If you were a passenger aboard the meteorite from Mars bearing down on the town of Tata, Morocco in July 2011, you would be in a decidedly unenviable position. For one thing you’d be a bacterium — a nifty Martian bacterium, to be sure, but still. For another thing you’d be either freeze-dried or in a state of suspended animation — the better to survive the thousands or even millions of years you might have spent in space. And the odds are that even if you were alive and well when you stowed away on the rock while it was on Mars, the life would have been snuffed out of you the moment the asteroid hit that blasted you into space in the first place.
On the other hand, maybe you’d survive — maybe the shock would not have been so great or you’d be tucked away deep enough in the meteorite that you were spared its full power. And if you did survive and arrived on Earth a few billion years ago, maybe you’d have have adapted well to your new home and grown and thrived and served as the seed for every organism that ever populated your new planet including, eons later, the human species itself. In which case, modern humans never have to contemplate meeting Martians again because we are the Martians.