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10 biggest unsolved mysteries about Earth

How did all this water get here?

What about all the oxygen?
What about all the oxygen?
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Another thing that’s proved very advantageous for the creatures living on Earth is the planet’s oxygen.

And while we actually do know how it originated—about 2.4 billion years ago, microscopic creatures called cyanobacteria released oxygen as a waste product, filling the atmosphere with it—the happenings of the next few eons are a little less clear.

After that, the level of oxygen in Earth’s atmosphere went wildly up and down until it finally stabilised around 540 million years ago.

Since then, it’s remained at about the breathable level we experience today.

But what caused it to suddenly stabilise? This remains one of the biggest scientific mysteries about our home planet.



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