Life-genic Atmospheric Alterations

…Their analysis revealed that atmospheric pressure 2.7 billion years ago was at most only half of its present value—a result that flies in the face of our understanding of the Earth during the Archaean period. … Now, scientists have to figure out what it means. … suggests something dramatic took place about three billion years ago to reduce the size of the atmosphere. And Som has a hunch as to what that something might be. … Other geochemical evidence suggests that around 3.2 billion years ago, bacteria developed mechanisms for transforming atmospheric nitrogen (N2 gas) into ammonia (NH3), a biologically-useful form. … nitrogen fixation, was utterly essential to the evolution of complex life. Without it, plants and animals would have no way of accessing the nitrogen our cells need to build proteins and DNA. Essentially, Som and others suspect that the ability to strip-mine the atmosphere for nitrogen caused air pressure to take a temporary nosedive.…