at home, just make a parfait or a layer cake.

Back to Akilia. The 2002 paper compared layers in Nutman’s proposed BIF and in neighboring rocks that were clearly volcanic. Apparently, they were all squeezed in the same direction, just like the coins on the table. In other words, the iron-rich rock wasn’t all that special from its’ volcanic neighbors, it just happened to look a bit different.

Which brings us to point number 2: If the mystery Akilia rock was just an old lava flow, what was all that rusty iron doing there? According to the 2002 paper, there wasn’t actually that much iron inside. A few layers had 5 to 10% iron, but most layers had none. The iron that was present was also seen in neighboring lava flows. Again, the rusty Akilia rocks might look different from their neighbors, but on closer inspection, were apparently very similar.

Finally, the 2002 paper investigated chemistry, including the 17 rare earth elements that have become a cornerstone of the show. Don’t worry, I’m not getting into specifics. The point is that once again, the Akilia mystery rock more closely resembled volcanic rocks than banded iron formations. At least, that’s what the authors argued.

These authors were Christopher Fedo at George Washington University in Washington, DC, and yet another name from last episode: Martin Whitehouse at the Swedish Museum of Natural History. Last episode, we saw Whitehouse square off against Nutman and Mojzsis about the age of Akilia rocks. Nutman and Mojzsis proposed an old date, Whitehouse countered with a young date. Like last episode, I’m using Team names here, but many other folks were involved, like Dr. Fedo in DC.

Today, we see a similar showdown. Teams Nutman and Mojzsis described a banded iron formation from the ancient seafloor, possibly with evidence of life. Team Whitehouse disagreed, saying this was just a messed-up lava flow. That’s a huge difference of opinion.

For fans of drama, grab your popcorn and soda, and take a seat. We’re going to discuss a part of academia we haven’t talked about before: comments and replies to publications. Usually, if you read a paper and you think it’s wrong, you go out, collect your own data, and write a paper yourself. This happened last episode: When Team Whitehouse said Akilia was young, Team Mojzsis went out and got new data arguing for an old date. This process usually takes a few years.

Sometimes you disagree with a paper so strongly, you need to respond right away. Usually these are high-profile papers in journals like Nature or Science, articles that have the power to change the field, and maybe the world. That might sound like hyperbole, but it has happened before in a different field. Let’s take a brief, but important digression. In 1998 an article was published in The Lancet, a high-ranking medical journal. Three weeks later, The Lancet published a dogpile of seven comments questioning the study, all saying it was fundamentally flawed. Many more have been published since. The original article was highly publicized, as medical articles usually are. The overwhelming outcry from other researchers did not make the news, such comments usually don’t. But truth will out.

In 2004, it was revealed the study had manipulated medical data and had not revealed conflicts of interest- over $1,000,000 in today’s money that was paid to tell a specific medical story. That story was that measles vaccines cause autism in children, a conclusion that has been proven wrong by hundreds of studies that didn’t cherry-pick data or take thousands in secret money. In 2010, The Lancet finally retracted this paper, but it was too little too late. One bad study has altered the face of global health. If the media focused on the early criticism in 1998, just weeks after publication, I might be telling a different story.

That is an extreme example of the comment process. Let me be clear: I’m not comparing Team Whitehouse, or any other Greenland team to that bad vaccine study - they’re not frauds. Team Whitehouse simply called the rocks on Akilia Island lava flows instead of banded iron formations. Team Nutman and Team Mojzsis felt so strongly, they reacted immediately with back-to-back comments.

Team Mojzsis focused on chemistry. Mojzsis took Whitehouse’s chemical results and split them into two groups. Some samples did indeed have a volcanic signature. But others fell far closer to the range of BIFs and seafloor sediments. There appeared to be a mixing of two different materials: lava and mud.

Team Nutman, led by Clark Friend at Oxford, focused on field geology. They critiqued the Whitehouse maps as not detailed enough and the Whitehouse samples as being too altered to show decent chemical data. Again, there were two distinct signatures in the Akilia mystery rock: one of deep-sea sediments, and the other of volcanics.

*Figure from Nutman et al., 2002, in response to Fedo & Whitehouse 2002*

Together, the comments paint a story. Imagine an undersea volcano, with dark lava flows instantly cooling underwater. As the volcano simmers down, the seafloor is covered with layers of iron-rich sediments. Eventually the volcano erupts again, sandwiching this iron formation, this BIF between lava flows. These eruptions also inject thin veins of lava into the poor BIF like doughnut filling. Many millions of years later, this rock sandwich is buried deep underground and squeezed together, mixing them even more. It's like that old candy commercial: “You got chocolate in my peanut butter! You got peanut butter in my chocolate!”

