How do I know something about everything

How do you know how the earth is structured?

We can fly to the moon, but a trip to the center of the earth will always be science fiction. Every drilling rig becomes soft at a depth of just a few kilometers because it cannot withstand the enormous pressure and high temperature. Nevertheless, researchers know very well how the earth is structured - but where from?

Similar to an X-ray machine, geologists can look inside the earth without having to cut open the earth. Your "X-rays" are earthquake waves: if there is a strong tremor in one place, the vibrations spread through the entire earth body, similar to sound waves in the air.

However, these waves are not always equally fast: In dense and hard material, the vibrations are transmitted faster than in lighter and softer material. If they hit a layer of rock with a higher density, they can also be refracted or reflected back, like rays of light on a pane of glass. And some waves can only move in solid or viscous substances and liquids cannot pass through them at all.

When the earthquake waves finally arrive on the other side of the world, they are recorded by a global network of highly sensitive measuring devices - so-called seismographs. From the patterns in these diagrams, the researchers can read off the type of waves and their speed and trace the path of the waves through the globe.

In this way, the researchers learn a lot about the interior of the earth - for example, at what depth there are layers of rock or metal and whether these are solid, viscous or thin.

How is the earth structured?

In the beginning, young earth was a hot ball of molten matter. All components were initially well mixed, just as they were distributed when the earth was formed: Metals, rocks, trapped water and gases and much more - a big mess.

But in the course of time that changed: The heavier substances sank down to the center of the earth - especially metals. Rocks, on the other hand, were a little lighter and rose, the lightest to the surface of the earth. There they slowly cooled down and froze.

So the material of the earth separated into the three spherical layers that we know today. You can imagine the structure of the earth like a peach: on the outside a wafer-thin “shell” made of light, solid rock - the Earth crust. On average, it is only 35 kilometers thick.

Under the crust is the "pulp" - the almost 3000 kilometers thick Mantle made of heavy, viscous rock. And inside the earth lies that Earth core from the metals iron and nickel.

The core of the earth itself consists initially of an outer layer about 2200 kilometers thick, the outer core. It is over 5000 degrees Celsius there, which is why the metal has melted and is as fluid as mercury.

That is right inside inner core, slightly smaller than the moon. At over 6000 degrees Celsius, it is a little hotter than the outer core - but surprisingly solid. This is because with increasing depth, not only does the temperature increase, but also the pressure. The outer layers that weigh on the earth's core compress its material so unimaginably that it cannot liquefy.

Why is the earth warm inside?

The liquid interior of the earth bubbles under our feet. Volcanic eruptions and geysers show the heat there - over 6000 degrees Celsius in the earth's core. But why is it so hot in the earth?

Much of the heat comes from Earth's childhood days when dust and rocks condensed into a planet. The word “condense” sounds a bit too harmless, however: In reality, you have to imagine how many large meteorite impacts - each impact a gigantic explosion that heated up the young planet and melted the material.

Since then it has become a little quieter and the earth is cooling down again. However, it does this extremely slowly, the heat in the interior of the earth can only very slowly escape into space. Hot magma flows in the tough earth mantle transport the heat upwards. There it remains enclosed under the rigid earth's crust as if under a lid. The crustal rock only slowly releases its heat into space.

In addition, heat is still being produced inside the earth. This is because the core of the earth contains a lot of radioactive substances such as uranium. Since our planet was formed, they have been disintegrating and giving off heat over a very long period of time. This “fuel” will last for billions of years.

When the earth shakes

The earth trembles, cracks gape in the ground, trees sway and houses collapse - earthquakes are forces of nature with destructive power. When the earth shakes, entire districts can collapse. The earth shakes particularly often in certain areas, namely where the plates of the earth's crust adjoin one another. This is the case, for example, in Japan, on the west coast of the USA or in the Mediterranean region.

The cause of earthquakes is the movement of the plates. These float on the viscous material of the earth's mantle, whose currents propel them like a motor. Where two slabs adjoin each other, their rock masses can get stuck and come to a standstill. The problem is: the current in the interior of the earth drives them on. This creates enormous tension between the two plates. If the tension becomes too great at some point, one of the plates jerks forward. The tension discharges: the earth shakes.

