Proc. Natl Acad. Sci. USA 10.1073/pnas.0809436106 (2009)

The Sun is growing brighter with age, and some argue that this will limit the lifespan of Earth's biosphere. The hotter the Sun, the more readily carbon dioxide will be removed from the atmosphere by chemical weathering; once levels fall too low, photosynthesis will cease and the biosphere will be radically diminished.

King-Fai Li and his colleagues at the California Institute of Technology in Pasadena offer a way out of this trap with the help of a simple model. A drop in overall atmospheric pressure, achieved perhaps through biological sequestration of nitrogen, would weaken the atmospheric greenhouse effect. This would make the world cooler for a given level of CO2. As a result, the weathering effects would be less marked and CO2 levels could stay higher for longer. This might extend the biosphere's remaining lifespan from around 1 billion years to something like 2.3 billion years.

The authors conclude that atmospheric pressure is also likely to co-regulate the climate of planets elsewhere in the Universe. If this means that the lifetimes of biospheres are longer in general, it might increase the chances of intelligent life evolving, and the chances that that life coincides with life on Earth.