What is gravity in the earth's core

What is happening inside the earth?

The lava lamp - cult from the 70s: thick bubbles rise slowly in a viscous liquid, sink back to the ground and bubble up again. A similar circular motion of hot, viscous rock also takes place directly under our feet in the interior of the earth. But what is the reason for this?

Regardless of whether it is a lava lamp, water in a saucepan or the earth's mantle, the reason is always the same: When a liquid is heated, warm bubbles rise to the top. This is because the tiny particles that make it up move back and forth more and more as the temperature increases. To do this, they need more space and no longer huddle together so closely. There are now fewer particles in the same volume than in the vicinity, so it is lighter and rises upwards. There this bubble cools down again and the particles take up less space. The volume piece becomes heavier than the surroundings, sinks again and the cycle starts all over again. When a liquid flows in a circle due to a temperature difference, it is also called convection.

In a lava lamp, the heat from the lamp sets the liquid in motion. In the interior of the earth, the hot, solid inner core of the earth is the heat source. It heats the overlying liquid metal of the outer core of the earth. This rises up and transfers its heat to the earth's mantle, which gradually cools it down. Then it sinks back down, where it heats up again.

A second, similar cycle takes place in the earth's mantle: its heated rock moves upwards from the core towards the earth's crust, to which it in turn gives off heat. After it cools down, it flows down to the Earth's core, where the cycle begins again. Because the earth's mantle rock is very tough, the convection current only moves a few centimeters per year - a cycle lasts a long time.

Due to the rock currents in the earth's interior, great heat and pressure act on the thin earth crust. It cannot always keep up: Every now and then it tears open in individual places and hot rock escapes through volcanoes to the surface of the earth.

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 little 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 earth's interior 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 the formation of our planet, they have been disintegrating and giving off heat over a very long period of time. This “fuel” will last for billions of years.

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.

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 exactly how the earth is structured - but from where?

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 body of the earth, 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.

What is the difference between lava and magma?

Magma and lava actually refer to the same thing, just in different places: Magma is inside the earth, lava is on the surface of the earth.

Magma arises where the heat and pressure in the earth's interior are very high. There the rock melts and a viscous rock slurry is created, the magma. The magma collects in underground cavities and flows up to the surface of the earth when the pressure rises. As soon as the magma swells out of the earth during a volcanic eruption, it is called lava. Gases that were trapped in the magma can then escape into the air. Therefore, lava and magma differ in their chemical composition.

As long as the lava is hot, it is soft and malleable. On the surface of the earth, the lava slowly cools down and solidifies. Then it can look very different, depending on where and how it flowed out of the earth: For example, if a volcano erupts underwater, the lava cools down very quickly. It forms into structures that look like lumps or pillows. This is why one speaks of pillow lava. Other lava flows look like long balls of wool and are therefore called knitted lava.

Over time, various rocks are formed from lava. Particularly thin lava turns into dark gray basalt after cooling. This rock is often used as a paving stone for roads and paths. When lava is thrown into the air during a volcanic eruption and puffs up like foam, it creates pumice stone. The trapped air makes pumice stone so light that a piece of it can float on the water. Volcanic ash and volcanic dust that solidify turn into tufa. Many houses in the Vulkaneifel, for example, are made of tuff.

What happens in the event of a volcanic eruption?

It steams and bubbles, it smokes and hisses. Glowing hot rock shoots up from inside the earth. An ash cloud rises, lava gushes out of the volcano and flows over the surface of the earth. When a volcanic eruption occurs, enormous forces are at work. But how does a volcano actually erupt?

In the earth's mantle, the rock layer under the earth's crust, temperatures of over a thousand degrees Celsius and very high pressure prevail. If the heat and pressure are high enough, the rock melts and becomes a viscous mass called magma. This magma expands and rises to the top. There it first collects in cavities, the magma chambers. None of this happens overnight, however, but takes tens of thousands or hundreds of thousands of years.

When the magma chamber is full and cannot hold any more material, the hot magma makes its way out. It penetrates through channels and crevices to the surface and emerges there as glowing hot lava - the volcano erupts. The channel through which the magma swells up is called a chimney, and its exit is called a crater.

Some volcanoes regularly spit lava, for example the Stromboli in southern Italy. One can observe its eruptions every day. Other volcanoes remain quiet for centuries but are not actually extinct. Often their craters are clogged with lava and debris. That makes them very dangerous because if they break out there can be huge explosions; well-known for this are, for example, Vesuvius near Naples or Krakatau in Indonesia. Such explosive eruptions blow up millions of tons of rock. The ash cloud that rises from the eruption can stay in the air for a long time and be widely dispersed by the wind. This cloud then only slowly settles on the earth as a fine layer of ash.

Lava that is not thrown into the air flows down from the crater rim as a scorching stream of molten rock. When this lava flow cools, it solidifies into lava rock. Little by little, lava flows, ash and debris build a mountain around the crater - the volcanic cone.

Why is the earth magnetic at all?

The fact that the earth has a magnetic field is very practical: Among other things, it protects us from charged particles from space (the “solar wind”) and was - at least from GPS - an important aid when navigating the sea and in unknown terrain. But why is the earth magnetic at all?

Explaining this in detail is not that easy - scientists are still researching the details to this day. One thing is clear: the earth's magnetic field is created in the earth's core. It consists mainly of the metals iron and nickel and has a temperature of over 5000 degrees Celsius. The metals in the outer core of the earth have melted and are therefore liquid, and further inside the pressure is so high that the inner core of the earth is solid.

