Some organisms which make their homes on — and in — the earth can be far stranger than most can realize. Thiobacillus thio-oxidans feed upon sulfur and can exist in concentrations of sulfuric acid strong enough to kill all other creatures or dissolve metal. Hyperthermophiles grow in temperatures approaching 350 degrees Celsius. Chemotrophs produce nutrition independent of the sun’s energy — complete ecosystems exist without ever seeing the sun and would die if exposed to the surface.
Such organisms are commonly referred to as “superbugs” or “extremophiles.” Many scientists feel that their apparently ancient nature makes they good candidates for being “living fossils.” These organisms might in fact make up a total of 10% of the Earth’s entire biomass, if they extend down to half a kilometer or more, as some research suggests.
In The Fifth Miracle, Paul Davies offers several reasons to suspect that life on Earth first developed either on the sea floor near a thermal vent or in the rocks deep under the surface.
Protection: Life there would be protected from the ever-present dangers which threaten from space — a much greater issue in the earlier millennia of Earth’s history. With the asteroids and comets zipping through the solar system, life on the surface would have led a perilous existence, possibly being exterminated at any time — in fact, the surface must have been sterilized a number of times in its early history.
Raw Materials: The basic materials needed for life would have been found in abundance. Even in the present day there exists a steady supply of vial elements like hydrogen, methane and ammonia. Because of such a context, simulations of geothermally heated ocean crust conditions have created a great deal more organic material than the Miller-Urey experiments ever could have hoped for.
Energy: On the surface, the sun provides the lion’s share of the energy needed to drive life. At the bottom of the ocean, there is a tremendous chemical and thermal energy which can be harnessed. In fact, the synthesizing of simple organic compounds can release energy. This would “pay” for the localized decrease in entropy with the formation of a complex organism. Everett Shock of Washington University at St. Louis estimates that in a vent, life can produce biomass at rates like two and a half kilograms per hour, vastly outpacing photosynthesis on the surface.
Genetics: I cannot go into all of the details here that Davies offers, but studies demonstrate that extremophiles like the hyperthermophiles reside in the lowest and shortest branches of the tree of life. Not only are they most closely related to the earliest common ancestors of all life on earth, but they have in fact have developed least since they split off.
Surely this is no surprise — conditions on the Earth’s surface keep changing over time and this has put pressure on life to adapt for the sake of survival. Adaptation means change, and so life has had to change regularly. Below the surface, in locations like sedimentary rocks or near thermal vents, conditions have barely changed in millions and billions of years. If life did begin in such places, it could have occupied its niche almost unchanged for all that time.
One implication of all of this is how tight the hold life has on our planet. Even dire fears of the most paranoid people, involving a massive asteroid impact upon the earth, almost certainly would not destroy all life. Certainly life on the surface could be eliminated, but life would continue an underground existence and would perhaps rise once again to the surface.
It would be an almost-literal phoenix coming up from the hot depths to reclaim a sterilized surface. One irony is that one of the most ancient hyperthermophiles is the sulfur-eater, suggesting a key role which sulfur may have played in the origin of life. The old term for sulfur was “brimstone,” the stuff of visions of hell.Davies states that “not only was the real Eden most likely a Hadean inferno, it may also turn out that life was created from brimstone.”
Researchers around the world are finding increasing evidence that deep-sea vents are key to life’s origins. Koichiro Matsuno at the Nagaoka University of Technology said he and his colleagues were able to produce some of the elementary building blocks of which proteins, essential to life, are formed. Matsuno's team built an artificial system simulating the environment at undersea thermal vents where water heated deep below erupts through the seabed into cooler ocean water.
