Mainly studying atmospheric thermodynamics and paleometeorology. 19 12 put forward the hypothesis of crustal movement and the distribution of oceans and continents-"the theory of continental drift". According to the very similar data on both sides of the Atlantic Ocean, especially on the coasts of Africa and South America, he thought that the Si-Al layer of the earth's crust floated on the Si-Mg layer, and assumed that the continents of the world were a unified whole (Pangaea) before the Paleozoic Carboniferous, surrounded by vast oceans. Later, especially at the end of Mesozoic, Pangu continent broke into several pieces under the action of tidal force of celestial bodies and centrifugal force generated by the earth's rotation, and drifted away on the silicon-magnesium layer, gradually forming the distribution of continents and oceans in the world today. However, this hypothesis is difficult to explain some big problems, such as the dynamics of continental movement, deep earthquakes and orogenic structures. [2]
Continental drift theory
Main evidence: the existence of Pan-continent and the rupture of the continent.
The evidence of drift mainly includes:
The coastlines on both sides of the Atlantic correspond to each other.
In particular, the right-angle projection of the eastern end of Brazil is very consistent with the Gulf of Guinea, which is a right-angle depression on the west coast of Africa.
② Structural echo on both sides of the Atlantic Ocean
America is similar to Africa and Europe in stratum, rock and structure. For example, the wrinkled mountain system in Newfoundland, North America corresponds to the wrinkled mountain system in Scandinavia, northwest Europe, both of which belong to the early Paleozoic orogenic belt; The tectonic orientation, rock sequence and fossils contained in the southern tip of Africa and southern Argentina in South America were consistent in the Late Paleozoic.
③ Adjacent continents.
Especially on both sides of the Atlantic. For example, the Carboniferous-Permian strata in Brazil and South Africa all contain a reptile, the middle dragon fossil, which lives in fresh water or brackish water, but it has not been found in other parts of the world so far. For another example, fossil ferns mainly growing in cold climates are widely distributed in the Carboniferous-Permian system in Africa, South America, India, Australia, Antarctica and other continents. But these continents are located in different climatic zones.
④ Carboniferous-Permian
Glaciation occurs widely in South America, central and southern Africa, India and Australia. Except South America and Antarctica, these areas are all in tropical or temperate regions. At the same time, in the vast areas of the northern hemisphere except India, no exact remains of late Paleozoic glaciers have been found, but many biological fossils with warm climate have been seen. This shows that the continents with ancient glaciers were connected at that time and became a unified continent.
⑤ The development of modern science
Provide more direct evidence for continental drift: accurate geodetic data confirm that the continent is still moving slowly and continuously horizontally; Paleomagnetic data show that the positions of many continental blocks do not represent their initial positions, but have undergone long or short migrations.
Continental drift theory is an active theory, which challenges the fixed theory, lays the foundation for the establishment and development of plate tectonics, and plays a great role in promoting the development of earth science. However, the mechanism of continental drift has not been solved so far.
The formation of continental drift theory
Development history
The theory of continental drift was put forward by Alfred Wegener (1880- 1930) in an important academic paper 19 12, and was developed and developed in a monograph (19 15) published several years later. Almost immediately, people realized that this assumption was potentially revolutionary, because it needed to revise all the foundations of geography. In the 1920s and 1930s, geographers extensively discussed the concept of continental movement, and as a result, the opposition was almost unanimous. Therefore, Wei Gena's theory of earth drift has been in what I call a theoretical revolution for a long time, and it was not until the mid-1950s that the new evidence constantly discovered became more and more favorable to the hypothesis that the mainland might move. But it was not until the 1960s that there was a real revolution in earth science.
Historical analysis
Historical analysis shows that the earth science revolution ended the theoretical revolution for half a century only because people reluctantly accepted a set of ideas or theories that had been dormant or abandoned earlier. This scientific revolution is accompanied by the emergence of new means to study the earth and new technologies to spread knowledge. Not only many earth scientists think along unconventional routes, but also many physicists have devoted themselves to the research of earth science and made great discoveries. Therefore, the ultimate earth science revolution is not only a simple resurrection of the long-resisted continental drift theory, but also a fundamental change of traditional concepts, and it also creates a new plate tectonic theory to describe continental drift. In a sense, Wei Gena's initial theory did not lead to a scientific revolution, but the final scientific revolution did embody the central idea of continental movement in Wei Gena's theory and the concept of dividing the surface into two types of regions (land and seabed).
