What was the snowball event

A. This term has been given to a series of geological event around 750 million years ago when the Earth was covered in ice. The Earth became a giant snowball, reflecting back any of the Sun’s heat, accelerating the process of freezing.

Q. What triggered the snowball event

A. The big freeze is thought to have been caused by a combination of a dimmer sun and lower levels of carbon dioxide, the so-called green house gas. Carbon dioxide levels were possibly depleted by evolving primitive plants and fungi. As the temperature dropped the polar icecaps spread over the globe.

Q. How do scientists know this event occurred

A. From reading carbon deposits in rocks. The drop in levels suggests that there was a virtual standstill in any biological activity during the snowball event.

Q. How cold was it during the snowball event

A. There may have been four periods of global glaciations between 750 and 570 million years ago and temperatures were probably the lowest that our planet has experienced so far.

Q. Did anything survive the snowball event

A. At the time of the first snowball event life on Earth was relatively primitive, just single-celled creatures and possibly plants, whose soft bodies haven’t survived in the fossil record. After the glaciations only a relatively small number of microbes would have survived.

However these events, especially the last one 570 million years ago possibly kick started evolution. Scientists believe that the fact that these snowball events preceded the first appearance of life on Earth isn’t a coincidence.

Q. What caused the end of the snowball event

A. The Earth remained ice bound until gradually volcanic activity had built up enough carbon dioxide in the atmosphere to warm things up.

The result was a greenhouse effect that raised global temperatures again.

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by Lisa Cardy