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.

The earth where human beings live has evolved step by step to the present and gradually formed today's face.