Atmospheric Biomarkers

In this 7th session of the internet-based live lectures between Universities and Institutes, Dr Lee Grenfell discusses briefly the question "what is life?" and explores some of the criteria and methods which could be applied to find life on planets beyond the Earth. We start with some definitions of the properties of life, their limitations, and how they could be used to define possible criteria for finding potential extra-terrestrial
life. We then provide a historical context related to the earliest ideas about whether or not life could exist beyond the Earth. An overview is provided on key methods for finding life signals ("biomarkers") and the underlying physical principles. A special focus is given to the so-called atmospheric biomarkers (e.g. oxygen and ozone) where we discuss the main processes which form and remove these species and their associated atmospheric spectral signals.
We discuss with examples some central caveats e.g. the case of a dead planet which could mimic life, or a planet having life but whose life signals may be concealed. Finally we present some examples of theoretical atmospheric biomarker studies which focus on potential "Earth-like" worlds beyond the Solar System and discuss which factors could influence the potential
biomarker signals there.