Why does the earth have a liquid core? Formation of the earth's core

After dropping the keys into the molten lava flow, say goodbye to them, because, well, dude, they are everything.
- Jack Handy

We all know why this is so: because the Earth's oceans rise above the rocks and mud that make up the land. The concept of buoyancy, in which less dense objects float above denser objects that sink below, explains much more than just oceans.

The same principle that explains why ice floats in water, a helium balloon rises in the atmosphere, and rocks sink in a lake, explains why the layers of planet Earth are arranged the way they are.

The least dense part of the Earth, the atmosphere, floats above water oceans, which float above the Earth's crust, which is above the denser mantle, which does not sink into the Earth's densest part: the core.

Ideally, the most stable state of the Earth would be one that would ideally be layered, like an onion, with the densest elements in the center, and as you move outward, each successive layer would consist of less dense elements. And every earthquake actually moves the planet towards that state.

And this explains the structure of not only the Earth, but all the planets, if you remember where these elements came from.

When the universe was young - only a few minutes old - only hydrogen and helium existed. More and more heavy elements were created in the stars, and only when these stars died did the heavy elements go out into the Universe, allowing new generations of stars to form.

But this time, the mixture of all these elements - not only hydrogen and helium, but also carbon, nitrogen, oxygen, silicon, magnesium, sulfur, iron and others - forms not only a star, but also a protoplanetary disk around this star.

The pressure from the inside out in the forming star pushes the lighter elements out, and gravity causes irregularities in the disk to collapse and form planets.

When solar system four inner peace are the densest of all planets in the system. Mercury is made up of the densest elements that could not hold a large number of hydrogen and helium.

Other planets, more massive and more distant from the Sun (and therefore receiving less of its radiation), were able to hold more of these ultra-light elements - this is how the gas giants formed.

In all worlds, as on Earth, on average, the densest elements are concentrated in the core, while the lungs form progressively less dense layers around it.

Not surprisingly, iron, the most stable element, and the heaviest element created in large quantities on the border of supernovae, and there is the most common element of the earth's core. But perhaps surprisingly, between the solid core and the solid mantle lies a liquid layer more than 2,000 km thick: Earth's outer core.

The Earth has a thick liquid layer containing 30% of the planet's mass! And we learned about its existence by a rather ingenious method - thanks to seismic waves coming from earthquakes!

Seismic waves of two types are born in earthquakes: the main compressional, known as P-wave, passing along the longitudinal path

And the second shear wave, known as the S-wave, similar to the waves on the surface of the sea.

Seismic stations around the world are capable of picking up P- and S-waves, but S-waves do not travel through liquid, and P-waves not only travel through liquid, they are refracted!

As a result, it can be understood that the Earth has a liquid outer core, outside of which there is a solid mantle, and inside - a solid inner core! This is why the Earth's core contains the heaviest and densest elements, and this is how we know that the outer core is a liquid layer.

But why is the outer core liquid? Like all elements, the state of iron, whether solid, liquid, gaseous, or otherwise, depends on the pressure and temperature of the iron.

Iron is a more complex element than many you are familiar with. Of course, it can have different crystalline solids, as shown in the graph, but we are not interested in ordinary pressures. We are descending to the core of the earth, where pressures are a million times higher than at sea level. And what does the phase diagram look like for such high pressures?

The beauty of science is that even if you don't immediately have an answer to a question, chances are that someone has already done the right research in which to find the answer! In this case, Ahrens, Collins and Chen in 2001 found the answer to our question.

And although the diagram shows gigantic pressures up to 120 GPa, it is important to remember that the pressure of the atmosphere is only 0.0001 GPa, while pressures in the inner core reach 330-360 GPa. The top solid line shows the boundary between melting iron (top) and solid iron (bottom). Did you notice how the solid line at the very end makes a sharp upward turn?

In order for iron to melt at a pressure of 330 GPa, an enormous temperature is required, comparable to that which prevails on the surface of the Sun. The same temperatures at lower pressures will easily maintain iron in a liquid state, and at higher pressures in a solid state. What does this mean in terms of the Earth's core?

