This is something I've thought about quite a bit, but never quite been able to look into. I suspect Esrolia: Land of 10k Goddesses might shed some light on it, but I haven't gotten around to it yet. Pardon the following mess of questions, it's just that so many things seem related/interconnected.
So basically, one of the things I noticed once I started getting into Glorantha was the ubiquity of "earth goddesses", which very, very often feature as partners in other-element-dominated pantheons or even histories. f.ex. Oria in Pelorian mythology, Erlanda in Orlanthi mythology, or even Seshna as a dynastic mother of the early Seshnegi Serpent Kings. There are tons of more stuff, of course. They are also paired with at least earth-related deities as well, like Flamal and Lodril, but neither are purely cthonic it seems.
We're also seemingly confronted with an array of regional goddesses (called land or grain goddesses, I believe) that very conveniently not only apply to named geographic regions, but even seem to alter as geography changes. Some of these goddesses however also seem to be "a-regional/global", like Erlanda herself (or is she?? There used to be a place called Erlandela, after all) and so on. Many of these feature in relations with whoever are the local male deity bigwigs, but rarely rule in their own stead, or even maintain their own kind of people. That doesn't seem to have been the case forever though, as very early Pelanda/Wendaria seems to indicate, and so on. Complex stuff.
Layered above these regional godesses we also have the cardinal-direction gods, or continental gods, like Genert and Pamalt, and arguably Malkion/Zzabur and Vith as well (which also parallel Pelorian cardinal administrators, and Orlanthi "camps", but that's neither here nor there, really). Out of these, Genert is the one most clearly defined as an earth-entity (even if it's likely he would've had his own unique proprietary rune as Pamalt has), to the point where he, apart from being called a giant, is also called an Earth Titan or Earth King (a great title that should be used more, imho), and ruled a garden-realm where everything grew aplenty. With his death central Genertela not only became a wasteland, but Genertela in general supposedly has become less fertile and more conflict-filled than Pamaltela in the south.
Now comes the God-Learnerism: do we have any good sources, or examples of whether there were independent Earth-folk (like Time's Solar folk, Storm folk, etc.) were extant, and if so, what their social practices were and other aspects of their lives? Given that most genealogies involving earth goddesses tend to be woven into other pantheons, do we have any good "earth-centric" genealogies perhaps including the Earth Kings/Directional Lords, the regional/featural land goddesses, the more general mother goddesses, and the primal earth? Do we have any indication what beliefs in other pantheons might have been appropriated into other belief systems from hypothetical Earth Folk? Or indeed what happened to them, physically? (The Durevings joining the Vingkotlings and becoming the Esrolians come to mind, as do the Praxians and Pentans forming from the survivors of Genert's Garden, or patriarchal urbanized Pelanda forming from pre-urban matrriarchal Wendaria). And lastly, is it even possible to talk about an "Earth people" in the first place, and not just various groups who were focused on chthonic powers unrelated to each other?
Pardon for the multitude of questions - I of course fully acknowledge that most of these things probably don't have one canonical answer, or were ever intended to be answered, but I find them interesting to think about.