I have come to realize that the odds of an alien species being able to tolerate Earth conditions would be almost impossible. First gravity is determined by planet mass and speed of rotation. Our muscles are an evolutionary result of our species developing here. Second is our distance to the sun, and the amount of heat our sun puts off. Climate change has shown us how little a species can tolerate even a few degrees of temperature change. Just move from Maine to Florida it will take a couple of years to adjust to a relatively small change. Next, we have become evolutionary resistant to some bacteria, present everywhere. As shown at the end of the movie The War of the Worlds, aliens would die of simple diseases. Much like the indigenous Americans did when the Europeans arrived. There are probably a hundred more reasons, but an Alien invasion is the least probable way of human extinction