Glaciers pulverised Earth's ancient rocks: Expert

Imagine floating in space, gazing at a frozen white orb. The ball hangs in the void, lonely and gleaming in the light from its star.

- CHRIS KIRKLAND

From the pole to the equator, the sphere is covered in a thick crust of ice. In orbit around the white planet is a single cratered moon.

You are gazing at Earth in the Cryogenian period, 700 million years ago. This is about three times as long ago as the earliest dinosaurs roamed—but still not long in the scheme of Earth's mind-bending 4.5 billion years of history.

During the Cryogenian, our planet was plunged into a series of deep freezes when enormous glaciers flowed across the globe.

In new research published in Geology, we show that these crushing rivers of ice, sometimes kilometers deep, pulverised the planet's rocky surface like enormous bulldozers. When the ice eventually thawed, the ground-up minerals washed into the oceans where they may have provided the nutrients needed for the evolution of complex life.

Into the fridge According to the Snowball Earth hypothesis, Earth underwent at least two extreme global glaciations during the Cryogenian. Traces of these events can be seen across the globe in sedimentary rocks formed under glacial conditions, strongly suggesting that ice spread from the poles to reach the equatorial region.

Nobody is sure exactly what triggered these deep freeze events, though scientists have proposed a range of possibilities. One key may have been a significant decline in atmospheric greenhouse gases, particularly carbon dioxide (CO2).