the Meteorites that fell billions of years ago, helped to understand what was in the air before life is saturated with oxygen. The results were unexpected.
Achievement is described in a scientific paper published in the journal PNAS.
Geologists usually determine the composition of the ancient atmosphere to minerals, which at that moment were on the surface. It was set, for example, that oxygen began to accumulate about 2.5 billion years ago. But from what substances was an early gas shell of the Earth and what were their proportions?
Data on this is scant and controversial. But now scientists have found a new source of information about those distant times.
“This is a promising new tool for determining the composition of the upper atmosphere billions of years ago,” says first author Rebecca Payne (Rebecca Payne) from the University of Pennsylvania.
we are Talking about the iron meteorites no bigger than sand grains that fell 2.7 billion years ago. In the fall they heat due to the friction of the air and, as shown by chemical analysis, was subjected to oxidation.
Micrograph of the iron micrometeoroid that fell 2.7 billion years ago.Illustration Andrew Tomkins.
What gas can be an oxidizing agent in an oxygen-free era? The authors of the new study believe that carbon dioxide. According to their calculations, the atmosphere at the time consisted of CO2 by 25-50%.
But here arises another difficulty. Such a huge concentration of carbon dioxide should provide a powerful greenhouse effect and therefore warm the climate. However, the geological strata of that time bear the traces of glaciation.
the Contradiction? Do not have. Scientists have found an unexpected solution to this puzzle.
According to them, the proportion of carbon dioxide in the air was great, but the air was then much smaller than now. Therefore, in absolute terms, the amount of CO2 in the atmosphere was small, and greenhouse the effect was more than modest.
Recall that the atmosphere of those times did not contain oxygen, now amounting to 23% of the mass of dry air (at the surface). But the absence of one gas does not make a gas shell is so thin as required according to the bold hypothesis of the authors. We have to admit that the air was much less nitrogen than they are now.
However, according to the authors, there is independent evidence of low nitrogen content at that time.
By the way, not the first time that meteorites are a window into the distant past of our planet. Earlier “Conduct.Science” wrote about how they helped me to understand why life on Earth was poisoned by Halogens.