For universe, earth is just a speck of dust, for man it is best home. Within universe known to mankind, no other planets with gods have been found. The Earth not only gave birth to life, but also advanced intelligent beings-humans. To understand history of mankind, we must begin with an understanding of earth. The space in which Earth is located, and process of evolution experienced by Earth, are closely related to emergence of all life.

1. The formation of ocean and first life

"From past to present is called universe, and four directions are called universe." The universe is not only infinite space, but also eternal time. We cannot judge where Earth is in Universe, we cannot guess where it was created on time axis. We can only measure in human time scales. The Earth formed about 4.6 billion years ago. But at this time, Earth is not yet captured by solar system.

Earth Parameters

The mass and volume of Earth are also moderate. If mass is too small, gravity will not be enough, and gas will escape. Mars is an example of this. The reason Earth has an atmosphere is because there is enough gravity to pull on these gases. If force of gravity is too strong, planet will become a gaseous planet and life will not be born. During gradual development of Earth, an atmosphere dominated by nitrogen and oxygen has formed, which can effectively reduce impact of asteroids.

At beginning of formation, earth was not suitable for emergence of life. For first 400 million years, Earth was still magma and very hot. However, under action of gravity, denser matter gradually moves towards center of Earth, while less dense one rises to surface of earth. At same time, surface temperature also gradually dropped, forming a solid layer of rock. During Archean period, earth's crust was relatively thin and volcanic activity was frequent. High-temperature magma continuously erupted outward, forming a thin, primitive atmosphere dominated by gases such as water vapor and carbon dioxide. The water vapor in original atmosphere continued to expand and then continuously condensed, collecting rainwater on surface and gradually forming an ocean.

The original ocean was only one tenth of modern ocean, but after ocean appeared, it effectively prevented ultraviolet rays from reaching water, and earliest life originated in ocean. The ancient Greek philosopher Thales once said that "water is source of all things." I think it's more appropriate to say this sentence as "water is source of life". Earth has oceans and can also produce life. 3.8 billion years ago, organic matter began to appear in ocean, gradually producing low-level primitive single-celled organisms. Living things also transform from non-living things. Organisms are organic polymers made up of various molecules. The development of organisms goes from lowest level to highest. During this period, life evolved from prokaryotes to eukaryotes, and Earth entered era of bacteria-algae. Algae are widespread, and they carry out photosynthesis, which gradually increases oxygen content in atmosphere.

2. The Earth that became planet Sun

Earth was not originally planet of sun, perhaps it was a lone wanderer. About 600 million years ago, Earth was captured by Sun's gravity and became third planet from Sun. From that moment on, sun began to heat up cooling surface. In solar system, almost all stars are in same plane, regularly revolving around sun, and direction is mainly from west to east, which creates a relatively calm working environment. The average distance between Earth and Sun is 149 million kilometers, that is, between Mars and Venus. This is a very moderate distance between sun and earth, so that temperature of earth will not be too high or too low. Beyond Mars is Jupiter, largest planet in solar system, whose powerful gravitational force is able to suck up a large number of asteroids flying towards sun, avoiding constant attacks on earth.

After entering solar system, earth has another rotation and autobiography, cold and heat, four seasons, day and night. Within Earth, core, or inner sphere, is offset in opposite direction from Sun's gravitational force, rather than at center of Earth. The self-biography of earth leads to movement of earth's crust from east to west, forming mountains, plateaus, valleys and plains. The equatorial plane and plane of solar system are 23°26', which is basis for formation of five climatic zones on earth.

250 million years ago, Moon was captured by Earth and became a satellite of Earth. Since then, Earth is no longer alone. The moon rotates around earth, which changes and shifts gravitational field and earth's magnetic field. The moon causes tides on earth, stabilizes tilt of earth's axis and slows rotation of earth. The movement of sun, earth and moon is basis for calculation of time by people.

The Earth entered solar system, allowing algae to carry out photosynthesis in sunlight, thus producing oxygen. Oxygen gradually accumulates, forming ozone layer. Together with Earth's magnetic field, ozone layer blocks harmful rays of universe, allowing life to land on land, and world begins to become rich and colorful. 600 million years ago, algae began to evolve into first invertebrates - trilobites, jellyfish, worms and many others. Trilobites once dominated Paleozoic era and did not completely die out until Mesozoic era. The earliest fish, amphiox, appeared 500 million years ago and represents transition from invertebrates to vertebrates. After that, earliest vertebrates appeared - armored fish. Devon was age of fish. About 300 million years ago, some animals began to live on land. By Carboniferous and Permian, almost all developed vertebrates were able to adapt to terrestrial environment, which was represented by amphibians, such as frogs.

Trilobite fossil

In plant kingdom, bare ferns appeared at end of Silurian period. During Carboniferous and Permian periods, plants entered a period of rapid development of ferns, for reproduction of which spores were used. The Carboniferous and Permian periods were an important coal-forming period in geological history due to presence of fern forests.

