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Has the biospehere done a flip-flop?

Has the biosphere done a flip-flop?

Today, plants depend on carbon dioxide and water to survive. In turn, they produce organic matter, which settles on the ground or in a body of water, and oxygen, which floats into the atmosphere. Animals consume some of the plants and give off their own by-products--and the closed cycle of photosynthesis and respiration continues.

However, during the Archean age more than 2.5 billion years ago, the biosphere lacked oxygen and was replaced in the cycle by dissolved iron, proposes James C.G. Walker, a University of Michigan atmospheric scientist, in the Oct. 22 NATURE. The presence of dissolved iron caused the Archean biosphere to be a total flip-flop of today's, he says. If accepted, this picture could change how geologists classify Archean fossils and how scientists view human evolution.

According to Walker, the oxygen-replacing dissolved iron, which is denser than organic matter, settled in sediments or stagnant pools, while volatile carbon and gaseous hydrocarbons scattered in the atmosphere and oceans. "My suggestion will profoundly change, if not turn upside down, how we look at the Archean environment,' Walker told SCIENCE NEWS.

The prevailing thought has been that yesterday's "animals,' or single-celled organisms, either fermented organic matter or consumed dissolved sulfate. The organisms then released organic matter or sulfide that settled on the ground or in the sea. According to this view, these substances would be plentiful in areas where life was flourishing.

Geologists have maintained that fossils found in Archean sediments rich in either carbon or sulfide are the remains of organisms that lived in productive areas. But according to Walker, a fossilized organism found in iron-rich and carbon-poor or sulfide-poor rock lived in a very productive area. Walker defends his theory by maintaining that iron was more plentiful than sulfur during the Archean.

"The Archean world has few fossils,' Walker says. "Maybe that's why no one has really thought about it. [But] it's important to figure out who was eating whom and what properties in the environment they were exploiting.'

Donald Lowe, an authority on early sedimentary rocks at Louisiana State University at Baton Rouge, says, "Right or wrong, [Walker's theory] will . . . make people think about the system in ways they haven't before.'
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Author:Eisenberg, Steve
Publication:Science News
Date:Oct 31, 1987
Words:371
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