Early Earth had upper atmosphere rich in oxygen, discover researchers

Scientists have gleaned fresh insights into the chemistry of early Earth's atmosphere 2.7 billion years ago by analysing fossilised micrometeorites. The study, published today , indicates that ancient Earth's upper atmosphere contained about the same amount of oxygen as today, and that a methane haze layer separated it from an oxygen-starved lower atmosphere. These findings challenge the accepted view that Earth's ancient atmosphere was oxygen poor 2.7 billion years ago. The researchers suggest their results can be explained if Earth at that time had an atmosphere that mixed very little between the different layers. A possible explanation for this may be that the methane haze layer at middle levels would have absorbed UV light from the Sun, which would have released heat and created a warm zone that would inhibit mixing between layers. The team suggest the upper oxygen layer may have been produced when CO? was broken down by ultraviolent light from the Sun. The research was carried out by a team from Imperial College London , the Australian Synchrotron and led by Monash University.