Home, sweet home

Natural History, June, 2003 by Stephan Reebs

On Earth, where there's water, there's usually life. But few people would expect to find life in an isolated reservoir of 4,300-year-old seawater locked inside the basalt crust that forms the bottom of the world's oceans. The water is hot--a sweltering 149 degrees Fahrenheit--and almost entirely isolated by hundreds of feet of impermeable sediment (the exceptions to total isolation may be a few scattered, rocky seamounts that pierce the sediment blanket). But a team of scientists led by James P. Cowen of the University of Hawaii in Honolulu decided to check it out for life anyway.

First they had to obtain water from the crustal reservoir without contaminating it--quite a feat in itself. In the mid-1990s the international research partnership known as the Ocean Drilling Program bored a hole in the Juan de Fuca Ridge, in the northeastern Pacific. The drilling, in 8,530 feet of water, went down through 810 feet of sediment and then an additional 157 feet of seamount crust. Pressures at the bottom of the ocean are enormous, but they're even greater within the crust's high points, and so crustal water gets pushed all the way up to the seafloor at the top of the drill-hole. Cowen and his team took advantage of a clever collection device, recently installed, that captures the fluid before bringing it to the surface. Samples can thus be examined for any micro-denizens of the deep that might reside there.

What did the team find? In the water were swarms of bacteria and archaea (ancient microorganisms that often thrive in tough places), as many as a few million per ounce--perhaps not as crowded as pond scum, but similar to the density near the seafloor. Some of the microorganisms are genetically similar to the heat-loving bacteria that live in the sulfurous hot springs of Yellowstone National Park. And some of the critters get their energy from nitrates, rendering the water around them rich with ammonia. However uninviting to most of Earth's inhabitants, the reservoir is further proof that even in what most life-forms would regard as noxious quarters, an empty niche is hard to find. ("Fluids from aging ocean crust that support microbial life," Science 299:120-23, January 3, 2003)