SPACE.COM - Earth is the only home we know, but it was not always one we could live in. The oxygen we depend on with every breath was essentially absent when Earth formed about 4.5 billion years ago. It wasn't until about 2.4 billion years ago, when our planet was nearly half its present age...
EARTH.COM - More than 2 billion years ago, oxygen became a permanent part of Earth’s atmosphere. What happened next has puzzled scientists for decades. Somehow, oxygen levels stayed high enough for millions of years to eventually support complex life. New research finally explains how, and the answer traces back to a nutrient most people rarely...