In 2012, scientists were puzzled by evidence of ice sheets advancing in the Ordovician period between 488 and 444 million years ago. At that time, the continents were all clustered over what is now the South Pole and stretched as far as the Equator. Some scientists now believe that plants were the culprits: As the plants spread across and took root over dry land, they extracted minerals from the rocks they lived on. The scientists further offered several scenarios involving what happens to these minerals—all of which could eventually cause carbon levels to lower, along with the temperatures (in other words, almost the opposite of what we call “global warming”). The researchers suggest that the spread of terrestrial plants could have brought about a series of ice ages.