For more than a decade, false posts on social media have claimed that Australia is a "hoax". The posts claim the continent does not actually exist and that Australia was invented to cover up "one of the greatest mass murders in history" when Britain moved some 162,000 convicts to the southern hemisphere. "If you think you've been to Australia," the posts say, you're wrong -- you've probably been to South America "where they have cleared space and hired actors to act out as real Australians". The claim has also been amplified on "flat earth" websites. Here we look at some of the reasons why Australia's existence is irrefutable.