Graham Hancock believes advanced humans were wiped out 12,000 years ago, while Sitchin claims the Anunnaki, an alien race, came to Earth 500,000 years ago.

Hancock believes that a great civilization existed long before ancient Mesopotamia, Babylonia, and Egypt. He thinks this civilization was destroyed by a comet about 12,000 years ago, erasing almost all evidence of it.
However, he believes some clues remain, including a warning that a similar disaster could happen again. He shares this idea in his book Magicians of the Gods (2015).
On the other side, Zecharia Sitchin claimed that the Anunnaki were actually a race of extraterrestrial beings from the undiscovered planet Nibiru, who came to Earth around 500,000 years ago in order to mine gold.
According to Sitchin, the Anunnaki genetically engineered homo erectus to create modern humans to work as their slaves. Sitchin claimed that the Anunnaki were forced to leave Earth when Antarctic glaciers melted, causing the Flood of Noah, which also destroyed the Anunnaki’s bases on Earth. These had to be rebuilt and the Nephilim, needing more humans to help in this massive effort, taught them agriculture.
Hancock believes that Göbekli Tepe in Turkey, with its huge stone pillars, shows evidence that ancient people, even before we had high civilizations, were capable of advanced skills. He thinks this means there were unknown civilizations thousands of years ago, possibly teaching others. However, some argue this idea is too simplistic. They point out that Göbekli Tepe was a religious site, not a city, and there’s no evidence of everyday things like farming, metal tools, writing, or pottery, which later civilizations had.
Despite years of research, Hancock has not found enough proof to convince archaeologists that the usual timeline of human history needs to be changed. He believes mainstream science only accepts slow, gradual change and cannot consider big, catastrophic events.