Geologists found more evidence that Earth was nearly completely covered with ice 716.5 million years ago, and remained in this state for at least five million years. It's still unknown what caused or ended this glaciation, but scientists believe volcanoes may have had something to do with it, as there's evidence of major volcanic activity at the time.
By analysing ancient tropical rocks that are now found in northwestern Canada, the team concluded this chilly state lasted for at least five million years.
"This is the first time that the Sturtian glaciation has been shown to have occurred at tropical latitudes, providing direct evidence that this particular glaciation was a 'snowball Earth' event," says lead author Francis Macdonald of Harvard University.
According to Enriqueta Barrera, program director in NSF's Division of Earth Sciences, the Sturtian glaciation, along with the Marinoan glaciation right after it, are the greatest ice ages known to have taken place on Earth. "Ice may have covered the entire planet then," says Barrera, "turning it into a 'snowball Earth.'"