Just how long have humans known of and revered the Asgardians? I know that in the real world it's only been several thousand years, but there are some indicates that in Marvel, it's been considerably longer. Each Ragnarok cycle lasts several thousand mortal years. In THOR: AGES OF THUNDER it's stated that there have been at least 23 cycles; this would push Asgardian activity back a long way into prehistory, and the same book indicates that humans already lived on Earth and acknowledged Asgard by the third cycle.
Interestingly, Marvel's old Conan comics had the human Nordheimr of the Hyborian Age, circa 10,000 BCE, frequently invoke Ymir, Woden, Thor and Balder. These stories are canon, as they occurred in the distant past of Reality-616. And a recent story showed Odin employing the forces of Heven to discourage Asgardians from wreaking havoc on Earth at a time when humans were still not very far removed from apes and hunted mammoths. Whether this is before or after the Hyborian Age, I'm unsure, but I'm personally inclined to place it before. And there were human civilizations on Earth many thousands of years prior to the Hyborian Age that could have had knowledge of Asgard.