The evolution of stars can be roughly divided into three stages. The first stage is the gravitational contraction stage, that is, the mutual attraction between dispersed nebulae is concentrated into clouds; The second stage is the nuclear reaction stage, in which primitive nebulae collide with each other to generate heat, and violent nuclear reactions occur inside; The third stage is the aging stage, that is, the hydrogen and nitrogen used as nuclear fusion fuel are gradually exhausted.
According to the general law of star evolution, it can be inferred that a nebula began to gather about 5 billion to 6 billion years ago. In the process of gravitational contraction, most of the matter in this nebula entered the center, formed the primitive sun, began to take shape and began to shine. After that, the huge energy generated by the internal nuclear reaction makes it emit light and heat all the time.
The earth may have been formed by the aggregation of large and small nebulae at the earliest. It is generally believed that it grew to a mass similar to that of the modern earth 4.7 billion years ago. At this time, the earth is only a collection of many microsatellites, called the original earth. Under the action of gravitational contraction and the heat generated by the decay of radioactive elements inside, the original earth is constantly heated. When the internal temperature of the original earth reached enough to melt elements such as iron and nickel, the elements such as iron and nickel quickly concentrated to the center of the earth, forming the core and mantle about 4.6 billion years ago, and the crust initially differentiated. The primitive crust is weak and the temperature inside the earth is very high. Therefore, volcanic activity is frequent, and many gases ejected from the volcano constitute the primitive atmosphere, such as CH4, NH3, H2, H2O (water vapor), H2S, HCH and so on. But there is no free oxygen (the oxygen in the atmosphere is accumulated for a long time after the emergence of photosynthetic cyanobacteria and green plants). This reducing atmosphere forms a series of small organic compounds, including amino acids and nucleotides, under the energy of lightning, ultraviolet rays, shock waves and rays (this has been confirmed by the experiment that the spark discharge device designed by American scientist Miller simulates lightning to make inorganic substances synthesize organic substances). These organic small molecular compounds either directly fall into the primitive ocean, or gather in the primitive ocean through lakes and rivers, and accumulate and interact in the middle layer of the ocean for a long time. Under appropriate conditions, they further condense into biological macromolecules such as protein and nucleic acid, with primitive structure and nonspecific function. These biomacromolecules accumulate in the primitive ocean, and their concentration increases continuously, and condense into droplets, forming a multi-molecular system. Under certain evolutionary probability and suitable environmental conditions, after a long period of continuous evolution, a primitive life with metabolism and self-reproduction ability was finally formed about 3.5 billion years ago. This is the first stage of life evolution, that is, the cell-free life stage, which realizes the transition from inanimate to living.
The childhood of the earth, from its formation 4.6 billion years ago, lasted about 3 billion years, a * * *151600 million years ago. Of course, we don't know much about the childhood of the earth now, and it is still a subject to be further explored.
Second, the youth of the earth.
From about 3 billion years ago to 570 million years ago, the earth entered a juvenile period, that is, pre-Paleozoic. Although this period lasted for a long time and the atmosphere, water and biosphere also developed greatly, the evolution of the biological world was very slow. Until the end of pre-Paleozoic, there were only fungi, algae, some lower protozoa and brachiopods on the earth. This is in sharp contrast with the rapid development of biology after CAMBRIAN.
A small continental nucleus appeared at the earliest, which indicated that the earth entered adolescence. Later, the continent was formed by the gradual expansion of the continental nucleus. The small stable continental nucleus found on the earth with conclusive evidence was formed in southern Africa 2.8 billion years ago. Until 2.5 billion years ago, each continent formed several small pieces of stable land. Later, around 654.38+0.7 billion years ago, the earth experienced the most important stable continent formation event, and the area of the stable continent increased greatly in a relatively short historical period, and the continent was almost close to the present scale. However, the already formed continental lithosphere (also known as primitive platform) is still relatively weak, with considerable activity and no real stability.
The transition period from the original platform to the platform was from 65.438+0.7 billion years ago to about 65.438+0.4 billion years ago. According to the research and analysis of the data by scientists, the original platform has been broken many times by forces from the inside of the earth and cemented by magma rising from below, making it thicker and more stable. Therefore, about 65.438+0.4 billion years ago was the final formation period of the stable continent.
