An article from last weeks Nature shows that the oxygenation (oxygen becoming part of the air we breathe) in the earth’s atmosphere started at least 300-400 million years earlier than previously thought. For the full article click here, subscription only.
To determine if oxygen was in the atmosphere and available at that time. The scientists showed that by analysing the amount of oxygen sensitive metals it is possible to determine the amount of oxygen that would have been present. This can be done by looking at isotopes of chromium metal (and other oxygen sensitive metals) and noticing what oxidation state they are in. Isotopes are the same element with a different structure in their nucleus. Oxidation state is how many electrons a metal atom has lost, so the metal can be in different forms like 1 or 2 or 3 etc. Very oversimplified but I think it conveys the message.
So why is this important? Because, for these oxidation states to exist in certain metals there is the requirement that micro-organisms exist!Now the authors do say they could be out by 5 to 10 million years, but even then using the maximum and minimum of both totals it is still only 3% difference in age. Additionally, extensive tests were carried out to show that the observed oxygen content was not from weathering of the rocks and inclusion from water filtration through the rocks.
So there you have it. Life may have existed 300-400 million years before the previously thought 2.6-2.7 billion years ago. I guess the young Earth creationists will say their age and that accepted by science is only out by a factor of 260 000, so clearly their age fits the science.