托福背景知识：地质学常识

地质学（geology）：地球的物质组成、内部构造、外部特征、各层圈之间的相互作用和演变历史的知识体系，是研究地球本身的学科。 地理学（geography），是一门描述地球表面的科学。地理学描述和发生在地球表面上的自然、生物和人文现象的空间变化，探讨它们之间的相互关系及其重要的区域类型。 一、 地球的内部结构是一个同心状圈层构造，由地心至地表依次分化为地核（core）、地幔（mantle）、地壳（crust）。地球地核、地幔和地壳的分界面，主要依据地震波（earthquake / seismic wave）传播速度的急剧变化推测确定。 二、 从地球的外部结构来看，则可以分成大气圈（atmosphere）、水圈（hydrosphere）、生物圈（biosphere）和岩石圈（lithosphere），岩石圈包括地壳和地幔上部。地球上有七大洲和五大洋，分别是亚洲（Asia），欧洲（Europe），北美洲（North America），南美洲（South America），非洲（Africa），大洋洲（Oceania）和南极洲（Antarctica）；太平洋（Pacific Ocean），大西洋（Atlantic Ocean），印度洋（Indian Ocean），北冰洋（Arctic Ocean）和南冰洋（Antarctic Ocean）。 三、大陆漂移学说（Continental Drift） 大陆漂移学说是有关于地球大陆之间关系的一种假说（hypothesis）。早在1596年，亚伯拉罕·奥特柳思（Abraham Ortelius）首次提出了这个观点，而对于这个观点我们比较熟悉的则是阿尔弗雷德·魏格纳（Alfred Wegener），他于1912年相对完整地提出了这套假说。到了二十世纪六十年代，随着板块构造学说（Plate Tectonics）的发展，大陆漂移学说得到了更多的支持。 如果仔细观察一下世界地图，我们会发现非洲和南美洲的海岸线（coastline）似乎能像拼图一样吻合在一起，早期的科学家们正是发现了这一点，才最终提出了大陆漂移学说。魏格纳提出在中生代(Mesozoic)地球表面存在一个泛大陆（Pangea），这个超级大陆经过了分裂和两亿多年的漂移形成了现在的海洋和陆地。 除了非洲和南美洲海岸线的“锯齿状吻合”，还有很多其他的证据能支持大陆漂移这个观点。魏格纳在研究古代气候的时候发现，各个大陆上存在某一个地质时期形成岩石类型出现在现代条件下不该出现的地区。例如，在南极洲地区出现古珊瑚礁（coral reef）和热带植物（tropical plants）化石（fossil）；在赤道（equator）地区发现有古代冰层。魏格纳还认为，大陆漂移对现代由海洋分隔的各大陆上动物和植物的显著相似性提供了最好的解释。例如中龙（mesosaurus）这种淡水爬行类动物（reptile），在南美和非洲都能找到；存在于南极洲三叠纪（Triassic period）有许多陆生爬行动物的化石在其他大陆同样存在。 板块构造学（Plate Tectonics） 板块构造学说以大陆漂移学说为基础，主要描述了地球岩石圈（lithosphere）的大范围运动。在二十世纪五十年代末六十年代初，海底扩张学说（Seafloor Spreading）发展起来了，大陆漂移学说也因此变得更为可信。1968年法国地质学家勒皮雄和麦肯锡、摩根等人提出了板块构造学说，作为一种新的大陆漂移学说，它是海底扩张说的具体延伸。所谓板块，指的是岩石圈板块，包括了地壳和软流层（asthenosphere）以上的地幔顶部。板块构造学说认为，不论大洋壳（oceanic crust）还是大陆壳（continental crust）都曾发生并且还在继续发生大规模水平运动，岩石圈板块在整个地幔软流层上像传送带般移动着。 1968年勒皮雄将地球的板块分为太平洋板块（Pacific Ocean tectonic plate）、亚欧板块（Eurasian tectonic plate）、非洲板块（African tectonic plate）、美洲板块（American tectonic plate）、印度洋板块（Indian Ocean tectonic plate）（包括澳洲）和南极洲板块（Antarctica tectonic plate）这六大板块，以及一些其他的小板块。这些板块在运动中相互影响，板块交界的地方即板块边界（plate boundaries）可以根据板块边缘的构造、活动性和板块内部整体性分为三种类型：离散型（divergent boundaries）、聚敛型（convergent/collisional boundaries）和剪切型(conservative transform boundaries)。板块边界是地壳上极不稳定的地带，几乎所有的地震（earthquake）都分布在此，火山(volcano)也大多数在边界附近，山脉的形成（mountain building）和海沟（oceanic trench）的出现也都沿着边界进行。 Continental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912. However, it was not until the development of the theory of plate tectonics in the 1960s, that a sufficient geological explanation of that movement was understood. In the 11th century, the Persian geologist, Abū Rayhān Bīrūnī (973-1048), observed the geology of India and discovered that the Indian subcontinent was once a sea and later became land. He attributed this the drifting of alluvium rather than continental drift. Abraham Ortelius (1596), Francis Bacon (1620), Benjamin Franklin, Antonio Snider-Pellegrini (1858), and others had noted earlier that the shapes of continents on opposite sides of the Atlantic Ocean (most notably, Africa and South America) seem to fit together. W. J. Kious described Ortelius' thoughts in this way: Abraham Ortelius in his work Thesaurus Geographicus ... suggested that the Americas were "torn