You might like to consider the way that Egdon Heath is linked to some sort of primeval past in the novel. This effect is achieved through the description we are given of the Heath in Chapter One on Guy Fawkes Night:
In the valleys of the heath nothing save its own wild face was visible at any time of day... None of its features could be seen now, but the whole made itself felt as a vague stretch of remoteness... Red suns and tufts of fire one by one began to arise, flecking the whole country round.
Note the way that Egdon Heath is presented as some sort of remote universe by itself. Often characters comment upon the way that Egdon Heath seems to be a universe on its own and they say that it is all they can see. The quote above includes a metaphor presenting Egdon Heath as its own galaxy, with the bonfires acting as the suns in the solar system of the Heath.
The bonfires also function in another way by linking the Heath to a more ancient, primeval past when bonfires were used for light and warmth in addition to celebration. The cultural background of the Heath is therefore linked to the dark ages (note the darkness in the quote above) and ancient times such as when the Celts and Romans variously dominated the land. This sense of age and timelessness is something that is deliberately refered to in Chapter One in the description of the Heath:
To know that everything around and underneath had been from prehistoric times as unaltered as the stars overhead, gave ballast to the mind adrift on change, and harassed by the irrepressible New. The great inviolate place had an ancient permanence which the sea cannot claim.
Not only is Egdon Heath "prehistoric," according to this quote, and we can imagine that Celts celebrated there just as the characters in this novel celebrate there now, but Egdon Heath is also timeless in the way that it remains unchanged by the ages that have gone by. The Heath is therefore presented as almost being outside of time and beyond the reaches of time and the way that it changes and withers everything else. This sense of permanence explicitly contrasts the Heath with the fate of individual humans, who so quickly fade and die.