main feature
One of the most prominent features of this revolution is that geographers engaged in subject research generally realize that they are experiencing a revolution in earth science. Many scientists write articles or monographs, emphasizing the revolutionary changes in the way of thinking of the mainland and the earth; Their books all have eye-catching titles, such as "Earth Science Revolution: From Continental Drift to Plate Tectonics" (Haram 1973) or "Severe Times of Earth Science Revolution" (Glen 1982). Emphasizing revolutionary is not only the characteristic of later historical or critical articles and books, but also the characteristic of academic papers in the era of earth science revolution. For example, the title of an innovative academic paper (Opdycke 1966) in Science magazine is "Paleomagnetic Research on Deep Sea Core in South China Sea" and the subtitle is "Revolutionary Method for Determining the Time of Earth Historical Events". 1970, when discussing "a new mistake", J.T. Wilson claimed that the discovery of geomagnetic inversion constituted a "revolution" in earth science. In the final report (1972) of the Upper Mantle Project (U.M.P.), the "unified concept of plate tectonics put forward by U.M.P. during its implementation" was described as a "revolution" in earth science (Sullivan1974,343).
detailed inspection
Wei Gena is famous for advocating the theory of continental drift. In his immortal book The Formation of the Continent and the Ocean, he tried to restore the relationship among geophysics, geography, meteorology and geology, which was separated by the professional development of various disciplines, and demonstrated the continental drift with a comprehensive method. Wei Gena's research shows that science is an exquisite human activity, not a mechanical collection of objective information. When people are used to explaining facts with popular theories, only a few outstanding people have the courage to break the old framework and put forward new theories. However, due to the limitation of the scientific development level at that time, continental drift was criticized by orthodox scholars because of the lack of reasonable dynamic mechanism. Wei Gena's theory has become an idea that transcends the times.
As early as 1620, British philosopher and politician Francis Bacon observed on the map that the east coast of South America and the west coast of Africa could be perfectly connected. Although Bacon shouted the famous saying "knowledge is power", he was not a real scientist. He just expressed his thoughts on the two continents, and did not try to find evidence to prove that the two sides had ever been in contact. It is understandable that people before Bacon didn't think of this, because Columbus discovered America in 1492, and the map at that time was full of mistakes. It was only in Bacon's time that the coastlines on both sides of the Atlantic were drawn decently. But nearly 300 years after Bacon, no scientist has seriously thought about why the land on both sides of the ocean can be put together in perfect harmony. Many people may have doubts in their hearts, but they have not put them into action. In the end, history awarded the honor to a German.
19 10 One day, a young German meteorologist Wei Gena was in poor health and was lying in a hospital bed. Bored, his eyes rested on the map of the world on the wall. He was surprised to find that the contours of the two sides of the Atlantic Ocean are so corresponding, especially the right-angled protruding part at the eastern end of Brazil, which is very consistent with the Gulf of Guinea, which is recessed into the west coast of Africa. From then on to the south, every prominent part of the Brazilian coast just corresponds to the bay with the same shape on the west coast of Africa; On the contrary, every bay along the coast of Brazil has a corresponding prominent part on the west coast of Africa. Is this a coincidence? The young scientist suddenly flashed an idea in his mind: Did the African continent and the South American continent ever stick together, that is, there was no Atlantic Ocean between them before, because the original continent was split and drifted by the component of the earth's rotation, which formed the present land-sea distribution?
The following year, Wei Gena began to collect information and test his ideas. He first tracked the mountains and strata on both sides of the Atlantic Ocean, and the results were encouraging: the folded mountains in Newfoundland, North America echoed the mountains in Scandinavia, indicating that North America and Europe had had close contact before; The fold belt of Appalachian mountains in the United States, whose northeast end sinks into the Atlantic Ocean and extends to the other side, reappears in western England and central Europe; The distribution area of ancient rocks in West Africa (more than 2 billion years) can be connected with the ancient rocks in Brazil, and the rock structure and structure between them are also consistent; The stratum corresponding to Mount Kepler at the southern tip of Africa is the rock in the mountain area near Buenos Aires, the capital of Argentina in South America.
Alfred Wegener made a very simple metaphor for this. He said, if two torn newspapers can be spliced according to their jagged rough edges and the printed words on them can be connected with each other, we have to admit that these two torn newspapers were torn from a complete newspaper. In addition to the evidence on both sides of the Atlantic, even between Africa and Indian, Australian and other continents, Wei Gena also found the connection between strata and structures, which was limited to those before Mesozoic, that is, 250 million years ago. It seems that the newspaper has a large layout.
