I know of nothing in the natural world of which there is just one. Just one flower? No. Just one bear? No. Just one cloud? No. Tree? No. Mountain? No. City? No. etc… So why would there just be one life sustaining planet? It makes no sense.
There are thousands, perhaps millions of life sustaining planets in the Universe. And there’s life out there; lots of it. It’s just too far away for us to see or hear.
Do you realize that by our best educated estimates there are at least 100 stars (in the universe) for each grain of sand on Earth? Astronomers believe most stars have planets. So there are trillions upon trillions of planets orbiting stars out there. You still think the one beneath your feet is the ONLY ONE CAPABLE OF SUPPORTING LIFE? I definitely think not.
It’s analogous to prehistoric man here on Earth; each tribe living in isolation, separated by thousands of miles of ocean, unaware other peoples even existed and having only very limited means (hollowed out logs) of navigating space (ocean). Very little has changed.
In the grand scheme of things, our Space Shuttle is comparable to that hollowed-out log used by ancient peoples to navigate the immediate ocean and rivers around them. In time we’ll develop great ships to quickly navigate space (AKA starwars/star trek).
Unfortunately it is possible for other life forms to find us before we find them. Think Europeans landing on North America about 600 years ago. Like wise, those aliens may posess superior weapons or host deadly germs and we, Earth humans, may not stand much of a chance. Scary stuff. But there is NOTHING that guarantees this can not or will not happen.
Imagine the native American’s long ago; going about their daily life, foraging for berries, hunting, war parties, etc… going about their business completely oblivious to the events transpiring thousands of miles away and the devistating consequences (MILLIONS OF THEM DIED) . Some things could come here and put us in the same shoes. It’s possible.