VOA慢速英语:Small Organisms in Deep Sea Rocks Eat Methane

The gas methane has been linked to rising temperatures on Earth. But methane does not stay in the atmosphere as long as another “greenhouse gas” -- carbon dioxide. Scientists say both gases trap heat from the sun. They prevent heat from escaping into outer space.

Methane can come from wetlands, as a byproduct of raising farm animals, and from human activities, such as leakage from natural gas systems. Methane is also plentiful in the ocean. It can be found in ice, but also rises from deep within the earth through small cracks, or holes, in the ocean floor.

Little of that methane reaches the atmosphere, thanks to methane-eating organisms that live in sea bed sediments – materials that sink to the sea floor. Now, an American scientist says other deep sea microorganisms are also attacking the gas. These organisms live in an unlikely place – inside rock on the ocean floor!

Victoria Orphan is with the California Institute of Technology. She studies microorganisms that live in sediment near methane vents in the ocean. These vents release methane trapped inside the earth. Ms. Orphan says the organisms have changed to survive in this extreme environment.

“These organisms would be able to extract energy from methane using sulfate found in sea water rather than oxygen. And as an end product, they would produce hydrogen sulfide, sort of that rotten egg smell. And also as another by-product, these organisms would produce carbonate, sort of like the pavement you see on the sidewalk.”

Over time, that calcium carbonate forms tall, rocky seamounts around the methane vents. Victoria Orphan suspected that these rocky areas served as a shelter for sea life. So she found a submersible -- a small vehicle like a submarine -- and went down 800 meters to the sea floor to prove it.              

Ms. Orphan made four such trips between 2006 and 2011. As part of her studies, she collected sediments and seamount particles from the near-freezing water. She says the rocks she collected confirmed her theory.

“These are not just simply end products of methane oxidation, but they actually maintain a viable community of microorganisms living inside the pore spaces of the rock that turns out are still capable of consuming methane.”

However, her research showed the seamount microbes attacked the gas at a slower rate than the methane-eating organisms in the sediment. That is because not as much methane reaches the small holes in the rock.

“But considering that the volume of rock that’s available to colonize down in these deep-sea environments, it still can be a significant potential source of methane consumption. So instead of just considering this a process that is going on in sediments, we now have this whole other expansive habitat to look at as a sink for methane over time.”

The journal Nature Communications published her findings. She says the large number of small organisms – both in the sediment and in rock – explains how the microbes can limit the amount of methane in the world’s oceans. As a result, the gas has trouble reaching the atmosphere. And she notes that the worms, crabs and other creatures living around the rocks eating the microbes may show evidence of an ecosystem formerly unknown to scientists.

I’m Anne Ball.

*This report was based on a story from VOA Roseanne Skirble. George Grow wrote it for Learning English. The editor was Ashley Thompson.