close
Advertisement

10 biggest unsolved mysteries about Earth

How did all this water get here?

What about all the oxygen?
What about all the oxygen?
Getty Images

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.



Advertisement
19 of the strangest unsolved mysteries of all time

19 of the strangest unsolved mysteries of all time

Get ready to have the hair on the back of your neck stand on end because these unsolved mysteries are among the most chilling we’ve ever heard.
10 secret messages hidden in world famous paintings

10 secret messages hidden in world famous paintings

Turns out Michelangelo, da Vinci, Van Gogh and company were even more brilliant than we’ve given them credit for.
Cancer June 22 – July 22

Horoscopes June 2019

Find out what the stars have in store for you this month, thanks to Reader’s Digest’s expert astrologist Janice Jones.
12 foods you didn’t know could kill your dog
Why we procrastinate and how to stop

Why we procrastinate and how to stop

These simple tools will stop you delaying what can be done today.

Advertisement