Microbes have been around for a lot longer than humans, and they were even around before the Dinosaurs! They’ve been on the Earth for around 3,500 million years, and were the only life forms on Earth for most of that time!
The first microbes appeared when the Earth cooled and liquid water formed.
At this time, there was still hardly any oxygen in the Earth’s atmosphere – less than 1%, compared to the 21% today! But then, 2,800 million years ago, something very important happened.
A group of microbes called cyanobacteria appeared and it is believed that these microbes were responsible for raising the level of oxygen to what it is today.
This allowed the evolition of knew aerobic (oxygen using) species of microbes to colonize every habitat on the planet, and slowly laid the foundations that would eventually lead to human life.
It took a while though! Mammals and flowering plants are relative newcomers and only appeared around 100 million years ago.
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