away from Europe and Africa ... by earthquakes and floods" and went on to say: "The vestiges of the rupture reveal themselves, if someone brings forward a map of the world and considers carefully the coasts of the three Wegener and his predecessors The hypothesis that the continents once formed a single landmass, broke up, and drifted to their present locations was fully formulated by Alfred Wegener in 1912. Although Wegener's theory was formed independently and was more complete than those of his predecessors, Wegener later credited a number of past authors with similar ideas: Franklin Coxworthy (between 1848 and 1890), Roberto Mantovani (between 1889 and 1909), William Henry Pickering (1907) ] and Frank Bursley Taylor (1908). For example: the similarity of southern continent geological formations had led Roberto Mantovani to conjecture in 1889 and 1909 that all the continents had once been joined into a supercontinent (now known as Pangaea); Wegener noted the similarity of Mantovani's and his own maps of the former positions of the southern continents. Through volcanic activity due to thermal expansion this continent broke and the new continents drifted away from each other because of further expansion of the rip-zones, where now the oceans lie. This led Mantovani to propose an Expanding Earth theory which has since been shown to be incorrect. Some sort of continental drift without expansion was proposed by Frank Bursley Taylor, who suggested in 1908 (published in 1910) that the continents were dragged towards the equator by increased lunar gravity during the Cretaceous, thus forming the Himalayas and Alps on the southern faces. Wegener said that of all those theories, Taylor's, although not fully developed, had the most similarities to his own. Wegener was the first to use the phrase "continental drift" (1912, 1915) (in German "die Verschiebung der Kontinente" - since Wegener presented and published in German, his ideas did not reach the majority of scientists until 1922, when his book was translated into English) and formally publish the hypothesis that the continents had somehow "drifted" apart. Although he presented much evidence for continental drift, he was unable to provide a convincing explanation for the physical processes which might have caused this drift. His suggestion that the continents had been pulled apart by the centrifugal pseudoforce of the Earth's rotation was rejected as calculations showed that the force was not sufficient. Controversial years Wegener's hypothesis received support from South African geologist Alexander Du Toit as well as from Arthur Holmes, but was not generally supported due to the lack of a known driving force and the absence of other evidence. The possibility of continental drift gradually became accepted by the late 1950s; by the 1960s, geological research conducted by Robert S. Dietz, Bruce Heezen, and Harry Hess, along with a revision of the theory including a mechanism by J. Tuzo Wilson, led to widespread acceptance of the theory among geologists.