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...