AsianScientist (Apr. 10, 2015) – According to a study published in Earth and Planetary Science Letters, the dramatic increase in atmospheric oxygen about 2.2 billion years ago was triggered by a melting ‘snowball Earth’.
As even schoolchildren know, the oxygen that makes up 21 percent of the atmosphere is essential for most lifeforms. However, the atmosphere two and half billion years ago only contained 0.001 percent the present atmospheric levels of free oxygen, rapidly rising 2.2 billion years ago in an event known as the Great Oxygen Transition.
Geological evidence from South Africa suggests that there was a global glaciation event that occurred just before the Great Oxygen Transition. Termed the ‘snowball Earth hypothesis’, it proposes that glacial deposits found in tropical regions can be explained by an almost complete freezing of the entire globe. However, the causal relationship between the snowball Earth effect and the mechanism for the rise of oxygen are unclear.
Using simulations based on theoretical modeling of climate, atmospheric chemistry and biogeochemical cycles, researchers from the University of Tokyo have shown that the rise of oxygen is an inevitable consequence of the snowball Earth event.
Their model also showed that the level of oxygen overshot up to the present level for 100 million years and then stabilized at 1/100 of the present atmospheric oxygen level. The oxygen level rapidly rose again to the present level at around 600 million years ago, an event which is also highly likely to have been triggered by another snowball Earth event in Earth’s history.
These findings provide important insights into the history of our planet; namely that the oxygen we breathe today was derived from snowball Earth events. To reveal a relationship between the rise of atmospheric oxygen concentration 2.2 billion years ago and the evolution of life is a critical issue for future research.
Source: The University of Tokyo; Photo: Kevin Gill/Flickr/CC.
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