Wave of massive volcanoes created Earth’s first supercontinent

The first supercontinent came into the world with a bang

Dana Stephenson/Getty

By Alice Klein

The world’s continents arrived in a blaze of fury. A pressure blow-out seems to have caused vast amounts of molten rock to spew out of the Earth and harden into solid land.
Until about 2.2 billion years ago, Earth was mostly underwater. A few small landmasses existed, but nothing like the vast continents we have today.
To understand how the continents formed, Christopher Spencer at Curtin University in Australia and his colleagues did the most comprehensive audit yet of the global geological record.
They found something strange: almost no volcanic rocks formed between 2.3 and 2.2 billion years ago. “Plenty formed before and after, but hardly any formed during this time,” says Spencer. “It was like there was this dramatic shutdown.”
At 2.2 billion years ago, the researchers found a sudden surge in the amount of land produced. They could tell because, when magma wells up from underground and crystallises, the resulting rock has giveaway chemical properties.
The researchers believe powerful whirlpool currents in the mantle, deep inside the Earth, may have been responsible for the lull and flare-up in geological activity.

Bursting at the seams

Between 2.3 and 2.2 billion years ago, they think these currents pulled together any small chunks of land that existed. “Once they became stuck in the middle, all volcanic activity on these land fragments pretty much stopped,” says Spencer.
Over time, heat built up under these static landmasses. Eventually, the enormous pressure sparked intense volcanic activity that spewed magma in all directions for millions of years.
“It would have been similar to how new land is forming today around Tonga, as lava erupts from volcanoes into the sea,” says Spencer. All the expanding landmasses gradually fused together to form the world’s first supercontinent, known as Nuna.
The Nuna supercontinent eventually broke into separate continents about 1.5 billion years go. Ever since, the continents have been continuously coming back together and breaking apart. This is called the “supercontinent cycle”.
The second supercontinent was Rodinia, which formed about 1 billion years ago. The third was Pangaea, which emerged about 300 million years ago. The next will be Amasia, when Asia and North America start to fuse in about 50 million years’ time.
It is still unclear why the supercontinents keep breaking up and re-forming, but currents in the mantle probably play a role, says Spencer. Previous research has pointed to a push-and-pull relationship between these currents and the continents, which could explain the supercontinent cycle.

Journal reference: Nature Geoscience, DOI: 10.1038/s41561-017-0051-y

https://www.newscientist.com/article/2159657-wave-of-massive-volcanoes-created-earths-first-supercontinent/