What is the origin of the moon?

The origin of the moon is uncertain. Regarding the origin of the moon, there are roughly three major schools in history. In the later period, the "Great Collision Theory" was newly formed on the basis of various theories and new research results.

1. Split theory

This is the earliest hypothesis to explain the origin of the moon. As early as 1898, George Darwin, the son of the famous biologist Darwin, pointed out in the article "Tides and Similar Effects in the Solar System" that the moon was originally a part of the earth. Later, due to the rapid rotation of the earth, part of the material on the earth was thrown away. When it came out, these materials separated from the earth to form the moon, and the large crater left on the earth is now the Pacific Ocean.

This view was quickly opposed by some people. They believe that with the speed of the earth's rotation, it is impossible to throw a piece of something that big. Besides, if the moon was thrown out by the earth, then the material composition of the two should be the same. However, through laboratory analysis of the rock samples brought back from the moon by the "Apollo 12" spacecraft, it was found that the two are very different. The age of the rocks on the moon's surface is extremely old. The age of the rocks on the entire moon's surface ranges from 3 to 4.2 billion years. The age of the oldest rocks on the earth's surface is limited to 3.8 billion-year-old metamorphic rocks exposed in some areas, while the Pacific Ocean The age of the ocean floor rocks is extremely young, completely contrary to the "split theory" theory.

2. Capture theory

This hypothesis holds that the moon was originally just a moon-sized asteroid in the solar system. Once, because it moved near the earth, it was captured by the earth’s gravity. Captured and never left the earth again. There is also a view close to the capture theory, which believes that the earth continues to accrete together the materials that enter its orbit. Over time, more and more things are accreted, and eventually the moon is formed. But some people point out that for a planet as big as the moon, the earth may not have that much power to capture it.

3. The theory of homology

This hypothesis holds that the earth and the moon are both diffuse nebula materials in the solar system, and have been rotated and accreted in almost the same solar nebula area. Celestial bodies of different sizes are formed at the same time. During the accretion process, the Earth is a little faster than the Moon and becomes the "elder brother". This assumption has also been challenged by objective facts. Through laboratory analysis of rock samples brought back from the moon by the "Apollo" spacecraft, it was found that the average chemical compositions of the earth and the moon are very different, and it was found that the moon's rocks are also much older than those of the earth.

4. Collision theory

This hypothesis holds that in the early stages of the evolution of the solar system, a large number of "planet particles" were formed in the solar system space, first forming a celestial body equivalent to 0.14 times the mass of the Earth. Planetesimals grew and merged to form a primitive earth through collision and accretion. During their respective evolution processes, these two celestial bodies formed a metallic core mainly composed of iron and a mantle and shell composed of silicate. Since the two celestial bodies are not far apart, the chance of encountering them is high.

By chance, the small celestial body hit the earth at a speed of about 5 kilometers per second. The violent collision not only changed the motion state of the Earth and tilted the Earth's rotation axis, but also caused the small celestial body to be shattered by the impact. The silicate shell and mantle were heated and evaporated, and the expanding gas carried a large amount of it at an extremely high speed and shattered it. of dust flying away from the earth. The material flying away from the earth is mainly composed of the mantle of the collision body. When the Earth was hit by a huge impact, most of the material in the mantle and crust was heated and evaporated, and the expanding gas carried a large amount of crushed dust flying away from the Earth at an extremely high speed. The metal core separated from the mantle when the impactor broke up was decelerated by the expanding and flying gas, and was accreted to the Earth in about 4 hours. The gas and dust flying away from the earth are not completely separated from the gravitational control of the earth. They are combined by mutual accretion to form an almost molten moon, or they first form a ring and then gradually accrete to form a large, partially molten moon. This version is universally recognized.

This model clearly explains that the average composition of the moon is compared with the average composition of the earth. The moon is relatively poor in iron and volatile matter, and the density of the moon is lower than that of the earth.

The isotope composition of certain elements that have contrasting characteristics of the "genes" of the Earth and the Moon, such as the isotopic composition of oxygen, chromium, titanium, iron, tungsten, silicon, etc., the measured values ??of the Moon and the Earth are consistent within the error range, indicating that the Moon is The "daughter of the earth." For 4.5 billion years, the earth has been carrying its daughter by its side, and the moon has been accompanying its mother, and together they have experienced 4.5 billion years of long and ancient times.