700 million years ago
The oxygen holocaust was a worldwide pollution crisis that occurred about two billion years ago. Before this time there was almost no oxygen in the Earth's atmosphere. The Earth's original biosphere was has different from ours as that of an alien planet. But purple and green photosyntetic microbes, frantic for hydrogen, discovered the ultimate resource, water, and its use led to the ultimate toxic waste, oxygen. All organisms are open thermodynamic systems which necessarily produce waste: our precious oxygen was originally a gaseous poison dumped into the atmosphere. The appearance of oxygen-using photosynthesis and the resulitng oxygen-rich environment tested the ingenuit of microbes, especially those producing oxygen and those nonmobile microorganisms unable to escape the newly abundant and reactive gas by means of motion. The microbes that stayed around responded by inventing various intracellular devices and scavengers to detoxify--and eventually exploit--the dangerous pollutant. Oxygen in the atmosphere was originally thought by scientists to be the reason for the proliferation of visible forms called the Cambrian explosion(because fossils of these animals were first found in Cambria, England). But an intriguin sign that oxygen prodeuction existed long before most think it did is displayed by banded iron formations--more commonly known as iron ore. These rocks show layers of relatively oxidized and non-oxidized iron, hematite and magnetite. They are probably testimony to oxygen-producing life--cyanobacteria--growing on top of each other with other bacteria long before the evolution of visible life forms. Learn More <
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