Last week a team of geologists from Princeton University published a paper in Science showing a massive change in the Earth’s carbon cycle some 720 million years ago. At the time, the Earth may have been in a “snowball” phase: a massive, global ice age in which glaciers and ice sheets covered the planet right down to the Equator.
From analyzing carbon isotopes in limestone rocks in Australia, the Princeton team think that there was a massive buildup of organic carbon in the oceans under the ice. That might have come from the ice sheets scraping material on land and dumping mineral nutrients into the ocean, they speculate.
The time in question is called the Neoproterozoic Era, from 1 billion to 540 million years ago. At the end of the Neoproterozoic, oxygen levels in the atmosphere rose rapidly, and complex animals appear in the fossil record for the first time. The Neoproterozoic “carbon excursion” might have had a long-term effect, leading to subsequent ice ages, the Princeton team say.
I asked UC Davis paleogeologist Isabel Montanez what she thought of the study. The carbon excursion associated with the appearance of multicellular life at the end of the Neoproterozoic has been described before, she said. What is new, she said, is that the new work identifies earlier carbon swings associated with each of the major glaciations during the Neoproterozoic. However, it’s not that surprising that these would occur, she said, given that the carbon cycle was less “buffered” than it is now and that the pool of carbon dissolved in the ocean was probably lower than it is now.
Any claims about the Neoproterozoic “Snowball Earth” period are quite speculative, Montanez notes.