38: Hidden Gems

Hello, and welcome to Bedrock, a podcast on Earth's earliest history. I'm your host, Dylan Wilmeth. Episode 38, Hidden Gems. Welcome back. It's been a while, and I thank you all for your patience and kind wishes. Here's a little housekeeping before we return to the rocks. If you want a detailed account of what I've been up to... please check out the last update, Bedrock Returns. In short, I still have my job in Michigan, but it's still not permanent, just one more year. The job hunt continues.

I'm on summer break now. On the plus side, that means time for more regular episodes, at least every other week. On the minus side, that means I'm not getting paid until September. Folks have asked me how you can support the show. Here are a few ways. If you want the full rundown, check out the last update. 1. Episodes will now have a donate button in their descriptions. Only give what you want. I know times are tough for a lot of folks, not just me. 2. Patreon

On Patreon, you can give a small monthly donation for some extra perks. I'm thinking mail time episodes or geology in the news. I'll start a Patreon soon, but I want a solid schedule first.

I don't think it's fair to ask for money if I'm not delivering. 3. Maybe some ads at the start and end of episodes, not interrupting the flow. If you love or hate any of these ideas please fill out the audience survey in the episode description I'd love to hear what you think if you can't or don't want to donate that's fine These main episodes will always be free. Which brings us back to today's scheduled program. Thanks for listening. We're in the final arc of Season 2.

Our destination is southwest Greenland, around the capital of Nuuk, a remote land of mountains, fjords, glaciers, and very old rocks. the area around nuke is the crown jewel of season two for three reasons one this is earth's oldest major slice of rock the size of a small nation far larger than anywhere else we have visited. 2. Nukes rocks cover a huge time frame, from February to March on the Earth calendar, 3.9...

to 3.6 billion years old. We are officially done with any date before 4 billion years. We're moving forward.

The rocks around Nuke are the most well-preserved of their age, though there is a range of quality. Last episode, we learned about three stages of metamorphism, three altered rocks... that tell us different stories. Do you remember their names? If not, then I don't blame you since it's been nearly a year. Here's a review. On the extreme end of metamorphism are the grand old granulites. They've been pressure cooked beyond imagination.

But they still tell large-scale stories of continents, mountains, and tectonics. Next is a group that's not great, not terrible. You can feel ambivalent about the rock. Amphibolite. Amphibolites give us more info than their great granulate cousins, but still not a lot. Finally, we have the lightly cooked green schists. giving us the green light to explore the surface world in greater detail, looking at oceans, volcanoes, and even fossils. When I say Green Chist, you should get excited.

In southwest Greenland, the rocks are mainly amphibolites, middle of the road. For other places on Earth, this is not exciting news, but for 3.9 billion years old, These Greenland amphibolites are looking pretty good. So, where do we go from here? We have an entire month of the Earth calendar before us, with many different rocks at our fingertips. This is our...

biggest buffet yet. As usual, we're going to divide and conquer. Today, we'll start with the bigger picture, with plate tectonics. In other words, what did Greenland look like? 3.9 billion years ago. Were continents smashing into each other? Were they pulling apart into seas? Were there any continents at all? Or was something stranger happening? These tectonic questions might sound esoteric, but they tell us how the hellish lava world from early season one became the earth we know and love.

They will set the backdrop for future Greenland episodes on oceans, volcanoes, and maybe even life. It's time to set the scene.

Part 1. A Quilt of Stone. Let's start by making a simple mental map of these Greenland rocks using our imagination. Remember... The island of Greenland is huge, the size of Mexico or Saudi Arabia. Don't worry, today we're zooming in on a small sliver on Greenland's southwest coast. I want you to imagine a long, thin banner hanging vertically. On this banner is embroidered a map of Greenland's oldest rocks. The top of the banner is north. The bottom...

is south. At the bottom of the banner is the cold, blue Atlantic Ocean. Here, tucked in the bottom left corner, is the harbor of Nuke, Greenland's capital of 20,000 people. It might not be large, but it is the gateway to Earth's oldest major slice of rock. If you were to wander around the streets of Nuke, you would see very old rocks, April to June.

On the Earth calendar, 3.2 to 2.5 billion for those keeping score. But we won't see rocks that age until seasons 4 and 5. We need to look elsewhere for the really ancient stuff. Back to our imaginary banner, we see islands and inlets lining the bottom of the tapestry, its ragged southern edge. These islands...

have some of the oldest rocks in the entire area, and folks have even argued for traces of life here. Both the dates and the possible fossils on these islands have been subject to heated debates. If you listen on the sea breeze, perhaps you'll hear the arguments of passionate scientists. We will focus on these islands and give them a name in two episodes. As we gaze upward...

