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Earth's Oxygen Enigma
by Kathy A. Svitil
February 11, 2003
Carrine Blank of Washington University in St. Louis
Scientists have long believed that blue-green algae arose 3.5 billion years ago, pumping out oxygen and causing the oceans to fill with rust. Over the next billion years the algae transformed Earth's atmosphere, allowing oxygen-breathing life to evolve. Carrine Blank of Washington University in St. Louis... compared genetic sequences from 53 different groups of bacteria -- including blue-green algae, also known as cyanobacteria -- to construct a detailed family tree. The results confounded her expectations. "Cyanobacteria arose fairly late, about 2.2 or 2.3 billion years ago. That explains why we see this very sudden increase in oxygen, around 2.2 to 2 billion years ago, which has always been a big mystery," she says. The finding implies that something else caused the ocean rusting.