Elementals are beings that are representative of the elements - especially the traditional four elements as found in Greek or Indian philosophy; earth; air; fire and water. These beings are something that appears to be, in my opinion, a demonstration of the way that the human mind more often than not likes to work with archetypes and to represent natural forces in a (roughly) anthropomorphic way. The abstract notion of an element is much easier to relate with, especially magickally, if it's in the form of an actual being, hence their commonality in Hermetic and alchemic texts. But the traditional four elements are only the basic bunch - in many philosophical systems there are others, such as wood, metal, space and consciousness etc. But could new ones develop in time?
Religious beliefs have changed over time, becoming more abstracted through history, and this is roughly indicated in the way in which the natural world has been personified and represented in religious and mythological terms. First nature was personified in a very direct way, with the likes of the Green Man and Pan being the mythological form - a very direct and personal way of relating to the world. But modern religions have a different way of approaching things, and God is a much more removed concept. The ultimate abstraction, since he's not actually a part of things in the Judeo-Christian description of the world. Although he may make his presence felt from time to time, he doesn't live in the nearby forest.
But the personification of things so that we can relate to them better is something that I think is very much alive and well. As we come into contact with new arenas of life and experience, we have to relate to them too, and may do so in the same way we have over thousands of years, albeit in an unconscious way. Inanimate objects, such as electrical goods and vehicles are given personalities, especially when they start acting up - when the gremlins have moved in.
Over the last century, humans have realised that our future may well lie outside this planet, and that we inhabit a small ball of rock in a massive and bewildering universe. So how have we dealt with this on murky level of the Collective Unconscious? I'd say what we've done is conjured a new elemental being with which to relate. One that represents the mysterious and possibly dangerous and unknowable nature of the cosmos. It's the alien, as typified these days by the Grey, that's become our new Space Elemental, becoming the personification of Out There, with its lack of emotions and its inky, black eyes.