ABSTRACT
Stromatolites are classically interpreted as “organo-sedimentary structures”, where layers and doming/branching result from microbial mats. As such, they could be considered quintessential ‘astrobiologic’ structures—a stromatolite, as a macroscopic manifestation of microbial processes, would be much easier to image remotely (on Mars, for example) than a microbe. While there is no doubt that some (perhaps most) stromatolites on Earth were formed with biologic influence, recent work has demonstrated that stromatolite-like structures have formed without biologic input. Can we tell the difference? When faced with determining the presence of life elsewhere in our solar system, “extraordinary claims require extraordinary evidence”—do stromatolites pass this test?