|An artist's impression of Titan shrouded in a haze of methane. |
This site may be very similar to the Earth of 2.6 billion years ago
When the Earth first formed, the atmosphere was composed of super heated steam, toxic gases and hydrogen. The atmosphere was in turmoil, constantly changing its nature.The modern form dominated by nitrogen and oxygen appeared around 2 billion years ago.
3.8 billion years ago, the atmosphere was devoid of oxygen. We know this because the chemicals required to form life can only be created in an environment which is devoid of oxygen. However from this point up until the 2 billion year mark, things get harder to unravel. Apart from a steady rise in oxygen to near enough modern day levels from around 2.9 billion years ago, we know very little about the gaseous compositions of the air at this time in Earth history.
Yet a team of geologists have found evidence in ancient rocks which offer some clues. The team sampled 2.65 to 2.5 billion year old carbonate rocks from a rock formation in South Africa known as the Ghaap Group. Carbonate rocks are almost exclusively marine. As the sea will contain dissolved compounds which were particularly abundant at the time, they will be included in the layers of rocks.
They were able to analyse the chemical signatures within the samples to reconstruct how the Earth's atmosphere changed at this point in the Earth's history. The study revealed high levels of carbon and sulphur isotopes, which indicate that the air was periodically rich in methane. This coincided with low oxygen levels and visa versa. All in all, this primordial version of the atmosphere would have been very similar to the methane rich atmosphere which covers Titan, one of Jupiter's moons.
The end result also showed that the thick, hydrocarbon haze did not permanently retreat until 100 million years later. Professor Malcolm Walter from the Australian Centre for astrobiology at the University of New South Wales has stated that the study confirms a very large change in the chemistry of the Earth's surface about 2.65 billion years ago.