Yes that is what I meant by there is a good case that life originated on Mars first.<p>This hypothesis also fits with the C12&#x2F;C13 enrichment in ancient sedimentary rocks (enrichment in C12&#x2F;C13 enrichment is a sign of living metabolic systems) almost as soon as water existed on the Earth’s surface - basically life appeared on Earth as soon as it was possible. It could also explain why the last common ancestor of all living cells was so complex - if life originated on Mars and came to Earth later then all the ancestral life would have been left on Mars.<p>Against the hypothesis that life originated on Mars is the fact that Mars is much smaller than the Earth (the surface area of Mars is about the same as Africa). All things being equal if the conditions for life originating were the same on both planets (at the same time) then we might expect life to be more likely to have originated on Earth.