Unknown. Some scientists, who support a hypothesis known as “Snowball Earth,” contend that at one time, about 650 million years ago, the Earth was in fact completely or mostly covered with ice. This hypothesis was developed in the 1960s to explain why sediments believed to have been deposited by glaciers were found in tropical regions. The “Snowball Earth” theory is not without controversy. Even one of the scientists who initially proposed it stated that while he thought it could happen, in his view it did not, because there would have been no way to escape from the scenario (meaning the Earth would still be a ball of ice today). Others say a greenhouse effect could have melted the glaciers. As to whether every square inch of the Earth’s surface could be covered by ice, without any dry land at all, that is not known but it seems unlikely. Today, Antarctica is about as cold as a “Snowball Earth” would have been, and there are isolated patches of ice-free terrain especially in rugged areas like mountains and jagged coastlines.
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