For the Earth to become as cold as it was during the “Snowball Earth” era, and stay there, required a combination of a reorganization of the Earth’s continents and the weathering of a vast volcanic province, scientists have argued. Another team, coincidentally publishing simultaneously, blames an asteroid instead. However, at this stage, they have less evidence to point to.
The periods known as
While some scientists
As the primary driver of changes in Earth’s temperature, there is no doubt carbon dioxide levels were very low during the Snowball Earth periods, but that leaves the question of why.
“We now think we have cracked the mystery,” said
“At this time, there were no multicellular animals or land plants on Earth,” Dutkiewicz noted. “The greenhouse gas concentration of the atmosphere was almost entirely dictated by CO2 outgassing from volcanoes and by silicate rock weathering processes, which consume CO2.”
Evidence for the weathering part is easy to find. The
That would not be enough on its own, however. Once the Earth became covered in ice it reflected more sunlight back to space, temporarily maintaining low temperatures. On the other hand, all that ice would also have slowed the rate of weathering. In normal circumstances, this would have caused carbon dioxide levels to rebound, warming the planet again. The fact this didn’t happen, Dutkiewicz and co-authors argue, indicates for tens of millions of years the release of CO2 must have been as slow as its removal.
They blame this on continental movements at the time. The longest Snowball Earth, known as the Sturtian after
Looking one step further back in the chain, Dutkiewicz told IFLScience, that responsibility lies with mantle convection processes, but “the problem [of what causes them] is not well understood. This is an area of intense study and has been for a long time.”
Almost the entire Earth froze over at least once more, in the Marinoan glaciation. Although Dutkiewicz believes there is some commonality to the two glaciations’ causes, she told IFLScience: “Marinoan was much shorter and happened a lot later. The Sturtian is the one that requires explanation.”
At the same time as Dutkiewicz and colleagues were publishing their work, another paper reported that an asteroid strike of similar size to the “dinosaur-killer” could have tipped the world into a similar frozen state. The authors of that paper conclude that such an event during a warm period, such as the Cretaceous, would have much more temporary effects. When carbon dioxide levels were already low, however, it could trigger something much bigger.
Dutkiewicz acknowledged to IFLScience that there could have been factors beyond the ones her team identified, but added the other paper “is purely a climate modelling study hypothesizing whether an asteroid impact of comparable size to the Chicxulub impact could have triggered a global glaciation. There is no evidence that such an asteroid impact actually triggered ‘Snowball Earth.’ It’s a highly speculative scenario. In any case, even if such an impact had occurred, it is unlikely to sustain a glaciation for very long (geologically speaking).”
Dutkiewicz’s work is open access in