Did Life’s Diversity Literally Spring Forth from Rock?

The trilobite, one of the first animals to make use of biominerals by forming a shell.

A new theory suggests that we may owe our existence – and the whole of Earth’s diversity – to rocks. If that sounds outrageous, read on and I’ll explain.

Mounting evidence suggests that evolution isn’t just a slow, diligently advancing wave of mutations. Instead, life makes giant leaps and bounds in relatively small amounts of time. Sort of like the X-Men all starting to appear in merely a couple of generations in the famous comics. Probably the most famous of these periods of time is called the Cambrian explosion.

The Cambrian explosion is a well-documented time in the Earth’s history roughly 530 million years ago where animals suddenly diversified from a bunch of soft-bodied, primitive life forms into a vast array of multicellular organisms, some sporting the first shells and skeletons. For four billion years, life on Earth had produced little beyond bacteria, plankton and simple animals. But thanks to the extensive fossil record from this period, we know that life suddenly advanced in many directions in less than 30 million years.

That may seem like a long time, but its paltry when compared to four billion, and the general timescale of evolution. The reason for this sudden diversification and evolution is a mystery. However, Shanan Peters of the University of Wisconsin believes the answer lies in the rocks in the Grand Canyon.

Another term you’ve probably never heard of – at least I hadn’t – is the Great Unconformity. You may know that looking at the layers of rock in the Grand Canyon is like looking at a time-capsule of Earth’s history. Each layer speaks to a different period of time where different types of rocks and fauna eroded to produce the various types of rocks seen in the canyon.

There are two layers, however, that don’t quite stack up correctly. At the canyon wall, ancient igneous and metamorphic rocks lie right on top of one another. That’s pretty normal, except for the fact that one layer is much older than the other. It appears that tens of millions of years of rock formation have been removed from the record.

The Great Unconformity.

There is a geological explanation, however. First, a giant lake or ocean  fills its bottom with sediment. Indeed, the southwestern United States was submerged in shallow waters around this time. As the water retreats, the sediment forms rock. Sedimentary rock. Get it?

But then plate tectonics take over. In a relatively short amount of time, the underlying bedrock is pushed up through the sedimentary rock as new mountains are formed. Because sedimentary rock is easily eroded, it gets washed away. As time continues on, the mountains are weathered down to nothing, and another layer of rock can now form on top of the flattened range. And because the sedimentary rock was washed away, you get two layers of rock on top of each other separated by hundreds of millions of years.

Now, according to Peters’ theory, the mountains began to form and push bedrock up through the sedimentary rock right before the Cambrian explosion. As the bedrock became exposed to the ocean, minerals in the rock began to dissolve, changing the chemistry of the oceans.

Pretend you’re a simple, multicellular organism swimming around. Suddenly, your body begins taking in all kinds of new minerals that you’re not used to. Some of them might even be toxic, unless you can figure out what to do with them. What could one do with a bunch of excess potassium, silica and iron?

How about make a mineral?

The fossil record shows that the three major biominerals — calcium phosphate, now found in bones and teeth; calcium carbonate, in invertebrate shells; and silicon dioxide, in radiolarians — appeared more or less simultaneously around this time and in a diverse array of distantly related organisms.

“It’s likely biomineralization didn’t evolve for something, it evolved in response to something,” said Peters. “In this case, changing seawater chemistry during the formation of the Great Unconformity. Then once that happened, evolution took it in another direction.”

Today, those biominerals play essential roles in shells, spines, bones, teeth and claws. The theory gives new meaning to the old myths that we sprung from the ground, made out of earth.


About bigkingken

A science writer dedicated to proving that the Big Ten - or the Committee on Institutional Cooperation, if you will - is more than athletics.
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