42: The Question of Life

Episode 42: The Question of Life

I didn’t plan for Episode 42 to be about life, but it’s a fitting number. For those who don’t know, 42 is the Answer to Life, the Universe and Everything. At least, that’s according to the Hitchhiker’s Guide to the Galaxy, the sci-fi comedy classic by Douglas Adams. If you’re even vaguely acquainted with nerds, you’ve probably heard all that before. Maybe you even have a 42 stamped somewhere around your home.

Here's what most people miss while laughing at the joke. In the book, 42 is the Answer to Life, the Universe, and Everything, but no one knows the actual Question. This puzzle is strikingly relevant to the actual search for life. In the rush to search for an answer, like the oldest fossil, or evidence for aliens, it’s easy to forget the question: what exactly are we looking for in the first place? Fortunately, for every proposed discovery, there are hundreds of scientists scrutinizing the evidence, making sure the best questions are asked.

Today, we examine another claim for the oldest fossils on Earth. This is not our first rodeo. In Episode 16, we saw ancient traces of carbon in the Jack Hills Zircons of Western Australia, diamonds and graphite over 4 billion years old. The diamonds turned out to be polishing grit, and the graphite remains ambiguous. In Episode 33, we saw thin, rusty, straw-like structures in northern Quebec, around 3.8 billion years old. They might be iron-rich cells, or chemical reactions with no influence from life. For now, there’s no smoking gun.

Everyone agrees that life was around during this time, but finding fossils remains difficult. You need a patch of seafloor or lakebed that’s been untouched for nearly 4 billion years. The older you look, the fewer rocks there are, and they’re very messed up. You take what you can get.

This episode concludes a trilogy on the island of Akilia, off the coast of Greenland. In Episode 40, we learned that Akilia is over 3.8 billion years old. On the great Earth Calendar, that’s February 25. In Episode 41, we learned that Akilia contains banded iron formations or BIFs, the remains of ancient iron-rich seafloors. All these points have been hotly debated over 30 years. Today, we’ll examine the last and largest debate: do these rocks hold fossils?

Part 1: Fertilizer

*Stephen Mojzsis in 1997, shortly after his major Akilia paper (photo from Science Photo Library)*

The year is 1996. The Olympics are celebrating their 100-year anniversary. The Macarena is taking the world by storm. As the planet cheers and dances, we zoom in to sunny San Diego, California. The Scripps Institute of Oceanography has a beautiful campus, looking out over green golf courses, hang gliders flying across seaside cliffs, and surfers on the beach. But today, we’re inside a laboratory, with sunlight streaming in from the outside.

Sitting at a microscope is a spectacled grad student named Stephen Mojzsis (moy-zish). If you’re searching his name, it’s spelled M-O-J-Z-S-I-S. Mojzsis has been with us for two episodes and is a major player on the Greenland stage, but in 1996, his story is just beginning. In front of Mojzsis is the world’s oldest slice of seafloor, a rusty, stripey slab of rock 3.8 billion years old named G91-26. If your goal is to find Earth’s oldest fossils, G91-26 is the best place to look. Mojzsis wasn’t looking for fossil bones or leaves or footprints- those bigger critters won’t appear for a long time. He was looking for ancient bacteria, the fabled “primordial ooze”. To do so, he had to look through the microscope. We’re going to follow his journey, shrinking smaller and smaller down.

The sample in question is a special type of rock: a banded iron formation. For more detail, check out last episode or Episode 32, but here are the relevant facts. Sample G91-26 formed at the bottom of the sea, as layers of red and gray iron collected on the seafloor, like sprinkles on a cake. Iron is not a fossil, but it’s a good clue that life was around- many types of bacteria love to munch on rust. Think of the iron layers like a watering hole on the African savannah, attracting critters who need to drink and eat.

Mojzsis scanned and scanned these rusty layers, looking for any signs of life. He didn’t see any fossil bacteria, but he found something interesting. Every so often, he would spot a weird crystal, an small speck of pale blue in a sea of rusty red. These scattered crystals made up less than 1% of the rock, but as Mojzsis found more and more, he grew increasingly excited. What is this mineral, and why do we care?

This new crystal will be a character actor, a friend appearing infrequently but dramatically in future seasons. You probably haven’t heard of this mineral, but it does have a memorable name. Meet apatite. You heard me: apatite. When I say “appetite”, you probably think of being hungry: working up an appetite, an appetite for destruction. This mineral’s name in pronounced the same but is spelled differently. Our mineral is A-P-A-T-I-T-E.

