Origin of the Ozone Layer and Evolution of Life

Early Earth atmospheres (>3 billion years ago) did not contain the 21% oxygen content that we have today. When life on Earth originated (~3.5 billion years ago) the first prokaryotic cells were anaerobic chemoautotrophs, most likely occupying deep ocean and subterranean habitats. With no oxygen in the atmosphere and no ozone layer, incident UVC and UVB levels would have been extreme, forcing life to remain in dim and unlighted habitats. It was the evolution of photosynthesis that added free oxygen to the atmosphere and resulted in the formation of the ozone layer. The subsequent removal of UVC and reduction of UVB from incident sunlight very likely contributed to life moving from the oceans into illuminated terrestrial environments.

10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

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