Australia's unusual fauna and flora is due to the continent having been isolated for millions of years. Continental drift tore Australia away from Africa and Antarctica and sent it on a 45 million year journey northwards. The original mammal passengers on this journey were the marsupials and egg layers (the monotremes). About 15 million years ago, as Australia drifted closer to Asia, rodents floated and bats flew over the sea to become the first placental mammal colonists. The journey north combined with global cooling to dry Australia out and give rise to its characteristic drought and fire-resistant plants.

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