Mumm-Ra: I have known of its power for a thousand years! From a time when this was still First Earth! Slithe: You know of the Eye of Thundera? Yessss? Mumm-Ra: You need only know that I am Mumm-Ra and that I know of your mission here on Third Earth. Mumm-Ra: As long as evil exists, Mumm-Ra lives! Within the show itself, the next closest thing we have to direct evidence is this bit from the episode The Unholy Alliance Also, Merlin has to stop by to save the day, and if he had to travel through time and space to get there, he didn't mention it. So unless the Lady of the Lake has a spaceship and map of the galaxy's best lakes, it was probably the original. In another episode, the Ancient Spirits of Evil tell Mumm-Ra that Excalibur was the greatest sword ever made, so Mumm-Ra disguises himself as King Arthur and borrows it from the Lady of the Lake. If humanity alone isn't enough to convince you, in the first episode, Mumm-Ra is shown clearly living in the great pyramid of Giza. Specifically, our earth is First Earth, and then it had a couple of calamities and so that the planet is now in its third… stage, I guess? But however weird Third Earth gets, what with the giant and the unicorns and the Berbils, it's still our planet in the future, hence the humans still living there, as well as the humans scattered across space. Why did Third Earth have Amazons? Well, because…

And there was even a tribe of Amazons living on Third Earth called the Warrior Maidens (a bit on the nose, if you ask me) who became friends with the ThunderCats. There were actually a bunch of humans already living on Third Earth as well, although 90% of them were royalty and/or wizards, like Queen Tartara and Brodo. There was an intergalactic big game hunter named Safari Joe (who dressed in traditional 'big game hunter' garb) a variety of bounty hunters a samurai from 'the Planet of the Red Sun' and many more. While the ThunderCats and their weird animal allies and foes were obviously ThunderCats' stars, the show was not devoid of humans, who stopped by on a reasonably regular basis.

IO9 wrote about this earlier this year, concluding that 'Third Earth' is actually just our Earth, far in the future.ģ) There were actually plenty of humans on the show.

Original thundercats