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.
History of African Americans in Chicago. The history of African Americans in Chicago dates back to Jean Baptiste Point du Sableâs trading activities in the 1780s. Du Sable is the city's founder. Fugitive slaves and freedmen established the cityâs first black community in the 1840s. By the late 19th century, the first black person had been elected to office. The Great Migrations from 1910 to 1960 brought hundreds of thousands of blacks from the South to Chicago, where they became an urban population. They created churches ...