Northward, into Greenland's interior, we see a broad stretch of dull gray stone, pushed upwards into snow-capped mountains and sliced through by modern blue fjords. These rocks have seen a lot of action, even in the distant past, in the middle of the tapestry sits a large patch of pink and brown, looking for all the world like a wine stain.

on the tapestry. This stain happened in Season 5, but we'll have to talk about it in a few episodes, since it dramatically altered the surrounding older rocks. If you look closely, In the gray background, beyond that gnarly pink stain, you'll see smaller flecks of color, peppered throughout the banner, patches of black, green, and even red.

Now that might ring a bell, especially for folks listening recently. These were the colors we saw in Nouveau Agatouk in the Canadian North, episodes 30 through 33. Those rocks, colorfully named greenstone belts, were windows onto the ancient surface, oceans, volcanoes, and maybe life. Most of Greenland's greenstone patches are far smaller than their Canadian cousins, just about football field size or so. But there's one major exception.

At the banner's northern boundary, we begin to see greater detail on a wider scale. It's a great curve of dark stone shaped like the letter U, or a welcoming smile. This northern greenstone belt is 200 square kilometers. That's 10 times larger than New Wackatuck. That's larger than Liechtenstein, larger than Washington, D.C.

Here we can see lava flows. Here we can see rusty iron seafloors. And wait, is that possibly some fossilized pond scum? When suddenly we're cut off by a wall of white... glacial ice at the northern border just like game of thrones the stone banner continues beneath the glaciers but for now those stories are hidden as humans continue to change earth's climate one

Unintended bonus could be revealing ancient secrets beneath the ice. Up to you if that's worth it. For now, let's appreciate what we have. This banner of stone. stretching from the sea to the glaciers, has a name. The Itzhak complex. That's I-T-S-A-Q. Itzhak. In the native Kalashasid language, the word Itzhak... means ancient. Pretty on the nose there. Again, apologies for any mispronunciations. The word complex is also there for a reason. This is a complex cluster of rocks.

I just described Itzhak like a single gray banner, but it's more like a giant, chaotic quilt. When geologists look closely at Itzhak, they find many different... gray patches shoved together, different rocks that formed at different times. A single cobblestone in your hand could have a 3.9... billion-year-old crystal, neighboring one, 3.6 billion years old. For context, that's February 23rd to March 19th on the calendar. Nearly a full month.

Even for geologists, you usually can't find a single small rock with two original ages that far apart. So what happened here? We'll learn the details in later episodes, but here's a handy visual for now. You can even follow along at home if you have a few different colors of Play-Doh modeling clay. Feel free to pause if you need to grab them or put them in your mind's eye. Take the pieces of Play-Doh and smash them together. The more colors, the better.

Now stretch them all out as long as you can. Take this colorful noodle and fold it in half, tip to tip. Repeat this stretching and folding two or three times more. In the end, you should have a demented rainbow of clay with many different pieces tortured into long stringy threads. Replace these colors with black, white, and gray. and you've made a rock we've met in episode 25. Nice. The most metamorphosed rock you can find.

More than 95% of the Yitzhak complex are these complex, stretched-out gneisses. You can tell some stories with them, but it's very difficult. even after 60 years of research, but in a few protected pockets. The rocks are less stressed out, keeping more of their original features. They're still messed up. but they can tell us what their neighbors once looked like. Today, let's focus on the most abundant rocks in the area. What would we see if we walked across the Itzhak Quilt?

Part 2. Stone Soup. More than 70% of the Yitzhak complex is, or more accurately was, Just one type of rock. An old friend of ours. It's a dull gray stone peppered with black crystals stretching from the fjords to the mountaintops. A non-listener. would say, well, that's just granite. They're close, but long-time listeners would know better. You would say, actually, that's tonalite. But I leave it up to you.

Whether pedantry is more important than pleasantry, especially on the Arctic tundra. For a refresher on Tonalite, check out episode 26. Here's the abridged version. Tonalites are one of granite's many cousins. Both form deep underground inside boiling magma chambers. The magma slowly cools into crystals the size of coins. making beautiful mosaics that look great on countertops. Some magmas make tonalites, many more make granites. Both cousins tell us stories of plate tectonics.

the birth and growth of continents so how can you tell a rare tonalite from a common granite color Granites usually have more pink or red or brown crystals, while tonalites have more gray and white crystals. Now for most homeowners, and... Honestly, for most geologists, the difference between granite and tonalite is seriously splitting hairs. You're not going to get more money for a great tonalite counter than a pink granite one. But for this show...

