I feel like the assertation that meteor impact ejecta would 'almost certainly' contain live bacteria spores and the implication that those spores would survive vacuum , radiation, heat cycling, and dessication for the very long trip from earth to mars is going to need a big old citation required here. That seems like a stretch.
In the abstract:
"The conclusion is that if microbes existed or exist on Mars, viable transfer to Earth is not only possible but also highly probable, due to microbes’ impressive resistance to the dangers of space transfer and to the dense traffic of billions of martian meteorites which have fallen on Earth since the dawn of our planetary system. Earth-to-Mars transfer is also possible but at a much lower frequency."
