By the Oligocene, the eroding had reached its peak. Two thirds of the present New Zealand was flooded over, leaving only a thin archipelago. As can be imagined, life on land was hard at this time. Animals may have coped by developing different species. Other species, trapped on islands, "developed separate geographical races". The soil was probably leached, making plant life strenuous. Due to arduous nature of life on New Zealand at the time, only the toughest plants and animals survived, clinging to the last remains of the land.