If you were over two billion years old, then you would remember that time that oxygen almost killed everything. 

Of course nobody is even close to being that old and even if they were, the Earth was so different then that it would be impossible for most of todays life to survive there. 

The Earth's atmosphere was mostly CO2 and Methane, with very little oxygen, which was okay because life on Earth was mostly anerobic. Then something changed. 

Check out the video below to learn what that change was and how it completely changed the future of our home planet. 

Leave a comment below to let me know what you thought about the video!