Earthquakes often happen where two plates slide past each other at different speeds, such as on the coast of California. This also does not go smoothly where plates collide. For example, the African drifts towards the Eurasian plate and dives beneath it. Because this plate boundary runs in the Mediterranean, the earth keeps shaking in Italy and Turkey. There are also tremors where the earth's crust is being pulled apart, for example in the Upper Rhine Rift. Although these were less strong in the past centuries, there have already been violent tremors here too: In 1356, a strong earthquake caused great damage in the city of Basel.

The movement of the plates is not "to blame" for an earthquake every time. Collapses can also shake the area. This happens when natural or man-made cavities collapse. Such quakes do not reach as far and are not as strong as quakes caused by the movement of the earth's plates.

The exact point from which an earthquake emanates is the focus of the earthquake, also known as the hypocenter. From here the earthquake waves spread in all directions - comparable to the waves after a stone has plopped into the water. The greater the distance from the focus of the earthquake, the weaker the earthquake waves that cause the earth to sway.

The epicenter on the surface of the earth lies directly above the focus or hypocenter. The destruction of an earthquake is usually greatest around this epicenter. How strong an earthquake is can be measured with special devices. Usually the strength is given with values ​​on the Richter scale, which is open at the top. The strongest earthquake recorded so far was that of Valdivia on May 22, 1960, also known as the Great Chile Earthquake. It reached a strength of 9.5 on the Richter scale.

12.10.1994

For years, the drill bit has laboriously hammered and twisted into the hard earth's crust. Again and again he got stuck. Now the press spokesman for the deep drilling program in Windischeschenbach has announced the end of the scientific project: On October 12, 1994, the drilling rig and its measurement technology had to be switched off at a depth of exactly 9101 meters and at a temperature of 265 degrees Celsius. Reason: The research project's coffers are empty. Overall, the drilling program is very successful, but it is too costly to continue.

The drilling at the Windischeschenbach site near Weiden in the Upper Palatinate was started in 1987 to investigate the earth's crust and the processes taking place in it. Originally, the geologists wanted to drill to a depth of 14 kilometers. According to their calculations, the electronic devices would have withstood the high temperatures of an estimated 300 degrees Celsius by then.

The deepest hole in the world

Kola, a Scandinavian peninsula on the icy northwestern edge of Russia. Here, where hardly a human soul strays, the earth's crust is over three billion years old. Such old crust is rare, and so a scientific drilling started in 1970. Researchers wanted to bring rock samples from the interior of the earth to the surface. But at a depth of a good 12 kilometers at a temperature of almost 200 degrees Celsius, the drilling rigs went soft and the electronics failed. The Russian deep drilling program had to be discontinued in 1989. But at 12,262 meters, it is still the deepest borehole in the world today. Over 45,000 rock samples were taken from the earth's crust during this time. Your exploration will take decades.

15.5.1992

No one has ever penetrated deeper into the earth: on the Kola peninsula, a Soviet team of researchers has drilled a hole over 12 kilometers deep in the earth's crust. Because of the unexpectedly great heat underground, the action was stopped after 12,262 meters.

The former Soviet Union had already started drilling on the Kola Peninsula in the north of the country in 1970. The aim of the “super-deep Kola borehole SG-3” was to reach the boundary between the earth's crust and mantle and to take rock samples. The choice fell on Kola because the rock here is more than two billion years old. This is where the “Uralmasch-4E” drilling machine comes in, which was also used for oil drilling. It was later replaced by a device that was supposed to penetrate up to 15 kilometers into the ground.

On the stony path underground, 45,000 rock samples were taken, various fossils were discovered and even gold was found. Copper and nickel deposits that are useful for industry could also be located. The biggest surprise, however, was: From a depth of 10 kilometers there was unimagined heat. At 180 degrees Celsius, the temperatures were much higher than expected. At a depth of 12,262 meters it was finally the end of the line. Technical breakdowns prevented the drilling work from proceeding. There is even talk of hellish noises underground. Whether the horrible sounds are a horror story, or whether the earth's crust is groaning here? In any case, the super-deep Kola borehole still poses a number of puzzles for science.

US record low broken

With the Kola borehole, the Soviet Union pursued another interest besides a scientific one:

They wanted to outdo the USA, which with its “Berta Rogers” well had reached a depth of 9,583 meters. This borehole, which was considered the deepest in the world from 1974 onwards, is located in the US state of Oklahoma. But the record only lasted five years. On June 6, 1979, the USSR broke the American record for depth with the Kola well. Despite all the records: With an earth radius of 6371 kilometers, both holes are just a small prick on the earth's surface.