*Apatite in its’ classic blue form, Irkutsk, Russia*

As a gemstone, apatite is usually blue or green but can come in any color. Because of its’ diversity and beauty, it can be mistaken for more precious gems like topaz or aquamarine. That deceptive nature gives apatite its name: apate is Ancient Greek for “deceit” or “fraud”, not to be confused with “Apt.”, the banger pop song by Rosé and Bruno Mars. Anyways, back to the minerals. Why was Mojzsis so excited, so hungry for this apatite? It’s not a fossil, but it is another strong clue that life was around.

Apatite is found in many locations, from lava flows to seafloors to the human body. In fact, apatite is the most abundant mineral in your body, but don’t worry- it’s supposed to be there. Apatite is the cornerstone of your skeleton. There are other materials mixed in, but the mineral apatite makes bones and teeth hard and strong. Without apatite, you would literally fall apart. For example, bad things happen when your tooth enamel wears away- that enamel is made from apatite. So even if the word apatite is new to you, you’ve literally seen it and carried it around every day of your life.

*An apatite crystal from Akilia, surrounded by a dark envelope of graphite. Scale bar is 20 microns. (Mojzsis et al., 1996)*

Does that mean the ancient Greenland apatites were once the bones of primeval creatures? Sadly no, but they can tell us about life. The most important ingredient in apatite is the element phosphorus. Phosphorus is an essential nutrient for life, even for creatures with no bones. DNA, RNA, and cell walls all have phosphorus inside. No phosphorus, no DNA, no life. This is why phosphorus is used as fertilizers on farms, it helps crops grow every year. Many of those fertilizers come from apatite mines. Geology and biology are closely linked. As we go forward, when I say “apatite”, I want you to think about fertilizer- it’s not alive, but it helps life grow. You can remember that life is “hungry” for apatite.

When Mojzsis found apatites in the ancient Greenland rocks, they were tiny and scattered, smaller than grains of sand. Not enough to fertilize plants, but perhaps enough to fertilize bacteria. Remember, the apatite wasn’t a fossil, but it was a great place to look for them. And finally, as Mojzsis zoomed even closer, inside the apatite crystals, he finally found what he was looking for, the strongest fingerprint for ancient life: carbon.

Part 2: Penciled In

The last time we talked about carbon was way back in Season 1, Episode 16, which kicked off a huge arc on the origins of life. Today’s conversation is a spiritual sequel to that episode, I’m going to reference it a lot. Here’s a quick recap.

All life on Earth, from bacteria to Bruce Springsteen, uses carbon as a fundamental building block. Inside you the listener, 20% of your body is made of carbon, from your DNA to your fingernails. It’s easy for the word “carbon” to become shorthand for life, but carbon by itself is not alive or a fossil. For example, a diamond on a wedding ring is pure carbon, but isn’t a living thing.

Mojzsis didn’t find diamonds inside the Greenland apatites, but he did find another carbon mineral: graphite. Like diamonds, graphite is formed when carbon is pressure-cooked deep underground. Unlike diamonds, graphite is much more common and much easier to make.

In fact, I’d bet good money that graphite is within 20 ft of you right now, inside a pencil. See if you can find one and look carefully at the tip. Every time you use a pencil, you’re grinding down dark graphite minerals onto paper. Sometimes graphite is called “pencil lead”, but that’s misleading- there’s NO lead inside your pencil, it’s pure carbon. Graphite just happens to look like shiny, dark lead minerals, but there’s no risk of poisoning if you chew a pencil. There’s enough lead around us without worrying about that.

Speaking of pencils, let’s get back to the point. Stephen Mojzsis was looking for fossils inside Earth’s oldest slice of seafloor. He was so close, and yet still so far. The iron was a good clue, but not a fossil. The fertilizing apatite was a good clue, but still not a fossil. Now he found tiny scraps of graphite, pure carbon, the building blocks of life. Furthermore, that carbon was nestled inside fertilizer, the perfect place for life to grow! But by itself, carbon still wasn’t quite enough. Fortunately, he had another trick up his sleeve: carbon isotopes.

Don’t sweat if you’re new, or not chemically inclined: here’s what you need to know about carbon isotopes. Again, this is summarized from Episode 16.

There are two main types of carbon atoms: light and heavy. Here’s the key thing to remember, burn it into your brain as we keep searching for fossils: life has light carbon. The carbon inside your body, or your pet, or your food, is much lighter than the average carbon of the universe. We’ll describe why this is in a future episode, but here’s a good analogy. If I asked you to carry an apple or a watermelon around all day, you’d probably choose the apple. Life is lazy, and doesn’t want to carry extra weight around.

