Every year, everyone will grow up by one year. A year is a long time for all of us, but it is a negligible moment in the history of the earth. Geologists have found that the layers of rocks covering the original crust are a "stone book" left by the evolution and development of the earth for billions of years, which is called stratum in geology. The stratum starts from the oldest geological age and reaches the surface layer by layer. Generally speaking, the stratum formed first is below, and the stratum formed later is above, and the stratum formed closer to the upper part of the stratum is shorter.
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, in science, the method of measuring the isotopic content of radioactive elements and their transformation in rocks is used as a "timer" to measure the age of the earth.
People use the characteristics of radioactive elements to calculate the age of rocks. Radioactive elements deteriorate at a stable speed and are not affected by external conditions. In a certain period of time, there is an exact amount of radioactive elements, how much they split and how many new substances they produce. For example, one gram of uranium splits into lead and helium in one year. Therefore, we can calculate the age of rocks according to the contents of uranium and lead in rocks now. The earth's crust is made of rocks, so we can know its age. Some people calculate that it is about 3 billion years.
The age of the earth's crust is not equal to the actual age of the earth, because before the formation of the earth's crust, the earth generally went through a period when the surface was in a molten state, and during this period, the age of the earth was estimated at about 4.6 billion years. This is a big number. But in the universe, there are more 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?
There are several methods to calculate the age of the earth, such as rock formation method, fossil method and radioactive element disintegration method. According to the identification, the oldest rock on the earth is Amizok gneiss discovered in St. Gotha, western Greenland, with an age of about 3.8 billion years. The debris of the solar system is between 4.5 billion and 4.7 billion years old. Therefore, it is believed 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 "periods", 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.
The primitive lithosphere, hydrosphere and atmosphere were formed on the earth's surface 2.4 billion years ago. But at that time, the crust was very unstable, volcanic activity was frequent, magma was everywhere, the ocean was vast, and the land was all bare mountains. This is an important era of iron ore formation, and the lowest primitive life began to appear.
From 2.4 billion years ago to Proterozoic 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-shaped 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 have appeared on the land in the northern hemisphere, some as high as 30 meters. These tall and dense forests later became big coalfields.
Mesozoic, from 250 million years ago to 700 million years ago, lasted about 65438+800 million years. This is the era of reptiles. Dinosaurs once ruled for a while, and then primitive mammals and birds appeared. Ferns are decreasing and being replaced by gymnosperms. The lush plants and huge animals in Mesozoic 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 face of the earth has been basically similar to today's situation. A new generation of angiosperms has developed greatly, and all kinds of herbivorous and carnivorous mammals have flourished unprecedentedly. The great development of nature creatures finally 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.
The earth where human beings live has evolved step by step to the present and gradually formed today's face.