Some materials or products are said not to be “earthly”.

It’s certainly possible, but I’m not aware of any irrefutable evidence for it.

Astronomers are convinced that there must be more than 1 planet in the universe to support life as we know it (which is understandable with billions of star systems).

So it is possible that there is a planet with life on it somewhere in the universe and it may also be intelligent (if we think of humanity as intelligent :D).

In order for potential aliens to land on the Earth before, today or in the future, they would need technologies unknown to us till now, enabling them to travel long distances.

We have only reached the Moon so far and we probably won’t get further than the borders of the solar system in this century, and traveling to distant stars is a task for perhaps the next millennium.

I recall that examples of “alien visits” are pyramids or simple chemical cells (or batteries that we put in remote controls), which is nothing that we could not build or manufacture at today’s level.

If aliens had been on the Earth before, they would have been technologically much further than we are and the findings should correspond to that, but I haven’t noticed that.

More likely, stories of alien visitation seem to me to be “discoverers” trying to apply our knowledge to historical finds.

By the way, we have been trying to detect the presence of advanced civilizations for decades by “listening” to the universe in radio waves, e.g. the SETI project.

And since the invention of wireless transmission, the Earth has been sending radio waves into the surrounding area.

So within 120 light years from the Earth, potential aliens would know that there is a planet in our part of the universe with animals capable of emitting radio waves.

No one has responded to these waves so far.