Article reprinted from Science and Humanities Online
The earth is evolved, it has "life", it has undergone the process of birth, growth and maturity; rocks are like bones and muscles, composing and supporting the earth's lattice and body; strata are like history books, can tell us the history of the earth's growth and evolution; magma and gas fluids are like blood and breathing, maintaining the life and operation of the earth; people know the life course of the earth according to the growth information recorded by the earth. The Earth is currently in the mature middle age stage.
How old is the earth?
According to the myths and legends of the continent, the earth is at least tens of thousands of years old. In the myths and legends of the mainland, 40,000 to 50,000 years ago, "heaven and earth were chaotic" and did not separate, when Pangu was born. He slept in the chaos for 18,000 years and woke up suddenly. When he saw that it was pitch black all around him, he slashed with a large axe, and the light rise became heaven, and the heavy descent became the earth ("Pangu Open Heaven"). However, the earth at that time, the "earth" was square and had four poles. Pangu was afraid that heaven and earth would merge into chaos again, so he stood on the ground and held the sky with his hands, and the sky grew taller every day, and Pangu grew taller with it. After 18,000 years, Pangu fell, his limbs became four poles, still "standing on top of the sky", his skin became earth, his blood became rivers, his breath became wind and clouds, and his sweat became rain and dew. After Pangu, Nuwa imitated herself and used "soil" to create all things ("Nuwa created man"), but then social unrest, the water god Gonggong clan and the fire god Zhu Rong clan fought, resulting in the Gonggong clan because of the great defeat and angrily crashed into the pillar of the world, Buzhou Mountain, so Nuwa used multicolored stones to make up the heavens ("Nuwa supplemented the heavens").
According to the Bible, the formation of the earth does not take more than 10,000 years.
At the beginning of the 18th century, the British physicist Edmond Halley proposed that assuming that the seawater was formed when it was light, then the age of the Earth was estimated to be about 100 million years based on the salt that was washed into the ocean by land every year, and the total salt content in the seawater. In 1854, the great German scientist Hermann von Helmholtz, based on his estimates of solar energy, concluded that the age of the Earth was no more than 25 million years. In 1862, the famous British physicist Joseph John Thomson proposed that it would take 20 million to 40 million years for the earth to cool from its early hot state to its current state.
In the early 20th century, scientists developed isotopic geological dating methods, proposing that the Earth was 3.5 billion years old, based on the oldest age of rocks obtained at that time. However, this rock is not necessarily the oldest on Earth. By the 1960s, scientists had measured rock specimens taken from the lunar surface, found that the age of the moon was 4.4 billion to 4.6 billion years old, and proposed that the earth was 4.4 billion to 4.6 billion years old based on the hypothesis that the earth and the moon formed at the same time. Later, more meteorites ageed the Earth to about 4.6 billion years.
New rocks are "born" every day on Earth, some formed in the process of volcanic eruptions, some formed in the process of lake and ocean sedimentation... After the rock is formed, some are gradually weathered, and some are melted by the magmatic process... Rocks also have a life cycle. How old are the oldest rocks on Earth? Were there rocks when the Earth formed?
The oldest rock on Earth that now has an exact age is located on a small island in the Acasta River in northern Canada, and this rock is known as "Akastaceta" (anglitter) gneiss, aged 4 billion years. Gneiss looks like hemp sugar, and there are different shades of mineral aggregates like sesame seeds arranged in a directional manner, intermittently distributed, forming bands, and the anglitter is a rock composed mainly of minerals such as feldsquartz. Such rocks are often formed in the crust below 10 km, and are formed by the differential distribution of different minerals in the rock under stress. Acastasia gneiss is found on a small island in the Akasta River in Canada's Northwest Territory with an area of less than 0.5 square kilometers. The only building on the island is a temporary circular tin house for geologists to work and live in, a "sanctuary" affectionately known by geologists as "Akasta City Hall". Canada's Northwest Territory covers an area of more than 3 million square kilometers, the indigenous people are Inuit, its capital is Yellowknife, and the permanent population is only more than 20,000 people. There are no roads to the "Akasta City Hall", and the most convenient way is to take a helicopter that can land on the lake. The Akasta gneiss are only a very small part of the island rock composition, and the other rocks are mostly gneiss and gabbros of 3.8 billion to 3.3 billion years old, with the youngest being about 1.2 billion years old (gabbro). Although these rocks are only a tiny fraction of the 4 billion-year-old continent that has been preserved, they provide the most precious samples for restoring the continent to what it was then.
