Counting the age of the earth is a difficult thing to understand, so there are often many people who do not believe that the age of the earth can be calculated, thinking that the data is unreal, and many people do not believe in how astronomers calculate the age of the sun, the milky way and even the universe. In fact, there are different methods of time determination for different things, and these methods must be based on science.
For example, the carbon-14 dating method often used in archaeology is a measurement method to calculate the approximate age of the sample according to the degree of decay of carbon 14, because carbon 14 is a radioactive isotope of carbon element, produced by cosmic rays hitting nitrogen atoms in the air, and the nucleus is composed of 6 protons and 8 neutrons, and its half-life is about 5,730 ±40 years, usually the organic material excavated by archaeology will contain carbon-14, so the approximate age of archaeological samples can be determined according to its decay.
So is this also the method used to measure the age of the Earth? No. Human measurement of the age of the earth has also experienced some processes, the methods used are different, there have been climate measurement, stratigraphic sediment measurement, paleontological method, seawater salinity method, etc., but these methods have obtained different results, science is not strong, to the middle of the last century, some scientists invented lead isotope measurement, which is a widely recognized earth age measurement method.
Why measure the age of the Earth with lead isomorphism, it turns out that part of the lead in nature existed in the early days of the formation of the earth, and the other part is derived from the decay of radioactive uranium. Speaking of this, we must talk about the formation of the earth, astronomers and geologists believe that the formation of such a planet as the earth is in a molten state, there are a large number of metal heavy elements sinking to the core of the earth to form the core, most of the lead elements sink to the core of the earth during this period, but most of the uranium elements come to the surface of the earth with the lava flow of silica and other substances, then in this case, there is most of the uranium near the surface, when this situation is formed, it is basically when the earth is formed. Then we can represent the composition of the lead isotopes in the core of the earth to represent the time when the Earth first formed.
So where does the lead in the Earth's crust come from? In fact, most of it is derived from the decay of uranium, so as long as you know the isotopic composition of lead in the earth's crust, you can get its time gap, because it is the result of the decay of uranium after hundreds of millions of years.
Uranium is mainly two kinds of radioactive isotopes uranium-235 and uranium-238, its half-life is 7X10^8 years and 4.47x10^9 years, that is, uranium-235 decays faster than uranium-238, this time difference is important, after decay to form lead-207 and lead-206, uranium-235's final decay product lead-207 growth rate faster than uranium-238 decay product lead-206. Therefore, as long as the composition of the lead isotope in the present and primitive state is known, the age of the earth can be deduced. The data obtained by this measurement is still relatively accurate.
In order to measure the age of the earth, scientists have collected a lot of minerals containing lead from different parts of the earth, and also referred to the lead element on many meteorites, because many metal meteorites come from the core of small bodies that continue to impact when the planet began to form, and the data from which the data is that the earth was formed about 4.55 billion years ago, which was obtained by the geochemist Claire Peterson in 1953 using the above method. Since the earth has basically formed at this time, it can also be pushed forward a little, so it is generally said that the earth is 4.6 billion years old, but this time also has a float up and down, and the floating value does not exceed 200 million years.