How did they determine that the earth's core is liquid? What's at the center of the earth

When you drop your keys into a stream of molten lava, say goodbye to them because, well, dude, they're everything.
- Jack Handy

We all know why this is so: because the Earth's oceans float above the rocks and dirt that make up the land. The concept of buoyancy, in which less dense objects float above denser ones that sink below, explains much more than just the 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 oceans of water, which float above the Earth's crust, which sits above the denser mantle, which does not sink into the densest part of the Earth: the core.

Ideally, the most stable state of the Earth would be one that would be ideally distributed into layers, like an onion, with the densest elements in the center, and as you move outward, each subsequent layer would be composed of less dense elements. And every earthquake, in fact, moves the planet towards this state.

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

When the Universe was young—just a few minutes old—only hydrogen and helium existed. Increasingly heavier elements were created in stars, and only when these stars died did the heavier elements escape into the Universe, allowing new generations of stars to form.

But this time, a 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.

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

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

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

On all worlds, as on Earth, on average, the densest elements are concentrated in the core, and the light ones form increasingly less dense layers around it.

It is not surprising that iron, the most stable element, and the heaviest element created in large quantities on the supernova boundary, and is the most common element earth's core. But perhaps surprisingly, between the solid core and the solid mantle lies a liquid layer more than 2,000 km thick: the Earth's outer core.

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

In earthquakes, seismic waves of two types are born: the main compression wave, known as P-wave, which travels along a longitudinal path

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

Seismic stations around the world are able to pick up P- and S-waves, but S-waves do not travel through liquid, and P-waves not only travel through liquid, but are refracted!

As a result, we can understand 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, gas, or other, depends on the pressure and temperature of the iron.

Iron is a more complex element than many you are used to. Of course, it may have different crystalline solid phases, as indicated in the graph, but we are not interested in ordinary pressures. We are descending into the earth's core, where pressures are a million times higher than sea level. What does the phase diagram look like for such high pressures?

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

And although the diagram shows gigantic pressures of up to 120 GPa, it is important to remember that the atmospheric pressure is only 0.0001 GPa, while in the inner core pressures reach 330-360 GPa. The upper 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 prevailing on the surface of the Sun. The same temperatures at lower pressures will easily maintain iron in liquid state, and at higher levels - in the solid. What does this mean in terms of the Earth's core?

This means that as the Earth cools, its internal temperature drops, but 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 slowly contracts, which leads to earthquakes!

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

If we want to look far into the future, we can expect the same properties to appear as those observed in Mercury.

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

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

Countless ideas have been expressed 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 iron meteorites arriving from space, considering them fragments of the core of a disintegrated planet. This means that the Earth’s core should also consist of heavy iron in a molten state.

In 1922, the Norwegian geochemist Victor Moritz Goldschmidt put forward the idea of ​​a general stratification of the Earth's substance at a time when the entire planet was in a liquid state. He derived 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 phase changes in matter intensify with increasing depth, as a result of which the matter is divided into shells. In this case, the core does not necessarily have to be iron. It may consist of overconsolidated silicate rocks that are 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 Earth’s core has a different physical state than the mantle, there is no reason to consider it to be composed of iron. After all, overconsolidated olivine could be as heavy as metal...

This is how two mutually exclusive hypotheses about the composition of the nucleus emerged. One is developed on the basis of E. Wichert'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 states 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.

To decide which way the scales should tip, scientists from many countries carried out experiments in laboratories and counted and counted, comparing the results of their calculations with what seismic studies and laboratory experiments showed.

In the sixties, experts finally came to the conclusion: the hypothesis of metallization of silicates, at the pressures and temperatures prevailing in the core, is not confirmed! Moreover, the research carried out convincingly proved that the center of our planet should contain at least eighty percent of the total iron reserve... So, after all, the Earth’s core is iron? Iron, but not quite. 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 material of the outer core consists of compounds of iron with lighter elements - 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 the course of his reasoning in a simplified form. 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 distributed approximately equally throughout the entire volume.

However, over time, heavier elements, such as iron, began to sink, so to speak, “sinking” into the mantle, going deeper and deeper towards the center of the planet. If this is so, then, comparing young and old rocks, we can expect lower content in young rocks. heavy elements, the same iron widely distributed in the Earth's matter.

