Wednesday, 3 June 2020

Snowball Earth and the GOE

What Caused the First Snowball Earth?

THIS ARTICLE discusses the effects of the Great Oxidation Event (GOE). Did it occur before or after the first snowball earth? We know both occurred about 2.4 billion years ago.

The method used in this study is the ratios of sulphur isotopes. Post GOE these are stable and predictable but before this photochemical reactions in the oxygen-free atmosphere are preserved as unpredictable sulphur isotope ratios. So pre GOE unpredictable; post GOE predictable. Therefore measure sulphur ratios and find the date of the GOE.

Using cores of sedimentary rocks, of the appropriate age, from the Kola Peninsula, the researchers in St Andrews, pin the GOE to a 70 million year interval between 2.50 and 2.43 billion years ago. In this context, a very short period!

This is before the snowball Earth deposits. It is postulated that rising oxygen levels lowered methane levels, weakening the greenhouse effect, and leading to a major period of glaciation.

If we looked at the Earth before the GOE would we have thought it a good prospect for habitation? And removing greenhouse gases from the atmosphere is not without risk!

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