Some people believe that aliens have visited our planet, but they did so during the ancient times. In fact, there is an entire tv series devoted to the phenomena of Ancient Aliens (website) on the history channel. This show describes its premise with: “According to ancient alien theorists, extraterrestrials with superior knowledge of science and engineering landed on Earth thousands of years ago, sharing their expertise with early civilizations and forever changing the course of human history. But how did this concept develop, and is there any evidence to support it?” The show then goes on to devote each episode to supporting evidence of this theory.
One such example cited as evidence such as ancient paintings like the one on the left (image taken from Wikipedia). Erich von Däniken was the first to bring this theory to the mainstream in the late 1960s and early 1970s with his publication of Chariots of the Gods? where he pointed to specific ancient iconography from the Mayans to support his theories.
Zecharia Sitchin was another such theories, but he turned to ancient Mesopotamian and Middle Eastern texts. He went so far to posit that an alien race named the Annunaki from the planet Nibiru came to the earth 400,000 years ago to mine the natural resources of the planet, and that in fact, they genetically engineered early human species to do the heavy mining work (we would be descendants of these people under this theory and our culture evolved from that of this race).
Of course, this material won’t be on a test, but if you are interested in more information, check out the show.