How to explain the theory of continental drift?

The theory of continental drift

was proposed by the young German scientist Wegener (pictured) in 1912. With the sober mind and keen insight of a scientist, Wegener raised questions and stimulated thinking by observing the outlines of land on both sides of the ocean on the map. Later, through inspection and research, he found evidence that the land on both sides of the Atlantic coincided with each other from the similarities and continuity characteristics of paleontological fossils, stratigraphic structures, and lithofacies; and then inferred that as early as 300 million years ago, there was a vast and vast land on the earth. A continuous body of water - "Pan-Ocean", surrounded by a huge primitive ancient continent - "Pangaea". About 200 million years ago, due to the long-term effects of the centrifugal force generated by the rotation of the earth and the tidal force of celestial bodies. This united ancient continent began to appear cracks and gradually separated and drifted. The light-weight silicon-aluminum land masses drifted on the heavier silicon-magnesium layer like ice floating on the water. Over a long period of geological time, they gradually formed the sea-land distribution that people see today.

At that time, Wegener's theory of continental drift was regarded as absurd and strange, and he himself was criticized. In order to further search for evidence of continental drift, he went to Greenland in the Arctic for an expedition alone. Unfortunately, he died on his 50th birthday. However, it is comforting that after Wegener, people gradually discovered some new evidence of continental drift, and the theory of continental drift was gradually accepted by people.

Why do continents drift on the silicon-magnesium layer? People continue to conduct in-depth research with various questions. With the new discoveries in paleomagnetism and new advances in marine science, a brand-new theory—the theory of plate tectonics—came into being.

Geological research proves that in the era when dinosaurs existed, there was only one continent on the earth, namely "Pangaea". Due to changes in the earth's crust, this continent experienced major divisions and drifts during the Jurassic Period, which eventually led to changes in the environment and climate, and the dinosaurs became extinct as a result.

From the "Continental Drift Theory" to the "Plate Tectonic Theory"

The once-rejected "Continental Drift Theory"

was first proposed in 1910 This question: Why are the coastlines of South America and Africa on both sides of the Atlantic so similar? This person was the German geophysicist and meteorologist Alfred Wegener. This idea became an opportunity for him to propose the "continental drift theory".

The phenomenon that the two sides separated by the ocean have similar coastlines has been noticed a long time ago. Wegener conducted scientific research on this fact from the perspectives of geology, paleontology, climatology and other perspectives. He proposed that based on the geological structures of orogenic belts and other small animals such as ferns and snails that could not cross the ocean, they were widely distributed in the South American continent and the African continent during the glacial period 300 million years ago. He concluded: Approximately 300 million years ago, the North and South America, Africa, Eurasia, Antarctica, etc. that we know today all belonged to a "supercontinent". Later, this "supercontinent" split into several continents and moved over a long period of time. , finally formed today’s continental location relationship.

The "continental drift theory" proposed by Wegener later developed into the "plate tectonics theory" and became the mainstream of earth science in the 20th century. The reason why the "continental drift theory" has such vitality is that it is a theory that can answer numerous questions so far in a wide range of fields including paleontology, paleoclimate, geological structure, topography, etc. However, Wegener's work "The Origin of Continents and Oceans" published in 1915 was not easily accepted. Although it was approved by geologists and paleontologists, it was dismissed by most geophysicists. , someone put forward a weighty rebuttal.

