One scientist is convinced that the crucial element that got life started here came from up there...

Evidence is mounting that life on Earth may have started on Mars. A leading scientist has claimed that one particular element believed to be crucial to the origin of life would only have been available on the surface of the red planet.

Professor Steven Benner, a geochemist, has argued that the "seeds" of life probably arrived on Earth in meteorites blasted off Mars by impacts or volcanic eruptions. As evidence, he points to the oxidised mineral form of the element molybdenum, thought to be a catalyst that helped organic molecules develop into the first living structures.

If this is true, then life must be very rare in the universe. It seems you need too many accidents to make it happen: the accident of some planet falling in the habitable zone from the right star, the accident of that planet having enough water (some scientists even think that we got a lot of our water from the accident of a comet or asteroid collision), and now we are speaking of the accident of interplanetary exchange of the principal chemical ingredients. Beyond all that, you also need, as the UW paleontologist Peter Ward once pointed out, some big planet like Jupiter to protect a core planet or planets in the habitable zone from repeated, surface-sterilizing asteroid and comet hits. Life appears to be a trick of the impossible.