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Allies and Enemies: How the World Depend... > 7. Climate, bacteria, and a barrel o...

7. Climate, bacteria, and a barrel of oil

A band of rock called the Isua formation runs along the edge of an inland ice cap from western Labrador to southwestern Greenland. The formation holds the oldest known rock found so far on Earth, dated at 3.8 billion years. Traces of fossilized life lace the Isua formation and analyses of its carbon content point to photosynthetic ancestors of cyanobacteria.

During the period in which the Isua formation developed, the Earth’s atmosphere held no oxygen. Primitive photosynthetic microbes used the sun, carbon dioxide, and the Earth’s elements (nitrogen, sulfur, phosphorus, salts, and metals) to sustain life. Their rudimentary photosynthetic reactions released little oxygen. Chemically unstable compounds in the atmosphere quickly captured what little oxygen the microbes liberated, and the oceans absorbed the rest. By 2.2 billion years ago, however, the oceans had accumulated enough dissolved oxygen to allow the gas to begin building up in the atmosphere. The oxygen levels in the atmosphere began to stabilize about 2 billion years ago.


  

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