To the naked eye, life gets scarce the deeper into the ocean one goes. But both the ocean's surfaces and its floors are teeming with microscopic life, and the deepest point of all—the Challenger Deep canyon in the Mariana Trench nearly seven miles below sea level—is home to an abundance of an "unexpected" bacteria called heterotrophs. Reporting in the journal Proceedings of the National Academy of Sciences, researchers in Japan say the microbes are incapable of producing their own food and must scavenge from their otherwise barren environment—likely surviving on dust, dissolved fecal pellets, or sediment from above that is loosened during landslides triggered by earthquakes, reports LiveScience.
"These big slope collapses are rare accidents in terms of human life spans, but they happen very frequently on a geologic timescale, and the release of organic compounds could continue for a very long time," one researcher said. The team also found that phytoplankton fill the surface waters, while chemolithotrophs (microbes capable of converting, say, sulfur and ammonia into sustenance) dominated down to around 3.7 miles, at which point their numbers gave way to heterotrophs. Other life forms are also capable of thriving at these depths, including yeasts and viruses. (Researchers also found hints of life in the Challenger Deep back in 2010.)