Evrim Yazgin
Cosmos science journalist
More than 700 million years ago, the entire globe was covered in ice in a period called “Snowball Earth”. At least, that’s what scientists think. Now geologists believe they’ve found the best evidence that the “Snowball Earth” was really a global event.
For reasons which remain unclear, a runaway chain of events caused a massive shift in Earth’s climate about 720 million years ago. Global temperatures plunged and ice sheets kilometres thick are believed to have covered the planet from the poles to the equator.
Called the Sturtian glaciation, Snowball Earth lasted about 60 million years. This was quickly followed by another global ice age called the Marinoan glaciation. Together, these big freezes made up the geological period called the Cryogenian (720–635 million years ago).
Evidence of the extent of ice cover during the Sturtian can be seen in rocks as far apart as Namibia, North America and Australia.
A new study published in the Proceedings of the National Academy of Sciences presents new evidence that these massive glaciers covered the entire globe.
“This study presents the first physical evidence that Snowball Earth reached the heart of continents at the equator,” says lead author Liam Courtney-Davies, a postdoctoral researcher at the University of Colorado Boulder (UCB).
The researchers examined a series of rocks nicknamed Tavakaiv, or “Tava” – sandstones found on the Front Range of Colorado’s Rocky Mountains which hold clues to Snowball Earth.
A technique called laser ablation mass spectrometry was used to date the rocks. The Tava had been forced underground between about 690 to 660 million years ago – likely from the weight of huge glaciers pressing down above them.
“These are classic geological features called injectites that often form below some ice sheets, including in modern-day Antarctica,” Courtney-Davies says.
These date to the Sturtian glaciation, showing they were pushed down during Snowball Earth.
“We’re excited that we had the opportunity to unravel the story of the only Snowball Earth deposits that have so far been identified in Colorado,” says Rebecca Flowers, also from UCB.
Before the Cryogenian period, life on Earth was dominated by single-celled organisms.
After Snowball Earth thawed are the earliest examples of large organisms during the Ediacaran period (635–541 million years ago).
Scientists still don’t understand the processes which led to this explosion in life, after which our planet was changed forever.
“You have the climate evolving, and you have life evolving with it,” Courtney-Davies says. “All of these things happened during Snowball Earth upheaval. We have to better characterise this entire time period to understand how we and the planet evolved together.”
