Of course. The universe is infinite, and constantly expanding. You would have to be awfully arrogant, and closed minded to not think somewhere out there, are other planets similar to Earth. They may not be in the Milky Way galaxy, but there are BILLIONS of stars out there, and each one could have its own system of planets. In fact I sort of have this fucked up theory that we never find the remains of Bigfoot, because he's from another planet, and his home planet sends a ship to pick up remains to keep Earthlings from finding any proof.