There are many assumptions;

one

Use the formation of the ocean to determine the age of the earth. When the earth was just formed, a large amount of water vapor was produced due to the cooling of the surface, which gradually accumulated more and more. Finally, it rained heavily for a million or even a thousand years. Add water separated from rocks and the ocean is formed. In this case, the age of the earth is 250 million years, but the formation time of the earth is much longer than that of the ocean. So this statement was quickly refuted.

two

According to the original distance from the moon to the earth and the current distance, but the answer is almost the same as above, 260 million years, which puzzles astronomers.

three

Is determined by the product layer of the earth. However, it is difficult to define the product layer. In addition, the interlayer change rate of product layer is very unstable. So this statement was overturned.

four

According to the oldest rocks on earth; For example, one in 7.5 billion uranium decays into lead and helium within one year. Therefore, some radioactive elements in rocks can be completely determined. As long as we know the current radioactive element content and the current decay element content, we can know its age according to the decay formula. The oldest known rock is 3.5 billion years old. But the oldest rocks on the earth are not necessarily the age of the earth. So this statement ran aground.

five

Because the ages of the earth and the solar system were formed at the same time, scientists have determined the ages of meteorites that landed on the earth and the moon respectively. The age of the moon is 4.6 billion years. At present, the oldest meteorite on the earth is also 4.6 billion meteorites from Mars.

So the last year is 4.6 billion years, which is the most recognized hypothesis in the world ~ ~

Recently, German and British scientists have analyzed different moon rock samples brought back by American Apollo spacecraft, and determined the relatively accurate rock age according to the number of tungsten-182 isotopes in the rocks. Scientists analyzed and calculated that the age of the moon was 4.527 billion years. This is by far the most accurate measurement of the moon's age. This latest data not only conforms to the commonly used theory of the formation of the moon, but also supports the theory of the formation time of the earth, which will help to study the formation history of the earth. According to the big collision theory, the moon and the earth were formed at the same time, and the age of the moon is certain, so it is expected to calculate the age of the earth.

The moon is a satellite of the earth, but scientists can't give the exact date of birth of the earth, because the oldest rocks on the earth are at least 500 million years younger than the earth, so they can't be used to determine the age of the earth. According to the big collision theory, the moon and the earth formed at the same time. If the age of the moon is recognized as mentioned above, it is undoubtedly determined.

At present, scientists estimate that the age of the earth is about 4.6 billion years.

Radioisotope method is based on the principle of isotope decay. After one half-life, the original isotope is only half, after two half-lives, it is only a quarter ... and so on. As long as the ratio of isotope content before and after decay is measured, its age can be calculated from the known half-life. This method measures the "radioactive age" of rocks and takes it as the age of the earth, which implies a hypothesis that the formation of such rocks is regarded as the birth of the earth, which is a problem. Radioisotope method is also used to measure the age of moon rocks, and the results are between 4 1 100-4.6 billion years. Some people regard it as the age of the earth, and the implicit assumption is that the moon rocks are the same age as the earth, which involves the formation of planets and satellites, and there is no conclusion yet. In fact, the radioisotope method measures the age of the crust when rocks solidify from hot lava slurry. Before that, the earth was born. It has been pointed out that "the Earth, as an independent planet in the solar system, was formed five to five billion years ago" (Sha Jingeng: Ancient and Vibrant Paleontology, published in Science,No. 1 2002). In short, there are still different opinions. So someone joked: Mother Earth is old and forgets her age. Let's start with her goose-skin crane.

Every year, everyone will grow up by one year. For all of us, a year is a long time, but in the history of the earth, it is only a negligible moment. Geologists have found that the layered rock layer covering the primary crust is a "stone book" left by the evolution and development of the earth for billions of years, which is called stratum in geology. Since the oldest geological era, strata have reached the surface layer by layer. Generally speaking,

The stratum is like a book that records the history of the earth, and the rocks and fossils in the stratum are like the words in this book. By measuring ancient rocks with modern scientific methods, people know that the earth has existed for 4.6 billion years.

So what scientific methods do people use to calculate the age of the earth? At present, the scientific method is to determine the radioactive elements in rocks and the isotope content produced by their transformation as a "timer" for determining the age of the earth.

People use the characteristics of radioactive elements to calculate the age of rocks. When radioactive elements change, the speed is very stable and is not affected by external conditions. In a certain period of time, a certain amount of radioactive elements has an exact number, how much they split and how many new substances are produced. For example, one gram of uranium splits into lead and helium in one year. So we can calculate the age of the rock according to the content of uranium and lead in the rock now.

The age of the crust is not equal to the actual age of the earth, because before the formation of the crust, the earth generally has to go through a period when the surface is in a molten state. In addition, the age of the earth is estimated to be around 4.6 billion years. This is a very large number. But in the universe, there are many planets older than the earth.

Geological scientists say that the earth is at least 4.6 billion years old. The recorded history of mankind is only a few thousand years. So, how do we know the age of the earth?

According to the identification, the oldest rock on the earth is Amizok gneiss found in St. Gotha, western Greenland, which is about 3.8 billion years old, while the fragments of the solar system are between 4.5 billion and 4.7 billion years old. Therefore, it is considered that most members of the solar system, including the earth, were formed at the same time.

According to the method of dividing dynasties in human history, the earth can be divided into five generations from its formation to the present: Archean, Proterozoic, Paleozoic, Mesozoic and Cenozoic. Some generations are further divided into several "times". For example, Paleozoic is divided into Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian from far to near; Mesozoic is divided into Triassic, Jurassic and Cretaceous; Cenozoic is divided into tertiary and quaternary. This is the roughest division of the earth's historical period, which we call "geological age". People in different geological ages have different characteristics.

Archaean, 2.4 billion years ago, primitive lithosphere, hydrosphere and atmosphere were formed on the earth's surface. But at that time, the crust was unstable, volcanic activity was frequent, magma was everywhere, the ocean was vast, and the land was covered with bare mountains. This is an important era of iron ore formation, and the lowest primitive life began to appear.

Proterozoic 2.4-600 million years ago. At this time, most of the earth is still covered by oceans. Later, a large area of land appeared on the earth. "Proterozoic" refers to the primitive era, when algae and marine invertebrates appeared.

600-250 million years ago was Paleozoic. "Paleozoic" refers to the era of ancient life. At this time, thousands of animals appeared in the ocean, and marine invertebrates flourished unprecedentedly. Later, fish-like animals appeared, and fish multiplied in large numbers. A fish crawling on its fins appeared and landed on land, becoming the ancestor of terrestrial vertebrates. Amphibians also appeared. Ferns appear on the land in the northern hemisphere, some of which are as high as 30 meters.

Mesozoic, from 250 million years ago to 700 million years ago, lasted about 65.438+0.8 billion years. This is the era of reptiles, dinosaurs once dominated, and primitive mammals and birds appeared. Pteridophytes are declining and being replaced by gymnosperms. The lush plants and huge animals in the Mesozoic era later turned into many huge coalfields and oil fields. Many metal deposits were also formed in Mesozoic.

Cenozoic is the latest stage in the history of the earth, with the shortest time, only about 70 million years. At this time, the appearance of the earth is basically the same as today. The new generation angiosperms developed greatly, and all kinds of herbivorous and carnivorous mammals flourished unprecedentedly. The great development of natural life eventually led to the emergence of human beings, and the ancient apes gradually evolved into modern people. It is generally believed that human beings appeared in the Quaternary, about 2.4 million years ago.