There have been a few claims of microfossils of bacteria found in meteorites.  One of particular interest is the Allan Hills 84001, a meteorite found in Antarctica.  The meteorite would have arrived on Earth after having been blasted off the surface of Mars.   In 1996 a several scientists found strange structures that could be interpreted as microscopic fossils of bacteria in it. Using a scanning electron microscope, the scientists found tiny formations similar to fossils of bacteria-like lifeforms.  Most scientists reject this hypothesis stating that there are non-biological means of creating similar structures.