Earth’s ancient atmosphere may have been much thinner

New Scientist : The atmosphere on Earth some 2.7 billion years ago may have been less than half as thick as it is today. That finding is based on a new study in which Sanjoy Som of NASA’s Ames Research Center and colleagues looked at gas bubbles trapped in ancient lava covering thousands of square kilometers in the Australian outback. By comparing the larger bubbles that rose to the top with the smaller ones that got trapped at the bottom, the researchers were able to determine that the air pressure billions of years ago when the lava hardened was probably 0–0.5 atmospheres; the best estimate is that the atmosphere was 23% as thick as it is today. That finding contradicts earlier theories that said the atmosphere must have been thicker to prevent Earth’s surface from freezing over when the Sun was much younger and fainter. The researchers say the key may be nitrogen, which might have dominated the primeval atmosphere, warming it and fueling nascent microbial life.