This means that as the Earth cools, its internal temperature drops, while the pressure remains unchanged. That is, during the formation of the Earth, most likely, the entire core was liquid, and as it cools, the inner core grows! And in the process, since solid iron has a higher density than liquid iron, the Earth is slowly shrinking, which leads to earthquakes!

So the Earth's core is liquid because it's hot enough to melt iron, but only in regions where the pressure is low enough. As the Earth ages and cools, more and more of the core becomes solid, and so the Earth shrinks a bit!

If we want to look far into the future, we can expect the same properties that are observed in Mercury.

Mercury, due to its small size, has already cooled and contracted significantly, and has fractures hundreds of kilometers long due to the need for contraction due to cooling.

So why does the Earth have a liquid core? Because she hasn't cooled yet. And each earthquake is a small approximation of the Earth to the final, cooled down and solid state through and through. But don't worry, the Sun will explode long before then, and everyone you know will be dead for a very long time.

There have been countless ideas about the structure of the Earth's core. Dmitry Ivanovich Sokolov, a Russian geologist and academician, said that substances inside the Earth are distributed like slag and metal in a smelting furnace.

This figurative comparison has been confirmed more than once. Scientists carefully studied the iron meteorites that came from space, considering them to be fragments of the core of a disintegrated planet. This means that the core of the Earth should also consist of heavy iron, which is in a molten state.

In 1922, the Norwegian geochemist Viktor Moritz Goldschmidt put forward the idea of ​​a general stratification of the Earth's matter even at a time when the entire planet was in a liquid state. He deduced this by analogy with the metallurgical process studied in steel mills. “In the stage of liquid melt,” he said, “the substance of the Earth was divided into three immiscible liquids - silicate, sulfide and metallic. With further cooling, these liquids formed the main shells of the Earth - the crust, mantle and iron core!

However, closer to our time, the idea of ​​a “hot” origin of our planet was increasingly inferior to a “cold” creation. And in 1939, Lodochnikov proposed a different picture of the formation of the Earth's interior. By this time, the idea of ​​phase transitions of matter was already known. Lodochnikov suggested that the phase changes of matter increase with increasing depth, as a result of which the matter is divided into shells. In this case, the core does not have to be iron at all. It may consist of overconsolidated silicate rocks in a "metallic" state. This idea was picked up and developed in 1948 by the Finnish scientist V. Ramsey. It turned out that although the core of the Earth has a different physical state than the mantle, there are no reasons to consider it to be composed of iron. After all, overcompacted olivine could be as heavy as metal...

Thus, two mutually exclusive hypotheses about the composition of the nucleus appeared. One - developed on the basis of E. Wiechert's ideas about an iron-nickel alloy with small additions of light elements as a material for the Earth's core. And the second - proposed by V.N. Lodochnikov and developed by V. Ramsey, which says that the composition of the core does not differ from the composition of the mantle, but the substance in it is in a particularly dense metallized state.

In order to decide in which direction the scale should tip, scientists from many countries set up experiments in laboratories and counted, counted, comparing the results of their calculations with what was shown by seismic studies and laboratory experiments.

In the sixties, experts finally came to the conclusion: the hypothesis of metallization of silicates, at pressures and temperatures prevailing in the core, is not confirmed! Moreover, the studies carried out convincingly proved that at least eighty percent of the total iron reserve should be contained in the center of our planet ... So, after all, the core of the Earth is iron? Iron, but not really. Pure metal or pure metal alloy compressed at the center of the planet would be too heavy for the Earth. Therefore, it must be assumed that the substance of the outer core consists of compounds of iron with lighter elements - with oxygen, aluminum, silicon or sulfur, which are most common in the earth's crust. But which ones specifically? This is unknown.