The solid inner core acts like a hotplate: it heats the liquid above, the heated liquid rises and finally meets a slightly cooler layer. There it passes on its warmth and cools itself down a bit in the process. As a result, it sinks back down. This cycle is called "convection flow".

In the outer core of the earth there are currents made of iron - a conductive material. You can almost imagine it like a wire that moves. And we know from a wire that moves in a magnetic field that a voltage is generated (“induced”) in it. This voltage in turn causes electrical current to flow and this again generates a magnetic field.

While the iron masses move in the earth's core, the earth also rotates on its own axis. This has the effect that these liquid flows are additionally twisted. With the right combination of flow movement and earth rotation, this can result in the generated magnetic field being oriented in such a way that it supports and strengthens the original magnetic field. And this amplified magnetic field induces a stronger voltage, which allows a stronger electric current to flow, which further amplifies the magnetic field. In this way, the magnetic field can ultimately keep itself stable.

So at the beginning there must have been a small magnetic field by chance. Driven by the rotation of the earth and geothermal energy, this mechanism has led to this mechanism becoming increasingly stronger. So strong that little by little a magnetic field with a uniform direction has prevailed in the entire earth's core. We can then measure this on the surface as the “Earth's magnetic field”.

However, it can also happen that the flow conditions in the core change a little. Then this mechanism, in which the magnetic field is self-sustaining, no longer works so well. As a result, the earth's magnetic field can become weaker overall - and it is even possible that suddenly in one part of the earth's core the opposite direction gains the upper hand and this gradually asserts itself throughout the whole of the earth's core. In the end, the earth's magnetic field has completely reversed: the North Pole became the South Pole and vice versa. Scientists have found that such a “pole reversal” has taken place many times in the past, on average about every 250,000 years.

Continents on the move

For a long time it was thought that the land masses of the earth would stand rigidly in place. It later turned out: the opposite is the case. The continents of our planet are moving! Like huge ice floes, they drift in different directions, albeit not very quickly. Their speed corresponds roughly to the growth of a fingernail. But why is it that the continents are constantly on the move?

The earth's crust that envelops our planet is brittle and cracked. It resembles a cracked egg shell and is made up of seven large and many smaller plates. Some of them make up the continents, others make up the ocean floor. These plates of the earth's crust drift around on a hot, viscous rock slurry and are driven by movements in the earth's interior, more precisely: by currents in the earth's mantle. Experts also say: you are drifting. All these processes related to the movement of the earth's plates are called plate tectonics, and the movement itself is also known as plate drift.

The earth is particularly active where the individual plates adjoin one another. At some of these plate boundaries, hot rock penetrates upwards from the earth's mantle and cools down. Here new earth crust forms: the two plates grow and are thereby pushed apart. On the other hand, where two plates collide, the lighter one of them - the continental crust - is crumpled up and unfolded to form mountains. The heavier of the two - the oceanic crust - is slowly disappearing into the depths. Due to the heat in the earth's interior, their rock is melted again. As the edge of the plate sinks into the depth, it pulls the rest of the plate behind it and thus additionally drives the plate movement.

Volcanic eruptions, earthquakes, long mountain ranges and deep ocean trenches accumulate along such plate edges. Most of the unrest on the earth's surface brings with it the largest of its plates: it is the Pacific plate, which is moving northwest at a rate of about 10 centimeters per year. Most of the world's active volcanoes can be found at their edges, and violent earthquakes shake the region. Because of the frequent volcanic eruptions and earthquakes, this plate boundary is also called the “Pacific Ring of Fire”.


30 kilometers south of Iceland, an island was born out of the sea. A young volcano has been spewing fire and ashes here since November 14th. Its lava masses have already given rise to an island 40 meters high and 500 meters long.

White-gray ash clouds hang in the sky and darken it. Fine volcanic rock patters the area, every lava discharge is accompanied by the rumble of thunder. The smoke column caused by the volcanic eruption rises 10 kilometers into the air. And an island off Iceland's south coast continues to grow.

The eruption of the underwater volcano came unexpectedly, but not without its harbingers. Seismologists had already measured smaller earthquakes a week earlier in the capital Reykjavik - signs that a lot is happening at the plate boundary of the Mid-Atlantic Ridge. In addition, a research ship had found that the sea was warmer than usual. And residents of the nearby coastal region believed they smelled hydrogen sulfide. When the volcano erupted on the seabed at a depth of 130 meters, it initially went unnoticed. Its explosions were weakened by the water pressure.But as it grew, it approached sea level and finally broke through it, spitting wildly. That was the birth of an island in Iceland.

The new island off the south coast already has a name: it is called "Surtsey" after Surt, the giant of fire. A Nordic legend tells of him that he hurls fire and destroys all life with his glowing sword.

How Iceland came into being

Iceland is actually nothing more than the peak of a huge mountain range in the Atlantic: The mid-Atlantic ridge, which stretches from north to south through the entire Atlantic, is almost 20,000 kilometers long. At the height of Iceland, the North American and Eurasian plates drift apart, by about two centimeters every year. Where they spread, hot magma penetrates from the interior of the earth to the surface. These volcanic eruptions have been piling up mountains underwater for millions of years and caused Iceland to appear above sea level 17 to 20 million years ago. These volcanoes are still active today. And now they have born another island: Surtsey.