snowball earth
Evidence has shown that the earth has undergone a series of dramatic cold periods. ... There were thought to have been ice formations two kilometers thick covering 30% of the surface of the earth. This explains what inspired Joe Kirschvink to term the occurrence “snowball earth”. It has been said that the snowball earth began when the earth’s continents were all lined up along the equator. ... Fortunately, volcanoes kept erupting trapping solar heat and putting back enough of the gas to prevent a permanent snowball earth. ... It may be too simplistic to state (as in the snowball earth theory) that floating ice could seal off the atmosphere from the ocean. ... The extreme conditions described in the snowball earth model may seem too far-fetched for some. An alternate theory called slushball earth has also been proposed as more credible, less dramatic version of the original.