• Although it is tempting to think of these natural landscapes as reflecting a stability in climactic and geologic forces, long periods of climactic and geophysical stability actually result in a rundown of the energy available to ecosystems and people. Geologically young regions with recent mountain building and volcanism tend to be much more biologically productive and have supported large populations of people despite their vulnerability to natural disasters. Geologically old regions (like most of Australia) tend to have low biological productivity and supported fewer people.