65.438+0.33 billion years ago, gravity gathered gas and heated it, and the first stars gave off light. Through nuclear reaction, the energy generated by stars competes with its gravity to produce heavier chemical elements. When the first generation of stars aged and died, heavy elements scattered into interstellar space, and the second generation of stars formed again under the action of gravity. The second generation of stars also experienced more intense nuclear reactions, produced heavier chemical elements and experienced more violent explosions. At this time, our common substances, such as iron or aluminum, have basically formed, and suddenly dust and steam, and even simple macromolecular substances have begun to form.
Against this background, about 5 billion years ago, our sun was born as the third generation star. Its gravitational field bound some huge rocks and air masses to keep them running in a specific orbit, and they became the planets of the sun. 4.5 billion years ago, the earth, as the planet of the sun, was also born in frequent and violent rock collisions.
At the beginning of its formation, the earth was devastated, and the outside was constantly hit by meteorites, and the inside was constantly collapsing and carrying out nuclear reactions, which made the earth heat up continuously, thus forming a hot lava body. Under the action of gravity, heavy matter began to collapse inward, forming the center of the earth, while light matter remained on the surface, forming the crust. The initial crust is extremely thin, so the earth's volcano moves frequently, and the gas emitted by the volcano rises, which constitutes the original atmosphere of the earth. Under the long-term influence of environmental factors such as thunderstorm, intense ultraviolet radiation and high temperature, many simple organic substances were formed in the primitive atmosphere.
About this time, a celestial body named Teia collided violently with our home. If the impact is more violent, it may completely destroy the earth. The impact tore off a large piece of material from the earth and formed the moon. The impact also caused the skew of the earth's axis and the differentiation of the four seasons on the surface, which is an important prerequisite for the development of life. But at this time, the earth is still a purgatory, a lava ocean, a highly toxic atmosphere, and it is still being hit by meteorites.
Meteorites keep coming to the earth, bringing water, which evaporates and gathers above the surface, forming clouds and bringing lasting rainfall, making the surface a Wang Yang. With the continuous cooling of the surface, the crust began to solidify. However, the hot magma inside the earth is still flowing, splitting the fragile crust into plates, pushing the plates to move and beginning to reshape the surface morphology. Plates collide, forming steep mountains, plates separate, forming deep trenches, and part of the surface rises, exposing the sea level and forming land.
3.7 billion years ago, in a hot spring mouth deep in the ocean, a group of molecules-genetic material molecules, which are important to all living things, were formed, and these molecules happened to be wrapped by an oily substance. This is the first cell on the earth and the ancestor of all living things. Cells begin to absorb substances from their surroundings and convert them into energy. It is influenced by the outside world and controls the deformation of some cells to realize movement. The genetic material sends out an electric signal, which makes the cell split into two, and the picture of life continuation and development begins.
3.3 billion years ago, primitive bacteria and bacteria differentiated due to variation. About 2.7 billion years ago, the first cell with nucleus was formed. Eukaryotic cells have three basic structures: nuclear membrane, genetic information expression system and cytoskeleton. The three basic structural systems constitute organelles with tight internal structure, clear division of labor and intelligence, and on this basis, the cell life activities are highly programmed and controlled. About 26,543.8 billion years ago, primitive multicellular plants also appeared.
About 654.38+0.25 billion years ago, some pan-plants containing chloroplasts appeared in the ocean, which can absorb the light energy of the sun, convert carbon dioxide and water into organic substances such as sugars, store energy and discharge a considerable amount of oxygen. Oxygen-enriched environment provides good conditions for the development of eukaryotic cells. 65.438 billion years ago, eukaryotic cells flourished.
In the early stage of life evolution, life thrives by monotonous self-replication and division, and the difference between parents and offspring is quite small, so life evolution is slow. About 654.38 billion years ago, two cells fused unexpectedly, and their genetic materials were combined. When the cells divide again, the newly formed cells contain the genetic material of their parents, which is the first sexual reproduction in the history of life. Sexual reproduction greatly increases the difference between offspring and parents, greatly improves the speed of life evolution, and life begins to develop rapidly in all directions.
