Introduced Species and the Australian Environment
- introduced organisms, how they affect the australian environment, how are organisms kept out, that kind of thing
Organic Geology - A Non-renewable Resource
- lots of stuff on rocks, oil and coal, factors that affect them
Mining and the Australian Environment
- mining, mines, effects of mining on the environment, rehabilitation after mining is complete
Oceanography
- oceans, ocean floors, rock types of the opcean floor, collecting data about the ocean
introduced species is probably the simplest topic to do, especially if you couldnt care less about the geology stuff (which most people dont).
like pretty much anything else whats easier depends on what youre good at and what youre interested in.
check out
http://www.hsc.csu.edu.au/earth_environmental/#106009, theres a fair bit on each of the 4 options there so that might help too.