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^{[citation needed]} The Antarctic ice cap was formed after Antarctica split from South America, allowing the formation of the Antarctic Circumpolar Current. The Arctic ice cap was partially caused by the Azolla event, where a large number of ferns in the ocean died, sank, and never decayed, which trapped carbon dioxide beneath the ocean.^{[citation needed]}

There is a hypothesis that around 650 million years ago, the entire planet was frozen, called Snowball Earth. Essentially the entire planet had an ice cap climate. However, this theory is disputed, and even proponents suggest there was an area of periodic melting near the equator.^[citation