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

What was iron's companion on its way to the center? The scientist tried many elements. But some did not dissolve well in the melt, while others turned out to be incompatible. And then Sorokhtin had a thought: wasn’t the most common element - oxygen - a companion of iron?

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

And again calculations, calculations. But what a satisfaction when the result obtained showed that the density and mass of the earth’s core, built from iron oxide, which has undergone phase changes, gives exactly the value required modern model cores!

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

Many outstanding geologists and geophysicists, oceanologists and seismologists - representatives of literally all branches of science that study the planet - are taking part in the creation of the modern hypothesis about the release 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 another couple of billion years ahead. Only after this immeasurable period of time will the Earth cool down and turn into a dead cosmic body. But what will happen by this time?..

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 people into space, automata to other planets of the solar system and mastered near space for technical needs.

The exploration and then the use of the deep bowels of our own planet is a program that is already knocking on the door of scientific progress.

The earth's core includes two layers with a boundary zone between them: the outer liquid shell of the core reaches a thickness of 2266 kilometers, beneath it there is a massive dense core, the diameter of which is estimated to reach 1300 km. The transition zone has a non-uniform thickness and gradually hardens, turning into the inner core. At the surface of the upper layer, the temperature is around 5960 degrees Celsius, although this data is considered approximate.

Approximate composition of the outer core and methods for its determination

Very little is still known about the composition of even the outer layer of the earth's core, since it is not possible to obtain samples for study. The main elements that may make up the outer core of our planet are iron and nickel. Scientists came to this hypothesis as a result of analyzing the composition of meteorites, since wanderers from space are fragments of the nuclei of asteroids and other planets.

Nevertheless, meteorites cannot be considered absolutely identical in terms of chemical composition, since the original cosmic bodies were much smaller in size than the Earth. After much research, scientists came to the conclusion that the liquid part of the nuclear substance is highly diluted with other elements, including sulfur. This explains its lower density than that of iron-nickel alloys.

What happens on the outer core of the planet?

The outer surface of the core at the boundary with the mantle is heterogeneous. Scientists suggest that it has different thickness, forming a kind of internal relief. This is explained by the constant mixing of heterogeneous deep substances. They differ in chemical composition and also have different densities, so the thickness of the boundary between the core and the mantle can vary from 150 to 350 km.

Science fiction writers of previous years in their works described a journey to the center of the Earth through deep caves and underground passages. Is this really possible? Alas, the pressure on the surface of the core exceeds 113 million atmospheres. This means that any cave would have “slammed shut” tightly even at the stage of approaching the mantle. This explains why there are no caves on our planet deeper than at least 1 km.

How do you study the outer layer of the nucleus?

Scientists can judge what the core looks like and what it consists of by monitoring seismic activity. So, for example, it was found that the outer and inner layers rotate in different directions Under the influence magnetic field. The Earth's core hides dozens more unsolved mysteries and awaits new fundamental discoveries.

In which time immemorial did this happen? All these questions have worried humanity for a long time. And many scientists wanted to quickly find out what was there in the depths? But it turned out that learning all this is not so easy. After all, even today, having everything modern devices To conduct all kinds of research, humanity is able to drill wells into the subsoil for only some fifteen kilometers - no more. And for full-fledged and comprehensive experiments, the required depth should be an order of magnitude greater. That's why scientists and we have to calculate how the Earth's core was formed using a variety of high-precision instruments.

Exploring the Earth

Since ancient times, people have studied naturally exposed rocks. Cliffs and mountain slopes, steep banks of rivers and seas... Here you can see with your own eyes what existed probably millions of years ago. And in some suitable places wells are being drilled. One of these is at its depth - fifteen thousand meters. The mines that people dig to also help study the inner Core, of course, they cannot “get” it. But from these mines and wells, scientists can extract rock samples, learning in this way about their changes and origin, structure and composition. The disadvantage of these methods is that they are only able to study land and only the upper part of the Earth's crust.

Recreating conditions in the Earth's core

But geophysics and seismology - the sciences of earthquakes and the geological composition of the planet - help scientists penetrate deeper and deeper without contact. By studying seismic waves and their propagation, it is determined what both the mantle and the core consist of (it is determined similarly, for example, with the composition fallen meteorites). Such knowledge is based on received data - indirect - about physical properties substances. Also today, modern data obtained from artificial satellites, located in orbit.