And so the Russian scientist Oleg Georgievich Sorokhtin undertook a new study. Let's try to follow in a simplified form the course of his reasoning. Based on the latest achievements of geological science, the Soviet scientist concludes that in the first period of formation, the Earth was most likely more or less homogeneous. All its substance was approximately equally distributed throughout the volume.

However, over time, heavier elements, such as iron, began to sink, so to speak, “sink” in the mantle, going deeper and deeper to the center of the planet. If this is so, then, comparing young and old rocks, one can expect a lower content of heavy elements in young ones, the same iron, which is widespread in the Earth's substance.

The study of ancient lavas confirmed the above assumption. However, the core of the Earth cannot be purely iron. It's too light for that.

What was the satellite of iron on its way to the center? The scientist tried many elements. But some were poorly soluble in the melt, while others were incompatible. And then Sorokhtin had an idea: was not the most common element, oxygen, a companion of iron?

True, calculations showed that the combination of iron with oxygen - iron oxide - seems to be light for the nucleus. But after all, under conditions of compression and heating in the depths, iron oxide must also undergo phase changes. Under conditions that exist near the center of the Earth, only two iron atoms can hold one oxygen atom. This means that the density of the resulting oxide will become greater ...

And again, calculations, calculations. But on the other hand, what satisfaction is it when the result obtained has shown that the density and mass of the earth's core, built from iron oxide, which has undergone phase changes, gives exactly the value that is required modern model kernels!

Here it is - a modern and, perhaps, the most plausible model of our planet in the entire history of its searches. “The outer core of the Earth consists of an oxide of the univalent phase of iron Fe2O, and the inner core is made of metallic iron or an iron-nickel alloy,” writes Oleg Georgievich Sorokhtin in his book. - The transition layer F between the inner and outer core can be considered as consisting of iron sulfide - troillite FeS.

Many eminent geologists and geophysicists, oceanologists and seismologists, representatives of literally all branches of science studying the planet, take part in the creation of the modern hypothesis about the separation of the core from the primary substance of the Earth. The processes of tectonic development of the Earth, according to scientists, will continue in the depths for quite a long time, at least our planet has a couple of billion years ahead. Only after this boundless period the Earth will cool down and turn into a dead cosmic body. But what will happen by then?

How old is humanity? A million, two, well, two and a half. And during this period, people not only got up from all fours, tamed fire and understood how to extract energy from an atom, they sent a man into space, machines to other planets of the solar system and mastered near space for technical needs.

Exploration, and then the use of the deep bowels of their own planet - a program that is already knocking on the door of scientific progress.

Why does the Earth's core not cool down and remains heated to a temperature of approximately 6000°C for 4.5 billion years? The question is extremely complex, to which, moreover, science cannot give a 100% accurate intelligible answer. However, there are objective reasons for this.

Too much mystery

Excessive, so to speak, the mystery of the earth's core is associated with two factors. Firstly, no one knows for sure how, when and under what circumstances it was formed - it happened during the formation of the proto-Earth or already on early stages the existence of a formed planet is all a big mystery. Secondly, it is absolutely impossible to get samples from the earth's core - for sure no one knows what it consists of. Moreover, all the data that we know about the nucleus is collected by indirect methods and models.

Why does the Earth's core stay hot?

To try to understand why the earth's core does not cool down for such a long time, you first need to figure out what caused it to warm up in the first place. The bowels of ours, like any other planet, are heterogeneous, they are relatively clearly demarcated layers of different densities. But this was not always the case: the heavy elements slowly descended, forming the inner and outer core, the light ones were forced out to the top, forming the mantle and the earth's crust. This process proceeds extremely slowly and is accompanied by the release of heat. However, this was not the main reason for the heating. The entire mass of the earth huge force presses on its center, producing a phenomenal pressure of approximately 360 GPa (3.7 million atmospheres), as a result of which the decay of radioactive long-lived elements contained in the iron-silicon-nickel core began to occur, which was accompanied by colossal heat emissions.

An additional source of heating is the kinetic energy generated as a result of friction between different layers (each layer rotates independently of the other): the inner core with the outer and the outer with the mantle.