During this period, the development of the biological world entered the second stage, namely the prokaryotic cell stage. At this stage, life has cell morphology and real cell membrane, but there is no real nucleus, so it is impossible to distinguish between real nuclear membrane and nucleolus. Cyanobacteria, mainly represented, flourished 2.8 ~ 2 billion years ago, which could carry out real photosynthesis, absorb carbon dioxide and release oxygen, so that the reducing atmosphere of the early earth was gradually replaced by oxidizing atmosphere, and then entered the third stage of evolution, and eukaryotic cells appeared. The development from prokaryotic cells to eukaryotic cells is the most important evolution completed in the biological world.
Third, the Paleozoic of the earth.
The Paleozoic strata can be divided into early and late stages, and the early Paleozoic can be divided into Cambrian, Ordovician and Silurian, about 570 million to 400 million years ago. Late Paleozoic includes Devonian, Carboniferous and Triassic, ranging from 400 million years ago to 230 million years ago. This 340 million years is the oldest age of life, and the earth has experienced billions of years of evolution by this time. The material composition and structure of the atmosphere, hydrosphere and lithosphere are worse than today's earth. Do you forgive us? ⑸? What's the first thing? What is the reason? What's the matter with you? Hey? Mechanical south is awkward? Sad? Beep? Excuse me. Hey? Forced burial of oxime amine pen [6]? Jun ⒅ rank howling up dark hexagrams? Thrilling and diarrhea? Pie? Does the mace shovel master bask in alpha?
Since CAMBRIAN, the platform has been weathered, denuded and transported for a long time, and the surface height difference has narrowed (that is, flattened). Low-lying areas have been submerged by seawater for many times, and the area of shallow sea has been expanding. This period is the earliest period when available coal appeared on the earth. For example, stone coal, a kind of coal in southern China, is formed by a large number of fossil remains of marine plants living in coastal and shallow seas. By the end of Silurian, great changes had taken place in the geosyncline around and between platforms, which lasted for millions of years. The original low-lying area has been raised again, and the simple landform has become complicated. After this change, some places were tilted and folded, others were broken, and the total area of the mainland expanded. With the further flattening, the terrain of the earth gradually tends to be flat, and some areas of the Pacific Ocean are submerged. In the middle of Carboniferous, the scale of seawater immersion reached the maximum. Since the Late Carboniferous, the strong tectonic movement has caused the sedimentary rocks and volcanic rocks in the geosyncline to fold strongly, and transformed them into folded mountain systems. Tectonic movements occurred one after another until the end of late Paleozoic. This movement is called the Wali West (Wali West Mountain in the Alps) movement.
The Variscan Movement turned the geosyncline between Europe and Africa, the Ural geosyncline between Eastern Europe and Siberia, the vast geosyncline between Siberia, Central Asia and China, and the Appalachian geosyncline on the eastern edge of North America into a folded mountain system, and the seawater withdrew, thus connecting Eurasia. The continents of the world are close to each other to the greatest extent, forming a unified global continent-Pangaya continent. The total area of this continent is almost as big as the total area of the earth today.
At the end of pre-Paleozoic, plants and animals had differentiated. In the plant kingdom, cyanobacteria and fungi flourish; In the animal kingdom, lower invertebrates have appeared. In the Cambrian, red algae and green algae in the plant kingdom began to flourish. In the animal kingdom, several invertebrates, especially trilobites, suddenly began to flourish. In the Ordovician sea area, algae are widely developed in the plant kingdom, and marine invertebrates are mostly cephalopods. In the late Ordovician, a primitive jawless fish-shaped vertebrate appeared. Real fish appeared in the late Silurian. By Devonian, fish had flourished and was the tallest animal at that time. One of them is a common fin fish, which later developed into an amphibian.
Due to the Caledonian movement, the mainland area expanded, some oceans disappeared, and the environment changed dramatically, which enabled those adaptable biological species to survive. In the Middle Devonian, terrestrial plants developed greatly, many species and genera grew into trees, and insects and amphibians appeared. By the middle of Carboniferous, forests appeared, insects further developed into the air, and reptiles evolved from amphibians also appeared. Later, the Variscan Movement made the sea water recede and the mainland area expanded, which greatly promoted the process of creatures marching to the mainland. Generally speaking, in Paleozoic, the plant kingdom evolved from lower aquatic algae to higher terrestrial plants, and the animal kingdom evolved from lower marine invertebrates to fish and terrestrial reptiles.
Fourth, the Mesozoic of the earth.
