# How is the age of the earth calculated? After listening to the explanation of the scientists, I understand

The earth is the home where human beings have lived for millions of years. We all know that all things in the universe have their ages. The age of the universe is about 13.8 billion years, the average age of human beings is about 80 years, and the age of the earth is about 4.6 billion years.

Many people understand that human beings begin to calculate their age from the moment they are born. Naturally, we also know how old we are. But how do we know that the earth is 4.6 billion years old when it is so long? How do scientists calculate the exact age of the earth?

The age of human beings is from the moment of birth, and scientists judge a person’s age not by the age of your appearance, nor by the date of birth shown on your ID card. You should know that a person’s appearance can not judge a person’s age. Some people are naturally tender and good at maintenance. Even if they are more than 60 years old, they will be regarded as 30 years old from the appearance About a month.

Scientists judge and analyze a person’s age by bone age, which is the abbreviation of bone age. No matter how you maintain and how young you look, your bone age is getting older every year. This can’t be changed, just like a person’s DNA information is very difficult to change. Scientists use specific images of bones in X-ray photography to determine a person’s age.

The X-ray film of the wrist of the left hand is usually taken. The doctor observes the development degree of the ossification center of the metacarpal and phalangeal bones, carpal bones and the lower end of the radius and ulna to determine the bone age. This technology is widely used in all walks of life, especially in case solving and archaeology. People’s reality can be judged by their bone age, so how can we judge the age of the earth?

Some people may think that judging the age of rocks may be able to get the age of the earth. Is it really so simple? Of course not. After billions of years of changes, the rocks on the earth have not been the original rocks, because it is difficult for scientists to accurately determine the age of the earth by judging the age of the rocks.

People’s interest in the age of the earth has been studied and explored in ancient times, but at that time, it was more calculated by astrology, and the answer was also very inaccurate. Until mankind began to walk out of the era of science and technology, science lovers began to use some scientific methods to calculate the age of the earth.

In the early days, scientists collected a lot of prehistoric fossils and determined the age of these fossils to determine the age of the earth. The answer is more than 75000 years. Of course, this age is far less than the real age of the earth. Later, physicists appeared. In the 1850s, the second law of thermodynamics proposed by German physicist Clausius and British physicist Lord Kelvin has become the consensus of the academic community. According to the second law of thermodynamics, the earth, the sun and even the whole universe are in the process of heat dissipation.

According to this theory, the earth is a high heat magma ball at the beginning of its birth, and its temperature decreases with time until the heat is completely dissipated and becomes completely cold and dead. In this way, as long as we know the initial temperature of the earth (that is, the temperature of the magma), the thermal conductivity of the rocks and the geothermal gradient, we can calculate the age of the earth according to the formula.

Kelvin published an article entitled “on the slow cooling of the earth” in 1862. He set the temperature of magma at 3870 ℃ (actually it should be 700 ℃ – 1200 ℃), and then estimated the average value of thermal conductivity and geothermal gradient. Kelvin’s final result is 98 million years. Considering the error caused by the estimation, he proposed that the age of the earth is about 20 million to 400 million years.

Kelvin’s assertion about the age of the Earth lasted for a long time. Until 1907, American chemist bolt wood thought that lead was the final product of uranium radioactive decay and put forward “uranium lead determination method”. After the discovery of isotopes, this method was further optimized by scientists, because uranium 235 and uranium 238 will decay into lead 207 and lead 206, respectively. So in theory, as long as we know the proportion of lead and uranium in a rock, we can calculate the age of the rock.

However, it’s not easy to find rocks that meet this requirement on the earth. The rocks on the earth’s surface have already experienced complex geological activities and years of weathering, and become brand new and no longer pure. They are not the rocks at the beginning of the earth’s birth. Later, scientists came up with the idea of using meteorites in space to make this calculation.

As we all know, there are many asteroids and other small stars in the solar system. These stars formed at the same time as the earth. They are the early materials of the solar system. Because these asteroids have no atmosphere and are completely exposed to the vacuum of space environment, even after billions of years, these asteroids still retain the material composition of the early solar system.

The low uranium content of meteorite iron in these meteorites means that the lead produced by uranium decay is very little. Therefore, the proportion of lead and uranium in meteorite iron is almost equal to that at the beginning of the formation of the earth. American geochemist Claire Patterson finally set the ratio of lead and uranium in meteorite iron as the initial value and the average ratio of lead and uranium in the earth’s rocks as the final value, and calculated that the age of the earth is between 4.1-4.6 billion years. In 1956, Patterson finally concluded that the age of the earth was 4550.7 million years.

The above method is the most advanced method for detecting the earth’s age. Is the earth’s age calculated by this method correct? I believe scientists are not 100% sure. One way to calculate the real age of the earth is to find the material that may exist at the beginning of the earth’s birth. As long as such material is found, it is not difficult to calculate the real age of the earth.

However, due to ecological changes on the earth’s surface, such rock material does not exist. That hope can only be placed in the earth’s interior. However, the deepest depth of human science and technology can only be more than 12000 meters underground. This depth does not even break the crust. If scientists want to get the early materials of the earth, they may need to go deep into the mantle layer. The deeper they go into the earth’s center, the more promising they are It can exist in the original material at the beginning of the formation of the earth.

Another method is to detect the age of asteroids near the earth’s orbit. These asteroids are probably born at the same time as the earth. They do not have their own ecosystem. The rocks and other materials on the asteroids still maintain the primitive formation of the early solar system. It is very possible. As long as we can accurately determine the age of these asteroids, the age of the earth should be about the same.

The “uranium lead determination method” currently used by scientists to calculate the ratio of lead and uranium in meteorites, so as to calculate the age of the earth, may not be completely correct. With the continuous progress of human science and technology, there may be more advanced and accurate calculation methods in the future, and the real age of the earth will be more and more accurate. It is possible that the real age of the earth will be far greater than 4.6 billion years.