Lately it seems to be popular to speculate that life may have originated on Mars through transfer of microbes through impact debris. Part of the mindset is that Mars cooled sooner than the Earth and may have been the source of life on Earth. http://www.space.com/22577-earth-life-from-mars-theory.html If this is true then this could explain the Cambrian "explosion", there are multicellular organisms tough enough to make the journey from Earth to Mars and by the time of the Ediacara life forms the Earth seems to have dominated by weird organisms with no modern counterparts. A meteor holding desiccated specimens of some tough creature or creatures, already the result of billions of years of evolution but from the same microbes that seeded early Earth, could have been thrown to Earth from Mars by an impact , some tough creature already adapted to a competitive life style, toughened by the deteriorating conditions on Mars, transferred by impact debris, unable to compete was Earth's Ediacara biota wiped out and replaced by Martians!
What do you think?