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In his controversial 1999 book, The Deep Hot Biosphere, late Austrian-born astrophysicist Thomas Gold speculated that, though there is certainly life on other planets, this life is likely to be in the ground and not the surface. Gold might have been a bit lost when it came to the whole abiogenic petroleum origin theory (nothing more will be said about that in this post); but it seems his theory on life and its grounded origin has a chance.

A recently completed 10-year scientific study of life in earth's "subterranean biosphere"—that is, life in the ground—concluded that there is much, much, much more life beneath us than we initially thought. A group of 1,200 scientists estimate the ground is "teeming with between 15bn and 23bn tonnes of micro-organisms." That is "twice the size of the world's oceans." Indeed, some of these forms of life are so deep that their metabolic processes have little and possibly nothing to do with sunlight. This should strike one as very strange. It opens up the possibility that life driven by light, by photosynthesis—the forms of life that we are familiar with and wholly depend upon (no plants, no us; no cyanobacteria, no plants)—may have arrived very late on the scene. Life can be driven by just enough energy.

Karen Lloyd, an associate professor at the University of Tennessee in Knoxville, told the Guardian: “The strangest thing for me is that some organisms can exist for millennia. They are metabolically active but in stasis, with less energy than we thought possible of supporting life.” And how deep is life? As far as our instruments can tell us. And our instruments can only go so far. So, in essence, we do not know. The subterranean biosphere could shock us and double its size. Triple its size. And this would radically change our understanding of the history of life on earth.

There has been, for sure, much discussion about deep sea "black smokers," a theory popularized by the British biochemist Nick Lane, as the first engines of life. It all sounds plausible. There are promising chemical patterns—or echoes—and so on. But as another star in the origin field, the mineralogist Robert Hazen, told the Guardian, "We must ask ourselves: if life on Earth can be this different from what experience has led us to expect, then what strangeness might await as we probe for life on other worlds?" (My origin theory requires, above all, a planet-rich solar system—I owe much to Peter Ward for this idea.)

It seems the more we look at life, the stranger it becomes. And this is, indeed, the most important lesson of Darwin's lovely "warm little pond" as the possible origin of life. What's important is not that he was completely wrong, but that he clearly looked at the garden in his fine manor in the Kent countryside, and imagined that life could get a pretty good start there. Why not? It was comfortable enough (a nice little pond, a little light, a little heat, some salt—how lovely). But that is exactly how we humans see the origin of life. Habitually or instinctually, it's from where we are, from what we can see. But we are much weird than we think, and life is mindbogglingly weirder than we are.

Gold:

The surface life on the Earth, based on photosynthesis for its overall energy supply, may be just one strange branch of life, an adaptation specific to a planet that happened to have such favorable circumstances on its surface as would occur only very rarely: a favorable atmosphere, a suitable distance from an illuminating star, a mix of water and rock surface, etc. The deep, chemically supplied life, however, may be very common in the universe. Astronomical considerations make it seem probable that planetary-sized, cold bodies have formed in many locations from the materials of molecular clouds, even in the absence of a central star, and such objects may be widespread and common in our and in other galaxies. It is therefore a possibility that they mostly support this or similar forms of life....