There are many people who believe in an alien ancient civilization that once came onto the Earth. Although no one knows for sure the purpose of the aliens coming to the earth, it is believed that they came to learn about humans and use humans to do work for them.
These ancient alien civilizations are also referred to as astronaut aliens, ancient aliens or ancient astronauts. There are some who even believe these ancient aliens have taken over the deities of many religions. Also, it is believed that some ancient alien bloodlines still exist and are being watched over still to this day.
The most talked about ancient alien civilization is the Anunnaki which some say created the Mesopotamian culture and first visited earth approximately 430,000 years ago in the Middle Eastern region. Many ancient ruins are said to be too technologically advanced to be have been built by humans without alien intervention or guidance.
Anunnaki are believed to also have altered the genes of humans to create the current evolution of the homo sapien species. They are said to have spliced some of their alien genes with the then human genes to create a specialized race to be controlled for mining of gold and other resources and building the early civilizations.
To learn about the scientific study of alien ancient civilizations, watch this video: