You may have seen it in the early spring in the north. The earth has just recovered, the river has just thawed, and large pieces of ice on the river collide and move. The power of their movement comes from the flow of the river under their feet. Can people imagine that the surface of the earth where we live is similar to this scene? The endless earth is not monolithic, but also made up of many small pieces. Just like the big ice cubes on the river, they are constantly moving and colliding, but this movement is slow and invisible to the naked eye. For example, the annual sea level rise 1 cm can't be observed without measuring instruments. If it passes 1000, it will rise 1 m! Some big coastal cities may be flooded.
Wei Gena is the founder of continental drift theory. Wei Gena, German, was born in Berlin in 1880. He is a doctor of astronomy. But it was this man who strongly shook the foundation of traditional geology, but he was not a geologist. Mainly as a meteorologist, how did he put forward the idea of continental drift? In his book The Origin of Land and Sea, he described it as follows: "The idea of continental drift was first obtained by the author in 19 10. Once, when I was looking at a map of the world, I was attracted by the similarity between the two sides of the Atlantic, but I gave up immediately at that time and felt that it was of little significance. In the autumn of 19 1 1, by chance, I saw a passage in a collection of essays: According to the evidence of paleontology, Brazil and Africa were once connected by land. This is something I didn't know before. This written record prompted me to make a hasty study of this problem within the scope of geodesy and paleontology for this goal, and I came to an important positive argument, from which I was convinced that my idea was basically correct. " Wei Gena published his research for the first time.
The hypothesis of split continental drift in America, Europe, Africa and Greenland originated from the matching of continental geometry. Then, Wei Gena made a lot of outstanding arguments on it from the aspects of geology, biology, paleontology and paleoclimatology, thus making it a scientific hypothesis in geology. But at that time, it was criticized and opposed by most scholars and gradually forgotten.
In the 1960s, the research results of paleomagnetism awakened people's memory of the continental drift hypothesis, strongly supported the drift hypothesis, and made most geologists in the world admit this theory and put it into vigorous research.
Just talk about what paleomagnetism is. The earth's magnetic field has existed for a long time. In ancient times, the earth's magnetic field magnetized ferromagnetic substances in rocks. For example, igneous rocks, that is, magma ejected during volcanic eruption, will be magnetized by the geomagnetic field at that time during the cooling process. This part of residual magnetic field remains to this day, which is called natural remanence. The example given here is a kind of natural remanence: thermal remanence, collecting suitable rock samples, measuring its geological age by radioactive method, and then measuring the magnitude and direction of remanence by micro-magnetometer, we can know the geomagnetic field at that time. The science of studying geomagnetic field in this way is paleomagnetism.
The Evolution of Pan-continent from 65438 to 0954 blackett, a British geophysicist and Nobel Prize winner, and his team studied the Triassic red sandstone fossil magnetic blocks in Britain and found surprising results. They calculated that the position of the geomagnetic pole at that time would deviate from the geographical pole of the earth by as much as 30; At the same time, the magnetic dip angle of Triassic England is about 34, which is more than 30 smaller than the current 65 dip angle in this area. The great difference between the present and Triassic relative positions in this area can only be explained by the movement of England itself. This explanation is so close to the hypothesis of continental drift put forward by Wei Gena, which encourages blackett to continue to explore the mystery of continental drift.
Blackett's explanation of paleomagnetism research results is based on the hypothesis of axial dipole, and the average position of paleomagnetism poles is taken as a reference for studying continental movement. On the contrary, another group of paleomagnetism experts, represented by Langken, used paleomagnetism research methods to explore the paleomagnetism pole shift with each continent as a fixed reference. But the ruthless facts forced them to give up the original assumption: the mainland's position remains unchanged. After many explorations, they finally formally admitted that only Wei Gena's continental drift theory can satisfactorily explain their achievements. Two paleomagnetic research groups, blackett and Langkern, studied from completely different starting points and reached the same conclusion: the continent drifted.
Now, for an interesting example, there is a string of volcanic islands in the Pacific Ocean, and their volcanic eruption time has a good order. This can be explained by continental drift: the upper continental plate is drifting, there is a fixed point below the plate, and the volcanic lava below is regularly ejected. It's like having a gun fixed under a piece of paper, firing it every once in a while and punching a hole in the paper, while the paper keeps moving horizontally, resulting in a series of intermittent holes in the paper.
The migration track of paleomagnetic poles The epicentres of most earthquakes in the world are distributed in some narrow strips, which actually outline the outline of the plate. For example, if the Pacific plate and adjacent plates are pressed against each other and an earthquake occurs, then there will be an earthquake zone around the Pacific Ocean.
Where does the power of plate movement come from? It's time to look under the earth's crust. Compared with the hard crust, there is a "asthenosphere" in the upper mantle. Below the ocean, this "asthenosphere" begins at a depth of about 60 kilometers, while below the mainland, it begins with mantle convection at a depth of 120 kilometers and reaches a depth of 200-250 kilometers. In the "asthenosphere", the hot material below rises from the bottom, then diffuses and cools, and finally sinks as a relatively dense material. This cycle will bring the rigid crust and crust of the upper mantle from the hot rising area to the cold sinking area, thus forming a convection system. It is this convection that becomes the driving force of plate movement.
The emergence of plate theory is undoubtedly an outstanding achievement and great progress of modern earth science, and it is a well-deserved second revolution of geological science. The first revolution in geological science was the theory of geosyncline and platform. It can be said that we are in an era of knowledge explosion, and the accumulated data and progress of geological science in the past 20 years have exceeded that in any previous 200 years. A series of new ideas and concepts are breaking through the pattern of plate tectonics and making great progress in explaining tectonic phenomena that plate theory cannot explain. These new ideas and concepts have merged into a huge trend, which is surging all over the world, opening the prelude to the third revolution of geological science.