About 700m years ago, the Earth froze over entirely – now we may know why

Researchers believe huge volcanic eruptions, and the absence of plants, turned our planet into one giant snowball

It's hard to believe, but about 700m years ago it's thought that our planet completely froze over with little to no liquid ocean or lakes exposed to the atmosphere, even in the tropics. But what tipped Earth's climate into Snowball Earth" state? A new study suggests a cold climate and massive volcanic eruptions set the scene.

The Franklin eruptions - about 720m years ago - spewed out vast amounts of fresh rock, stretching from what is now Alaska, through northern Canada to Greenland. Similarly large eruptions have happened at other times, but this one happened to coincide with an already cold climate. And combined with a lack of plants (they hadn't evolved yet) these eruptions exposed a huge carpet of fresh rock to intense weathering.