Fossil Microorganisms at Methane Seeps: an Astrobiological Perspective

The recent detection of methane in the martian atmosphere has stimulated a debate on its source, including speculations on a possible biological origin as in the Earth’s atmosphere, where methane is present as a trace gas and is mostly produced by life. Large amounts of methane seepage flows from the subsurface are documented on Earth since the lower Paleozoic by the formation of authigenic carbonate deposits. Methane-derived carbonates also precipitate in the modern continental slopes throughout the world with a great variety in size and shape, and document a still active methane advection from deep sources. The interest of seep carbonates in an astrobiological perspective relies on their relationship with microbiological communities that inhabit the methane seep ecosystems and establish the base of their food chain. They also might represent terrestrial analogues for martian environments and possible models for microbial life on other planets.