【正文】 本文與TPO中Orientation and Navigation一篇較為對應，可作為參考。最后還有一些動物靠磁場導航。最開始金星和地球性質相似，后來因為地球較太陽更近，溫度高，逐漸蒸發(fā)，造成不同。Great PlainsThe northern and southern Great Plains are a broad expanse of flat land, much of it covered in prairie,steppe and grassland,which lies west of the Mississippi River and east of the Rocky Mountains in the United States and area covers parts of the . states of Colorado, Kansas, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, and Wyoming, and the Canadian provinces of Alberta, Manitoba and Saskatchewan.The Canadian portion of the Plains is known as the Prairies. Some geographers include some territory of Mexico in the plains, but many stop at the Rio Grande. The region is known for supporting extensive ranching and agriculture.GeologyThe Great Plains are the westernmost portion of the vast North American Interior Plains, which extend east to the Appalachian Plateau. The United States Geological Survey divides the Great Plains in the United States into ten physiographic subdivisions:During the Cretaceous Period (14565 million years ago), the Great Plains was covered by a shallow inland sea called the Western Interior Seaway. However, during the Late Cretaceous to the Paleocene (6555 million years ago), the seaway had begun to recede, leaving behind thick marine deposits and a relatively flat terrain where the seaway had once occupied.Paleontological finds in the area have yielded bones of woo