The Sahara Desert includes a wide variety of ecosystems. The arid climate and hot weather dominate the eco-system. Within the Sahara Desert there are oasis ecosystems, which have date palm, trees freshwater, and animals such ascrocodiles. The Sahara also has dune ecosystems, with the changing landscape determined by the wind. The animals in these ecosystems such as snakes or scorpions, must be able to survive in sand dunes for long lenghs of time. The Sahara even includes a marine environment, where the Atlantic Ocean creates cold fogs on the Northwest Africa.Shrubs and animals that feed on small trees, such as goats, live in this Sahara ecosystem. Its forbidding landscape took shape over many years ago, but even today, the Sahara Desert is constantly changing. The Sahara since the middle Holocene has destroyed most archives recording its transition from a 'green Sahara' to the present barren desert. Strong reductions in tropical trees and then Sahelian grassland cover allowed large-scale dust mobilization from 4300 calendar years before the present (cal yr B.P.). Today's desert ecosystem and wind system was established around 2700 cal yr B.P.