19 12 In the spring, German meteorologist Alfred Wegener first put forward the theory of continental drift. He believes that the earth and the mainland were once closely connected, and then drifted to the present position. Nowadays, the theory of continental drift and plate tectonics have become the basis of geology, but when Wei Gena first put forward this hypothesis, just like Copernicus put forward "Heliocentrism", it was questioned endlessly.
With a fixed mind, skeptics focus their doubts on two points: first, Wei Gena only found that there is huge energy in the earth's crust, but there is no evidence to show how the plates are connected; Second, he doesn't have a good model to explain how the mainland is divided.
In fact, Wei Gena stumbled upon the theory of continental drift, but his hypothesis was not just an epiphany. Two years ago, when Wei Gena was ill, he carefully observed the map hanging on the wall. He found that the Atlantic coast of Brazil seemed to be in perfect harmony with West Africa, so he cut out the maps of all continents and put them together, trying to show what the mainland used to look like.
At the same time, Wei Gena began to collect evidence of plants and animals on land on both sides of the ocean. He found that not only marsupials in Australia and South America are highly similar, but also parasites. A freshwater reptile named Zhonglong can be found in Permian glacial sediments in South America and Africa, and it can also be found in many other continents. The Appalachian Mountains in the United States and the Caledonian Mountains in Scotland can be merged.
Wei Gena called this once supercontinent Pangea, or Pangea. By 19 15, Wei Gena officially published the book The Origin of the Continent and the Ocean, explaining his theory in detail.
As a meteorologist, Wei Gena was questioned and ridiculed by scientists from different countries and disciplines. Geologists call him "crazy narcissism" and paleontologists call him "German pseudoscience". In the eyes of traditional geologists, the plates on the earth are fixed, and similar fossils on the African continent in South America are completely connected by ancient bridges and have sunk to the bottom of the sea, while paleontologists directly deny the similarity of fossils from different continents.
Until 1950s, new evidence and data made people re-examine Wei Gena's theory, and geoscientists and physicists made scientific research on the evolution of the earth from a new angle. By the 1960s, scientists discovered the plate edge through submarine magnetic survey and seismic monitoring of underground nuclear test. The alternating pattern of submarine magnetic anomalies indicates the expansion of the seabed and the birth of the plate.
Facts have proved that most of Wei Gena's observations on fossils and rocks are correct. According to the data of US Geological Survey (USGS), Pangea is a supercontinent, which was formed 200 million to 250 million years ago. However, it is undeniable that Wei Gena's "continental drift" theory does not explain how the continent moves on the earth, and the plate tectonics theory in the 1970s gave a detailed explanation on this issue.
Now we all know that there are six major plates in the world, namely, the Pacific plate, the Eurasian plate, the African plate, the American plate, the Indian Ocean plate and the Antarctic plate. In addition, there are about 20 smaller plates. This division was put forward by Xavier Le Pichon in 1968, and these plates have been moving slowly.
The motive force of plate movement is convection in the mantle, that is, mantle convection. The mantle is composed of high-temperature hot matter. With the increase of heat, upward heat flow is generated. When the heat flow meets the bottom of the earth's crust, it will be diverted around. With the decrease of temperature, hot matter will sink into the mantle again, thus forming mantle convection ring. This convection is not only a kind of heat transfer, but also a way for the energy inside the earth to be transported to the surface of the earth.
In this process, three different boundary types are formed between plates. Hot matter rises along the mid-ocean ridge, forming a new oceanic crust and expanding to both sides, which is a discrete boundary.
There is also a subduction zone between the oceanic plate and the continental plate. When two tectonic plates meet, the denser oceanic plate will dive under the continental plate, which is the convergence boundary. There is also a plate boundary called the conservation boundary.
Through rock and fossil evidence, earth scientists reconstructed the history of the earth's continent. In the earth's 4.5 billion-year history, plate tectonics began about 3 billion years ago. About 1 1 100 million years ago, there was only one supercontinent called Rodinia. About 600 million years ago, the Rodinia supercontinent began to split, and then it was polymerized to form Gondwana and Laos. Now our continent was formed 300 million years ago and is called Pangu continent. At that time, Africa, South America, North America and Europe were very close. With the disintegration of Pangu/KLOC-0.5 billion years ago, today's continental form was formed.
From the theory of continental drift to the theory of plate tectonics, the scientific exploration of the formation process of the earth's ancient land has been updated. Wei Gena, who laid the foundation for these explorations, was questioned far more than praised. Wei Gena died in a scientific expedition to Greenland in 1930. During his lifetime, he failed to see his theory widely accepted by academic circles, but the theory of continental drift became one of the most important and widely used geological theories, which had a great influence on geology, geophysics, oceanography and biology.
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