From "continental drift theory" to "plate tectonics theory"
The once-denied "continental drift theory"
19 10, someone first asked this question: Why are the coastlines of South America and Africa on both sides of the Atlantic so similar? This man is German geophysicist and meteorologist Alfred Wegener, and this idea became an opportunity for him to put forward the theory of continental drift.
The phenomenon that two banks separated by the ocean have similar coastlines was noticed long ago. Wei Gena made a scientific study of this fact from the perspectives of geology, paleontology and climatology. He pointed out that according to the geological structure of orogenic belts and other small animals, such as ferns and snails, they could not cross the ocean and were widely distributed in South America and Africa during the ice age 300 million years ago. He concluded that about 300 million years ago, all the continents we know today belonged to a "super continent", and later this "super continent" split into several continents. After a long time,
The theory of continental drift put forward by Wei Gena later developed into the theory of plate tectonics and became the mainstream of earth science in the 20th century. The reason why "continental drift theory" has such strong vitality is that it is a theory that can answer many questions in a wide range of fields, including paleontology, paleoclimate, geological structure and topography. However, the book The Origin of the Continent and the Ocean published by Wei Gena in 19 15 is not easily accepted. Although recognized by geologists and paleontologists, it has been despised by most geophysicists, and some people have put forward a weighty rebuttal.
The main argument of the opponents is that the motive force that can make the mainland move thousands of kilometers horizontally has not been found. Although geologist Alsa Holmes thinks that mantle convection may be the driving force of continental drift, with the disappearance of Wei Gena in Greenland exploration in 1930, the theory of continental drift was gradually ignored, so that it was forgotten in the 1940s. The theory of "continental drift" is finally popular again in the spring breeze.
In the 1950s, the "continental drift theory" made a comeback in completely unrelated fields. This completely irrelevant field is the subject of studying the ancient earth's magnetic field-paleomagnetism. Today, the two magnetic poles of the earth-the south magnetic pole and the north magnetic pole-are almost fixed, but with the passage of time, their positions have moved and reversed in the long geological history. According to paleomagnetism, scientists restored the original magnetic field of rocks produced in previous geological periods, and inferred the position of the north and south magnetic poles from this. The trajectory of the magnetic pole moving with time is called "pole shift curve". 1950, British Keith Lancan and Patrick Blancott successfully obtained the "pole shift curve" based on the accurate measurement of the residual magnetic field in rocks of various geological periods in the European continent and the North American continent. The earth has only two magnetic poles: the south magnetic pole and the north magnetic pole, and the "magnetic pole motion curve" of the south magnetic pole or the north magnetic pole studied from all continents should be consistent. However, the two "pole shift curves" obtained by Lankan et al. are similar in shape, but deviate along the meridian direction. If the North American continent and the European continent on both sides of the Atlantic Ocean are combined, the corresponding "pole shift curves" can just coincide. This fact just shows that continental drift is possible. Because the dynamic problems leading to continental drift have not been solved, all earth scientists have always ignored the "continental drift theory", but the "continental drift theory" reappeared because of the discovery of paleomagnetism. "Ocean Expansion Theory" came into being.
In the early 1950s, new technologies developed in World War II were widely used in ocean observation, such as observing seabed topography with sonar devices and detecting seabed magnetic field anomalies with marine magnetic instruments. Through these explorations, scientists finally figured out that the huge undersea mountains called "Hailing" on the global seabed are interconnected.
Wei Gena is no stranger to the central ridge of the Atlantic undersea mountains. However, similar ridges exist in all the oceans of the earth, such as the Pacific Ocean, the Indian Ocean and the Arctic Ocean, and are distributed on the seabed like a network. There is also a "large-scale valley" in the middle of the central ridge, which stretches for more than 654.38+00000 kilometers in the north-south direction in the middle of the Atlantic Ocean. Scientists also found that this "central valley" is connected side by side with the central ridge. So some scientists have suggested that the Atlantic Ocean is a crack in the earth, and the seabed may expand here. Later, scientists measured the crustal heat flow from the interior of the earth, and learned that hot matter seemed to spew out from the depths below the ridge.
According to the above detection results, scientists have concluded that the convection uplift of the mantle under the central ridge forms an oceanic crust and the seabed expands, which supports the "ocean expansion theory" and explains the division and movement of the mainland. When the density of the materials that make up the continental crust is small, the mantle will float. According to the "ocean expansion theory", the convection uplift of the continental lower mantle leads to the division of the continent, and then the horizontal movement of the mantle pushes the continent away.
