Scientists Figure Out Why Earth Froze Over 700 Million Years Ago

Throughout its approximately 4.54 billion-year history, Earth has undergone several ice ages ranging from relatively mild to extreme. Researchers believe our planet has endured five ice ages belonging to the latter category, with one particularly severe ice age occurring during the Cryogenian period 720 to 630 million years ago. During what’s referred to as the Sturtian glaciation, Earth essentially froze over: Temperatures plummeted, and masses of thick, crusty ice formed all over the planet’s surface. The freeze was so severe that scientists now use “Snowball Earth” to refer to the planet’s Sturtian condition. 

How and why Earth underwent such a drastic metamorphosis roughly 700 million years ago has long remained a scientific puzzle. But researchers in Australia believe they’ve finally determined how Snowball Earth came about. In a Geology paper published Wednesday, a team of sedimentologists and tectonic geologists write that modern tectonic models have unearthed the likely cause behind this brutal ice age and its 57 million-year duration.

The University of Sydney’s EarthByte computer models allowed the team to simulate the behavior that would have characterized Earth’s tectonic movements, geodynamics, and surface processes hundreds of millions of years ago. The model showed that after a “plate tectonic reorganization” broke up the ancient supercontinent Rodina, Earth saw an all-time low in volcanic degassing, responsible for most of the planet’s atmospheric accumulation of greenhouse gasses. After all, multicellular animals and land plants were absent from the Earth, so “geology ruled climate,” according to study co-author Professor Dietmar Müller. 

Chunks of ice floating in the sea


Credit: Ivan Bandura/Unsplash

At the same time, a continental volcanic province in Canada started eroding. Called the ca. 718 Ma Franklin province, this geological feature is believed to have formed roughly 718 million years ago after massive quantities of magma erupted from Northern Canada’s Franklin Mountains and solidified into igneous rock. The researchers note that the ca. 718 Ma Franklin province underwent a relatively sudden period of silicate weathering, which absorbs carbon dioxide from the atmosphere over long periods. 

“The result was that atmospheric CO2 fell to a level where glaciation kicks in—which we estimate to be below 200 parts per million, less than half today’s level,” Müller said in the University of Sydney’s statement. 

This marked decrease in atmospheric carbon dioxide allowed Earth to cool drastically, enabling the severe glaciation that marked the Cryogenian period. In essence, this was the opposite of what we see today with the buildup of atmospheric greenhouse gasses and an increasingly problematic global temperature increase. Why are these things related? It all comes down to Pangea Ultima, the ultra-hot supercontinent scientists believe might form in 250 million years. Using discoveries about the Stutrian glaciation, researchers can more accurately predict how Pangea Ultima might come about and how human-induced climate change could alter its development. 

“Whatever the future holds, it is important to note that geological climate change, of the type studied here, happens extremely slowly,” Dr. Adriana Dutkiewicz, the study’s lead author, said. “According to NASA, human-induced climate change is happening 10 times faster than we have seen before.”

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