The predecessor of animals is simple single-celled organisms, which only rely on specialized organelles in cells to survive and continue their offspring, and carry out actions, nutrition, respiration, excretion and reproduction, which is inefficient. Shortly after the emergence of sexual reproduction, social flagellates formed the simplest multicellular animal body-sponge. These sponges have simple cell differentiation, including digestive cells, sertoli cells, spore cells and epidermal cells, and form the differentiation of endoderm and ectoderm. Each cell does its own job and completes life activities together, but in fact, sponges can only be attached to rocks and do not have the ability to carry out complex movements. In coelenterates, besides cell differentiation, tissue differentiation also occurs, forming mesothelium between two germ layers. There are special fibers in the epithelial muscle cells of coelenterates, which enable them to move in a small range. In addition, coelenterates also formed a simple nervous system. The differentiation of cells and tissues makes animals begin to have the ability to carry out complex life activities, making animal activities more effective and convenient.
About 700 million years ago, a jellyfish adapted to crawling on the seabed flattened and its nervous system moved to its head, gradually forming the first worm on earth. Between ectoderm and endoderm, mesoderm is formed. The appearance of mesoderm is of great significance to the further development of animal body structure and function. On the one hand, the formation of mesoderm lightens the burden of endoderm and ectoderm, which leads to a series of new differentiation and provides necessary material conditions for the further complexity and integrity of animal body structure. The formation of mesoderm promotes metabolism, also forms complex muscular layer, and enhances motor function. Coupled with the symmetrical body shape on both sides, it is possible for animals to eat more food in a wider range. Muscles also appeared on the digestive tract wall, which strengthened the peristalsis ability of the digestive tract, which undoubtedly promoted the strengthening of metabolic function. Due to the strengthening of metabolic function, the metabolic waste produced also increased, thus promoting the formation of excretory system, and flat animals began to have protonephric ducts. Because of the improvement of motor function, animals often contact with the changeable external environment, which promotes the further development of nervous system and sensory organs. Compared with coelenterates, the nervous system of flat animals has made remarkable progress, and it has begun to concentrate into a stepped nervous system to form a central nervous system. In addition, the parenchyma formed by mesoderm has the function of storing nutrients and water, which makes animals have the ability to resist hunger and drought to a certain extent, and creates preparation conditions for animals to go ashore in the later stage. [ 1]
In the Cambrian period 540 million years ago, life experienced an unprecedented explosive development. With the rapid development of invertebrates, the body system is becoming more and more perfect, and higher invertebrates appear. Linear animals have specialized excretory organs, and the digestive system has been improved. In annelids and echinoderms, a fissure cavity is formed between the body wall and the intestinal wall. The formation of fissure cavity promotes the further differentiation of digestive tract function, strengthens digestive function, and then strengthens the demand of excretion function, and the posterior renal duct begins to form. During the formation of the fissure cavity, some remains formed blood vessels and the circulatory system was improved. The appearance of fissure cavity also provides a basis for animal body segmentation. A class of echinoderms undergo metamorphosis in the embryonic stage, and a part of mesoderm thickens, differentiates and protrudes, and finally leaves the intestinal wall to form a notochord. The notochord constitutes the main beam supporting the body, is the bearer of weight, and also provides strong support and protection for internal organs. Exercise muscles can get a strong fulcrum, so that the body will not be shortened or deformed because of the contraction of muscles during exercise, and the animals will develop on a large scale. At the same time, the central axis support of the notochord can also enable animals to complete directional movement more effectively, which is more accurate and rapid for actively hunting and avoiding enemies. The ectoderm invades, forming the internal neural tube of primitive chordates. The pharynx at the front end of the digestive tract forms a branchial cleft, which is filled with tiny blood vessels for breathing. A closed circulatory system is formed, and a heart is also formed on the ventral surface of the digestive tract. The heart is like a water pump, which provides power for blood flow, nutrition for cells and takes away the waste produced by metabolism, making the circulatory system run more efficiently and providing conditions for animals to move quickly and persistently.
