If you were to hop in a time machine and travel back about 717 million years, you’d be greeted with scenes reminiscent of the ice planet Hoth from Star Wars. But exactly how the Earth came to resemble a giant snowball has long been up for debate.


Now, a team from Harvard University thinks that the runaway glaciation event that froze the entire surface of the planet could have been triggered by a huge volcanic eruption that devastated an area stretching from present-day Alaska to Greenland and happened to coincide with several other specific atmospheric conditions.

“It is not unique to have large volcanic provinces erupting,” said researcher Robin Wordsworth. “These types of eruptions have happened over and over again throughout geological time but they’re not always associated with cooling events. So, the question is, what made this event different?”

Great snowballs of fire

The team’s computer models show that volcanoes may have emitted large amounts of sulphur dioxide into the atmosphere as the volcanic rocks pushed their way through the sulphur-rich sediment. As sulphur dioxide is highly reflective, this would’ve created an umbrella-like effect that shielded the Earth from the Sun’s rays. The fact that the eruptions took place near the equator would’ve further exaggerated the effect, as this is where most solar radiation reaches the Earth.

Ice created by this umbrella’s cooling effect would have then reflected more sunlight away from the surface, cooling the planet further. This in turn would’ve created more ice, reflecting more and more sunlight. Eventually a positive feedback loop would’ve taken over, making the runaway snowball essentially unstoppable.

“Cooling from aerosols doesn’t have to freeze the whole planet; it just has to drive the ice to a critical latitude. Then the ice does the rest,” said researcher Francis Macdonald.

The theory was published in the journal Geophysical Research Letters.

  • This news story first appeared in the May 2017 issue of BBC Science Focus magazine - for the latest news subscribe here.


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Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.