There are many examples of UFOs and aliens in ancient art. There are theories about ancient gods being aliens; aside from these, as they will be addressed elsewhere on this site, here are a few of them:

Kiev 4,000 B.C.

Carmonica 10,000 B.C.

France 17,000 B.C.

Russia 10,000 B.C.

Tanzania 2,900 B.C.

Tassili 6,000 B.C.