What object did ptolemy claim was at the center of the universe

How do convection currents form underwater mountains?

How have ethnic groups shaped the population in central america and the caribbean? how has migration shaped the population in central america and the caribbean? how has small land areas shaped population in central america and the caribbean? how has a rapid population growth shaped the population in central america and the caribbean?

The first atomic explosion was detonated in the desert north of alamogordo, new mexico, on july 16, 1945. what percentage of the strontium-90 ( yr) originally produced by that explosion still remains as of july 16, 2016?