Som, S.M., Buick, R, Hagadorn, J.W., Blake, T.S., Perreault, J.M., Harnmeijer, J.P. & Catling, D.C.
Nature Geoscience, available online.
Air pressure has changed markedly over time. In a paper published in Nature Geosciences, Dr. Sanjoy Som (Blue Marble Space Institute of Science / NASA Ames Research Center) and co-authors measure the air pressure on the Earth 2.7 billion years ago, at a time when the Earth was markedly different compared with the modern day. Using gas bubbles trapped in ancient lava flows that solidified at sea-level, the researchers found that the air weighed at most half of what it does today.
As the lava cooled, it solidified from the bottom-up, trapping the bubbles at the base of the flow, and from the top-down, trapping bubbles at the top of the flow. By measuring the difference in size between the bubbles at the top and at the bottom using sophisticated instruments, the researchers were able to determine how much the air was pushing down on the lava flows as they cooled. An imbalance in the biological cycle of nitrogen, the dominant constituent of air pressure on Earth, is thought to be the reason for this surprising result.
This result has two important implications. First, it shows that biology can have a very strong influence on the evolution of a planetary atmosphere. Scientists have known for along time that biology can affect the chemistry of an atmosphere, such as the oxygenation of our air which began halfway through our planet’s history, but it had not been appreciated that biology can affect that actual amount of air around a planet. Secondly, this study demonstrates that microbial life can survive and thrive on planetary surfaces that are very different than modern Earth. This is important for astronomers as they seek out evidence of life far beyond our home planet.