Jordana Cepelewicz writes:

Energy drives the planet; it’s the currency that all living things use to grow, develop and function. But just how little energy do cells need to get by? Sediment-dwelling microbes below the seafloor — which may outnumber the microbial cells found in the oceans themselves — are providing some surprising answers. The organisms not only challenge what scientists thought they knew about life’s energy needs, but hint at new ways of defining what life is and where we might find it.

Last week in Science Advances, researchers presented the most complete picture to date of the strange, hidden biosphere beneath the seafloor. Ocean drilling expeditions have repeatedly probed those lightless depths and uncovered cells that survive almost in suspended animation, consuming orders of magnitude less energy than their neighbors at the surface. But the model presented in the new study shows that this zombielike state probably applies to the vast majority of microbes in ocean sediments — and that they typically subsist on energy budgets approaching a theoretical minimum for life.

“This entire biosphere of cells, equivalent in size to the world’s soils, hardly has enough energy to survive,” said James Bradley, a geobiologist at Queen Mary University of London and the lead author of the new modeling study. [Continue reading…]