1969-Humans, and billions of bacteria, on the Moon. The Humans return to Earth.
Date: 20th of June, 1969
Fact: 96 bags of human feces have been left on the Moon. Each of these containing billions of bacteria (up to 55% of the bags mass). Some might be revivable, might have survived, or even might have evolved to adapt to the local conditions (of the inner of the bag).
The possibility is investigated, that some extremophile microorganisms in the bags are still revivable (source, Mark Lupisella, NASA). As such, those bags on the moon could be interpreted as a depository for Earth originated DNA base life.
Even if remote, for the conditions on the Moon are really harsh, the possibility exist that some live colony eventually evolved into microorganisms capable of surviving out of the bags. In such a case, we would have forced an adaptation of terrestrial life to the lunar environment, and possibly seeded a new biosphere along the way.
It is possible (while the possibility is remote) that we have seeded the moon with terrestrial life, "inadvertently"
Thoughts about this
While Musk is keeping it up with his target of a million people on Mars, dreaming of making earth a "multilpanetary species", from a microbial point of view, Humans have already set 17 colonies of billions of microbial spationautes. On the moon We've not heard from these yet. Maybe they're all dead. Maybe not. The Apollo Contamination Environment (ACE) Sample Return. project, in this perspective, holds an extremely rich promess, for the understanding of the capability of microbial life to adapt to space environment.
footprints - and a bag of feces/NASA
I strongly recommend the reading of the article in Vox, from which the above image, and the lovely astronaut poop video have been extracted. Also of interest: