Australia is a continent which broke off from Gondwanaland (Africa, India, Antarctica and South America). New Zealand is a distinct continental fragment. The Islands of the Pacific are also fragments and include sea mounts - isolated volcanoes rising to the surface.
The Islands of the Atlantic are formed over the Mid-Atlantic Ridge where the plates of Africa and Europe on the east separate from the American plates.
The islands to the north of Australia are included in the Asia section of this work.
Humans entered Australia at least as early as 20,000 years before the present, but then appear to have been isolated from the rest of humanity. From linguistic and genetic evidence the other islands seem to have been settled from the Asian mainland.