At the edge of prehistory, this color difference tells us a story. The key players are those pink crystals in granite. If you really want a name, they're called orthoclays. But that is not on today's test. We'll do a deeper dive in a later episode. Just remember that granites are usually pinkish. As a magma chamber cools underground. The pink crystals in granite are some of the last to form very late to the party. Furthermore, our pink pals are picky.

They can only form in magmas that have been repeatedly recycled upward from the mantle, into seafloors, into continents. Check out episode 12 for more detail on that cycle. In short, a pink or red or brown granite takes a lot more work, a lot more refinement than dull gray tonalite. If our old friend tonalite is grape juice, granite... is wine. I'm not ragging on totalites here. They're crucial rocks in Earth's early history. And we've seen them in episodes 26, 27, and 30.

For example, Earth's oldest surviving rock, the Acastan Ice, was once a tonalite. Back to today's episode, most of Greenland's Itzhak Complex, that Great Stone Banner, was once tonalite. this rock will be a constant companion for the next few seasons. Tonalite was extremely common on the early earth, but is relatively rare today, replaced by its more popular cousin, granite.

So what changed? What does Tonalite tell us about Greenland 3.9 billion years ago? It was all over the place, so what? For that answer, we need to return.

to the original magma chambers of their birth. When most people think of magma, they imagine a thick, bubbling, red-hot liquid, deadly to the touch. And they're absolutely right. A geologist would see and feel the same thing you do. But there's another way that geologists think of magma, one that gives us even more info. To us, that pot of magma is a giant stew of minerals and chemicals, one whose recipe changes as rocks melt and recrystallize. To start...

I want you to imagine a rock sitting in a pot. As we turn up the temperature, the rock begins to melt. Softer, wimpier crystals melt first, while tougher crystals stick it out until the bitter end. If you removed some of that very early partial melt with a ladle, it would have a different chemistry, a different flavor than the later completely molten rock.

Now, let's cool the temperature back down. The hot magma begins to freeze into different crystals at different times. Tough ones first, wimpy ones last. If you plucked out the very first crystals as they cooled, they would have a different chemistry from the later, completely frozen rock. These ideas have names in geology, partial melting, and what I call partial freezing. For sticklers, the freezing process is actually called fractional recrystallization.

But I think partial freezing describes it far better for non-science folks. You've only frozen a part of the magma. If you want more info... Episode 26 is dedicated to partial melting, and 27 for partial freezing. Let's bring this back to the oldest Greenland tonalites, 3.9 billion years old.

We can't watch these ancient rocks melt and freeze from scratch, but we can look for clues in their chemistry. Just like certain crystals melt more easily or freeze more easily, Certain elements on the periodic table jump immediately into magma, while others cling desperately to the last remaining crystals until they're forced into the pool.

In short, the chemical patterns of tonalite can tell us where it melted and where it froze, and if there are any modern spots where we see the same patterns. The smallest elements can tell us stories about the birth of continents. Part 3. The Great Carbuncle

In the 1960s, a Kiwi geologist named Vic McGregor began to untangle the contorted Greenland rocks, the Play-Doh knot we made earlier this episode. Vic realized that the oldest rocks... might be older than any known at the time, but he needed dates. He sent the samples to Oxford, where they confirmed his suspicions, kicking off a string of publications dating these incredibly old rocks. Break out the champagne. The year is now 1974, a decade...

after Vic's research began. And we're back in Oxford, England. The initial rush of dating has cooled down, as it does for many relationships. And the crew now turns to deeper questions beyond age alone, questions of chemistry. In all honesty, the chemical nitty-gritty is less important. than the larger story. But I do want to highlight a group of elements we've met before, and we'll meet again many times. The rare earth elements.

I've described the rare earths as 17 sisters, 17 soft metals that behave similarly, but have their own unique quirks. Despite their relative rarity, These elements are increasingly important ingredients for technology, from electric cars and smartphones to cancer treatments and lasers. For those of you up on the news, hearing the words Greenland and Rare Earth Elements might make your ears perk. A huge mine.

on Greenland's southern tip has been in the geopolitical crosshairs for decades. It's a long, tangled, and honestly tense story that weaves together nuclear physicists. like Niels Bohr, Chinese mining firms, the 2021 Greenland election, environmental concerns, and this year, heightened interest from the U.S. government. If I start a geology in the news series, this would probably be the first story. Otherwise, we'll see these contentious rocks in Season 7, September, on the Earth Calendar.

