OBJECTIVE LIFE SCIENCE
MOLECULAR BIOLOGY
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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4.2 BYA, dissolved calcium carbonate
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2.4 BYA, dissolved calcium carbonate
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4.2 BYA, precipitated iron as iron oxide
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2.4 BYA, precipitated iron as iron oxide
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Detailed explanation-1: -For the most part, scientists agree that oxygen, though lacking in the atmosphere, was likely brewing in the oceans as a byproduct of cyanobacterial photosynthesis as early as 3 billion years ago.
Detailed explanation-2: -Description: The Great Oxygenation Event occurred when cyanobacteria living in the oceans started producing oxygen through photosynthesis. As oxygen built up in the atmosphere anaerobic bacteria were killed leading to the Earth’s first mass extinction.
Detailed explanation-3: -These studies indicate that the chemistry of the earth’s atmosphere changed dramatically as oxygen levels rose and replaced methane (methane is still present today, but in very minute amounts). Further, it is hypothesized that accumulation of oxygen in the atmosphere led to one of the earliest ice ages on earth.