Actually it wouldn't suprise me at all if there were a few bacterial colonies scattered in the 5 feet or so around the Viking landers. Not native of course, but life, just the same. And Thrilla, I'd agree with you except that Earth's global ecosystem has suffered at least 1 cataclysmic disaster since the rise of higher animals. I don't know if the line that were dinosaurs would have evolved into intelligent life ultimately, but we are about 80 million years behind where we could have been as a planet. If life is as common as it would seem, then the possibility exists that it could have developed somewhere where no global extinctions happened.
Then again, western civilization needed the Dark ages to take a fresh look at advanced mechanics and science in general, so maybe one has to go back in order to go forwards, so to speak.