Since then, scientists from Scripps Institute of Oceanography, University of California, USA have observed geomagnetic anomalies in the Pacific Ocean near the west coast of the United States, which can explain the formation of the seabed crust, and found that there is a magnetic anomaly of 1% in the width of 20 km to 30 km, which is strip-shaped in the range of hundreds of kilometers from north to south. In addition, with the progress of rock dating technology in the same period, scientists have figured out the history of repeated inversion of geomagnetic field in the past millions of years.
1963, Fred Vain and Dramondo Matthews put forward a bold hypothesis: the geomagnetic anomaly zone in California is a reflection of the reversal of the earth's magnetic field. On the central ridge, the submarine crust was formed due to the cooling of high-temperature magma, and rocks with the same magnetic field as that of the earth at that time were also formed. Vain and others believe that the earth's magnetic pole has been reversed many times, and the seabed crust with the characteristics of magnetic field direction in each geological period is striped side by side on the seabed, which is confirmed by observation. Because the seabed extends to both sides of the ridge, if the opinions of Vain et al. are in line with reality, then the observed stripes reflecting magnetic field anomalies should be symmetrical about both sides of the ridge. This symmetry is also confirmed by practical observation. The collected observation data all support the "ocean expansion theory", and according to the data of submarine magnetic field anomaly, the reversal history of the earth's magnetic field currently mastered by scientists is expanded to 200 million years at once. Plate tectonics
Because of the evidence provided by the "pole shift curve" and submarine expansion, continental drift is indeed a fact that is happening. In 1965, scientists used computers to put together the continents on the earth according to their existing shapes. Moreover, Haiti's topography, earthquake location, volcanoes and other active parts are all connected into a strip, so the revolutionary view of "plate tectonic theory" has emerged.
After 1970, the theory of plate tectonics was established. According to this new theory, the earth's surface is covered with undeformed solid plates (crust), and these plates are indeed moving at the speed of 1 cm to1cm every year. Due to the limited surface area of the earth, the earth plates can be divided into three States: one is the boundary of convergent plates close to each other; The second is the boundary of separated plates far away from each other; The third is the boundary of the interlaced transformation plates. The plate itself is not deformed, and the earth's surface activities are concentrated in these three States. For example, ridges are formed under the boundaries of separating plates, while trenches are formed under the boundaries of converging plates, where ocean plates collide with each other and one plate subducts under the other. The San Andreas fault along the west coast of the North American continent was formed under the boundary of a typical transitional plate formed between the Pacific plate and the North American continent plate.
Because it is related to the state around the Pacific plate called "Pacific Rim", earthquakes, deep earthquakes and volcanic activities in this area are very active. Due to the collision between the Indian subcontinent and Eurasia, the Himalayas and the Qinghai-Tibet Plateau were formed. Under the boundary of convergent plates where continental plates collide with each other, the conflict zone between continents is formed, and large folded mountains are also created.
Due to the development of plate tectonic theory, most of the earth activities that have been regarded as mysteries so far have been explained. Since 1970s, the world-scale earth observation aimed at confirming the theory of plate tectonics has developed vigorously. Through these observations, the age distribution of the seabed is determined in detail, and the plate movement process in previous geological periods is clarified. Moreover, due to the development of space observation technology, even the plate movement of one centimeter per year can be observed for several years. Interpret the history of the whole earth.
The theory of plate tectonics confirmed Wei Gena's theory of continental drift. Because the "continental drift theory" depends on plate movement, it solves the dynamic problem of the "continental drift theory" which has long been regarded as an unsolved mystery. However, the theory of plate tectonics cannot understand all the earth's activities. The theory of plate tectonics only confirms the fact of the last 200 million years in the 4.6 billion-year history of the earth. Previous earth activities are still an important research topic today, and the activities in the deep mantle that lead to plate movement need further observation and research.
Since 1980s, scientists have used the technology called "seismic X-ray tomography" to study the uneven structure in the earth by using seismic waves, and have made progress in their research. The results show that the actual state of mantle convection, once considered as the driving force of plate movement, seems to be touchable. As for when the plate structure of the earth began to form in the evolutionary history of the earth, scientists will further study some submarine crusts that are older than 200 million years ago.
The "continental drift theory" put forward by German scientist Wei Gena in the early 20th century was explored and developed in the above tortuous process, until the plate tectonics theory recognized by the scientific community came out in the 1970s. The latest earth observation results provide new clues for solving the mystery of deep mantle and core activities, which are also hesitant about plate tectonics theory, and for clarifying the evolution history of the earth for 4.6 billion years.
Looking back on the development history of earth science in the 20th century, Wei Gena's "continental drift theory" created an opportunity for studying earth activities, and also provided us with a good opportunity to fully understand the earth science fields that have been subdivided into geology, paleontology, observation and seismology. In the above sense, "continental drift theory" has played a pioneering role.