At first glance, there doesn't appear to be much happening in the mud buried 30 meters below the Pacific Ocean sea floor. But this ancient muck, which hasn't had a fresh shot of food or sunlight since the days of the dinosaurs, still harbors life—if just barely. Scientists have discovered that deep-sea microbial communities, buried for 86 million years, are still consuming oxygen, albeit at extraordinarily low rates. These microorganisms eking out an existence in slow motion reveal just how little it takes to sustain life on our own planet, and potentially on others.
Microbes such as bacteria are the most numerous organisms on Earth, and about 90% of them live in sediments buried under the sea floor. To take a peak at this microscopic life in its natural habitat, a team of scientists including Hans Røy, a microbiologist at Aarhus University in Denmark, traveled to the tropical waters of the Pacific Ocean. There, they collected mud from the sea floor, which builds up for millions of years like a giant layer cake as newer sediments pile on top of older ones.
The scientists jammed a large metal pipe 30 meters into the sea bottom and used a piston to suck out a long column of reddish clay. After hauling the sediment onboard, they probed the core with a needlelike sensor to measure the oxygen concentration in each layer. The researchers knew how much oxygen should have diffused down into each section of sediment from the seawater, so any "missing" oxygen meant microbes had consumed it.
Moving deeper through the core is like moving back in time, studying older and older communities of microorganisms. "We can use the Pacific as a natural experiment that has been running for 86 million years," Røy says.
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