Most experts now believe that the rock art tradition in Africa may go back at least 50,000 years, however the vast majority of the rock art we see today is much more recent than these discoveries. Unlike the rock paintings of Europe which are typically found in deep limestone caves most of Africa's rock paintings are on exposed surfaces and in shallow shelters usually open to heat and cold, sun, wind, rain and natural erosion. Meanwhile the rock engravings and carvings are found out in the open on cliffs and boulders. Except in special circumstances most rock art in Africa is probably not more than 7,000 years old. The likelihood of art surviving any longer in exposed situations is very slim. Exceptions to this may exist in places like Zimbabwe's Matobo Hills and in Algeria's Tassili n'Ajjer where rock paintings have been dated to nearly 10,000 years old and some of Libya's and Algeria's deeply etched engravings may be even older.