地球内部过程 Plate Tectonics The Topography of the Sea Floor: 000620233040247950 8O 165 Bt/ 916卷 illion Years B. P Figure 3.9 Age distribution of the sea floor, Note relative spreading rates of Mid-Atlantie Ridge(Slower) and East Pacilie Rise n by wider color bands in the Pacific Seafloor relief is superimposed in grey on age data. Souree MarineGeologyan. eophysics Division of the NOAA National Geophysical D)ata Center. 环境迪顶学 minoucntalocelogu ,率
地球内部过程 • Plate Tectonics The Topography of the Sea Floor：
地球内部过程 Plate Tectonics I Figure 3.10 goods pait Magnetic north, however, has not -cm always coincided with its present position. In the early 1900s scientists investigating the direction of magnetization of a sequence of volcanic rocks in France discovered some flows that appeared to be magnetized the opposite direction from the rest: their magnetic minerals pointed south instead of north Confirmation of this discovery in many places around the world led A to the suggestion in the late 1920s that the earth's magnetic field had flipped翻动," or reversed polarit!y; that is that the north and south poles had switched转换 places During the time those surprising rocks had crystallized. a compass needle would have pointed to the 环境地质学∠wwe, not north tic so ,率
地球内部过程 • Plate Tectonics Magnetic north, however, has not always coincided with its present position. In the early 1900s, scientists investigating the direction of magnetization of a sequence of volcanic rocks in France discovered some flows that appeared to be magnetized in the opposite direction from the rest: their magnetic minerals pointed south instead of north. Confirmation of this discovery in many places around the world led to the suggestion in the late 1920s that the earth’s magnetic field had “flipped翻动,” or reversed polarity; that is, that the north and south poles had switched转换 places. During the time those surprising rocks had crystallized, a compass needle would have pointed to the magnetic south pole, not north