Whenever comments are made to a scientific paper, the original authors have a chance to get the final word in, to defend their point of view. Fedo and Whitehouse struck back hard. They were not willing to concede that any BIF was involved in Akilia. Their response gets a bit personal. According to Team Whitehouse, the original descriptions in the 90s way oversold the mystery rock, they focused on only one sample from the area, and that they glossed over major alteration issues. Now the same people, Teams Nutman and Mojzsis, were contradicting their former work, saying “of course these rocks are altered, of course there’s other data out there”. To Whitehouse, it seemed like a bait-and-switch.

Reading all the comments and replies, you can feel a sense of frustration and unfairness, whether you agree or not. Sometimes I sympathize, sometimes it feels like “he said, she said”. It’s not all semantics, they also use hard evidence, but neither side would budge. It was back to the drawing board.

Part 3: Ironing Out the Details

Here’s where we stand. On Akilia Island, there is an old stretch of rock with rusty red layers. According to Teams Nutman and Mojzsis, the rocks were seafloor sediments intermingled with volcanic rocks. If so, they could have evidence for life inside. According to Team Whitehouse, the rocks were only volcanic, they were super messed up, and had no chance of preserving fossils. Both teams had used field geology and rare earth elements, and had not reached any common ground, except to say the rocks were metamorphosed. Hmph.

Clearly, some different data was needed. In 2004, a new team proposed a new way to test the mystery Akilia rock. Forget all these crazy rare earth elements, let’s return to a fundamental fact: this rock is rusty, it has some iron inside. If you could interrogate that iron, you could figure out the rock’s history. Specifically, this new team was investigating iron isotopes.

The last time we seriously talked about isotopes was Episode 16, so let’s brush off some dust before we continue. There are two main types of iron atoms: one is lighter and one is heavier. These light and heavy versions are called isotopes. I think of isotopes like dog breeds- Chihuahuas are lighter than Great Danes, but both are clearly dogs. There are some places Chihuahuas can go that Great Danes can’t, like the space under a couch. Likewise, a Great Dane can reach your dinner table, while a Chihuahua can’t get there.

In the same way, light and heavy isotopes move in different ways. A piece of rust will have a certain ratio of light and heavy iron, while a glass of water will have a different ratio. So what about the mystery Akilia rock? Let’s look at our options. According to Teams Nutman and Mojzsis, the rusty rock is a banded iron formation, a slice of ancient seafloor sediment. If they’re right, the rock should have heavier iron, more Great Danes than Chihuahuas. According to Team Whitehouse, the rocks were once lava flows. If so, the rock should have lighter iron. Once again, if the rock is a BIF, it’s heavy. If it’s a lava rock, it’s light.

Place your bets! Are you on team BIF, or on team lava? Drumroll, please!

The winner is… Team BIF. When the mystery rock was analyzed, it was heavy, resembling other BIFs around the world. Just to confirm, neighboring lava rocks were also tested, and were clearly much lighter. This new team was headed by Nicolas Dauphas (nee-ko-la dough-fawss) at the University of Chicago. Don’t worry about yet another name. Unlike the other guys, Dauphas gets in, makes his point, and leaves. Another author on this team will play a much larger role next episode, when we finally get to these fossils I’ve been teasing. I won’t name him yet, partly to avoid name fatigue, and partly out of suspense. This mystery guy is a good friend of mine and a former boss, but those are stories for next episode.

Before we finish, we have to ask: what did Team Whitehouse think about the iron isotopes? Remember, they’ve been arguing for years that the rusty Akilia rocks were lava flows, not BIFs. The iron seems to prove them wrong. Ten years later, in 2015, Team Whitehouse released their own iron isotope data. Broadly, their results agree with Dauphas: most lavas were light, most of the mystery rock was heavy like a BIF. There’s one interesting wrinkle, just a brief coda before we finish.

In some places, the mystery rock is a tight mixture of BIF and lava. The isotopes here are mixed, they are smeared between light and heavy like that chocolate and peanut butter. Whitehouse notes that metamorphosis should still not be ignored, that there’s still more to be revealed. While they don’t completely concede, they admit that BIFs are a potential possibility for the mystery rocks. The text is much less heated than the great debates of 2002. Who knows? Perhaps with more evidence, both sides can finally reach an agreement. Or it might cause a whole new string of debates. In either case, you’ll be the first to know.

Summary:

Sample G91-26 was likely a banded iron formation. If so, it is the oldest slice of seafloor on Earth. It formed as iron crystals gently rained onto dark seabeds, 3.8 billion years ago. These rusty layers were entombed by lava flows as surrounding volcanos erupted underwater. As these layers were buried, both iron and lava were squeezed and warped into a tight sandwich. Deconstructing the layers of this sandwich, both physically and chemically, has sparked intense debates over 30 years of research. For now, Team Iron has taken the lead.

Why do we care about this rusty old rock, what’s the big deal? Next episode, we’ll finish out the Akilia trilogy with the most important debate of all. The rock finally has an age, the rock finally has a name, but does it have any fossils of ancient life, 3.8 billion years old? Find out in Episode 42: The Question of Life.

40: The Time War