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Team Totals Immense Amount of Carbon in Zombie Bacteria, Other De*p Life Microbes harvest energy from methane at seafloor seeps. These organisms have very slow growth rates with a minimum doubling time of a few months, very slow growth rates with a minimum doubling time of a few months, making them very difficult to cultivate and study in the lab. Image courtesy Katrin Knittel (MPI Bremen) Barely living “zombie” bacteria and other forms of life constitute an immense amount of carbon de*p within Earth’s subsurface—245 to 385 times greater than the carbon mas* of all humans on the surface, according to scientists nearing the end of a 10-year international collaboration to reveal Earth’s innermost secrets. are reporting on several transformational discoveries, including how much and what kinds of life exist in the de*p subsurface under the greatest extremes of pressure, temperature, and low energy and nutrient availability. is akin to exploring the Amazon rainforest. There is life everywhere, and everywhere there’s an awe-inspiring abundance of unexpected and Drilling 2.5 kilometers into the seafloor, and sampling microbes from continental mines and boreholes more than 5 km de*p, the team has used the results to construct models of the ecosystem de*p within the planet. “Molecular studies raise the likelihood that microbial dark matter is much more diverse than what we currently know it to be, and the in 1977,” Sogin said. “Perhaps we are approaching a nexus where the earliest possible branching patterns might be accessible through With insights from now hundreds of sites under the continents and seas, they have approximated the size of the de*p biosphere—2 to 2.3 The work also helps determine types of extraterrestrial environments that could support life. domains of life: bacteria and archaea (microbes with no membrane-bound nucleus), and eukarya (microbes or multicellular organisms with cells Among them are millions of distinct types, most yet to be discovered or characterized. This so-called microbial “dark matter”