Panspermia is the concept of taking one in a trillion odds of a shot hitting the target and firing that shot a trillion times. I'm not particularly advocating for it, but it has at least some basis in plausibility.
We know that rocks from others planets can and do get shot out by meteor impacts on a routine basis as some have landed on Earth. We know that these impacts shoot out large quantities of rocks at a time into space at random directions. We also know that gravitational currents can help objects naturally move between planets.
We also know that bacteria can survive being left in outer space for years at a time. We know that the interior of a meteorite does not particularly heat up upon re-entry into the Earth's atmosphere. We know that bacteria are found inside of rocks inside the Earth when we look for them.
Now I'm not going to get into life (bacteria etc) evolving and everything that goes with it. I'm certainly not saying that Panspermia has any evidence of having ever occurred. I'm simply saying that the idea of Panspermia has at least some plausibility as a delivery mechanism for bacteria like life that had already evolved on it's own.