3. Biological prosperity and continental drift in Mesozoic

The so-called "Natural Selection, Survival of Fittest" means that all living beings must face enormous challenges in way of evolution and must constantly adapt to changes in natural geography. In Mesozoic era, a large number of animals came to live on land from ocean, which is an important milestone in biological evolution. Due to influence of continental drift, glacier activity and other factors, land climate changes are very frequent, which will create serious problems for habitat of organisms and accelerate the evolution of organisms.

Tree of biological evolution

In Paleozoic era, primitive continents were formed, many huge folded mountain systems appeared in world. The ancient land of Gondwana in southern hemisphere and ancient land of Laurasia in northern hemisphere merged into Pangea. But Pangea in Mesozoic was in a state of division. During Cretaceous period, Gondwana continent began to split into South America, Antarctica, Australia and Africa, and South Atlantic and Indian Oceans began to appear. The movement of plates caused a large number of mountains to appear on sea floor, and sea level rose rapidly, and about one third of earth's surface was covered by ocean. The movement of plates and drift of continents will inevitably lead to regional climate changes

In general, plate change is slow, so organisms have enough time to adapt to climate change. But climate change caused by glaciers is happening quickly. So far, three major glaciers have formed on Earth, namely Blue Glacier, Carboniferous-Permian Glacier, and Quaternary Glacier. After arrival of glaciers, temperature of earth will drop sharply, which will lead to extinction of a large number of organisms. But some organisms that are better adapted to their environment will also evolve.

The Mesozoic era was age of reptiles. The land at that time was full of jungle, gymnosperms and ferns flourished. But flowers and plants did not appear until Late Cretaceous, so although entire era was full of greenery, it was very monotonous. Reptiles live in such an environment, they have completely escaped from aquatic environment, adapted to life on land, and use their lungs for breathing. Crocodiles and turtles are representatives of reptiles, but main characters are dinosaurs. Dinosaurs are largest animals that have ever appeared on earth, they can weigh tens of tons and can be called giants. There are many types of dinosaurs, mostly carnivores and herbivores

The Jurassic period was era of prosperity of dinosaurs, and Cretaceous period was era of extinction of dinosaurs. The reason for extinction of dinosaurs is still a mystery. Some people think it was caused by an asteroid hitting Earth, and some people think it was caused by climate change. Either way, climate change is inevitable. During Cretaceous period, plants eaten by dinosaurs disappeared, angiosperms appeared, herbivorous dinosaurs began to die out, and then carnivorous dinosaurs also died out. At same time that dinosaurs died out, a large number of marine life also died out, which shows that a huge catastrophic event occurred at that time. During this extinction, mammals survived.

Fourth, evolution of a new generation of advanced animals.

After Cretaceous extinction, earth began to enter Cenozoic era. During this period, main continents of Earth formed their current shape, but position of land and sea is still very different from present. At that time ocean was huge and land was small. The Mediterranean Sea was twice as large as it is now, and most of south of North America was covered by ocean. In China, everything is different, Bohai Sea and Yellow Sea are dry land. Due to movement of earth's crust during this period, main mountains and plateaus of earth were mainly formed. The climatic zonality of earth is becoming more and more obvious, and natural environment on earth is developing towards diversity

Angiosperms flourished, gymnosperms declined, and ferns were mostly confined to warmer regions. In animal kingdom, reptiles have become extinct, replaced by mammals, birds, and teleosts. Mammals were produced as early as Mesozoic, but at that time, under threat of dinosaurs, living space was very limited. Their bodies are small and covered with hair, which can effectively maintain a constant body temperature. The perfect circulatory system enhances metabolic function and makes them more adaptable to external environment. Most of them do not need hibernation and can adapt to cold winters. Although mammals have small bodies, evolution of brain has accelerated significantly. During Cenozoic, brain size of many mammals increased 6–10 times.

Large mammals that existed in early days included thunder beasts, four-tusked elephants, mammoths, saber-toothed cats, etc., but they all died out later. Relatively isolated places like Australia still have early mammals like platypuses and kangaroos. Among many animals, we pay more attention to primates. They also appear in Cenozoic and there are a large number of varieties. Primates live in forest, climb trees, have flexible limbs, and hands and feet began to have a division of labor. Their brains are highly developed, they can distinguish different colors, sounds and smells, and they have a highly developed sense of curiosity. Thus, one branch of primates was able to develop into humans.

About 30 million years ago, primates evolved into great apes. Compared to monkeys, monkeys have larger bodies, more developed brains, and no tails. They mainly search for food on ground in rainforests, and they can use natural tools to obtain fruits that are not available to them. But they can also climb trees and cannot escape forest environment. Engels called it "the tree-climbing monkey". About 5 million years ago, East African Rift Valley formed, East African plateau rose, and forests turned into pastures. These monkeys had to move through meadows, they learned to walk upright and began to make stone tools, so earliest australopithecine man appeared.