The moon is the only natural satellite on Earth. It has been hanging quietly in the sky for billions of years, and it seems to be an eternal existence. People have long been accustomed to this, but when we look at the moon, maybe you can never imagine that the planet has been gradually moving away from the earth.
1969 On July 21, 1969, the Apollo 11 lunar module landed in the southern part of the tranquil sea of the moon. This is the first time that humans have left footprints on other planets.
Apollo 11 crew conducted many activities and experiments on the surface of the moon. One of them was to install the mirror . These mirrors were used to reflect the laser light emitted from the earth to the moon. Scientists will measure the distance between the earth and the moon through the time required for the laser to go back and forth.
In the past few decades, scientists have discovered that the moon is moving away from the earth at a rate of 3.8 cm per year. If we simulate at the current rate of the moon far away from the earth, we will find that the earth collided with the moon about 1.5 billion years ago. However, based on the age of the lunar soil, the moon has existed for about 4.5 billion years.
This means that if the current fallback model is accurate, then the velocity of the moon's distance may not be constant.
From the University of Utrecht, Netherlands and , a researcher from the University of Geneva, Switzerland, recently discovered rock formations that can reveal the history of the moon's distant past, but the rock formations are not on the moon, but in the Karigini National Park, Australia on Earth.
In Karigini's National Park are some stratified sediments from 2.5 billion years ago, which are composed of unique iron layers and silicon-rich minerals. In the past, these substances were widely deposited on the seabed, but now they are the oldest part of the earth's crust. In , the red-brown iron layers alternate at regular intervals, while the darker intervals are some softer rocks that are more easily eroded. Their surfaces are polished by rivers that once flowed through the canyon, showing an alternating pattern of white, red and gray.
1972, Australian geologist A.F. Trendel proposed that the periodic patterns presented by these ancient rock formations may be related to climate change caused by the Milankovic cycle. The Milankovic cycle describes how the shape of the earth's orbit and how the slight periodic changes in the rotation axis affect the sunlight received by the earth and the climate change affected. The cycle changes every 400,000 years, 100,000 years, 41,000 years and 21,000 years, which has an impact on the evolution and climate of animal and plant migration. The characteristics of these changes can be interpreted through the periodic changes of ancient rock formations.
Earth-moon distance is directly related to Milankovic's cycle frequency. When the moon and the earth are closer, the cycle time will be shorter. This means that we can first find the Milankovic cycle in the ancient rock strata, and then find the period of the earth swing, thereby estimating the distance between the earth and the moon during the rock strata.
Researchers' analysis of rock formations shows that these rock formations contain periodic changes of multiple scales, is repeated at intervals of 10 and 85 cm, and combines the thickness and sedimentary speed of the rock formation, and it can be found that these periodic changes occur every 11,000 years and 100,000 years.
The cycle of 11,000 years is much shorter than the current 21,000 years. Scientists use this difference to calculate the distance between the earth and the moon 2.4 billion years ago. found that the distance between the earth and the moon was about 60,000 kilometers at that time.
At that time, the earth's rotation speed was much faster than now, only had 17 hours a day . The gravity generated by such a fast speed was enough to lock the moon firmly around the earth. As the earth's oceans increased, everything changed.
The original water source of the earth comes from meteorite . External meteorites are rich in water. The early Earth is very susceptible to impacts, so meteorites bring rich water sources to the earth. After the solar system is stable, the number of meteorites hit is very small. At this time, the water resources on the earth are basically maintained at a relatively stable level.
Later, the glaciers on the earth continued to melt, increasing the earth's water resources again.
Because the direction of the object's movement is opposite to the friction force, the increasing number of ocean water causes the earth to suffer from the reverse friction during rotation. The moon's tidal effect on the earth's ocean further aggravates the resistance to the earth's rotation, and finally causes the speed of the earth's rotation to continue to decline. The gravitational binding effect of on the moon is getting smaller and smaller. Until now, the moon can continue to stay away from the earth.
In addition, asteroid impact is also the reason why the moon is far away from the earth.
Every larger mass celestial body passes through the moon or directly against the moon will affect the moon's movement posture and orbit. It can be seen from the dense craters of the moon that has experienced many impacts in the past few billion years.
As the speed of the earth's rotation continues to slow down, the difference in the angular velocity between the earth's rotation and the moon's revolution will become smaller and smaller, and the speed of the moon's distance from the earth will also decrease.
Tens of billions of years later, the moon will tidal locks with the earth and become the Earth's synchronous satellite . By then, the distance between the earth and the moon will increase to 550,000 kilometers, and the Earth-1 rotation period of the Earth and the moon's revolution period will last for 1,100 hours.
