Geologists have long known that around 155 million years ago, a 5,000 km long piece of continent broke off western Australia and drifted away. They can see that by the 'void' it left behind: a basin hidden deep below the ocean known as the Argo Abyssal Plain. The underwater feature also lends its name to the newly formed continent: Argoland. The structure of the seafloor shows that this continent must have drifted off to the northwest, and must have ended up where the islands of Southeast Asia are located today.