The Mesozoic is divided into Triassic, Jurassic and Cretaceous, which lasted from 230 million years ago to 67 million years ago, lasting about 65.438+0.6 billion years.
Since the beginning of Mesozoic, there has been a new turning point in the development of the earth's history, Pangea has gradually disintegrated, various landmasses have gradually drifted towards modern positions, and a series of important changes have taken place in the lithosphere. From Mesozoic to the end of Triassic, it split between North and South America, Europe, Asia and Africa, and also split between several landmasses in the south, and began to move away from each other. In the late Jurassic, various landmasses further split, resulting in huge north-south cracks between North America and Eurasia, and between South America and Africa. The land mass moves to both sides and the sea is immersed. This is the future Atlantic Ocean. After another 70 million years, in the late Cretaceous, the situation changed further and the continents continued to move away from each other. The most remarkable thing is that the distance between South America and Africa has increased, which means that the South Atlantic has obviously expanded.
What is the historical basis of the above continental division in Mesozoic? What is the reason for the split? This has to start with the following assumption.
First, Austrian geophysicist Wei Gena (1880 ~ 1930) put forward the continental drift hypothesis in 19 12. He believes that the earth is a celestial body from heat to cold, and its surface layer cools first and then condenses into a solid crust, and the upper layer of the crust is a lighter silicon-aluminum layer. Just as ice floats on water, the mainland also floats on its basement-silicon-magnesium layer. Due to the eastward rotation of the earth and the action of tidal force, the original Panga continent slowly moved westward, and then cracks and disintegration appeared. He also believes that the Pacific Ocean is an ancient ocean and coexists with the primitive continent. Later, due to the westward drift of the American continent, its scope gradually narrowed, and the reduced area was equal to the expanded area of the Atlantic Ocean. After the separation of Australia and the Antarctic continent, the Indian Ocean appeared. As for the Arctic Ocean, it is originally a part of the Pacific Ocean. In the literature of geology and paleontology, the argument of continental drift was found: the Sierra Mountains on the east coast of South America and the Cape Mountains on the west coast of Africa not only have the same geological structure, but also have the same ore beds. Secondly, paleontological data. At that time, paleontological research proved that 64% of Carboniferous reptiles in several continents in the southern hemisphere were the same. By Triassic, that is to say, after several continents in the southern hemisphere were divided for a period of time, the same reptile in several continents had dropped to 34%. Thirdly, according to the data of paleoclimate, the special sediments of paleoclimate conditions such as coal seams and salt deposits formed by tropical plants reflecting dry and hot climate conditions are analyzed, and it is found that they have all moved to today's high latitudes, while moraines reflecting ancient polar regions have moved to today's equatorial regions, which is the so-called pole shift. However, this assumption was ignored after a period of popularity.
Until the early 1950s, with the rise of paleomagnetism, research proved that the trajectory of continental drift was consistent with paleomagnetism. The earth's magnetic field is divided into North Pole and South Pole. In the rock formations formed hundreds of millions of years ago, the magnetic records at that time were preserved. By measuring the remanence of rocks with precision instruments, we can know the position and movement of geomagnetic North Pole in different geological ages and continents. The research shows that the geomagnetic north pole of different continents has different moving routes in corresponding geological years, and finally meets the magnetic north pole today.
Secondly, in the early 1960s, American scholar Hess (H.H. Hess, 1906 ~? ) and Dietz (R.S. Dietz, 19 14 ~? ) put forward the hypothesis of submarine expansion. The basic idea of this hypothesis is: Thermoplastic substances upwell from the asthenosphere below and invade the axis of the future ocean ridge through cracks in the lithosphere, and the magma that gushed out condenses into a new ocean floor, pushing the original ocean floor to expand to both sides, and the mainland drifts with it. After a period of time, the new ocean floor was widened, and the cracked continental crust was taken farther away from the ocean rift.