The main argument of opponents is that no driving force has been found that can move continents thousands of kilometers horizontally. Although geologist Alsa Holmz considered that mantle convection might be the driving force behind continental drift, he kept a low profile. With Wegener's disappearance during the Greenland expedition in 1930, the "continental drift theory" gradually fell into disrepute. In the 1940s, people had forgotten the "continental drift theory". The "continental drift theory" finally made a comeback

In the 1950s, the "continental drift theory" actually made a comeback in a completely unrelated field. This completely unrelated field is the study of ancient Earth's magnetic field - paleomagnetism. Today, the Earth's two magnetic poles, the South and North Magnetic Pole, are almost stationary, but over time, their positions have moved and reversed throughout the long geological history. Based on paleomagnetism, scientists have restored the original magnetic fields of rocks generated in various geological periods in the past, and thus deduced the positions of the north and south magnetic poles. The movement trajectory of the magnetic poles over time is called the "pole movement curve". In 1950, Keith Lancahn, Patrick Blancott and others from the UK successfully obtained the "polar movement curve" based on the precise measurement of the residual magnetic fields in rocks from various geological periods on the European and North American continents. The earth has only two magnetic poles, the south magnetic pole and the north magnetic pole. The "pole movement curves" of the south magnetic pole or the north magnetic pole studied from various continents should be consistent. However, the two "polar motion curves" obtained by Rankan et al. have similar shapes but deviate along the longitude. If the North American continent and the European continent on both sides of the Atlantic Ocean are combined, then the corresponding "polar motion curve" will just match.

This fact just illustrates the possibility of continental drift. Since the dynamic problem that caused continental drift has not been solved, all earth scientists have always ignored the "continental drift theory". However, the "continental drift theory" has reappeared in a majestic way due to the discovery of paleomagnetism. The "ocean expansion theory" came to the fore

At the beginning of the 1950s, new technologies developed during World War II were widely used in ocean observations, such as using sonar devices to observe seafloor topography and using ocean magnetic field instruments to detect the seafloor. Magnetic field anomalies, etc. Through these detections, scientists finally figured out that the huge submarine mountains called "sea ridges" on the global seafloor are connected to each other.

The Central Atlantic Ridge, located in the middle of the Atlantic Ocean among the submarine mountains, was familiar to people when Wegener was alive. However, similar ridges exist in all oceans on earth, including the Pacific, Indian, and Arctic oceans, and are distributed on the seafloor like a network. There is also a "large-scale valley" in the middle section of the Central Ridge, which stretches from north to south for more than 10,000 kilometers 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 proposed that the Atlantic Ocean is a crack in the earth, and the sea floor may be expanding here. Scientists then measured the flow of crustal heat flowing out of the Earth's interior, and learned that hot material seemed to be spewing out from deep beneath the ocean ridges.

Based on the above detection results, scientists concluded that the mantle convection under the central ridge rose to form the ocean crust, and the seafloor expanded. This conclusion supports the "ocean expansion theory", and the "ocean expansion theory" Also explains the breakup and movement of continents. The material that makes up the continental crust is less dense, so the mantle rises. According to the "ocean expansion theory", the mantle convection rising under the continent caused the continent to split, and then the horizontal movement of the mantle pushed the continent apart.

Since then, scientists from the Scripps Institution of Oceanography at the University of California, USA, have observed geomagnetic anomalies that can explain the formation of the Pacific Ocean crust near the west coast of the United States, and found out that the width of the ocean floor is between 20 kilometers and 30 kilometers. There is one percent magnetic field anomaly, which is distributed in stripes within a few hundred kilometers from north to south. In addition, with the advancement of rock dating technology during the same period, scientists have clarified the history of geomagnetic field reversals that have repeated many times in the past millions of years.

In 1963, Fred Vine and Dramondo Mathews proposed a bold hypothesis: The geomagnetic anomaly in California is a reflection of the reversal of the Earth's magnetic field. In the Central Ridge, seafloor crust was formed due to the cooling of high-temperature magma, thus forming rocks with a magnetic field in the direction of the Earth's magnetic field at that time. Vine and others believe that the earth's magnetic poles have been reversed many times, and the seafloor crust with the magnetic field direction characteristics of various geological periods is juxtaposed in stripes on the seafloor. This fact has been confirmed by observations. Since the seafloor expands to both sides of the ridge, if the opinions of Vine and others are realistic, then the observed stripes reflecting magnetic field anomalies should be symmetrical relative to both sides of the ridge. This symmetry is also confirmed by actual observations. The collected relevant observational data all support the "ocean expansion theory", and based on the data on seafloor magnetic field anomalies, the reversal history of the Earth's magnetic field that scientists have known so far has only been known for a few million years, suddenly expanded to 200 million years. The theory of plate tectonics

