Location of discovery: Aurora borealis, by NASA
Source NASA photo: https://spaceflight.nasa.gov/gallery/images/station/crew-13/hires/iss013e69634.jpg
Here is a cool photo from the NASA Spaceflight site. The photo supposedly shows the Aurora borealis in all its glory, however it accidentally caught a large UFO in it. The UFO was clearly inside the green area and was taking samples and taking readings from the Aurora. Aliens are interested in everything about Earth, not just the humans, not just the life forms, but all area of our planet. It wouldn't surprise me if several aliens species terraformed earth long ago as an experiment so they could record the entire planet evolving and growing through time. Why? Because those alien species are billions of years old, and have long since forgotten or lost their own history that far back. Even us humans have lost a lot of our own history of what happened just a few hundred years ago, and lost most of our history of what happened two thousand years ago. So yes, we can assume the same has happened to the alien species, but for them, they lost it many times over.
Scott C. Waring