So what happens if the aliens land? Here, on Earth. I'm not talking about detecting a radio signal or a laser flash from hundreds of light-years away. I'm speaking of visitors who actually set their boots on the ground. What do we do? It may surprise you to learn that there's precious little preparation for such an eventuality.
Being in a planet so abundant in water, oxygen and resources, it is hard to imagine that life could thrive in any situation but everything seems to be so perfectly balanced for the existence of life, perhaps that's why till now, the search for Extraterrestrial life has only been confined to planets with resources of air and water. Till now.
Unless Earth is special beyond reason, you can confidently assume there are plenty of societies out there. That doesn't mean that they'll come to Earth (or, as many believe, already have). Interstellar travel, despite what you've seen at the local multiplex, is hard. But we could easily get in touch via radio signals or flashing laser lights.