The dark abyss of the Mariana Trench in the western Pacific Ocean hosts a surprisingly active bacterial community.

By using an automated deep-sea instrument that they designed, a team led by Ronnie Glud at the University of Southern Denmark in Odense measured rates of biological oxygen consumption in the almost 11-kilometre-deep ocean trench. The high rates they found there suggest that degradable organic matter is being deposited at the bottom of the trench, allowing microbes to thrive in this secluded habitat.

A second team reports that life exists in an even more unlikely environment. While at the University of North Carolina at Chapel Hill, Mark Lever and his colleagues found hydrogen-loving microbes in the oceanic crust, deep beneath the seabed off the west coast of North America. An incubation experiment over several years showed that the organisms can derive energy from geochemical reactions between iron compounds and the sea water that permeates through cracks in the rocky crust.

Nature Geosci. http://dx.doi.org/10.1038/ngeo1773 (2013); Science 339, 1305–1308 (2013)