Tham khảo tài liệu 'earth sciences - notable research and discoveries part 2', khoa học tự nhiên, địa lý phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 4 EARTH SCIENCES The uppermost layer of Earth called the crust contains the mountains plains and deserts of the continents and the seafloor. Most of the rocks of the crust are composed of silicates compounds containing the elements silicon Si and oxygen O such as silica SiO2 a molecule which consists of one silicon atom and two oxygen atoms. Sand and quartz are common examples. Another common silicate known as olivine contains iron and magnesium along with silicon and oxygen. In terms of chemical elements the weight of Earth s crust is about 46 percent oxygen 28 percent silicon 8 percent aluminum 6 percent iron 4 percent magnesium and a small percentage of other elements. Major features such as mountains do not seem to change much in a human lifetime yet Earth is a dynamic place. The top of Mount Everest which soars more than 29 030 feet 8 850 m above sea level is rich in Despite seemingly permanent features such as Mount Rushmore in South Dakota Earth is constantly albeit slowly changing. William Walsh iStockphoto Exploring Earth s Depths 5 limestone a sedimentary rock that contains marine fossils and was once under water In 1912 the German researcher Alfred Wegener 1880-1930 noticed that the coasts of continents such as Africa and South America seemed to fit together and displayed remarkable similarities in the kind of fossils they contained as if these now-separated continents were once adjoined. He proposed the notion of continental drift and hypothesized that continents had once been joined. Wegener had a difficult time convincing people that something as massive as a continent moves and he was wrong as it turned out in some of his ideas Wegener was unable to propose a viable mechanism by which continents move and he incorrectly believed continents float across oceans. But anyone who has ever lived through an earthquake knows the ground can certainly move. SEISMIC WAVES Wiechert Wegener and other researchers encouraged their colleagues to reexamine assumptions
