Correct Response: D. The geographic area of the United States was located near the equator and subtropics during the Paleozoic era. The shift in tectonic plates that formed Gondwanaland in the Early Paleozoic and Pangea in the Late Paleozoic is responsible for the tropical climate conditions in the region at that time. The concentration of oxygen in the atmosphere (A) and the intensity of solar radiation (B) during the Paleozoic era were not primarily responsible for the region's tropical climate.
Ocean currents during the 300 million years of the Paleozoic era likely changed dramatically over that time period and certainly must have affected climate. However, it was primarily the geographic location that was responsible for changes in ocean currents and the region's tropical climate (C).
