False biosignatures from micrometeorite strikes onto a planetary atmosphere

Extrasolar Planets And False Atmospheric Biosignatures: The Role Of Micrometeoroids
http://www.sciencedirect.com/science/article/pii/S0032063312002735?v=s5

A high micrometeorite flux onto a planet can create methane in the atmosphere that could be mistaken for an atmospheric biosignature. However the amount of material falling onto the planet would require a very dense debris disk to provide, and is thus likely to be seen only in very young systems.