Hourly Forecast Detailed. 1  0am:The Santee, SC forecast for Apr 11 is 63 degrees and Clear. There is 74 percentage chance of rain and 4 mph winds from the South-Southeast. 2  3am:The Santee, SC forecast for Apr 11 is 55 degrees and Clear. There is 79 percentage chance of rain and 4 mph winds from the South.
Most Important Organism? Marine plants produce between 70 and 80 percent of the oxygen in the atmosphere.
Today oxygen makes up about 20 percent of Earth's atmosphere, but for the first two billion years after Earth formed, its atmosphere was anoxic (oxygen-free). About 2.3 billion years ago, oxygen increased from a trace gas to perhaps one percent of Earth's atmosphere.Another jump took place about 600 million years ago, paving the way for multi-cellular life forms to expand during the Cambrian Explosion.ndeed, the jumps in atmospheric oxygen at 2.3 billion years ago and 600 million years ago do seem to be associated with Snowball Earth episodes (Fig. 14). However, scientists are still unsure exactly what the connection might be between the extreme ice ages and changes in the oxygen content of the atmosphere.