A Walk on the Wild Side

If you haven't heard of Olivia Judson then you are living an impoverished life. She is a delightful biologist & writer who does popular science on "curious animals" as well as a research scientist. She wrote the tantalizing book Dr. Tatiana's Sex Advice to All Creation: The Definitive Guide to the Evolutionary Biology of Sex. She has a blog on the NY Times that is well worth reading. The following is an extract from a longer article to give you a taste of her writing:

...many bacteria live deep in the oceans and deep in the earth, far from light, far from what we normally think of as good, comfortable places to live.

For example: the bottom of the Mariana Trench. This is a seam on the sea floor in the northwestern Pacific, not far from the island of Guam; it’s where the Pacific plate is sliding under the Philippine plate. The ocean is deeper here than anywhere else in the world: the seabed is 11 kilometers (almost 7 miles) below the surface of the sea. Yet even here, where the pressure of the water would crush you or me, there are bacteria. Some of them won’t grow at all unless the atmospheric pressure is at least 50 megapascals (around 7,000 pounds per square inch), and they grow better if the pressure is greater — 70 megapascals (more than 10,000 pounds per square inch). For comparison, the pressure at sea level — the pressure we have evolved to bear — is 700 times less.

Then there are the “intraterrestrials” — the organisms that live in rocks deep in the earth, the creatures of the “deep subsurface biosphere.” Bacteria have been found in rock samples taken several hundred meters below the sea floor, even when the sea floor itself is 4 kilometers (2.5 miles) below sea level.

We don’t know how many organisms are living in this (to us) alien environment. But based on what’s been found in rock samples so far, the numbers are likely to be gigantic. One recent study found between 1 million and 1 billion bacteria per gram of rock (a gram is 1/28 of an ounce). It may be that a large proportion — perhaps as many as a third — of all bacteria on Earth live in rocks below the floor of the sea. That would be a lot of bacteria.