Moss and the air that we breathe

The evolution of land plants, include photosynthesizing green mosses could help explain how atmospheric oxygen levels rose to the levels we enjoy today. Atmospheric oxygen first appeared some 2.4 billion years ago, during the Great Oxidation Event but was just 400 million years ago that this vital gas first started to approach modern levels in the atmosphere. Tim Lenton and colleagues at the University of Exeter, UK, explain how, using computer simulations, they have estimated that bryophytes, such as moss, which are non-vascular plants, could have generated almost one third of today�s global terrestrial net primary productivity as early as 445 million years ago.