But nick's right...
If there's anything at all to that theory, that horse left the barn a long time ago, including a chance of abundant Earth life being transported around the Solar System. While ejecta hitting escape speed is a lot harder on Earth than it would be on Mars, the odds of such Earth ejecta over the past billion years containing microbial life at the moment of impact are almost certain. Whether it survived the impact, or years in space, is, of course, another matter.