Thanks to chemical proxies in the geological record, we have been able to reconstruct the composition of the atmosphere with a fair degree of accuracy. However, the older the time period being reconstructed, the less accurate the reconstructions become. Ice cores from the past few hundred thousand years actually contain samples of the atmosphere present when they formed. There is an abundance of strata from the past few hundred million years which provide enough data to reliably reconstruct the atmosphere in older geological periods. Yet as we start to look at the atmosphere billions of years ago, available rock samples become scare. Many have also been metamorphosed, rendering their geochemical composition useless.
As a result, the earliest atmosphere has been a highly contentious subject, based primarily on the atmospheres of other planets and a fair degree of speculation. Yet now a study of the most ancient rocks on the planet has given scientists an indication of the atmosphere from an incredible 4.3 billion years ago, just 200 million years after the formation of the planet. The Nuvvuagittuq Greenstone belt is a mix of volcanic and sedimentary rocks in northern Canada dating from the Hadean eon. Analysis of samples taken from the greenstone belt was conducted by researchers from McGill's Earth and Planetary Sciences Department, Canada. They used mass spectrometry to measure the cyclical changes of concentrations of sulphur isotopes across time, finding that the atmosphere 4.3 billion years ago extremely oxygen-poor compared to today, with potentially more methane and carbon dioxide.
|The Nuvvuaqittuq Greenstone Belt in northern Canada contains |
the oldest rocks on the planet at 4.28 billion years old
The research team's next product is to determine whether the cycling was as a result of biological or geological processes. The results of this future study should prove invaluable as there is an on-going debate as to whether the early Earth could have supported life. The Nuvvuaqittuq greenstone belts indicate that temperatures may have been cool enough to sustain liquid water. Conversely, the Hadean Earth may have been too tectonically unstable to support cells. By understanding the interplay between biological, atmospheric and geochemical processes we will be able to ascertain when life first appeared on our planet.