Slow life

Here’s another example of an article from the popular press that uses the potential for apocalypse (“huge tsunamis, runaway global warming, and extinctions”) as the hook. But it turns out that many researchers are skeptical about the most drastic claims, feeling that the potential of massive, microbial belches to alter the earth’s atmosphere may be completely overblown. In my view, just as with the recent Science Times article on cosmology, the “gee whiz” aspect of this story is way more compelling. One third of all life on earth, measured by biomass, may occur beneath the seafloor, in the so-called deep biosphere. This life consists of archaea and primitive forms of bacteria: microbes for which oxygen is poison, because they evolved before the existence of green plants. The final paragraphs of this article are worth quoting in full. From the cover story of the March issue of Discover magazine, “20,000 Microbes Under the Sea,” by Robert Kunzig:

“The researchers found microbes in all the sediments they examined. There were more under the coastal waters of Peru than in the open Pacific; more near the seafloor than 1,400 feet below it. But there were intact microbes everywhere. In the upper layers, typically, they were reducing sulfate; in the lower ones they were making methane; and in between they were oxidizing methane.

“The existence of the deep biosphere is established – but it remains an astonishing paradox. ‘From all we understand about the energy requirements just to stay alive, it’s much higher than the energy they have,’ says Barker Jørgensen. If the deep microbes spend as much on maintenance as the surface microbes do, he says – repairing radiation damage to their DNA, keeping their membranes intact – they should have nothing left for the microbial prime directive: divide and multiply. Barker Jørgensen’s expedition looked for some new energy source in the sediment, some exotic new combination of fuel and oxidant, and found none.

“[John] Parkes thinks the microbes’ secret is their slowness: ‘These things are dividing every thousand, every ten thousand, every hundred thousand years. There’s nothing to eat them; bacteria near the surface have to grow fast because they get eaten by protozoa and ciliates, but we’ve not detected those kinds of organisms in the subsurface. So bacteria there can concentrate on maintenance, rather than wasting energy on division.’ And they must have lived long enough and divided often enough and mutated often enough to evolve through natural selection, because they are well adapted to their environment. Parkes has found microbes in deep sediments that grow best at precisely the pressure at which he found them. ‘They are responding at geological timescales,’ he says. ‘That’s the fascinating thing.’

“Microbes living under the seafloor today, Parkes speculates, may have survived the growth and splintering of continents, the opening and closing of oceans; they may have been buried, subducted, frozen in hydrate, and spat out of a mud volcano, only to be buried, subducted, and spat out again. While we were waiting for our evolutionary fast lane to be paved, racing through all of human prehistory and history in the time it takes one of them to divide once, they have been living in time with the planet’s deepest, slowest rhythms. They have been living almost like rock, which is precisely what made them so easy to miss. They have always been there, from our deepest past, but only now have they fully penetrated into our awareness. Given their collective influence, it’s about time.”

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