Have you ever noticed on a map of the Atlantic how the east coast of South America seems to coincide with the west coast of Africa? If you combine the Brazilian hump with the Gulf of Guinea in Africa, the coast from Guyana to Argentina blends beautifully with the line from Ghana to Cape Town. The two continents seem like pieces of a big puzzle.
Maybe when you first did, you thought that South America and Africa at some point came together and somehow merged. melted and melted. In that case, you probably dismissed the idea as absurd, just a strange coincidence.
But did you know that most geologists take this idea seriously? A theory that the continents actually move here and there in the floating mantle of the earth's crust has gained wide acceptance since the 1960s.
Theory of continental drift
The theory was originally proposed not by a geologist but by a German meteorologist named Alfred Wegener. He suggested that not only were South America and Africa already connected but all the continents were part of a single landmass. He called this hypothetical ancient continent Pangea (meaning "whole earth"). He found that when the contours of the continental shelf were used, the alignment of the continent was better than the current coasts.
Today, geologists use computers to draw and rotate continental contours on a globe to get the best possible fit. In a typical reconstruction of the supposed ancient supercontinent, the southeast coast of North America lies on the northwest coast of Africa. Eurasia is in line with Spain, so Europe's west coast collides with Newfoundland and Greenland. Antarctica is facing Southeast Africa, Australia is connected to the opposite side.
When Wegener first proposed this revolutionary concept in 1912, it aroused mixed feelings among geologists. All theories that contradict the prevailing belief in science are generally met with caution. Continental drift was registered even colder than normal, possibly because the author was not a member of the geological group. Although there is strong evidence to support this theory, it has been mathematically "proven" that the earth's crust is too thick to allow continents to move sideways. And he wondered where some power would come from to advance the continents in one way or another. No one could suggest anything that would pass the test. The idea was gradually ignored by leading researchers.
Theory test: compliance
So why did geologists change about continental drift? First, different types of evidence gradually accumulate, making it difficult to explain otherwise. This includes the similarity between geological formations and fossil deposits on continents that are now very separated, as well as the displacement of the earth's magnetic poles.
As an example of geological agreement, we are informed about a series of sedimentary deposits that were deposited during the so-called Paleozoic geological era and later exposed to their ascent in the mountains. Deposits of red sandstone, gray slate and coal beds are found in the Appalachian rock system in eastern North America and extend as far east as Greenland. They are also found in the highlands of the British Isles. Similar sediments are found in the Kjölen Mountains in Scandinavia and along the Atlas Mountains in northwestern Africa. On the originally theoretical continent of Pangea, all these rock formations would have been part of a continuous rock system, the remains of which are now very distant on three continents.
The similarity of the fossils found in these strata on either side of the Atlantic is used as an additional argument for the theory. Fish fossils are plentiful, including land plants, including forests with large arboreta and tall trees. Another example of the oft-mentioned fossil record is the Mesosaur, a small dinosaur that lived during the so-called Paleozoic era. Its fossils are found in southwest Africa and Brazil, but have not been found anywhere else in the world. If South America and Africa had been united at this time, the Mesosaurus area would have been a continuous area.
Stray magnetic poles
Other compelling evidence comes from studies of the mysterious phenomenon of polar migration. The belief that the Earth's magnetic poles have shifted is based on measurements of the magnetization of volcanic rocks. When hot rock is cooled in a magnetic field, it becomes weakly magnetized as the magnetic mineral particles in the rock propagate in the direction of the magnetic field. This shows the direction of the Earth's magnetic field when the rock formed like a "frozen compass".
You can now expect all of these fossil compasses to point north, but surprisingly, rocks of different geological ages are showing magnetization in many different directions. It is as if the magnetic pole is moving universally and aimlessly on the Earth, hence the term "polar migration".
However, when the directions are organized according to the apparent age of the rocks, it turns out that the pole follows a defined path from one epoch to another. In addition, when the magnetism of rocks is measured elsewhere on the same continent, it turns out that they consistently follow the same path.
This discovery put the geophysicist in difficulty. Although no one knows what causes the Earth's magnetic field, it seems that it must be related to the rotation of the Earth in some way or another and it is hard to believe that the magnetic pole could be much different. from the geographic pole, it is certainly not known which equator is indicated. . of the mountain compass. . Of course, the migratory magnetic orbits would have been explained even if the pole had stopped as the continents glided around the world, but it seemed even harder to believe.
What struck the balance between two incredible explanations was the discovery that magnetic measurements on different continents often point to completely different routes to Poland. It cannot be explained by polar movements, because the earth has only one north pole and cannot go in several different directions at the same time. To geologists, this seemed to be a strong sign that continents were moving independently for thousands of kilometers.
