The author is saying that because of humans and the ways they are impacting earth is causing irreparable changes like causing animals to go extinct, etc.
When Grendel says Unferth's "beard and hair hung straight down like seaweed", the literary device used is SIMILE.
Simile is comparing two unrelated and dissimilar things, people, beings, places, and concepts using the words "like", "as" or "such as"
Beard and Hair was compared to seaweed using "like".
Though a bit lengthy (which is absolutely fine!) you seem to go into some good detail while withholding main points for the rest of your paper and it is very well done!
