Since War of The Worlds, we give credit to our sci-fi novelist even people from SETI/Search for Extra Terrestrial Intelligence, to scare people of life forms aside from our own. The scary vision of them invading the planet and make Earth habitual to their way of life especially removing oxygen in our planet. We do not need any little green fellows to do that since our major industrial countries already poisoning the air from China and India. Not to mention over mining of minerals from precious metals, stones, rare earth to make consumer products from our cellphones and luxury cars and planes. Over fishing again by China from the West Philippine sea to as far from African coastlines. Rain forest of the Amazon gone. And the most important aside from oxygen, fresh water, being polluted and over use for watering golf courses , mansions of Hollywood celebrities and exclusive hotels.
So who needs terraforming of our planet by aliens when your next door neighbor is not an advocate of waste segregation anyway.
Clean our Earth. Its the only rock we live in.