The Allan Hills meteorite, found in Antarctica in 1984, lead to speculation that bacteria from Mars may have traveled from Mars to Earth between 17 million and 13 000 years ago - blasted from Mars 17 million years ago and landing on Earth 13 000 years ago.
This is not the only situation that I have come across, over time, where scientists have mentioned that life may have originated on Mars and then seeded Earth via meteorites.
I am not disputing that life on Earth has existed for billions of years. The Allan Hills meteorite is just an example of how a chunk of Mars can end up on Earth via natural processes.
But if life were to have originated on Mars, what would make Mars a better candidate for life to originate on?