About 450 million years ago, the first fish and the first vertebrate appeared in the ocean. On its body, an obvious head is formed. The nervous system is tubular, its front end expands into the brain and its back end differentiates into the spinal cord. The spinal cord is replaced by a spine connected by a single vertebra. It has jaws that form the mouth. As a tool for asking for food, there are teeth in the mouth, which play the role of biting and grinding, transforming substances that cannot be directly used into food, thus opening up the range of ingestible food sources. At the same time, the circulatory system is more perfect, and a contractile heart appears, which promotes blood circulation and is conducive to improving physiological functions. The complex kidney replaces the simple kidney tube, which improves the excretion function and enables a large amount of waste produced by metabolism to be excreted more effectively. [2] Since then, vertebrates have entered a period of rapid development, all kinds of fish have flourished unprecedentedly, the number and species of jaw fish have increased, and modern fish bony fish have also begun to develop. Invertebrates also continued to develop, and early insects appeared. The increase of oxygen in the atmosphere forms an ozone layer in the stratosphere that can absorb most ultraviolet rays, thus creating conditions for the landing of animals and plants.
About 400 million years ago, some green algae in the ocean evolved into gymnosperms with land life ability. Vascular bundle system transports water and nutrients up and down in plants; The rhizomes support plants and absorb nutrients in the soil. Keratinization of stem surface can prevent evaporation of water in plants and prevent plants from dying in aquatic environment; Stomata can complete the gas exchange between plants and the outside world. All these structures make gymnosperms get rid of the complete dependence on water and adapt to the humid and lowland environment along the coast. [3] Plants began to spread to the land, which had a revolutionary impact on the land environment. As pioneers, insects became the earliest land animals. The hard exoskeleton can protect the internal structure of insects, reduce water loss and make insects adapt to the dry land environment. At the same time, a large number of eggs enable insects to reproduce successfully. Insects successfully adapted to the land environment in 40 million years and became the masters of the land.
367 million years ago, huge meteors broke through the night sky and fell into the ocean. The global climate dries up, the temperature drops, and the ocean currents swirl in a new form, which further cools the ocean, increases the salinity of surface water, and reduces the oxygen content in the ocean to a very low level, leading to the extinction of many marine life. With the deterioration of the earth's climate, fish are facing great threats. During this long period of time, a certain species of total fin fish climbed onto the land in search of water and food. Over time, some of them gradually evolved into primitive amphibians. Terrestrial plants provide sufficient food for amphibians, and amphibians spread rapidly because there is no bigger animal to compete with them.
After a period of time, the climate was warm and humid, swamps were everywhere, terrestrial animals flourished further, and amphibians gradually occupied the dominant position. At the same time, ferns continued to grow and spread from coastal lowlands to Chinese mainland, forming a large-scale forest. About 300 million years ago, Cycas evolved the first batch of gymnosperms. Pollen tubes appear for the first time in gymnosperms, which send sperm into egg cells, thus freeing plants from the restriction of water. In addition, gymnosperms can also produce seeds, and the formation of seeds can protect embryos and obtain sufficient nutrition. Seeds also have a structure suitable for spreading or resisting adverse conditions, which creates good conditions for the racial continuation of plants. Meanwhile, reptiles evolved from amphibians. Reptiles have dry skin and a layer of horny scales on the surface, which reduces the water loss in the body and enables reptiles to adapt to the dry climate on land. A neck is formed between the head and trunk, so that the head can rotate flexibly, which is convenient for finding food and avoiding enemies on land. Reptiles have more developed lungs and can get oxygen directly from the air. Reptiles can lay eggs on land. The eggs are large, nutritious and protected by eggshells, which makes reptiles get rid of the restriction of water and become vertebrates that really adapt to the land environment. 290 million years ago, reptiles began to develop rapidly in four directions.
250 million years ago, due to sea level change, ocean hypoxia, pan-continental formation and other factors, there was a dry climate. Coupled with violent impact events, super volcanic eruption and ocean warming, the most serious extinction event occurred in the history of life. This catastrophe wiped out most marine life, and the creatures that ruled the ocean for nearly 300 million years declined, and the era of reptiles began.
