This past summer, oceanography grad student Justine Sauvage headed to sea aboard the Japanese Deep Sea Drilling Vessel (D/V) Chikyu for a two-month expedition studying life deep beneath the seafloor. She had no idea at the time that she’d become part of an international team of scientists who would dig deeper than humans ever have before. Her team drilled 2,446 meters below the seafloor off the coast of Japan, far surpassing the previous record of 2,112 meters.

Justine is studying the microbial activity deep in the sediment in the South Pacific gyre, the farthest place from land on Earth, where very few cells live and where even less organic matter ever reaches the seafloor. Why? Well, “if we can understand all of the places where life is capable of living, then that may give us a link to finding life on other planets,” of course.

Every day while aboard the ship, Justine collected sediment cores from the drill team, put the sediment in a press, squeezed out the water, and analyzed the chemistry of the water. “The water tells us what microbial processes are going on, what they are doing and eating and the chemicals they are releasing,” she said. The sediment she collected contain numerous radioactive elements, and it appears likely that the living organisms there may be feeding on the hydrogen produced from the radioactive splitting of water, since there’s little else available to eat.

“If that kind of ‘nuclear life’ is taking place on Earth, then we can extrapolate that it may be happening in less-hospitable environments characterized by wet sediments rich in radioactive elements, like subsurface Mars and Europa.”