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小学自然第五册第二十课中讲道根据“近来,人们在喜马拉雅山发现了海螺的化石”的事实,推断:现在喜马拉雅山脉的广大地区,“在古代,是一片汪洋大海。”那末,喜马拉雅山地区何时曾是海洋呢?我们可用放射性同位素法来进行测定。放射性同位素,就是指某同一种元素的不同原子(原子量不同)能自发地不断地发射出不可见的射线,它们即是放射性同位素。例如钾的同位素,有原子量为39的叫钾——39,有原子量为40的叫钾
According to the fact that “Recently, people found the conch fossils in the Himalayas,” it is inferred that the vast area of the Himalayas today “was an ocean in ancient times.” Then, When was the Himalayas a sea? We can use the radioisotope method to determine. Radioisotopes, refers to the same element of different atoms (atomic weight) can spontaneously emit invisible rays, they are radioactive isotopes. For example, the isotope of potassium, there is an atomic weight of 39 called potassium - 39, there is an atomic weight of 40 called potassium