One topic for an essay about A Friend of the Earth could be a drawing of the parallels between the people and the animals in this novel. Certainly, their Adam and Eve stunt makes Tyron Tierwater and former wife Andrea as susceptible to the elements as the animals. For, this grueling test of their survival skills demands that they pull from their inner beings whatever resources they have, and they come out successfully. Of course, there are other struggles in this "Brave New World" of ecological disaster, struggles which lead Ty to re-evaluate his life and make one final attempt at love, all the while that he works to help save the Earth.
One quote that is worth exploring is
Live in the present, that's what I say, one step at a time, and forget nostalgia, forget history, forget the sketchy chain of loss, attrition and disappointment that got you into bed last night and out of it this morning.
This is what Ty and Andrea do when they reunite and shed their history along with their clothing as they set forth on their rebirth in Nature.