main idea. A. The plants and animals collected during the eighteenth- and nineteenth-century voyages of discovery made it possible to advance important scientific theories. B. By 1828, fossils of Glossopteris had been discovered to have inhabited both the Northern and Southern Hemisphere continents in the remote geological past. C. To explain the observed distribution patterns of flora and fauna, scientists hypothesized that land bridges had linked the widely separated Southern Hemisphere continents in the geological past. D. The theory of continental drift, proposed in 1912, held that the Southern Hemisphere continents once formed an unbroken landmass and subsequently moved apart to their present locations. E. To support their hypothesis that continents are not fixed in their relative positions, Alfred Wegener and Alex Logan du Toit used paleomagnetic evidence to develop the theory of plate tectonics. F. Continental drift explained the distribution of organisms as well as the similarities in rocks and the geometric fit of Africa and South America, but the theory was not generally accepted until the 1960s.