What is the core of the planet. How do we know what is in the Earth's core? Earth's magnetic field
By tightly squeezing both substances using diamonds, the scientists were able to force molten iron through the silicate. “This pressure significantly changes the interaction properties of iron with silicates,” says Mao. - At high pressure, a “melting network” is formed.
This may indicate that the iron gradually slipped through the Earth's rocks over millions of years until it reached the core.
At this point you may ask: how do we actually know the size of the kernel? Why do scientists believe that it begins 3000 kilometers away? There is only one answer: seismology.
When an earthquake occurs, it sends shock waves throughout the planet. Seismologists record these vibrations. It's like we're hitting one side of the planet with a giant hammer and listening to the noise on the other side.
“There was an earthquake in Chile in the 1960s, which gave us a huge amount of data,” says Redfern. “Every seismic station around the Earth recorded the tremors of this earthquake.”
Depending on the route these vibrations take, they pass through different parts of the Earth, and this affects what "sound" they make at the other end.
Early in the history of seismology, it became apparent that some oscillations were missing. These “S-waves” were expected to be seen at the other end of the Earth after originating at one end, but were not seen. The reason for this is simple. S-waves reverberate through solid material and cannot travel through liquid.
They must have encountered something molten at the center of the Earth. By mapping the paths of S-waves, scientists concluded that at a depth of about 3,000 kilometers, rocks become liquid. This also suggests that the entire core is molten. But seismologists had another surprise in this story.
In the 1930s, Danish seismologist Inge Lehman discovered that another type of wave, P-waves, unexpectedly passed through the core and was detected on the other side of the planet. The assumption immediately followed that the core was divided into two layers. The "inner" core, which begins 5,000 kilometers below, was solid. Only the “outer” core is melted.
Lehman's idea was confirmed in 1970, when more sensitive seismographs showed that P waves did indeed travel through the core and, in some cases, reflected from it at certain angles. It's no surprise that they end up on the other side of the planet.
It's not just earthquakes that send shock waves through the Earth. In fact, seismologists owe a lot to the development of nuclear weapons.
A nuclear explosion also creates waves on the ground, which is why states turn to seismologists for help during nuclear weapons testing. This was extremely important during the Cold War, so seismologists like Lehman received a lot of support.
Competing countries were learning about each other's nuclear capabilities and, at the same time, we were learning more and more about the Earth's core. Seismology is still used to detect nuclear explosions today.
Now we can draw a rough picture of the structure of the Earth. There is a molten outer core that starts about halfway to the center of the planet, and within it is a solid inner core with a diameter of approximately 1,220 kilometers.
This does not make the questions any less, especially on the topic of the inner core. For example, how hot is it? Figuring out this was not so easy, and scientists have been scratching their heads for a long time, says Lidunka Vokadlo from University College London in the UK. We can't put a thermometer in there, so the only option is to create the required pressure in a laboratory setting.
Under normal conditions, iron melts at a temperature of 1538 degrees
In 2013, a group of French scientists produced the best estimate to date. They subjected pure iron to half the pressure of what is in the core, and proceeded from there. The melting point of pure iron in the core is approximately 6230 degrees. The presence of other materials may lower the melting point slightly, up to 6000 degrees. But it's still hotter than the surface of the Sun.
Like a jacket potato of sorts, the Earth's core remains hot thanks to the heat left over from the planet's formation. It also extracts heat from the friction that occurs as dense materials move, as well as from the decay of radioactive elements. It cools by about 100 degrees Celsius every billion years.
Knowing this temperature is useful because it affects the speed at which vibrations travel through the core. And this is convenient, because there is something strange in these vibrations. P-waves travel surprisingly slowly through the inner core—slower than if it were made of pure iron.
“The wave speeds that seismologists have measured in earthquakes are much lower than what experiments or computer calculations show,” says Vokadlo. “Nobody yet knows why this is so.”
Apparently there is another material mixed in with the iron. Possibly nickel. But scientists calculated how seismic waves should pass through an iron-nickel alloy, and were unable to fit the calculations to the observations.
Vokadlo and her colleagues are now looking at the possibility that other elements, such as sulfur and silicon, may be present in the core. So far, no one has been able to come up with a theory of the composition of the inner core that would satisfy everyone. Cinderella problem: the shoe doesn't fit anyone. Vokadlo is trying to experiment with inner core materials on a computer. She hopes to find a combination of materials, temperatures and pressures that will slow down seismic waves by the right amount.
She says the secret may lie in the fact that the inner core is almost at the melting point. As a result, the exact properties of the material may differ from those of a completely solid substance. It could also explain why seismic waves travel slower than expected.
