As far back as 4.4 billion years, we think Earth was an ocean world. This was partly supported by research last year, looking at some of the oldest rocks on the planet. A new study has now suggested when the first land might have emerged.
In this new study published in Nature, scientists led by Ilya Bindeman from the University of Oregon went a step further. They said that Earth’s first supercontinent, Kenorland, likely emerged from the ocean about 2.4 billion years ago. And it changed our planet dramatically.
"What we speculate is that once large continents emerged, light would be reflected back into space and initiate runaway glaciation," Bindeman said in a statement. "Earth would have seen its first snowfall."
They came to this conclusion after studying chemical signatures in Earth’s most common sedimentary rock, shale. Looking at the changes in oxygen in the shale, they pinpointed the time when Earth’s crust was exposed to weathering as it emerged from the ocean.
And about 2.4 billion years ago, it’s thought that the total amount of landmass on Earth would have been about two-thirds of what we see today, with the emergence of new land happening rapidly.
This timing also coincides with the arrival of Kenorland, when our planet got its first high-mountain ranges and plateaus. The crust needed to be thick to stick out of the water, but when Earth was hot earlier in its life, it was unable to support such large landmasses.
“Our data indicate that this changed exponentially 2.4 billion years ago,” said Bindeman. “The cooler mantle was able to support large swaths of land above sea level.”
The temperature would have been much hotter when this land emerged, by tens of degrees. But the land would have sucked carbon dioxide out of the atmosphere, cooling the planet. And the land would also have made Earth more reflective, bouncing more of the Sun’s rays back into space and further cooling the planet, eventually leading to the first snow.
The emergence of land 2.4 billion years ago is also around the time when life moved from water-based things like bacteria to land-based like fungi and plants. The arrival of land may also have kickstarted the Great Oxygenation Event 2.4 to 2.2 billion years ago, as our atmosphere changed dramatically.