It’s complicated…
In the old days, which was up until the mid-sixties in many countries, so not ancient history, you could apply for a patent for something that was common or even patented in other countries. The word ‘invention’ comes from the Latin ‘invenire’ - or ‘to bring in’. This let people patent stained glass techniques that had existed in history and been lost, or the means to make porcelain or silk, which existed but elsewhere. This allowed entrepreneurs to recoup the expenses of sailing to Cathay or wherever, and bringing back the expertise. This argument got harder to defend as world travel got easier
The other thing you could patent was something that you had, erm, invented in your head. For this, you wold have to come up with a new idea which would have be non-obvious to those skilled in the particular field. In theory, you would have to have someone that was completely skilled in your field, and yet unable to come up with anything original, to test novelty. This is never practical, so in general patent offices settle for a lot less. They have a good, indexed database of existing patents. But if you idea is not on that database, they can issue the patent, assuming that if someone else comes up with evidence of prior art, the patent can be dismissed. In the early days of software patents, there were no software patents, and people went about trying to patent basic maths.
It is unlikely you could patent an oak tree. But I could imagine it could be possible to patent an oak tree being planted to attract harmful insects away from crops (I made that up. It’s not very good, I know).
Suppose we contacted intelligences from the stars. We might have lots of new inventions from the stars, but a huge cost for getting the ideas, and trading them for other ideas. To recoup these costs, we might bring back the idea of patenting ideas that are known abroad.
