Snowball Earth

A theory postulating the existence of several periods of time, in a remote past, in which the Earth was covered in ice in its entirety. The hypothesis - also known as Snowball Earth - was proposed in 1998 by researchers at Harvard University (USA) Paul Hoffman and Daniel Schrag, based on the discovery of traces of ice in certain geological strata, corresponding to the end of the Proterozoic eon (Upper Precambrian). Those remnants of primitive ice have been found throughout the planet, suggesting that both continental and oceanic areas across the entire Earth (including the equatorial band) became covered by a thick layer of ice, which could have brought the global average temperature down to –50°C. Several of these superglaciations have been dated over a period spanning between 800 and 550 million years before the present.