How much do you know about the earth? Take you deeper into this "blue star"

The earth is the third closest planet to the sun in the solar system and the only celestial body with life so far. Although the earth is the fifth largest planet in the solar system, it is the only planet with liquid water on its surface. The earth is the largest of the four planets closest to the sun. These four planets are all made of rocks and metals, and the earth is only a little bigger than nearby Venus.

The word earth has a history of 1000 years. Except the earth, all the other planets are named after the gods in Greek and Roman mythology. The word earth comes from Germanic language, which means "land".

Radius of the earth is 63,765,438+0 km, the largest terrestrial planet and the fifth largest planet in the solar system.

The average distance between the earth and the sun is 65.438+0.5 billion kilometers, which is only an astronomical unit (abbreviated as A.U., whose value takes the average distance between the earth and the sun). Astronomical units provide a simple way to compare the distances between planets and the sun in the solar system.

It takes about 8 minutes for sunlight to reach the earth.

When the earth revolves around the sun, it is still rotating, and it takes about 23.9 hours to rotate once. It takes about 365.25 days to make a revolution around the sun. The calendar system we use now defaults to 365 days a year, and the extra quarter of the day when the earth revolves around the sun has a certain influence on this system. In order to keep the time of our calendar year consistent with the time when the earth revolves around the sun, one day is added to the calendar every four years, that is, there are 366 days in that year. The added day is leap day, and that year is leap year.

There is an included angle of 23.4 between the earth's rotation axis and its orbital plane, thus forming the alternation of four seasons. For part of the year, the northern hemisphere leans towards the sun, while the southern hemisphere is far away from the sun. As the height of the sun in the sky increases, the more sunlight and heat the ground in the northern hemisphere gets, and it is summer in the northern hemisphere. At the same time, the southern hemisphere can only get less sunlight and heat, and it is winter in the southern hemisphere. After half a year, the situation reversed. In spring and autumn, the sunlight and heat received by the northern and southern hemispheres are roughly the same.

About 4.5 billion years ago, when the solar system formed its present celestial layout, under the action of gravity, the rotating gas and dust formed the earth and became the third planet according to the distance from the sun. Like other terrestrial planets, the earth consists of a central core, a rocky mantle and a hard crust.

The earth is a rocky planet similar to the earth, with mountains, valleys, canyons, plains and other landforms on its surface. At the same time, the earth is special. Up to 70% of its surface is covered by water, and the title of "water polo" is worthy of the name.

The earth's atmosphere is mainly composed of nitrogen, but there is enough oxygen for us to breathe. The atmosphere also protects us from meteoroids, most of which break up before hitting the earth.

The earth consists of four main layers, from the center of the earth to the surface, namely, the inner core, the outer core, the mantle and the crust.

The core is a solid sphere with a radius of about 1, 22 1 km, and the temperature is as high as 9800 degrees Fahrenheit (5400 degrees Celsius). Outside the inner core is an outer core, which is about 2300 kilometers thick and consists of liquid iron and liquid nickel.

The mantle is the middle layer between the earth's core and the earth's surface, with a thickness of about 2900 kilometers, which is the thickest layer. It itself is a hot and viscous lava mixture, a bit like caramel. The outermost layer is the crust, and the average thickness of the mainland is about 30 kilometers; The ocean crust is very thin, extending from the seabed to the top of the mantle for about 5 kilometers.

Like Mars and Venus, there are volcanoes, mountains and valleys on the earth. The earth's lithosphere, including the crust (continent and ocean) and the upper mantle, has split into huge plates and is constantly moving. For example, the North American plate moves westward above the Pacific basin at a speed equivalent to the growth rate of human nails. When the plates collide with each other, or rupture and dislocation, earthquakes occur and mountains may form.

About 70% of the earth's surface is ocean, with an average depth of about 4 kilometers, accounting for 97% of the earth's total water. Almost all the volcanoes on the earth are hidden under these oceans. Monaque volcano in Hawaii is higher than Mount Everest from top to bottom, but most of it is underwater. The longest mountain range on earth is also underwater, located at the bottom of the Arctic Ocean and the Atlantic Ocean, that is, the mid-ocean ridge, which is about four times that of the Andes, Rockies and Himalayas combined.

The atmosphere near the surface is 78% nitrogen, 2 1% oxygen, and 1% argon, carbon dioxide, neon and other gases. The atmosphere will affect the long-term climate and short-term weather of the earth and protect the earth from most harmful radiation from the sun. The atmosphere also protects us from meteoroids, most of which burn in the atmosphere before hitting the earth, that is, meteors in the night sky.

Illustration: NASA photographed the moon partially wrapped by the earth's atmosphere.

Life is possible because the earth has a suitable temperature and a mixture of its own chemicals. Most uniquely, most of the earth is covered with water, because its temperature allows liquid water to exist for a long time. About 3.8 billion years ago, life was born in this vast ocean.

Unfortunately, due to the continuous impact of climate change, some features on the earth that are conducive to maintaining life are changing.

The earth is the only planet with only one natural satellite. For us, the moon is the natural satellite of the earth and the brightest and most familiar object in the night sky. In many ways, it is because of the moon that the earth can become the beautiful homeland of life. It has stabilized the wobble of the earth and made the climate change little for thousands of years.

Asteroids and boulders sometimes appear temporarily in the earth's orbit, and they are often bound by the earth's gravity for months or even years before returning to their orbits. Some asteroids will orbit the sun with the earth for a long time.

Illustration: The reddish moon during the eclipse.

Some satellites are rock fragments captured by planetary gravity, but the moon may be the result of collisions billions of years ago. When the earth was a young planet, a big stone hit it and became a part of the earth. The resulting stones gathered together to form the moon. With a radius of about 1738km, the moon is the fifth largest satellite in the solar system, and the other four satellites are Ganymede, Titan, Callisto and Io in turn.

The distance between the moon and the earth is farther than most people think, with an average distance of 384,400 kilometers. In other words, there are theoretically 30 planets the size of the earth between the earth and the moon.

The earth has no planetary rings.

The rapid rotation of the earth and the iron-nickel core make the earth produce a geomagnetic field, which makes the solar wind twist into tears in space. The solar wind is a stream of charged particles continuously emitted by the sun. When the charged particles in the solar wind are trapped in the earth's magnetic field, they will collide with the air molecules above the earth's magnetic pole, and the air molecules will start to glow, forming aurora.

Illustration: Schematic diagram of the earth's magnetosphere. The solar wind goes from left to right.

Because of the magnetic field, no matter which direction you turn, the pointer of the compass will always point to the south pole. But the magnetic pole of the earth can be changed, and the magnetic field will be reversed. According to geological records, magnetic pole inversion occurs once every 400,000 years on average, but the time is very irregular. As far as people know, this magnetic pole reversal will not cause any harm to life on earth, and it is unlikely to happen for at least 1000 years. But when the magnetic pole reversal does happen, the needle of the compass may point in many different directions for centuries until it finally points to the south.

1.WJ encyclopedia

2. Astronomical terminology

3. Floating life is like a water-solar system.

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