Millions of Years Ago Earth’s Atmosphere had almost No Oxygen
We all know how important carbon and oxygen are in the development of life on Earth. But millions of years ago, there wouldn't have been enough oxygen for animals to exist. What changed?
Between 750 and 580 million years ago, the Earth was almost entirely encased in thick glaciers and ice sheets. When the ice finally started to recede, the oceans were now oxygen-depleted. This made them poor candidates to support life, or at least anything more complex than simple anaerobic bacteria. If complex life was ever going to emerge, then the oceans would need a massive spike in its oxygen levels.
That's where phosphorus enters the picture. Conventional wisdom had long held that phosphorus has been scarce on this planet throughout its history, but new work on ancient minerals has revealed at least one period when the element was plentiful - 750 and 635 million years ago, which is when complex life began to develop.
Researchers say that isn't a coincidence. Phosphorus was probably washed into the oceans by glacial debris, and the element would have jump-started the growth of cyanobacteria, also known as blue-green algae. That algae creates oxygen as a byproduct of its own metabolic process, which would have slowly raised oxygen levels in the oceans. Given enough time, there was finally enough oxygen for animals and other complex forms of life to develop - all thanks to phosphorus.