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 prevailing theory about the origin of indigenous Americans is that they came to the continent from Asia thousands of years ago, which would make purely indigenous Latinos ... Asian. That's a concept that would make some Asians laugh. And, well, most Latinos are mixed with European blood, though plenty of Jews, Germans, Austrians and Japanese (none of them races unto themselves) ended up south of the border too, particularly in the last 200 years.