In At the Mountains of Madness by H.P. Lovecraft a group of antarctic explorers discover the evidence of an ancient, prehuman civilization. While exploring the ruins of a vast and abandoned city the explorers find and interpret a series of carvings and hieroglyphs that seem to tell a history of both the “Elder Things” and, basically, the evolution of life on Earth. I say “seem to tell” because the explorers are only able to spend a few days in the city and are forced to leave it under terrifying and sanity disturbing circumstances. Their understanding of the story told in the carvings shouldn’t be assumed to be perfect. It might be missing important information. It might be completely wrong. Human beings have a hard enough time understanding the languages and art left by extinct human cultures. It’s unlikely that a human could get an accurate reading of non-human culture without being able to interact with representatives of that culture.
That’s one of the things that I enjoy about the Cthulhu Mythos. Humanity and the Earth itself are not central. Sure, most Mythos stories feature human protagonists and deal with human adventures but that’s because human authors are writing the stories for human readers. But the Mythos features beings and species and civilizations that existed long before mankind learned to make fire and who will exist long after mankind’s story ends. Earth is just one of the places these creatures have visited. The Universe is vast and full of strangeness and wonder. (Or terror and madness, if you’re a xenophobic New Englander.)
The Elder Things came from the stars to the Earth, presumably, before fish evolved in the seas. Their civilization here lasted for millions of years. That civilization might continue, somewhere in secret, here on Earth. In all likelihood there are Elder Things civilizations scattered across this and other galaxies. If humans made it out to the stars, would we find the Elder Things welcoming? Threatening? Dismissive? All of the above?