In China's ancient books, it seems that Qin Shihuang met with aliens. Volume 41 of Notes on the Collection of Leftovers records: "There are people in Wanqu, and they come by boat. The shape of the ship is like a snail, which sinks to the bottom of the sea, but the water is not immersed. It is a' boat braving the wind and waves'. Its people are ten feet long and cover their shapes with the hair of birds and animals. The first emperor spoke to him and opened the shirt of heaven and earth. " They also have amazing high-efficiency energy. If they are used for night lighting, only one grain "like millet" can "shine together". If you throw it into a stream, it will boil for dozens of miles. At that time, aliens were described by the ancients as whispering, and the gas they spit out when they came by spaceship was regarded as "weather"
It is also recorded in the Western Bible that Ezekiel mistook aliens for gods. Therefore, I believe that aliens must have been to the earth.
But maybe aliens are our descendants. In a few years, our technology will be much more developed than it is now. At that time, maybe we invented flying saucers, which can travel back in time. At that time, maybe our appearance evolved into what we now call "aliens". At that time, in order to study "the ancients" (that is, now we) and "the ancient earth", we returned to the present earth by flying saucer.