Anyone can find carbon inside a rock like graphite or diamonds. That carbon could be a trace of life, or just plain old chemistry. But if that carbon is extremely light, that’s a much stronger sign that it was once a living thing. When Stephen Mojzsis looked inside the ancient Akilia seafloor, that’s exactly what he saw. The carbon had the same isotope signatures as bacteria- full of light carbon atoms. Here’s the model that Mojzsis proposed:

Once upon a time, bacteria were living and dying on the seafloor, 3.8 billion years ago. The bacteria were attracted to plentiful fields of iron and especially attracted to little seeds of fertilizer, apatite crystals. The bacterial were filled with light carbon atoms, just like bacteria today. As this seafloor was buried, the tiny cells became pressure-cooked into shiny graphite crystals. Even though the cells were obliterated, the light carbon atoms remained behind inside graphite.

*A potential vision of the ancient Akilia seafloor (modern Papua New Guinea)*

In 1996, Mojzsis published this research in the journal Nature, the highest place a geologist can go. Since then, Mojzsis has been a researcher at UCLA in Los Angeles and is currently a professor at the University of Colorado in Boulder. We first met him way back in Season 1, Episode 15, looking at the oldest evidence for Earth’s oceans, a paper with nearly 1000 citations, huge for a geologist. Today’s paper, the one discussing ancient fossils, is approaching 2000 citations, his most cited work.

One of the reasons for all these citations is 30 years of intense debate. As you can imagine, such a large claim, one that would change the history of life on Earth, was met with intense scrutiny. It was time to test Mojzsis’ idea: were these graphite flecks actually fossils?

Part 3: Don’t Panic

For the past two episodes, we’ve met three different research teams battling over Akilia Island off the Greenland coast. Each team has dozens of folks, but for simplicity we’ve named them after their major players: Team Nutman from Australia, Team Mojzsis from the USA, and Team Whitehouse from Sweden. Teams Nutman and Mojzsis have been on the same side this entire season, agreeing on the age and nature of Akilia rocks. You might wonder why they’re not one mega-team, why they don’t publish together. I don’t know the full story, and I’m not going to turn this into speculative gossip- it’s still a bit recent for that. There might not even be any gossip, it could simply be an issue of timing. Here are my observations from the literature.

Nutman and Mojzsis and friends did publish two papers together in the 1990s: one with each at the helm. One is the huge paper I just described, Mojzsis’ great fossil discovery of 1996, the light graphite from this episode. The next year, Nutman described the banded iron formation itself- less flashy, but very important. Since then, the two authors have not written any other papers together.

The disagreement came three years later. Nutman and a team led by Yuji Sano in Hiroshima, Japan published a short comment on the fossil paper. We learned about such short comments last episode. If you feel a paper is very wrong, but don’t have enough time to write your own paper, a comment is your place for a quick argument. These short comments are usually a bit punchier, written from a place of disagreement with a need to get a point across quickly and clearly. Whenever we talk about comments, feel free to get out the popcorn and soda, these are the dramatic moments in academia.

So why did Sano, Nutman and crew disagree with Mojzsis’ fossils? Remember, Nutman was on the original fossil paper with Mojzsis- what evidence changed his mind? Dates.

*Apatite from Akilia island. The lines on the inside form as uranium decays and carves paths in the crystal. Cool stuff! (Mojzsis et al., 1996)*

On this show, nearly all our age dates come from the mineral zircon- it’s the clock that sets the Earth Calendar. The ticking of the clock comes as uranium atoms decay into lead. Zircon crystals are great timepieces because they trap and hold uranium. Our new mineral friend apatite can also trap uranium, it’s an alternate clock. One difference is that apatite is much wimpier than zircon, it can’t take the heat as well. That wimpiness is a key part of the argument.

Sano and Team Nutman dated the Greenland apatites, the little seeds of fertilizer that cradled the precious carbon. Surprisingly, the dates were much younger than other studies- September on the Earth Calendar instead of February. For folks keeping score, that’s 1.5 billion vs 3.8 billion years old. We won’t see rocks that young until Season 7!

Does this mean the entire rock is young, and should be thrown out? No. The Hiroshima crew argued the rock was still February in age, but was squeezed and pressure-cooked much later in September. This metamorphosis had altered Mojzsis’ apatite crystals, had literally reset their internal clocks. If the apatite was messed up, maybe the graphite was as well. In other words, even though the rocks were old, the carbon inside might be young.