Wei Gena, immersed in joy, examined the fossils in the rocks. Before him, paleontologists had discovered that some continents separated by oceans were closely related. For example, Zhonglong is a small reptile that lived in fresh water on land in ancient times. It is found in the strata formed from Carboniferous to Permian in Brazil, and also in similar strata in Carboniferous and Permian in South Africa. So far, no such animal fossils have been found on other continents in the world. How did the dragon living in fresh water swim across the Atlantic Ocean made of salt water?
More interestingly, there is a kind of garden snail, not only in Germany and Britain, but also in North America across the Atlantic. Snails are famous for walking slowly, but they have the ability to cross the thousands of waves of the Atlantic Ocean and spread from one shore to the other. At that time, there were no airplanes and ships invented by human beings, and there were not even birds on the earth. How did the snail get there?
Let's take a look at the plant fossil-Tongyangya, which is an ancient fern widely distributed in the Late Paleozoic strata in Australia, India, South America, Africa and other places, that is, the continent relatively south on the modern map. Plants have no legs and can't swim. How can they cross the ocean?
In order to explain these phenomena, paleontologists put forward the "land bridge theory" before Wei Gena. They imagined that in the ocean between these continents, there was once a long and narrow land or a series of islands connecting distant continents, and animals and plants traveled thousands of miles to another continent through a continental bridge; Later, these land bridges sank and disappeared, and the mainland was completely separated by the sea. This view is called "fixation theory", that is, the mainland and the ocean are fixed. Wei Gena's explanation is "activity theory". The similarity of paleontological characteristics between continents is not because there is any land bridge between them, but because these continents are directly connected, and only later did they split, drift and go their separate ways. The debate between fixed theory and activity theory, together with the debate between deep formation theory and water theory, and the debate between gradual change theory and sudden change theory, is called the three major debates in geology. As a pioneer of radicalism, Wei Gena was almost alone at first.
The distribution of ancient glaciers also supports Wei Gena's view. In the Late Paleozoic, large-scale glaciation occurred in South America, Africa, Australia, India and Antarctica about 300 million years ago. In some areas, the flow direction of ancient glaciers can be judged from the scratches of glaciers. Judging from the scale and characteristics of the distribution of glacial remains, the type of glaciers at that time was continental glaciers produced near the polar regions. Moreover, the remains of ancient glaciers in South America, India and Australia remain on the continental margin, and the direction of glacier movement is from the coast to the inland. Obviously, glaciers will not fall or move to high places, which shows that the ancient glaciers on these continents are not indigenous. Faced with the distribution and flow characteristics of this ancient glacier, geologists in the past were at a loss. However, it is these characteristics that provide strong evidence for the theory of continental drift.
In Wei Gena's view, continents with ancient glaciers were connected at that time, and the whole continent was located near the South Pole. Glacier center is located in southern Africa, and ancient continental glaciers flow radially from the center in all directions, which reasonably explains the distribution and flow characteristics of ancient glaciers. The emergence of glaciers moving inland is actually because the original huge continent has split and the original inland has become a coastal area.
In addition to the remains of ancient glaciers, paleoclimatic indicators such as evaporated salt and coral reefs can also be used to infer the paleolatitude when they were formed. The ancient latitude and the location of the mainland are in conflict, which also shows that the previous continent is not the location of today.
The evidence seems to be sufficient. On the basis of rigorous scientific research, Wei Gena's masterpiece The Origin of Land and Sea was published in 19 15. In this book, Wei Gena expounded the view that the ancient continents were originally united, but later separated due to continental drift, and oceans appeared between the separated continents. According to Wei Gena, the mainland is composed of light siliceous and aluminous rocks such as basalt, which, like huge icebergs, float on heavy siliceous and magnesian rocks such as granite (the seabed is composed of siliceous and magnesian) and drift on it. In Permian, there was only one huge land in the world, which he called Pangaea (or United ancient land). After the calm Permian, the turbulent Mesozoic began. Pan-continent was first divided into two parts, with Lauea in the north and Gondwana in the south, and gradually split into several smaller lands, scattered and drifted, and some of them regrouped, eventually forming today's land-sea pattern.
Wei Gena's "rock-breaking" view immediately shocked the scientific community at that time, attracting far more attacks than support. On the one hand, the problems involved in this hypothesis are too grand. If established, the whole earth science theory will be rewritten. There must be enough evidence, and every link of the hypothesis must stand the test; On the other hand, Wei Gena received a doctorate in astronomy at the university, mainly studying meteorology. He is not a geologist, geophysicist or paleontologist. If you express your opinions in a field other than your own, people will inevitably doubt the scientific nature of their assumptions.
