This workshop explored the key questions and challenges associated with detecting life on an extrasolar planet. The biogeochemistry session reviewed the processes whereby biogenic gases are produced in aquatic environments and on land.
Gas production is an unavoidable byproduct of biological oxidation-reduction reactions.
Later still, abundant O 2 and O 3 were the most distinctive signatures. Future research should explore the mechanisms whereby the abundances of these gases are regulated. Also, we must better define the composition of a life-sustaining atmosphere in the absence of O 2 . O. A Venus-like planet could develop a wet stratosphere, lose its water by photodissociation and subsequent loss of hydrogen, and thus accumulate O 2 abiotically. However, additional critical information about a planet, such as its radius, albedo and effective radiating temperature, could differentiate between O 2 accumulation by these nonbiological mechanisms and O 2 accumulation by life.