These "seeds" of life probably arrived on Earth in meteorites blasted off Mars by impacts or volcanic eruptions, Geochemist Professor Steven Benner claims.
Prof Benner, from The Westheimer Institute for Science and Technology in the US, said: "The evidence seems to be building that we are actually all Martians; that life started on Mars and came to Earth on a rock."
Speaking at the Goldschmidt 2013 conference in Florence, Italy, he said: "It's lucky that we ended up here nevertheless, as certainly Earth has been the better of the two planets for sustaining life.
"If our hypothetical Martian ancestors had remained on Mars, there might not have been a story to tell."
Prof Benner said the element molybdenum was thought to be a catalyst that helped organic molecules develop into the first living things.
"This form of molybdenum couldn't have been available on Earth at the time life first began, because three billion years ago the surface of the Earth had very little oxygen, but Mars did.
"It's yet another piece of evidence which makes it more likely life came to Earth on a Martian meteorite, rather than starting on this planet."
He added: "Analysis of a Martian meteorite recently showed that there was boron on Mars; we now believe that the oxidised form of molybdenum was there too."
Another reason why life would have struggled to start on early Earth was that it was likely to have been covered by water, said Prof Benner.