(The separation rate is actually about 2.5 cm per year.) Figure 4.5 Carboniferous and Permian Karoo Glaciation in the southern hemisphere. He also cited evidence (based on his own astronomical observations) that showed that the continents were moving with respect to each other, and determined a separation rate between Greenland and Scandinavia of 11 m per year, although he admitted that the measurements were not accurate. He argued that this could only have happened if these continents were once all connected as a single supercontinent. Wegener also called upon evidence for the Carboniferous and Permian (~300 Ma) Karoo Glaciation from South America, Africa, India, Antarctica, and Australia (Figure 4.5). Figure 4.4 Diagram from Alfred Wegener’s book Die Entstehung der Kontinente und Ozeane comparing rock types on Canadian Arctic Islands and Greenland. He relied heavily on matching geological patterns across oceans, such as sedimentary strata in South America matching those in Africa, North American coalfields matching those in Europe, the mountains of Atlantic Canada matching those of northern Britain-both in structure and rock type-and comparisons of rocks in the Canadian Arctic with those of Greenland (Figure 4.4). Wegener pursued his idea with determination, combing libraries, consulting with colleagues, and making observations in an effort to find evidence in support of it. Watson, USGS (1999) Public Domain view source During the Permian, the supercontinent Pangea included the supercontinent Gondwana, shown here, along with North America and Eurasia. Figure 4.3 The distribution of several Permian terrestrial fossils that are present in various parts of continents now separated by oceans. He described the motion of the continents reconfiguring themselves as continental drift. Wegener envisioned a supercontinent made up of all the present day continents, and named it Pangea (meaning “all land”). He concluded that because these organisms could not have crossed the oceans to get from one continent to the next, the continents must have been joined in the past, permitting the animals to move from one to the other (Figure 4.3). In 1911 Wegener happened upon a scientific publication that described matching Permian-aged terrestrial fossils in various parts of South America, Africa, India, Antarctica, and Australia. Source: Alfred Wegener Institute (2008) Public Domain view source
4.1 Alfred Wegener’s Arguments for Plate TectonicsĪlfred Wegener (1880-1930 Figure 4.2) earned a PhD in astronomy at the University of Berlin in 1904, but had a keen interest in geophysics and meteorology, and focused on meteorology for much of his academic career.įigure 4.2 Alfred Wegener during a 1912-1913 expedition to Greenland.
0 kommentar(er)
