Soon afterward, the earliest life forms began changing the same chemistry that formed them. About 2.3 billion years ago, photosynthetic organisms started consuming carbon dioxide and sunlight and exhaling oxygen. For the first time, our planet had free oxygen floating around in the atmosphere. "Before that, if you left a piece of iron or steel on Earth's surface, it wouldn't rust," Hazen said. "But all of a sudden, life produced oxygen, and you start getting get rust -- and oxides of copper, manganese, and cobalt. There are literally thousands of minerals analogous to rust. You wouldn't have these without oxygen." If all life were suddenly wiped out, the 20-percent-oxygen atmosphere we currently enjoy would vanish in a matter of years. Along with the O2, all those minerals would go extinct. Minerals containing radioactive elements with short half-lives, such as plutonium, melted into extinction long ago (all plutonium on Earth today is man-made). And Heaney suspects there's a new field of mineral archaeology just waiting to be born. "No one has ever mapped out mineral extinction in Earth's history," Heaney said. "In a way, [Hazen's] work forces us to think in those terms and look for the mineral equivalent of a fossil record." Related Links: |
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