How is it formed?

It was not until the sixteenth century that man realized that the earth was only a planet in the solar system.

We can know the earth without a space probe, but it was not until the twentieth century that we really outlined the whole picture of the earth. Of course, it is very important to get its image from space. The spatial influence of the earth is very helpful for weather forecast, especially for typhoon (hurricane) forecast. The earth seen from space is really beautiful, lovely and spectacular.

According to the chemical composition and seismic characteristics, the earth can be divided into several layers, and their names and ranges (depth in kilometers) are as follows:

0 ~ 40 crust 40 ~ 2890 mantle 2890 ~ 5 150 outer core 5 150 ~ 6378 inner core

The thickness of solid crust varies greatly, and the crust in marine areas is thin, with an average thickness of about 7 kilometers; The continental crust is much thicker, with an average thickness of about 40 kilometers; The mantle is also solid, but there is a very small partially melted area on it, called asthenosphere. The top of the mantle and the whole crust above it are called lithosphere. As for the outer core is liquid and the inner core is solid. These different layers are bounded by discontinuities, the most famous of which is the Mo Holovics discontinuity between the crust and mantle.

The mantle occupies the main part of the earth, while the core occupies the second place. As for the space where we live, it is only a tiny part of the whole earth (mass, unit is 10 to the 24th power kilogram: atmosphere = 0.000005 1, ocean = 0.00 14, crust = 0.026, mantle = 4.043).

The main component of the core is iron (or iron-nickel), but there may be some lighter substances. The core temperature is about 7,500K, which is higher than the surface temperature of the sun. The main components of the lower mantle may be silicon, magnesium and oxygen, plus some iron, calcium and aluminum; The main components of the upper mantle are olivine and pyroxene (iron magnesium silicate rocks), but there are also calcium and aluminum. All the above knowledge comes from seismic data. Although the material in the upper mantle is sometimes brought to the surface by lava from volcanoes, we still can't reach the main part of the solid earth, and the current seabed drilling operation has not even dug through the crust. The crust is mainly composed of silicate such as quartz (silica) and feldspar. Generally speaking, the geochemical components are: iron 34.6%, oxygen 29.5%, silicon 15.2%, magnesium 12.7%, nickel 2.4%, sulfur 1.9% and titanium 0.05%.

The earth is the main star with the highest average density.

Other terrestrial planets also have structures and compositions similar to those of the Earth, but there are some differences: the moon nucleus accounts for the smallest proportion; Mercury has the largest proportion of nuclei; The letters of Mars and the moon are thicker; There is no difference in chemical composition between the moon and mercury. The earth may be the only one that can be subdivided into an inner core and an outer core. However, please note that our understanding of the interior of the planet mainly comes from theoretical deduction, even for the earth.

Different from other terrestrial planets, the outermost layer of the earth (including the crust and the top of the upper mantle) is divided into several pieces and "floats" on the fiery mantle below, which is the famous theory of plate tectonic movement. This theory mainly describes two kinds of movements: extension and dive. The former occurred in the place where the two plates were far apart, and the magma below them spewed out to form a new crust; The latter occurs when two plates collide with each other, one of which dives under the other plate and finally disappears into the mantle. In addition, there are some plate boundaries that cross each other or two continental plates collide with each other.

Most of the earth's surface is very young, only about 500 million years old, which is really short from an astronomical point of view. However, there are few places where the basement of the earth's crust is exposed, such as Suizhong County, Huludao City, Liaoning Province, China. Because of the long cooling time when granite is formed, the crystals in granite are very developed, and the side length is 1-2 cm, so it is named Suizhong granite. Because erosion and tectonic geological movement continue to destroy and rebuild most of the surface, it is not easy to find early geological records of the surface, such as impact craters, so most of the early earth history has disappeared. The earth is about 4.5 to 4.6 billion years old, but the oldest known rocks are only about 4 billion years old (the earth was a fireball formed by molten magma a long time ago), and rocks over 3 billion years old are very rare. The oldest biological fossils are not earlier than 3.9 billion years ago, and there is no record of the critical period of the origin of life.

7 1% of the earth's surface is covered with water, and the earth is the only planet in the solar system that can have liquid water on its surface (liquid ethane or methane exists on Titan's surface, while liquid water may exist under Europa's surface, but it is still unique that liquid water exists on the earth's surface). Liquid water is an indispensable element in our known life forms; Because of the large specific heat of water, the thermal volume of the ocean has become a great contributor to keeping the earth's temperature constant; Liquid water is also the main force of erosion and weathering on land, and land is the only place in the solar system that has this effect (it may have had this effect in the early days of Mars, but it is no longer there).

In the composition of the earth's atmosphere, 77% is nitrogen, 265,438+0% is oxygen, followed by trace amounts of argon, carbon dioxide and water vapor. Most of the atmosphere at the beginning of the earth may be carbon dioxide, but most of it has been combined with carbonate rocks, and the rest is dissolved in the ocean and discharged by green plants; Nowadays, plate tectonic movement and biological action are the continuous masters of the growth and decline of carbon dioxide in the atmosphere. The greenhouse effect caused by moisture and trace carbon dioxide in the atmosphere is very important to maintain the surface temperature. The greenhouse effect increases the surface temperature by about 35℃, otherwise the average surface temperature will be extremely cold -2 1℃! Without water vapor and carbon dioxide, seawater would freeze and life forms as we know them would be impossible to develop. In addition, water vapor is an indispensable angle in the earth's water cycle and weather changes.

The existence of free oxygen is also a major feature of geochemical composition, because oxygen is a very active gas and should be easily combined with other elements in the atmosphere. Oxygen on the earth is produced and maintained entirely by biological action. Without life, there is no free oxygen.

The tidal force between the Earth and the Moon will increase the rotation period of the Earth by about 2 milliseconds every century. The latest research shows that 900 million years ago, there was only 18 hours a day, while there was 48 1 day a year. The earth has a moderate magnetic field, which should be caused by the current in the liquid outer core. Due to the interaction between the solar wind and the earth's magnetic field and the outer atmosphere, the aurora is produced. The imbalance of the above factors causes the magnetic poles to move on the surface. At present, the magnetic North Pole is located on the northern border of Canada. Due to the interaction between the solar wind and the earth's magnetic field and the outer atmosphere, the aurora is produced.

The earth's magnetic field and its interaction with the solar wind also cause the Van Allen radiation belt, which is a pair of annular belts around the earth, like doughnuts, composed of gas ions (plasma), and the outer circle extends from 19000km above sea level to 4 1000km. The elevation of the inner ring is between 13000-7600 km.