The earth's crust can shift

plate tectonics Continents in motion

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On January 6, 1912, Alfred Wegener formulated the hypothesis that the continents "migrate" over time. A hundred years ago this idea still seemed absurd. But his theory has long been proven.

Status: 02.03.2021

The continents move: they drift apart, collide, slide over one another. A hundred years ago this idea still seemed absurd. But our earth's crust is far from being as solid as it was previously thought. The reason for the constant shaking of our planet are the movements of the continental plates. It wasn't that long ago that researchers realized that the continents were shifting. How the complicated interaction of the tectonic plates works is still not fully understood.

Moving theory of Galilean proportions

The meteorologist and polar researcher Alfred Wegener formulated the theory of continental drift.

The German meteorologist and polar researcher Alfred Wegener first formulated his theory of continental drift on January 6, 1912. However, he only got a shake of the head in the professional world. The idea that the continents were once connected and then drifted apart seemed too absurd. But how else could the bulge of the South American fit so well into the indentation of the African continent? However, Wegener still lacked an explanation of how the huge continental plates are moved.

Convection comes into play

Plate tectonics of the earth: heat flows in the earth's mantle form the engine.

In 1929 the Englishman Arthur Holmes had an idea for the mechanism of the plate displacement. When rock material in the earth's mantle heats up, its density is reduced and it rises to the surface, where it then cools down and sinks again. This process of heating up, rising, cooling and sinking - similar to boiling water in a pot - is called convection current. This convection current, in turn, could be the motor for the shifting of the continents.

This is how the plates have moved over the past billion years

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This is how the plates have moved over the past millennia

New ocean floor is emerging

But evidence of such a mechanism was only provided by improvements in echo sounder and sonar technology. Columbia University researchers carried out numerous depth measurements in the Atlantic Ocean and, based on these measurements, created a profile of the sea floor. The American oceanographers Bruce Heezen and Maurice Ewing presented a map in 1959 that shows a mountain range under the sea of ​​14,000 kilometers in length. This mountain ridge with a central trench that is up to 3,000 meters deep and twenty to fifty kilometers wide is part of a volcanic mountain system that has a total length of 75,000 kilometers and winds around the earth like the seam of a tennis ball: the so-called mid-ocean ridges . This is the place where new ocean floor is created.

Old Lady Continent - Young Hopper Oceanic Crust

Where the convection currents descend, cooled older oceanic crust penetrates back into the earth's mantle at the deep ocean trenches. The sea floor is expanding and shifting at the same time. For example, while the Atlantic is expanding by two centimeters per year, the Pacific is shrinking at the same time as the crustal plates subside. The further you move from the ocean ridges towards the continents, the older the rocks get. Due to the constant formation of new oceanic crust with simultaneous subduction, there is currently no sea floor older than 200 million years. But this also means that during this time the continents, such as South America and Africa, were still connected. The final proof of continental drift was provided by the magnetic survey of the underwater ridges in the early 1960s.

The late victory of plate tectonics

Forms of movement of clods of earth in an earthquake

The earth's magnetic field reverses every few hundred thousand years. Rock from different geological time periods can therefore have opposing magnetic polarization. On the sea floor, these reversals occur in adjacent layers, i.e. in strips. A specific time can be assigned to each polarity of a strip of rock. New ocean floor is being formed in the middle of the rift; strips of rock further away from the rift are of older date. For many geologists, this was a decisive indication that the earth's crust is not static, but is in constant motion. Wegener himself no longer lived to see his triumph. He had already died in 1930 on an expedition to Greenland.

  • The structure of our earth - crust, mantle and core: April 4, 2019, 3:05 p.m., radioWissen, Bavaria
  • The 4 elements - the history of the continents (episode 15): on February 16, 2017 at 5 p.m., ARD-alpha
  • Background earthquake: on August 24, 2016 at 6.30 p.m. in the "Rundschau", BR television
  • The formation of the continents - Alfred Wegener and plate tectonics: on July 4th, 2016 at 1:45 p.m., ARD-alpha