Earth’s extraordinary deep biosphere is our next great frontier

Intractor
Karen G. Lloyd (Princeton University Press)

I can think of a shelf full of books on the forests, and almost as much on the ocean or deserts. And consider the amount of ink that has been overthrown on expeditions to distant ecosystems, from the Amazon to Antarctica. However, with a few notable exceptions, such writing has neglected one of the greatest most fascinating habitats on the earth. It is microbial life in the crust of the planet: the deep biosphere.

More now. Intraterrestrials: discover the strangest life in the world By Karen G. Lloyd is an essential guide to the underground life of the earth – at least the parts of it, we have been able to probe so far. “In fact, we have not yet encountered a depth to which life ceases to exist,” she writes.

The fact that the very existence of the deep biosphere is not a public notoriety reflects our understandable concern of the surface. We live here after all. But Lloyd, a microbial biogeochemist at the University of Tennessee, Knoxville, argues that learning it more about this life can change the way we think of life in general.

As it sees, the deep biosphere includes any place under the ground or under the seabed, where life exists without exposure to the sun, the main source of energy for most of life on the surface. Such a definition extends through a wide range of metabolic contexts, methanogens living rotten plants under a few centimeters of marsh mud to chemiolithriversary breathing at the top of the rock at 3 kilometers.

For these microbes, she writes: “It is as if there were millions of small low -power suns distributed throughout the crust of the earth, each with their own little orbit of an underground ecosystem”.

How many life is there? We don’t really know. But all our estimates are too low, maintains Lloyd. She quotes a claiming that marine sediments alone could contain 2.9 × 10²⁹ Cells, with twice as much again to do in continent fractures and pores. These are amazing numbers.

We now learn more about these teeming ecosystems, thanks to a combination of genetic sequencing technology and field work. The first, explains Lloyd, helps researchers to distinguish the different species of microbes and to make inferences on their metabolism based solely on DNA. This is useful since most of these deep and archaee bacteria have proven to be impossible to cultivate in surface laboratories.

The field work part concerns how researchers are getting their hands on a new DNA, whether hydrothermal vents on the seabed, drilled from the continental rock or collected in water in deep mines. “To study the extremophiles, you sometimes have to become one yourself,” writes Lloyd.

Thanks to a full -minded prose, it brings us to some of its own adventures in pursuit of the high desert microbes of the Andes at the perilous summit of a Costaorian volcano. These are scenes from an action film: be careful not to slide on the shards of volcanic glass, for fear of falling into the acid lake!

Fortunately, the book is much more than a report of daring expeditions. It has extended and accessible explanations of chemistry which makes the biosphere deep possible. It’s a complicated thing. The equations are involved. You will see a lot of ΔG – The very important measurement of the energy that a microbe could extract from a given chemical reaction. However, in a way, incredibly, Lloyd helps us to start seeing the chemical contours that allow these organizations to live on the “energetic edge”.

To shoot us in this steep learning curve, it is based on analogies with surface ecosystems, as well as our own eating habits, to develop the underground world. For example, sulphide mastery bacteria are “sofa potatoes”. They compete with methanogenic “freeloaders” by holding hydrogen, universal food, in an ecological drama worthy of Serengeti. Sulfate reducers in Svalbard fjords “have access to a perpetually supplied refrigerator”. All this makes reading fun and evocative about biogeochemistry – not an easy task.

The culmination of the book, however, is Lloyd’s discussion on how certain forms of deep life have extremely slow metabolisms that could allow individuals to live for millennia, or perhaps millions of years. These “eonophiles” (should they prove to be so long) continue to “break our preconceived concepts on the way life is supposed to work,” she writes. Indeed, these are really foreign lifestyles. How lucky we can know more about them on earth.

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