Not entirely sure what the measurement means but this much is easy to grasp:
The scientific team, which includes hundreds of researchers from all over the world, drilled boreholes kilometers below the continents and seafloor to sample microbes. The information collected by the scientists has allowed them to build models of the deep ecosystem and make the estimates of the deep life biomass.
The researchers found a stunning array of life, mostly microbial, and estimate that approximately 70 percent of the total number of Earth’s bacteria and archaea organisms live in this realm. These microbes live at extremes of pressure, temperature, and nutrient and energy availability. Carolyn Wilke, “Life Deep Underground Is Twice the Volume of the Oceans: Study” at The Scientist
The find is a boost for the search for subsurface life on other planets.
From the Guardian:
One organism found 2.5km below the surface has been buried for millions of years and may not rely at all on energy from the sun. Instead, the methanogen has found a way to create methane in this low energy environment, which it may not use to reproduce or divide, but to replace or repair broken parts.
Lloyd said: “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.”
Jonathan Watts, “Scientists identify vast underground ecosystem containing billions of micro-organisms” at The Guardian
Presumably, these millennia-old subsurface organisms don’t reproduce much, as it is more economical to just stay alive and do nothing. What then of evolution? If the millennial organism changes a fair bit over the centuries, is that evolution?
Also, what if we examine the organisms without preconceived ideas about natural selection, longevity, or information transfer? Would we favour the same theories? For the same reasons?
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See also: “Fairly sophisticated” bacterial communications pose stark question re evolution
Light-loving cyanobacteria found, improbably, nearly 2,000 feet underground
Will a new type of photosynthesis, just discovered, change the hunt for alien life?