Major ice ages

There have been at least four main ice ages in the Earth's past.

The earliest hypothesized ice age is believed to have occurred around 2.7 to 2.3 billion years ago through the early Proterozoic Age.

Main article: Snowball Earth.

The most primitive well-documented ice age, and probably the most harsh of the last 1 billion years, occurred from 800 to 600 million years ago and it has been suggested that it formed a Snowball Earth in which permanent sea ice extensive to or very near the equator. It has been not compulsory that the end of this ice age was responsible for the subsequent Cambrian Explosion, though this theory is current and contentious.

The timing of ice ages all through geologic history is in part prohibited by the position of the continental plates on the surface of the Earth. When landmasses are determined near the Polar Regions, there is an increased chance for snow and ice to build up. Small changes in solar energy can tip the balance between summers in which the winter snow mass completely melts and summers in which the winter snow persists until the following winter. Due to the positions of Greenland, Antarctica, and the northern portions of Europe, Asia, and North America in Polar Regions, the Earth today is considered prone to ice age glaciations.

Proof for ice ages comes in a variety of forms, including rock scouring and scratching, glacial moraines, drumlins, valley cutting, and the deposition of till or tillites and glacial erratic. Successive glaciations be inclined to distort and erase the geological proof, making it difficult to interpret. It took some time for the current theory to be worked out. Analyses of ice cores and ocean sediment cores unmistakably show the record of glacial and interglacial over the past few million years.