Migration to the Australian continent for these travellers was a difficult task. Australia is separated from South East Asia by a great expanse of water. During the last Ice Age, the distance was smaller because so much water was locked up in glaciers. But before 50,000 years ago humans would still have faced a voyage across fifty miles of open sea to get to Australia. They must have built sea craft strong enough to survive the voyage, a technological feat that went beyond making spears or lighting fires.