"I'm pretty sure. If you are talking about life made of atoms and that uses energy. I am 100% sure."

I don't think we can be 100% sure at all - I don't think we can be 5% sure, if that.

We recognise carbon-based life forms on earth (and find new ones all the time) but we have no way of knowing how the chemistry might work and give rise to non-carbon-based life forms, or what processes such a life form might use to gather nutrients, breathe (if it needs to), replicate or communicate. It's thought processes might take eons, it might not have a physical body in the sense we understand it, it might be too tiny to see or too huge to comprehend as a living entity.

We might land on a planet of silicon-based life forms and see rocks, when what we might be looking at is a thriving advanced civilisation that takes years to say 'hello' - and they might not use sound to do that but change colour slowly over time. or whatever.

The real point about alien life forms is they will be, er, alien and probably unlike anything we can imagine. The fact most of these cover-up stories are about humanoid aliens with two eyes, a nose, mouth and the same limbs as us, the same basic skeletal configuration suggests to me who started these theories had a singular lack of imagination.