Since when?Last i checked we were an island continent,sharing no borders,and California is closer to NK than Australia is.If you mean due to proximity,then Hawaii is part of Asia too:P.And btw,i dont think it's safe to say no one would like to see Sydney nuked,Australia isnt so far behind the US when it comes to hostility from most of the world.
Maybe 20,000,000 years ago I am guessing.
It all depends on how one talks of "Asia". If "Asia" means only "East Asia" or rather "North East Asia" then no they are not in there.
If Asia is meant as most mean it, yes they are. As is Hawaii. The "Asia Pacific" or "Pacific Rim" could be debated on semantics also.
Australia is just across the way from South East Asia. Continental Australia is about 400 miles from Timor.
But hey, depending on the definition Indonesia might not be in "Asia" either.
They are all neighbors. What the hey...