“If this effect is real, we could reconcile the results of mineral physics with the results of seismology,” says Vokadlo. “People can’t do that yet.”
There are still many mysteries related to the Earth's core that have yet to be solved. But unable to dive to these unimaginable depths, scientists are accomplishing the feat of figuring out what lies thousands of kilometers below us. The hidden processes of the Earth's interior are extremely important to study. The Earth has a powerful magnetic field that is generated by its partially molten core. The constant movement of the molten core generates an electric current inside the planet, and this, in turn, generates a magnetic field that extends far into space.
This magnetic field protects us from harmful solar radiation. If the Earth's core were not the way it is, there would be no magnetic field, and we would seriously suffer from it. It's unlikely that any of us will be able to see the core with our own eyes, but it's good to just know that it's there.
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 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 thicknesses, forming a peculiar 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 we study the outer layer of the nucleus?
Scientists can judge what the core looks like and what it consists of by monitoring seismic activity. For example, it was found that the outer and inner layers rotate in different directions under the influence of a magnetic field. The Earth's core conceals dozens of unsolved mysteries and awaits new fundamental discoveries.
When you drop your keys into a stream of molten lava, say goodbye to them because, well, dude, they're everything.
- Jack Handy
Looking at our home planet, you will notice that 70% of its surface is covered with water.
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 lighter elements out, and gravity causes irregularities in the disk to collapse and form planets.
In the case of the Solar System, the four inner worlds are the densest of all the planets in the system. Mercury consists of the densest elements, which could not hold large amounts 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 at the edge of supernovae, is the most abundant element in 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: 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 capable of picking 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 there is 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 greater 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 research that might lead to 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 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, 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.
MOSCOW, February 12 - RIA Novosti. American geologists say that the inner core of the Earth could not have arisen 4.2 billion years ago in the form in which scientists imagine it today, since this is impossible from the point of view of physics, according to an article published in the journal EPS Letters.
“If the core of the young Earth consisted entirely of pure, homogeneous liquid, then the inner nucleolus should not exist in principle, since this matter could not cool to the temperatures at which its formation was possible. Accordingly, in this case the core may be heterogeneous composition, and the question arises of how it became this way. This is the paradox we discovered,” says James Van Orman from Case Western Reserve University in Cleveland (USA).
In the distant past, the Earth's core was completely liquid, and did not consist of two or three, as some geologists now suggest, layers - an inner metallic core and a surrounding melt of iron and lighter elements.
In this state, the core quickly cooled and lost energy, which led to a weakening of the magnetic field it generated. After some time, this process reached a certain critical point, and the central part of the nucleus “froze”, turning into a solid metal nucleolus, which was accompanied by a surge and increase in the strength of the magnetic field.
The time of this transition is extremely important for geologists, as it allows us to roughly estimate at what speed the Earth’s core is cooling today and how long the magnetic “shield” of our planet will last, protecting us from the action of cosmic rays, and the Earth’s atmosphere from the solar wind.
Geologists have discovered what flips the Earth's magnetic polesSwiss and Danish geologists believe that the magnetic poles periodically change places due to unusual waves inside the liquid core of the planet, periodically rearranging its magnetic structure as it moves from the equator to the poles.Now, as Van Orman notes, most scientists believe that this happened in the first moments of the Earth's life due to a phenomenon, an analogue of which can be found in the planet's atmosphere or in soda machines in fast food restaurants.
Physicists have long discovered that some liquids, including water, remain liquid at temperatures noticeably below the freezing point, if there are no impurities, microscopic ice crystals or powerful vibrations inside. If you shake it easily or drop a speck of dust into it, then such a liquid freezes almost instantly.
Something similar, according to geologists, happened about 4.2 billion years ago inside the Earth's core, when part of it suddenly crystallized. Van Orman and his colleagues tried to reproduce this process using computer models of the planet's interior.
These calculations unexpectedly showed that the Earth's inner core should not exist. It turned out that the process of crystallization of its rocks is very different from the way water and other supercooled liquids behave - this requires a huge temperature difference, more than a thousand kelvins, and the impressive size of a “speck of dust”, whose diameter should be about 20-45 kilometers.
As a result, two scenarios are most likely - either the planet’s core should have frozen completely, or it should still have remained completely liquid. Both are untrue, since the Earth does have an inner solid and outer liquid core.
In other words, scientists do not yet have an answer to this question. Van Orman and his colleagues invite all geologists on Earth to think about how a fairly large “piece” of iron could form in the planet’s mantle and “sink” into its core, or to find some other mechanism that would explain how it split into two parts.