Whovever assigned you that topic is the definitive feckin eejit. The short answer is to write about the Mayan collapse secondary to overpopulation/drought. But how does that advance anyone's knowledge of "sustainability"? It was a specific event fed by lots of unlucky, ancillary events. That a global climate revision with dreadful effects (at best)on all living organisms is on its way is (a) well known old news,(b) inevitable,(c) a perfect example of the preposterous phrase "hoist by one's own petard", and (d) so dwarfs the very idea of a school paper on "the current sustainability issues" that one wants to make the comparison to a young German 68 years ago asked to write a paper about "the Jewish Problem." "Sustainability" is such cant, such a green, feel-good topic. In truth it's a smoke screen which conceals the opposite of sustainability. It's truly Nero fiddling while Rome burns. Good luck with your paper. Archaeology abounds with object lessons in sustainability (again,the Maya, who created fertile, floating islands on which to plant crops). Perhaps more important than this make-work paper, you should find high ground in an area of reliable rainfaill. Good luck.