The oldest rocks in the group are in the north west of Scotland, Ireland and North Wales and are 2,700 million years old. During the Silurian period the north-western regions collided with the south-east, which had been part of a separate continental landmass. The topography of the islands is modest in scale by global standards. Ben Nevis rises to an elevation of only 1,344 metres (4,409 ft), and Lough Neagh, which is notably larger than other lakes on the isles, covers 390 square kilometres (151 sq mi). The climate is temperate marine, with mild winters and warm summers. The North Atlantic Drift brings significant moisture and raises temperatures 11 °C (20 °F) above the global average for the latitude. This led to a landscape which was long dominated by temperate rainforest, although human activity has since cleared the vast majority of forest cover. The region was re-inhabited after the last glacial period of Quaternary glaciation, by 12,000 BC when Great Britain was still a peninsula of the European continent. Ireland, which became an island by 12,000 BC, was not inhabited until after 8000 BC. Great Britain became an island by 5600 BC.