First, think in the cold winter, you wear a thick sweater, what will happen? Is the inside of the sweater warmer than the outside of the sweater? Or the lake freezes in winter. The water below the surface of the ice can still exist as a liquid and it can reach 4 degrees Celsius in the deeper layers, why doesn’t this melt the ice above the lake?
Although the principles of these two examples are slightly different, both can illustrate that temperatures can be reliably separated if there is a “shield” in between. So does our Earth, the nearly 3,000 km thick rock mantle on our planet’s surface acts like a sweater and ice on the lake. This layer of rock is very thick and helps the Earth’s core not lose heat.
Or to put it another way, our planet has not yet reached thermal equilibrium and therefore heat cannot be transferred efficiently from the core to the surface.
The Earth’s core is the innermost part of the Earth, and as found by seismic studies, it is a mostly solid sphere with a radius of about 1,220 km, only 70% of the radius of the Moon. It is said to contain an iron-nickel alloy.
In addition to the initial accretion heat, most of the new heat generated in the Earth’s core comes from the radioactive decay of some long-lived isotopes (mainly 4 radioactive isotopes of uranium- 235, potassium-40, uranium-238 and thorium-232), this process continuously generates heat and transfers it to the outside. However, soon this heat will have to pass through the ice and cold air. Therefore we cannot feel this heat.
According to Fourier’s law, the steeper the thermal gradient, the faster the conduction of heat, and the surface radiates heat to the cold night sky very quickly, just like the water on the surface of a lake in early winter, it loses heat faster than the There is a lot of water below.
About 1.5 billion years ago, the Earth had a hot core that was losing heat inexplicably. Then, after moderately cooled, part solidified (the Earth’s inner core) and sank to the rest (outer core), taking with it most of the iron and nickel. It is the process by which the inner core and outer core are formed.
About 4.6 billion years ago, after the birth of the Solar System, some cosmic debris and dust began to collide continuously, and slowly mixed together through gravity to form the original Earth. . But our planet at that time had a rather terrible environment, everywhere there were red rifts, magma could suddenly erupt from the ground at any time.
Along with the constant collisions with asteroids and comets from the outside world, the temperature of the entire Earth now exceeds 1,200 degrees Celsius. In essence, the Earth is now like a mass of mud. high temperature, high pressure and constantly impacted by objects in outer space. Geologists often refer to this initial 500 million year period of Earth as hell on earth.
During this time period, the temperature of outer space is much lower than that of Earth. Therefore, after each collision, the surface of the Earth also rapidly cools and turns black, like red iron bars dipped in water. Over time, a layer of rock formed on the Earth’s surface and became the original crust of the entire planet.
In addition, under the rate of heat absorption from the inside, this imbalance caused the surface to lose thermal energy and cool. As a result, the temperature will drop rapidly until the surface begins to solidify into stone. The deeper the solid rock, the hotter the lava underneath, but this process doesn’t happen fast enough to melt the surface rock.
In this way, each of the Earth’s mantles would have a near-stable temperature, and each would release excess thermal energy at the same rate. Accordingly, the Earth also gradually differentiates into a hot core, a mantle layer and a less hot mantle.
In fact, this surface cooled much faster than we imagined, the original crust after several million years was able to achieve stability and cool enough to ensure liquid water could be stored on the surface. planet face.
This is like when you take a hot dumpling out of the oven, the outside crust will cool down quickly, but actually the inside of the dumpling is still very hot, as long as you don’t break it, that dumpling It will still keep the heat inside.
According to scientists’ calculations, the temperature inside the Earth’s core will remain at the current high level for a period of time lasting 1 billion years.
Mechanically, it is divided into 5 main layers: lithosphere, mantle, mantle, outer core, and inner core. Chemically, it is divided into crust, upper mantle, lower mantle, outer core and inner core.
In fact, there are still places where we can feel the heat from the Earth’s core passing through to the outside. They are hot spring geysers, volcanic ridges near the ocean…
Source: Earthlymission; Nature; NASA