It’s difficult to imagine now, but at certain points in Earth’s history, ice covered the entire planet. This frozen Earth, nicknamed snowball Earth, was a setting “so severe, that the Earth’s entire surface, from pole to pole, including the oceans, completely froze over,” said Melissa Hage, an environmental scientist and assistant professor at Oxford College of Emory University in Georgia.
In 1840, Louis Agassiz, a Swiss natural scientist, was among the first to acknowledge and provide evidence that Earth had gone through ice ages, according to the University of California Museum of Paleontology. Joseph Kirschvink, an American geologist, later coined the term “snowball Earth,” in a 1992 textbook. Kirschvink’s work was based on evidence provided by Agassiz and others.
Scientists believe that three to four severe ice ages, which froze nearly or all of the surface, occurred between 750 million and 580 million years ago, probably because Earth’s land masses were all located at or near the equator, which resulted in increased weathering. Weathering is when wind and precipitation break down rocks and minerals on the planet’s surface. The process leads to decreased carbon dioxide levels in the atmosphere, which allows more heat to dissipate from the surface and into space, cooling the planet.