Chemical weathering is the process by which rocks are broken down by chemical reactions. There are different types of chemical weathering. Hydrolysis is the chemical breakdown of a substance when combined with water. The most common example of hydrolysis is feldspar in granite rocks changing to clay.
Racially Africans originated in Africa, Europeans in Europe and so on. (before that the human species originated in Africa, but that's ancient history) African Americans are an ethnic group, or a subrace of the African race.
The history of Africa begins with the emergence of Homo sapiens in East Africa, and continues into the present as a patchwork of diverse and politically developing nation states. The recorded history of early civilization arose in Egypt, and later in Nubia, the Sahel, the Maghreb and the Horn of Africa.During the Middle Ages, Islam spread through the regions. Crossing the Maghreb and the Sahel, a major center of Muslim culture was Timbuktu.uropean colonization of Africa developed rapidly in the Scramble for Africa of the late 19th and early 20th centuries. It is widely believed that Africa had up to 10,000 different states and autonomous groups with distinct languages and customs before it was colonized.