The earth moves around the sun in an approximate circle at a certain speed, and the centrifugal effect produced in this process can resist the gravity of the sun, thus avoiding falling on the surface of the sun. In this way, the earth seems to be "suspended" in the universe. By the same token, satellites and the moon can orbit the earth at a certain speed, and they can also avoid being dragged to the ground by the gravity of the earth.
In addition, the solar system will move around the center of the Milky Way to avoid falling into the center of the Milky Way. The earth is not "floating" in the universe, which is just an illusion caused by the invisible and intangible effect of gravity. Being in the sun is equivalent to observing all the planets with the sun (or the earth) as a fixed point, and there are reasons why these planets go around the sun without falling into the sun.
Just like the illusion of floating in the sky, in fact, for the planet, the gravity of the sun (almost) completely provides centripetal force, so the planet can always rotate around the sun spontaneously and continuously, just like someone is throwing a ball with a rope. As long as there is traction, the planet can always rotate around the center, and when we replace the traction provided by this rope with the gravity of the sun, the planet looks like it is suspended in the universe.
: introduction to the earth:
1. The earth is one of the eight planets in the solar system, ranking third in the order from near to far from the sun. It is also the earth-like planet with the largest diameter, mass and density in the solar system, with a distance of1.500 million kilometers from the sun. The earth rotates from west to east and revolves around the sun at the same time. 4-4.6 billion years ago. It has a natural satellite-the moon, forming a celestial system-the earth-moon system. It originated from the primitive solar nebula 4.6 billion years ago.
2. The equatorial radius of the earth is 6378. 137km, the polar radius is 6356.752km, the average radius is about 637 1km, and the equatorial circumference is about 40076km. It is an irregular ellipsoid with slightly flat poles and slightly bulging equator. The surface area of the earth is 5 1 100 million square kilometers, of which 7 1% is ocean and 29% is land. Seen from space, the earth looks blue.
3. There are core, mantle and shell structures inside the earth, and hydrosphere, atmosphere and magnetic field outside the earth. The earth is the only known celestial body with life in the universe at present, and it is the home of millions of creatures, including human beings. ?
446 million years ago, the earth was born. The evolution of the earth can be roughly divided into three stages. The first stage is the formation of the earth's sphere, and its time limit is about 4600 ~ 4200ma ago. The earth when it was born 4.6 billion years ago is very different from the earth in 2 1 century. According to scientists' inference, at the beginning of the earth's formation, it was a hot ball composed of hot liquid substances (mainly magma).
5. With the passage of time, the temperature of the earth's surface has been decreasing, and the solid core has gradually formed. Dense matter moves toward the center of the earth, and less dense matter (rocks, etc.). ) floats on the surface of the earth, thus forming the earth whose surface is mainly composed of rocks.
6. The second stage is Archean and Proterozoic. Its time limit is 4200-543Ma. The earth constantly releases energy, and the steam, carbon dioxide and other gases released by the continuous eruption of high-temperature magma constitute a very thin early atmosphere-primitive atmosphere. With the increase of water vapor in the primitive atmosphere, more and more water vapor condenses into small water droplets, and then gathers into rainwater and falls to the surface. In this way, the primitive ocean was formed.
7. The third stage is Phanerozoic, with a time limit of 543Ma. Phanerozoic lasted relatively short, but during this period, biology flourished, geological evolution was very rapid, and geological processes were rich and colorful. In addition, geological bodies are distributed all over the world and widely preserved, which makes it possible to observe and study them well, become the main research object of geological science and lay the basic theory and knowledge of geology.
8. Human scientists have been able to reconstruct information about the earth's past. The material in the solar system originated 4,567.2 million 600,000 years ago, about 4,540 million years ago (with an error of about 65,438+0%), and the earth and other planets in the solar system began to form in the solar nebula, leaving gas and dust after the formation of the sun.
9. 1 After 20 million years, the earth will basically take shape. From the initial melting state, the outer layer of the earth cooled and solidified into a solid crust, and water began to accumulate in the atmosphere. The moon formed late, about 4.53 billion years ago. A celestial body (usually called Theia) with a volume equivalent to Mars and a mass of about 65,438+00% of the Earth had a fatal collision with the Earth.
10. part of the mass of this celestial body is combined with the earth, part of it is splashed into space, and enough material enters the orbit to form the moon. The released gas and volcanic activity produce primitive atmosphere, and the water carried by asteroids, larger protoplanets, comets and celestial bodies outside Neptune increases the water content of the earth, and condensed water produces oceans.
1 1. The brightness of the newly formed sun is only 70% of that of the sun, but there is evidence that the early ocean is still liquid, which is called the weak young sun paradox. The combination of greenhouse effect and higher solar activity increases the temperature of the earth's surface and prevents the condensation of the ocean. There are two main theories of mainland growth: stable growth in modern times and rapid growth in early history. Studies show that the second theory is more likely, that is, the early crust grew rapidly, followed by long-term stable continental regions.
12. In the last hundreds of millions of years on the time scale, the earth's surface constantly reshaped itself, and the mainland constantly formed and split. Occasionally, a supercontinent will be formed in the continent where the surface moves. About 750 million years ago, Rodinia, the earliest known supercontinent, began to split, then merged into a pan-oceanic continent between 600 million and 540 million years ago, and finally a continent formed 65.438+0.8 billion years ago.
Reference: Baidu Encyclopedia Earth