Early reptiles included large carnivores, light hunters, heavy herbivores and crocodiles. At this time, the dominance of early dinosaurs has not yet been established. About 220 million years ago, a class of reptiles in theropoda evolved into the earliest mammals. Mammals have formed a perfect blood circulation system, with hair on the body surface and good thermal insulation performance, and also formed other mechanisms of body temperature regulation, providing a stable internal environment and reducing dependence on the external environment. Mammals also have a highly developed nervous system and senses, which can coordinate complex functional activities and adapt to changing environmental conditions. Mammals also have the differentiation of incisors, molars and canine teeth, which improves chewing ability and greatly increases energy intake. Mammalian mothers can breastfeed their offspring, which greatly increases their chances of survival. [4] In the era of dinosaur rule, our ancestors always huddled in the dark, but after the era of reptiles, mammals rose rapidly and occupied a dominant position.
From 208 million to 654.38+46 million years ago, reptiles reached their peak. In addition to dinosaurs on land and ichthyosaurs in water, pterosaurs and birds also appeared one after another, and vertebrates occupied the three ecological fields of land, sea and air for the first time. Dinosaurs ruled the earth. They developed into herbivorous dinosaurs and carnivorous dinosaurs. At the same time, a single continent on the earth has been divided into two continents, and plants and climate have become more diverse. But the earth is still warm on the whole.
After 65438+46 million years, dinosaurs still flourished. 65438+300 million years ago, flowering plants appeared. The appearance of flowers improves the probability of successful fertilization of plants and is beneficial to the spread of plant genes. Flowering plants have occupied a dominant position in the ecological environment in a short time, and many insects including bees and ants have also appeared. About 70 million years ago, mammals divided into two categories, placental mammals and marsupials. About 65 million years ago, a meteorite the size of Mount Everest hit the earth, causing great changes in the surface climate and the extinction of all large reptiles. Reptiles, which once dominated, never recovered, and mammals and birds also took this opportunity to enter the historical stage.
65 million to 50 million years ago, mammals developed rapidly.
60 million years ago, rats and primates appeared.
55 million years ago, mammals dominated. Carnivores appear, whales appear.
Fifty million years ago, odd-numbered hoofed and cloven-hoofed animals appeared.
45 million years ago, bats appeared.
40 million years ago, elephants appeared.
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654.38+0.8 million years ago, Homo sapiens stood out from other primates. Compared with other animals, Homo sapiens' brain is obviously bigger and has dexterous hands and feet. Human beings invented agriculture, obtained sufficient surplus means of production, liberated their hands, began to engage in other activities, invented literature, art, trade and handicrafts, and began to accumulate scientific knowledge in production. Uneven distribution of wealth breeds exploitation, ruling groups appear, and human beings enter the stage of slave society. For thousands of years, the ruling group has increasingly monopolized power and enslaved the thoughts of the exploited. At the same time, the world is gradually connected with the trade among regional civilizations. At the end of feudal society, the commodity economy was highly developed, the self-sufficient natural economy was destroyed, and social wealth began to occupy the labor force. In order to accumulate wealth, capitalists began to plunder workers' means of production, making them proletarians, and at the same time colonized overseas and plundered colonies. The great development of science and technology led to the industrial revolution and the capitalist system was finally established. With the establishment of the capitalist system and the awakening of the people's democratic consciousness, the national superstructure has to comply with the people's wishes and begin to implement democratic politics. The proletariat began to struggle and formed the communist theory. With the further deepening of the contradiction between productive forces and production relations in capitalist society, capitalism has developed from the stage of free competition to the stage of monopoly, and the deepening of political and economic contradictions within capitalist countries has expanded monopoly capital to the outside, and capitalism has begun to carve up the world. Due to the unequal distribution of spoils by imperialism, two world wars broke out, which caused great damage to human material civilization and spiritual civilization. After the war, the old imperialist countries declined, and the emerging United States finally occupied the dominant position, forming a confrontation with the socialist country Soviet Union, and the world formed a confrontation between the two camps of capitalism and socialism. At the same time, the oppressed and exploited countries got rid of colonial rule and embarked on the road of national rejuvenation through struggle. At the end of last century, the world political situation changed suddenly, the Soviet Union disintegrated, the socialist countries in Eastern Europe were transformed into capitalist countries one after another, and the world bipolar structure collapsed and began to develop in the direction of one superpower and many powers. Faced with various development problems, all countries in the world must work together and strengthen their actions.