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How many weeks' holiday a year are there? viagra4675 The new date places oxygen on the Earth more than 600 million years before the Great Oxidation Event, when levels of atmospheric oxygen rose dramatically. In the last six years, a handful of geologic studies have dated transient wisps of oxygen to 2.6 billion to 2.7 billion years ago. Scientists think that photosynthetic microorganisms such as cyanobacteria produced the oxygen. So the timing of the first atmospheric oxygen has implications for how photosynthetic life evolved on the planet.

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