Ancient Earth was probably a Big, Blue Ocean, New Evidence Says

Imagine, having to swim your way everywhere, probably, having a blubber, and communicate like a whale. Imagine how life would have been in a water world.

According to a new analysis of the features of Earth’s mantle over its long history, our whole world was once engulfed by a vast ocean, with very few or no land masses at all. It was an extremely soggy space rock.

So where the heck did all the water go? According to a team of researchers led by planetary scientist Junjie Dong of Harvard University, minerals deep inside the mantle slowly drunk up ancient Earth’s oceans to leave what we have today.

“We calculated the water storage capacity in Earth’s solid mantle as a function of mantle temperature,” the researchers wrote in their paper.

“We find that water storage capacity in a hot, early mantle may have been smaller than the amount of water Earth’s mantle currently holds, so the additional water in the mantle today would have resided on the surface of the early Earth and formed bigger oceans.

“Our results suggest that the long‐held assumption that the surface oceans’ volume remained nearly constant through geologic time may need to be reassessed.”

The scientists focused on different types of oxygen that seawater had carried into the crust. In particular, they analysed the relative amounts of two isotopes, oxygen-16 and the ever-so-slightly-heavier oxygen-18, in more than 100 samples of the stone.

They found that seawater contained more oxygen-18 when the crust was formed 3.2bn years ago. The most likely explanation, they believe, is that Earth had no continents at the time, because when these form, the clays they contain absorb the ocean’s heavy oxygen isotopes.

“Without continents above the ocean, the oxygen value would be distinct from today, which is exactly what we found,” Johnson said. “And it’s different in a way that’s most easily explained without land to get rained on and without soil formation.”