Eucalypts began between 35 and 50 million years ago, not long after Australia and New Guinea separated from the rest of Gondwana. Their coming coincides with an increase in fossil charcoal deposits (which might mean that fire was important to them even then). They stayed a minor component of the rainforest until about 20 million years ago, when the gradual drying of the continent and lessening of soil richness led to the growth of a more open forest type, with mainly "Casuarina" and "Acacia" trees. With the arrival of the first humans about 50 thousand years ago, fires became much more frequent and the fire-loving eucalypts soon came to account for roughly 70% of Australian forest.