1912-1913 winter in Greenland.
The main weakness of Wei Gena's theory is: What is this huge continent drifting? Where does the driving force of continental drift come from? Wei Gena thinks that the silicon-aluminum continent floats on the earth's silicon-magnesium layer, that is, the solid floats and moves on the solid. As for the power to push the mainland, Wei Gena guessed that the tides in the ocean beat the coast of the mainland, causing tiny movements and drifting the huge land into the distance with the passage of time; It may also be the gravity of the sun and the moon. According to Wei Gena, physicists at that time immediately began to calculate the quality of land by using its volume and density. Then, according to the friction between aluminosilicate rocks and silicomagnesian rocks, how much force is needed to make the continent move. Physicists found that the gravity of the sun and the moon and the tidal force were too small to push the vast continent.
When the continental drift was said, it was a sensation, but it soon disappeared in ridicule. Although Wei Gena has found a lot of evidence, if others find evidence against this scientific theory, such as the lack of motivation for continental drift, this theory can only be called a hypothesis, not a real theory. When people explain the distribution of ancient creatures such as dragons, tongues and ferns, they still use continental bridges to prevaricate. Although the land bridge theory seems absurd, at that time, people thought that there was another theory that was even more absurd, and that was Wei Gena's continental drift theory. Some people joke that the theory of continental drift is just "the dream of great poets".
Only Wei Gena sings his own poems alone. 1930, when Wei Gena visited Greenland for the fourth time, he was unfortunately buried in the ice and snow. He was only 50 years old, and his body was found the next summer. He left a little early, because a German scientific research ship just returned from the Atlantic Ocean, bringing a message that there is a long mid-ocean ridge in the middle of the Atlantic Ocean, where there is a huge rift valley. With Wei Gena's extensive knowledge, it will be possible for him to find a solution to the dynamic problem of continental drift, and the movement of the seabed will provide clues for continental drift. It's a pity that he is cut off from the news forever. Like many scientists who were ahead of the times, he was born a little earlier and could not wait until his theory was accepted by the world. Perhaps, only the lonely land of ice and snow can understand Wei Gena's loneliness before his death. Wei Gena's soul was frozen in the snow in Greenland, and the theory of continental drift was dusty on the library shelves.
1912 65438+16 October, Wei Gena delivered a speech entitled "the origin of the continent and the ocean" and put forward the hypothesis of continental drift. After that, I went to Greenland for the second time to study glaciology and paleoclimatology. In the subsequent World War I, his research work was interrupted and he was seriously injured on the battlefield. During his illness, he published the book Origin of Land and Sea in 19 15, which systematically expounded the theory of continental drift.
As soon as the theory of continental drift was put forward, it caused an uproar in the field of geology. The younger generation cheered for this theory, thinking that it had created a new era of geology, while the older generation did not recognize this new theory. Wei Gena continued to collect evidence against his theory, so he visited Greenland twice and found that Greenland was still drifting relative to the European continent. He measured the drift speed of about 1 m per year. 1930 In April, facing the snowstorm in the Arctic, Wei Gena led an expedition to visit Greenland for the fourth time. In the cold of-65℃, most people lost their courage, only he and two other followers continued to move forward, and finally successfully reached the Esmit base in the middle. 1 65438+1October1,he ventured back to the west coast base after celebrating his 50th birthday. 1930165438+1On October 2nd, Wei Gena was hit by a snowstorm when he visited Greenland for the fourth time and fell on the vast snowfield. He lost his way in the white ice and snow. His body was not found until the following April. He froze like a stone and merged with the glacier.
Six plates
From 65438 to 0968, French geologist Lei Bixiong put forward the viewpoint of six plates on the basis of previous studies, namely Eurasia plate, Africa plate, America plate, India plate, Antarctic plate and Pacific plate. Plate theory solved the problem of drift dynamics that Wei Gena could not solve before his death, and made geology comprehensive to a new height. With the establishment of plate movement as the basic form of earth geological movement, earth science has entered a new stage of development. The continents will unite and separate for a long time, and the oceans will sometimes expand and close, which has become a recognized crustal structure map. In the 1980s, people really believed that the proposition of continental drift theory and the establishment of plate theory constituted a truly great revolution in the field of modern earth science.