As new marine lithosphere keeps popping up from every ocean, the old marine lithosphere is moving outward and the ocean is expanding. At this rate, isn't the volume of the earth expanding? It was not until the hypothesis of seafloor spreading was combined with the hypothesis of continental drift that this problem was explained, that is, the increasing marine lithosphere returned to the asthenosphere in other parts of the earth and died out, which was closely related to the study of the global seismic activity zone. Thus, a complete and systematic plate tectonic theory is formed in earth science, and various movements of the upper layer of the earth are explained from a macro perspective. This theory divides the earth's crust into the Pacific plate, the Indian Ocean plate, the Eurasian plate, the African plate, the Antarctic plate and the American plate, and each plate is divided into several small pieces. All these plates form a lithosphere. The boundary of the plate is the active zone of the crust, and the plate moves with the expansion of the seabed. Near the ocean ridge is a plate growth zone, including the mid-Atlantic ridge, the mid-Indian ridge and the eastern Pacific uplift. Near the trench is the plate subduction zone, which is the part of the trench located on the east and west edges of the Pacific Ocean. When the denser plate subducts into the denser plate, it will cause strong earthquake and volcanic activity; The upward thrust forms an island or mountain system.
Generally speaking, the climatic conditions in Mesozoic are favorable for the development of animals and plants. In the early Mesozoic, gymnosperms such as conifers, cycads, ginkgo biloba and some true ferns were dominant. By the late Mesozoic, angiosperms appeared and could really blossom and bear fruit. Angiosperms are the highest class in the plant kingdom and have obvious advantages in spreading and reproducing offspring. In the animal kingdom, the Mesozoic era is often called the reptile era. Dinosaurs flourished in this era and became the overlord of the earth in Jurassic, but suddenly became extinct in Cretaceous. The reason is still a scientific mystery and has not been properly explained. Two kinds of higher vertebrates, birds and mammals, developed from reptiles also appeared in Mesozoic.
Five, the new generation of the earth
Cenozoic is the latest era in geological history. The whole Cenozoic, including modern times, is about 67 million years old and consists of Tertiary and Quaternary.
Although the Cenozoic lasted for a relatively short time, it was during this period that the land and sea distribution, climatic conditions and the appearance of the biological world on the earth's surface gradually evolved into a modern face.
The most prominent events in the Cenozoic era are the approach of Africa to Europe and the collision between India and Pakistan subcontinent and Asia. As a result, some upper lithospheric materials pushed each other, forming the most magnificent mountains and plateaus that span the northern and southern hemispheres and last almost half the earth's week. It starts from Atlas Mountain in northern Africa in the west, crosses the Alps in southern Europe, reaches Carpathian Mountain in the east, and connects the plateaus and mountains of Caucasus, Turkey and Iran, Pamirs and mountains in the east. This is the product of alpine orogeny and Himalayan orogeny.
The mutual compression between the Pacific Ocean and the surrounding continents also caused strong deformation and magmatism in the continental margin structural belt, accompanied by strong seismic activity, which lasted until modern times. The faults formed by movements in various geological historical periods are cut into large and small fault blocks. Under the influence of various movements of continental margin and lithosphere materials, they push, pull apart or rise and fall relatively, forming mountains, plateaus, basins and plains.
There are two main types of animals in the early Cenozoic: ancient ungulates and ancient carnivores. With their evolution, in the middle and late tertiary, the ancient ungulates first appeared strange ungulates, such as horses and rhinoceroses, and then even ungulates, such as sheep and cattle. Ancient carnivores gradually evolved into various beasts, such as lions, leopards and tigers. After billions of years of evolution, organisms have gone through many stages of development from scratch, from low to high, and finally flower of life-human was born in the latest geological history. The evolution of human beings is the result of the long-term evolution of the biological world.
Generally speaking, the factors contributing to the evolution of the earth are nothing more than internal and external aspects. The external cause is the force in the atmosphere, hydrosphere and biosphere outside the earth, and its geological functions are weathering, erosion and deposition. Its main energy sources are solar energy and gravity. In addition, there is the tidal force of the sun and moon on the earth, and the meteorite impact in the history of the earth. There are two main internal factors: one is the heat generated by the decay of radioactive elements contained in the earth; One is the energy converted from gravity energy. Internal and external factors are interdependent and contradictory, and * * * determines the material movement on the surface and inside of the earth.
It has been over 100 years since Ryle's magnum opus Principles of Geology was published in the mid-9th century. With the efforts of many earth scientists and the development of basic disciplines such as astronomy, physics, chemistry, biology and mathematics, great progress has been made in the study of earth evolution. However, due to the complexity of the problem, scientists are playing a role in some projects involving the earth. Why not go back and ask for advice first?
Looking at the development of scientific earth history, it can be said that earth scientists are on the eve of a new leap in understanding. Future earth scientists will surely push the important basic discipline of scientific earth history to a brand-new development period.