Early solar system had plenty of impact events happening. Mars has less gravity than Earth, so it's easier to eject material from there. Picture a comet or asteroid hitting early mars. Most ejecta falls back to Mars, but still tens of thousands of rock fragments are ejected into space, in random directions. Some fraction of them are likely to reach Earth a few years later, potentially carrying any microbial stowaways present in Mars by then.

We already know the meteorites from Mars probably do make their way to Earth on occasion. [1] From there, imagining some primitive life managing to hitch a ride is easy. Even quite advanced life, like tardigrades, have demonstrably survived days of exposure to outer space, and successfully procreated afterwards. [2]

[1] - https://www.space.com/mars-meteorites-on-earth-mystery

[2] - https://en.wikipedia.org/wiki/Tardigrade#Survival_after_expo...

> Martian meteorites experience shock pressures of less than 30 GPa on ejection from the Red Planet

Is that enough energy to boil the living things that might be in the rock?

I guess we can somehow bind an asteroid, alongside a spaceship crashing in.