With one crack revealed, the floodgates of criticism were now opened, and attacks came in from all sides. We don’t have time for every single debate, but some papers went wild. For example, two separate studies looked at the same rocks, and couldn’t find any graphite, any life-giving carbon at all! For context, imagine visiting a desert and finding ancient human footprints, perhaps the oldest on Earth. Now someone else visits the same spot, and says “Sorry buddy, I don’t see any footprints here”! That’s some serious pushback.

By the 2010s, the debate had calmed down a bit. Everyone now agreed that the Greenland rocks did indeed have graphite inside, a little bit of ancient carbon. The question now was: was this graphite the original remains of ancient fossils, or was it added later during metamorphosis? For a kitchen analogy, consider a cake full of sprinkles. Were the sprinkles baked inside the original cake, or were they sprinkled on top later?

Let’s examine three lines of evidence and reach our own conclusions, mostly from teams led by Dominic Papineau and Aivo Lepland, now in London and Norway, respectively.

1: Isotopes. Carbon isotopes can be strong evidence for ancient life. The lighter the carbon, the more likely it came from a living critter. This was the lynchpin of Mojzsis’ fossil argument: the Greenland graphites had the same carbon isotopes as bacteria! But more recent studies have only found heavier carbon- it might have come from life, but it might have come from a non-living source like limestone or carbon dioxide. If you’re looking for a bona fide fossil, you need evidence that can only be made by life.

2: Apatite. The relationship between crystals of graphite and apatite is important. According to Mojzsis, the flecks of graphite were fossils of ancient life, while the apatite was the fertilizer that helped life grow. He described tiny bacteria-sized graphite nestled inside larger, sand-sized apatite crystals, like sprinkles baked inside a cake. More recent studies do not see this pattern. Instead, they see dark graphite scattered around the outside of larger apatite crystals. In short, the sprinkles were put on the cake later, not baked inside from the beginning.

3: Other minerals. Until now, I’ve described graphite and apatite hand-in-hand, the fossils and the fertilizer that fed them. In 2010, graphite was found hanging out with hotter mineral friends. Don’t worry, I’m not unleashing any more names at you today. All we should know is this group of crystal “bad boys” were new kids in town, added during high-temperature metamorphosis billions of years after the rock formed. Other studies found graphites concentrated along cracks where hot groundwater had once seeped in.

All together, these three clues tell a story. Once upon a time, about 3.8 billion years ago, there was an ancient seafloor. That seafloor was buried and cooked deep underground over billions of years. As the rocks were warped, groundwater infiltrated the cracks like a leaky basement, dumping many new crystals into the old stone, including carbon-rich graphite. That carbon might have come from life, but it wasn’t the original inhabitants.

This is the third time we’ve looked for fossils, and the third time we’ve drawn a bust. If you’re bummed out, there is a faint glimmer of hope. Some of the Greenland graphite is clearly not original- everyone agrees about that now, even Stephen Mojzsis. But there is still the chance that somewhere, in a pristine pocket, there could be original carbon from 3.8 billion years ago. The chances of finding it are now much trickier, but not impossible. And if there’s one thing ancient geologists are good at, it’s meeting those odds and beating them. So while there are no definitive fossils on Akilia Island, the chance of discovery is still out there.

Summary: For the past three episodes, we’ve focused on just one frigid little island: Akilia, off the Greenland shore. The isle is a few city blocks wide, and the area of interest is the size of a large sports stadium. The story of the island is more than just the rocks, it’s about all the people who have studied and fought over them. We’ve focused on three teams led by three men: Allen Nutman, Stephen Mojzsis, and Martin Whitehouse, though many others are involved. Their disputes might seem incredibly minute at times, but together, they have painted a more detailed vision of the island’s past. In 2025, here is the broad consensus:

Akilia contains the oldest slice of Earth’s seafloor, or at least in the top three, over 3.8 billion years old. This seafloor was mostly dark and volcanic, but every so often a pause in eruptions would let iron rain down from the ocean above. This iron was likely a feast for microbes, supplemented with tiny grains of fertilizer like apatite. Life was almost certainly around, but if any fossils were preserved, they have been overprinted during burial and metamorphism. Who knows what future studies will reveal about Akilia Island?

Next episode, we enter the last leg of our Greenland adventure, and the final arc of Season 2. I’ve saved the best for last, these are truly the most well-preserved rocks of their age. Join me at the foot of the Greenland glaciers for Episode 43: Postcards from the Edge.

41: The Oldest Seafloor