Planet structure

Scientists were able to understand, by summarizing the data obtained, that the structure of the Earth is complex. It consists of at least three unequal parts. In the center there is a small core, which is surrounded by a huge mantle. The mantle occupies approximately five-sixths of the total volume Globe. And on top everything is covered by a rather thin outer crust of the Earth.

Core structure

The core is the central, middle part. It is divided into several layers: internal and external. According to most modern scientists, the inner core is solid, and the outer core is liquid (in a molten state). And the core is very heavy: it weighs more than a third of the mass of the entire planet with a volume of just over 15. The core temperature is quite high, ranging from 2000 to 6000 degrees Celsius. According to scientific assumptions, the center of the Earth consists mainly of iron and nickel. The radius of this heavy segment is 3470 kilometers. And its surface area is about 150 million square kilometers, which is approximately equal to the area of ​​​​all the continents on the surface of the Earth.

How was the Earth's core formed?

There is very little information about the core of our planet, and it can only be obtained indirectly (there are no core rock samples). Therefore, theories can only be expressed hypothetically about how the Earth’s core was formed. The history of the Earth goes back billions of years. Most scientists adhere to the theory that at first the planet formed as a fairly homogeneous one. The process of isolating the nucleus began later. And its composition is nickel and iron. How was the Earth's core formed? The melt of these metals gradually sank to the center of the planet, forming the core. This came at the expense of more specific gravity melt.

Alternative theories

There are also opponents of this theory, who present their own, quite reasonable, arguments. Firstly, these scientists question the fact that an alloy of iron and nickel passed into the center of the core (which is more than 100 kilometers). Secondly, if we assume the release of nickel and iron from silicates similar to meteorites, then a corresponding reduction reaction should have occurred. This, in turn, should have been accompanied by the release of a huge amount of oxygen, forming Atmosphere pressure several hundred thousand atmospheres. But there is no evidence of the existence of such an atmosphere in the past of the Earth. That is why theories were put forward about the initial formation of the core during the formation of the entire planet.

In 2015, Oxford scientists even proposed a theory according to which the core of planet Earth consists of uranium and has radioactivity. This indirectly proves the long existence of the magnetic field near the Earth, and the fact that in modern times our planet emits much more heat than previous scientific hypotheses assumed.

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 there is a monstrous pressure of 3 million atmospheres and incredible high temperature- 5000°C. It took scientists several centuries to find out what was in the center of the Earth. 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. It's a long way from the center of the Earth.

History of the discovery of the earth's core

One of the first to guess about the presence of a core in the center of the planet was the English physicist and chemist Henry Cavendish at the end of the 18th century. By using physical experiments he calculated the mass of the Earth and, based on its size, determined average density substances of our planet - 5.5 g/cm3. Density of known rocks and there were approximately two times less minerals in the earth’s crust. This led to the logical assumption that in the center of the Earth there is a region of denser matter - the core.

In 1897, the German seismologist E. Wichert, studying the passage of seismological waves through the interior 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 nucleus formation were born. It is assumed that it was formed due to the settling of heavier elements towards the center, and initially the substance of the planet was homogeneous (gaseous).

What does the core consist of?

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

At the moment, scientists assume that the central part of the planet is heterogeneous. What is at the center of the Earth? The part adjacent to the mantle is the liquid core, consisting of molten matter. Apparently it contains a mixture of iron and nickel. Scientists were led to this idea by a study of iron meteorites, which are pieces of asteroid cores. On the other hand, the resulting iron-nickel alloys have more high density than the estimated core density. Therefore, many scientists are inclined to assume that in the center of the Earth, the core, there are lighter chemical elements.

Geophysicists explain the existence of a magnetic field by the presence of a liquid core and the rotation of the planet around its own axis. 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.

Interior core, despite the temperature of several thousand degrees, is solid. This is because the pressure at the center of the planet is so high that hot metals become solid. Some scientists suggest that hard core consists of hydrogen, which under the influence of incredible pressure and enormous temperature becomes like metal. Thus, even geophysicists still do not know for certain what the center of the Earth is. But if we consider the issue from a mathematical point of view, we can say that the center of the Earth is approximately 6378 km away. from the surface of the planet.