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The snowball was smaller

Afonso Nogueira

Terconi Stone Quarry, in the town of Mirassol D’Oeste, State of Mato Grosso: rocks from Brazil were used to calculate ancient levels of CO2Afonso Nogueira

Between 710 and 635 million years ago, the Earth was allegedly undergoing a severe ice age and was totally covered in ice. It is widely believed that the end of this ice age was caused by intense volcanic activity, which spewed out so much carbon dioxide that the gas concentration point in the atmosphere is believed to have achieved levels 300 times higher than present-day levels. Thus, the planet got warmer and the ice melted. This hypothesis, called “Snowball Earth,” was put forth in the early 1990s. However, it has recently been challenged in a study conducted by Brazilian, French and American geophysicists (Nature, October 6). Based on carbon deposit samples obtained in the State of Mato Grosso, which cover the sediments of the so-called Marinoan glaciation, the researchers calculated the concentration of CO2 in that period and concluded that the concentration was probably close to present-day levels. In other words, it is likely that the ice age was not as severe as previously believed and that the end of the ice age was probably not caused by global warming resulting from excessively high carbon dioxide levels. Geophysicist Ricardo Trindade, from the University of São Paulo, and geologist Afonso Nogueira, from the Federal University of Pará, are the Brazilian members of this research team.