Continental drift is indeed a fact that is occurring due to evidence provided by the "polar motion curve" and seafloor expansion. In 1965, scientists used computers to fit the Earth's continents exactly into their current shapes. Furthermore, Haiti's topography, earthquake locations, volcanoes and other active parts were all connected into a band, and the revolutionary idea of ??"plate tectonics" came into being.

After 1970, the theory of plate tectonics was established. According to this new theory, the surface of the earth is covered with undeformable and solid plates (crust). These plates are indeed moving at a rate of 1 to 10 centimeters per year. move. Since the surface area of ??the earth is limited, the earth's plates are classified into three states: one is the convergent plate boundary that is close to each other; the other is the separated plate boundary that is far away from each other; and the third is the transformation plate boundary that is intertwined with each other. The plates themselves do not deform, and the activities on the earth's surface all occur in these three states. For example, ocean ridges are formed under detached plate boundaries, and trenches are formed when ocean plates collide with each other, and one plate subducts into another. Formed under the convergent plate boundary below. The San Andreas Fault, which runs along the west coast of the North American continent, was formed under the typical transform plate boundary between the Pacific Plate and the North American Continental Plate.

Due to the conditions surrounding the Pacific Plate known as the "Pacific Rim Belt", large earthquakes, deep earthquakes and volcanic activity are very active in this area. The collision between the Indian subcontinent and Eurasia resulted in the formation of the Himalayas and the Tibetan Plateau. Under the convergent plate boundary where continental plates collide with each other, a conflict zone between continents is formed, which also creates large fold mountains.

Due to the progress of the plate tectonics theory, most of the earth's activities that have been regarded as unsolved mysteries have been explained. Since the 1970s, world-scale earth observation has been vigorously carried out with the purpose of confirming the plate tectonics theory. Through these observations, the age distribution of the seafloor has been determined in detail, and the process of plate movement in past geological periods has been clarified. Due to the development of space observation technology, even plate movement of one centimeter per year can be observed for several consecutive years.

Interpreting the history of the entire earth

The theory of plate tectonics has confirmed the "continental drift theory" proposed by Wegener. Since the "continental drift theory" relies on plate movement, it has been regarded as an unsolved problem for a long time. The driving force behind the mysterious "continental drift theory" has been solved. However, the plate tectonics theory has not clarified all the earth's activities. The plate tectonics theory has only confirmed the facts of the last 200 million years of the earth's 4.6 billion years of history. Previous earth activities are still an important research topic to this day, and have led to The activities of plate movements deep in the mantle require further observation and research.

Regarding the activities of the Earth's lower mantle and core, since the 1980s, scientists have used a technology called "seismological X-ray tomography" to study the uneven structure of the Earth's interior using seismic waves. This scientific approach enables research to progress. The results show that the actual state of mantle convection, once thought to be the driving force of plate movement, seems to be palpable. As for when the Earth's plate tectonics began to form in the Earth's evolutionary history, scientists will further study part of the seafloor crust that is older than 200 million years ago.

The "continental drift theory" proposed by the German scientist Wegener in the early 20th century was explored and developed in the above-mentioned tortuous process. It was not until the 1970s that the theory of plate tectonics was approved by the scientific community. The latest results of earth observation have provided new clues to unravel the unsolved mysteries of the activities of the earth's deep mantle and core, which the theory of plate tectonics is hesitant about, and to clarify the 4.6 billion-year evolution history of the earth.

Looking back at the history of the development of earth science in the 20th century, Wegener's "continental drift theory" created an opportunity to study earth activities. At the same time, our comprehensive understanding has been divided into geology, paleontology, observation Science, seismology, etc.