Seabed testing
New evidence leading geologists to believe in continental drift has come from the bottom of the ocean. Exploration of the ocean floor actually began during the International Geophysical Year 1955. Oceanographers used detailed sound equipment to map the ocean floor. By adjusting the echoes, they not only examined the sediment floor at the bottom, but also the depth of the basalt rock below. They came to a surprising conclusion about the seabed: They came to the conclusion that the seabed is not fixed, but seems to continually form at certain limits and spread globally.
Let's take a look at the results that led to this surprising hypothesis. The first clue was a long ridge in the middle of the Atlantic. Since then, geologists have mapped a system of ocean ridges that literally surround the earth. A typical ridge rises from the seabed about 50 km deep to a peak about 30 km above the ground. It is flanked on both sides by a strip of mountainous terrain several hundred kilometers wide. What is striking is a valley that flows like a crack along the ridge and then divides it into two parallel ridges.
The acoustic sounds of the surface were supplemented with the help of boats equipped to drill holes in the seabed. They've developed rock cores for careful inspection and analysis, some up to 460 meters from many parts of the ocean. These studies show that the ridges themselves are bare rock and that there is little or no sediment on either side for a distance of up to 970 km. In addition, they have increasingly thick layers of sediment, up to a mile thick.
Magnetic studies of the oceans near the ridges led to another remarkable discovery. In parallel with the projections, there are projections where the magnetism is reversed. It is as if the north and south poles were turned when the rocks were formed. This reverse magnetization has already been observed in some volcanic lava flows, but near the middle of the ocean ridges there seems to be a continuous registration of frozen normal and reverse magnetic polarities on the seabed. There is no explanation for this mysterious change; After all, no one knows why the earth has a magnetic field, let alone why it spins. It is just an observed fact of creation.
Expansion of the seabed
Geologists explain these three observations with a single hypothesis called diffusion from the seabed. They believe that the central ocean chain is continuously formed by the upward movement of magma in the earth's plastic mantle through a crack in the earth's crust and that the seabed folds on both sides of the crack. how it is formed. The new rock is clean and the sediment builds up slowly and becomes visible only after the new rock has been exposed for a while and has moved away from the ridge. Parallel bands with normal and reverse magnetic polarity occur when magma seeps and solidifies for a while, while the earth's poles are normal, and then for a while they are reversed.
The results show that the Atlantic bottom currently extends just over 2.5 cm per year and the Pacific Ocean about 15 cm per year. . But if the earth forms a new crust on the seabed to this incredible point, it must throw its old crust elsewhere. After all, the total surface area of the earth does not increase. Geophysicists believe that this occurs along certain boundaries, where one part of the crust slides under another part and sinks into the hot interior, where it melts and is consumed again in the liquid layer. They believe that it is not a common process but is accompanied by earthquakes and volcanic eruptions. It forms deep sea graves and high mountains along consumption limits.
The theory of sheet metal tectonics
Using a world map of Mediterranean mountain ranges and consumption limits, geologists divided the entire earth's surface into six large (and several smaller) slabs of rigid rock. These plates, they postulate, form on ridges and move like a conveyor belt to the boundaries of other plates, where one of them is pushed into the mantle and dissolves. The continents are transported on these plates like an Eskimo igloo on an ice floe.
This is called the theory of sheet metal tectonics, from the Greek word "builder". Continental drift and the expansion of the seabed are part of the larger theory.
Let us look at some examples of how this theory is used to explain the observed properties of the earth's crust. The American plate, which supports North and South America and the western half of the Atlantic, is theoretically formed in the middle of the Atlantic and moves west. Along the west coast of South America, a smaller plate that forms in the eastern Pacific collides and falls under the American plate. This probably creates a deep rift in the ocean off the coast of South America and raises the Andes to the highest peaks in America. The waveform of the sea plate causes frequent earthquakes along the entire Pacific coast. When the lightest rock is theoretically washed, it melts through cracks in the overlapping continental crust and forms volcanoes in the Andes.
A detailed map of the ocean line shows that it is not really continuous, but is compensated for by a lot of rectangular errors. The two theoretical tables horizontally follow these transformation errors, as they are called. Geologists suggest that the friction of this movement is another cause of earthquakes. One of the biggest transformation errors is found between the American and Pacific plates along the west coast of North America. Along this line, known in California as the San Andreas Fault, the Pacific Plate moves northwest toward the United States Plate at a rate of about 5 inches per year. The resulting tensions cause frequent earthquakes.
The city of San Francisco faces this fault, and the southern California coast lies to the west of it in the Pacific. If the current movement is not stopped, the location of Los Angeles should be close to the current location of San Francisco in the distant past.
Geologists who follow the continental drift theory suggest that some places had a very different climate than today. In the Pangea postulate, with the exception of Antarctica, today's continents were all much further south than they are now. North America and the Spanish Peninsula were on the equator. South America, Africa, India and Australia have gathered around Antarctica in the South Pole regions.
Continets are indeed amazing