It's going to be a while. My point here is that we'll talk about rare earths in Greenland today, but they're not the newsworthy ones. Mining them in Itzhak would be a total waste. Scientists must sift the old tonalites with a fine-toothed comb to get anything. Which brings us back to Oxford in the 70s. Keith Onions and Robert Pankhurst are looking at a chart.

of rare earth elements from their samples, 3.9 billion years old. They've laid out the 17 sisters all in a row, lightest on the left, heaviest on the right. They see a clear, repeatable signal. These ancient tonalites had lots of light elements, but very few happy ones. Imagine a bar chart, with the highest bars on the left getting smaller.

and smaller to the right. Something had stolen those heavy elements away. Now you, the listener, might be bracing yourself. Whenever I bring up a new dataset... There's usually a heavy debate, one that's still unresolved. What will they fight about this time? Well, you can unclench yourself. I've got some rare good news.

When the Oxford bunch saw this rare earth data, they knew exactly what was going on. After decades and dozens of new samples, scientists see the same signals and reach the same broad conclusions. Peace, love, and harmony have finally been achieved, so what do we all agree on? I'm going to answer that question visually first, and then chemically.

Let's return to our imaginary rock in our imaginary pot. This time, we don't have just any old rock. This rock is scattered through with beautiful dark red crystals. As we crank up the heat, wimpier minerals start melting into magma. But these red gems remain stable, cool as a cucumber. We've only melted part. of this original reddish rock, but that's okay. That's all we need. If we remove that little bit of early magma into another pot and let it cool, voila, it turns into dull.

gray, tonalite. And meanwhile, all those hardy red gems remain in the first pot. If we zoom into the chemical scale... we would see these beautiful red crystals have hoarded all the heavy rare earth elements for themselves. Very little of these heavy hitters are left for our poor dull totalites. which is exactly what the Oxford crew saw. Lots of light stuff, not a lot of heavy stuff. The red crystals have taken away all of it.

If you're wondering where this is all going, let's take a step back. The big question we're trying to answer is, how did all those Greenland tonalites form 3.9 billion years ago? We know they formed underground, inside boiling magma chambers, but we're trying to get more specific. Was this magma below the ocean, or a continent? Was the crust pulling apart or smashing together?

The chemistry tells us what minerals were around, and the minerals tell us where this was all happening. To wrap up this episode, let's meet this red mineral and learn where... it forms. We first met this gem way back in Episode 7 in the early Magma Ocean. I mentioned, then, it would be a character actor, appearing infrequently but dramatically. This old friend is garnet. Garnet is a mineral most folks are at least familiar with.

Here are a few random facts before getting into the science Garnet comes in almost every color, but it's usually dark red or bright green as a gem It's not as fancy as diamond or ruby, but it can fetch a pretty penny. It's been used as jewelry ever since ancient times, and has importance, or shoutouts, in texts from Hinduism.

Buddhism, and Judaism. A more poetic name for Red Garnet is a carbuncle, which you'll see in literature from Shakespeare to Sherlock Holmes. In more practical terms, Garnet... is used as an abrasive because it's very tough. Which brings us back to science. Garnet is one of my favorite minerals, and not just because it's my birthstone. Garnet

forms under intense pressure, deep, deep in the crust. In the last episode, we took an elevator ride down into Earth's crust. Garnet begins to form at the bottom. of that elevator ride, the real basement of the crust. As a reminder, that's 40 kilometers or 20 miles deep, hotter than a flame, and 10 times the pressure of the deepest ocean. If you see a rock with garnets in it, it likely formed in the deepest parts of the crust. Our Greenland totalites, 3.9 billion years old, don't have garnets.

But their chemistry tells us they were born in the same deep basement. It's like footprints in concrete. The people are gone, but were clearly once here. Okay, after all that story, we actually have a location to set our ancient-owned lights. Magma chambers, at the very bottom of the crust, right next door to the mantle below.

there are still many questions to answer what does this deep horizon tell us about ancient plate tectonics was it anything like modern earth or was it completely alien those are questions for The next episode, which I promise is in two weeks, not another year. Summary Greenland contains the largest slice of rocks in Season 2, the Itzhak Complex. This area is a complicated patchwork quilt that formed over a month of the Earth calendar, February 23rd.

to March 19th, 3.9 to 3.6 billion years old. Most of these rocks were tonalites, the dull gray cousins of granite, but don't let that dullness fool you. These totalites were born deep in the crust, 40 kilometers down near the mantle boundary. We know this because they have the fingerprints of garnet, a gemstone forged under intense pressures.

Next time, we will learn more about this deep realm, we'll visit one of our cosmic neighbors for guidance, and we'll referee one of the biggest debates in early Earth history in episode 39. The Shattered Planet. Thank you for listening to Bedrock. If you like what you've heard today, please take a second to donate using the link in the description. Every dollar helps make this show possible.

and keep your eyes open for a patreon coming soon if that doesn't work just tell a friend rate the show or leave a comment that makes us more visible to curious folks it always makes my day and that one person Could be you. You can drop me a line at bedrock.mailbox at gmail.com. See you next time, and rock on!