Denizens of the Underworld
Earth’s Deep Biosphere (here’s a link) , It dismantles that assumption, and ioes so with findings that are genuinely hard to absorb on first hearing.
Beneath us, reaching at least five kilometres into the continental crust and ten kilometres below the seabed, there is a living world that owes not a penny to sunlight. This is no marginal world by the way.Researchers estimate that the deep biosphere may hold as much as fifteen per cent of all the biomass on Earth – Intraterrestrials all of them.
The first clues to the existence of this world emerged from mineshafts and boreholes, where fluids drawn from deep rock carried the chemical signatures of biology. The obvious objection — that drilling had simply dragged surface microbes downward — fell away as scientists learned to sample cleanly. The cells were already there. Wherever water could move through cracks and pores, something was living in it.
What lives down there is not what lives up here. The deep biosphere is the domain of bacteria and of archaea, single-celled organisms that resemble the earliest life on Earth and are well suited to heat, pressure and starvation. Near deep-sea hydrothermal vents, some microbes function at the boiling point of water, and a number of microbiologists now suspect the true ceiling for life lies closer to 150°C! The pressure is tough – at vent depths it runs to several hundred times that at the sea surface, and the organisms that love it are are called piezophiles, rather beautifully,.One of them, Photobacterium profundum, not only tolerate the crush of the deep but requires it.
Time is different down there. In seafloor sediment off Peru, a microbial community forty metres down was reckoned to have passed through some 11,500 generations across roughly four million years — an average generation lasting close to 350 years. That’s serious longevity for a microbe, compared to the laboratory favorite bacterium E. coli which lives about 20 minutes between each mitosis. These creatures live in a different time zone, preserving energy so sparingly that, by one recent estimate, the average deep microbe uses fifty billion billion times less energy than a human body. At the far extreme, where even buried organic matter gives out, life subsists on nothing more than the hydrogen released when water reacts with rock.
The numbers attached to all this verge on the comic. A 2018 review by the Deep Carbon Observatory put the continental subsurface alone at between 200 and 600 octillion cells, dwarfing the thirty trillion cells in a human body by a factor of around twenty quadrillion. The volume these organisms occupy is reckoned at over two billion cubic kilometres — nearly twice that of all the oceans — and we have surveyed almost none of it.
The oddities keep pace with the statistics. In a South African platinum mine, researchers found a bacterium whose cross-section is neither rod nor sphere but a star, a shape that maximises the surface available for absorbing nutrients where nutrients are scarce. Deeper still, in water that had lain undisturbed in gold-mine rock for at least three thousand years, they found multicellular animals: minuscule nematode worms, including one new to science, named Halicephalobus mephisto after the devil who shuns the light.
In 1992 the astrophysicist Tom Gold argued, in a paper titled “The Deep, Hot Biosphere,” that subsurface life might be as widespread as surface life, governed by chemistry rather than light and limited chiefly by temperature. If he was right, the reasoning travels off-world with unsettling ease. And that perhaps is the most interesting aspect of this. If life can establish itself down there then why not any any planet or moon that you care to name. There is a possibility that life is pretty much ubiquitous– maybe not on the surface of our fellow planets, but down there among the geology.