The bowels of the planet (the proportions are not met). Friction between the three inner layers serves as an additional source of heating.

Based on the above, we can conclude that the Earth and, in particular, its bowels are a self-sufficient machine that heats itself. But it cannot continue so naturally forever: the stocks of radioactive elements inside the core are slowly disappearing and there will be nothing left to maintain the temperature.

It's getting cold!

In fact, the cooling process has already begun a very long time ago, but it proceeds extremely slowly - by a fraction of a degree per century. According to rough estimates, it will take at least 1 billion years for the core to cool completely and stop chemical and other reactions in it.

Short answer: The earth, and in particular the earth's core, is a self-sufficient machine that heats itself. The entire mass of the planet presses on its center, producing phenomenal pressure and thereby starting the process of decay of radioactive elements, as a result of which heat is released.

Our planet Earth has a layered structure and consists of three main parts: earth's crust, mantle and core. What is the center of the earth? Core. The depth of the core is 2900 km, and the diameter is approximately 3.5 thousand km. Inside - a monstrous pressure of 3 million atmospheres and an incredibly high temperature - 5000 ° C. In order to find out what is in the center of the Earth, it took scientists several centuries. Even modern technology could not penetrate deeper than twelve thousand kilometers. The deepest borehole, located on the Kola Peninsula, has a depth of 12,262 meters. Far from the center of the earth.

The history of the discovery of the earth's core

One of the first to guess about the presence of a nucleus in the center of the planet was the English physicist and chemist Henry Cavendish at the end of the 18th century. With the help of physical experiments, he calculated the mass of the Earth and, based on its size, determined the average density of the substance of our planet - 5.5 g / cm3. Density known rocks and minerals in the earth's crust turned out to be about two times less. From this followed a logical assumption that in the center of the Earth there is an area of ​​denser matter - the core.

In 1897, the German seismologist E. Wiechert, studying the passage of seismological waves through the inner parts of the Earth, was able to confirm the assumption of the presence of a core. And in 1910, the American geophysicist B. Gutenberg determined the depth of its location. Subsequently, hypotheses about the process of formation of the nucleus were also born. It is assumed that it was formed as a result of the settling of heavier elements to the center, and initially the substance of the planet was homogeneous (gaseous).

What is the core made of?

It is quite difficult to study a substance whose sample cannot be obtained in order to study its physical and chemical parameters. Scientists have only to assume the presence of certain properties, as well as the structure and composition of the nucleus by indirect signs. Especially helpful in the study of the internal structure of the Earth was the study of the propagation of seismic waves. Seismographs, located at many points on the surface of the planet, record the speed and types of passing seismic waves arising from tremors of the earth's crust. All these data make it possible to judge internal structure Earth, including the core.

To date, scientists suggest that the central part of the planet is heterogeneous. What is at the center of the earth? The part adjacent to the mantle is a liquid core, consisting of molten matter. Apparently, it contains a mixture of iron and nickel. This idea led scientists to the study of iron meteorites, which are pieces of asteroid nuclei. On the other hand, the obtained iron-nickel alloys have a higher density than the expected density of the core. Therefore, many scientists tend to assume that in the center of the Earth, the core, there are also lighter chemical elements.

The presence of a liquid core and the rotation of the planet around its own axis of geophysics explain the existence magnetic field. It is known that an electromagnetic field around a conductor arises when current flows. The molten layer adjacent to the mantle serves as such a giant current-carrying conductor.

The inner part of the nucleus, despite the temperature of several thousand degrees, is a solid. This is due to the fact that the pressure in the center of the planet is so high that hot metals become solid. Some scientists suggest that the solid core consists of hydrogen, which, under the influence of incredible pressure and enormous temperature, becomes like a metal. Thus, what is the center of the Earth, even geophysicists are still not known for certain. But if we consider the issue from a mathematical point of view, we can say that the center of the Earth is located approximately 6378 km. from the surface of the planet.