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.
1 There were 1.4 million foreign born from Africa residing in the United States in 2007. 2  African immigrants made up 3.7 percent of all immigrants in 2007. 3  About one-third of African immigrants were from West Africa. 4  The top countries of origin for African immigrants were Nigeria, Egypt, and Ethiopia.f the African immigrants residing in the United States in 2007, 10.9 percent were minors (under age 18), 76.3 percent were of working age (between ages 18 and 54), and 12.8 percent were seniors (age 55 or older).