In about 2015 the terrestrial planet finder will look for atmospheric signature molecules in the atmospheres of earth-like exoplanets indicating the presence of life there.
Will that allow biologists to finally settle the question of how life originated on earth? For instance, suppose TPF finds oxygen in the atmosphere of exo-Earth. Does this prove that life originated by chemical reactions in the planet's atmosphere?
Or is Stan Friedman correct, could life travel around like Johnny Appleseed and colonize the local star systems?