In Greenland, Australia, Siberia and other places, rocks slightly younger than 4 billion years old have been found – 3.9 billion to 3.8 billion years old gneiss. There are also rocks of this age in the Anshan area of the mainland, which are produced in the Dongshan-Baijia tomb area and are now protected. The ancient rocks of Anshan and Australia are smaller, some the size of pillows, piece by piece, and irregularly shaped. The area of ancient rocks exposed in Greenland is very large (on the scale of kilometers), and scientists believe that these rocks roughly preserve the oldest crust on Earth.
Can you still find older rocks? The answer is almost yes! Scientists have discovered zircon, a mineral that has survived from 4.4 billion years of rock. The mineral has a negligible amount in rocks, but it is not easy to melt even at a high temperature of 1000 ° C, so it is easy to preserve. Found in sedimentary rocks (conglomerates) at Jack Hills in Western Australia, these minerals show a ring of zircon mineral growth that retains 4.4 billion years of age information. The rock was formed by detritus deposited 2.5 billion to 1.8 billion years ago by rivers. Studies have shown that these minerals record information about interactions with surface water, and that they formed in granites that resemble the dominant rocks of today's continents, such as those at the summits of Mount Huangshan and Taishan. This shows that 4.4 billion years ago, there were not only rocks on the earth, but also continents of a certain size, and that the continental rocks at that time had some similarities with those of today. Since theories speculate that there are more ancient rocks, it is possible to preserve them and wait for us to discover them.
Is there a rock older than 4.4 billion years? Did the Earth form rocks when it formed 4.6 billion years ago? Scientists believe that the surface of the Earth at the beginning was very hot, no rock, no crust, in a magmatic state, called the "magma ocean" or "magma sea". Magmatic ocean cooling may form oblique rocks. Plagioclase is a rock formed almost entirely by plagioclase minerals (which can be used as ceramics and glass, and some luminous stones also belong to the same group of minerals), which is a mineral with less crystalline density than magma in the magma ocean, which floats and gathers in the surface layer of the magma ocean to form rocks. The brighter-looking parts of the Moon (the "Highlands") are formed by oblique rocks. The oldest rock on the Moon is the oblique rock, which is isotopic geologically aged 4.5 billion years. Although the earliest type of rock crystallized by Earth was gneiss, some scientists believe that the surface of Earth's earliest crust (the original crust) may have looked like the high ground on the moon, composed of oblique rocks. The oblique rock is slightly weathered, it appears porcelain white, imagine the porcelain white earth without vegetation at that time, it must be very spectacular! Unfortunately, it is difficult for scientists to determine the exact age of the plagioclase, and it has not yet been confirmed whether there are more than 4.4 billion years of oblique rocks on earth.
Rocks that are 4 billion to 3.8 billion years old are only smaller rock fragments that remain in younger rocks. Where is the earth's large-scale old crust? Isua in Greenland. Part of the region's crust was formed 3.8 billion years ago and covers an area of 500 square kilometers. This is the largest piece of crust known to be more than 3.8 billion years old on Earth.
The history books of the earth
Consulting the classics and exploring the ruins, we can perceive the development process of human history, lament the rise and fall, the vicissitudes and great changes, just like the "Book of Poetry" said that "the high shore is the valley, the deep valley is the mausoleum". The history of mankind is only a few thousand years, while the history of the earth is more than 4 billion years, how can these histories be explored? The history of the Earth also has "writers", they are widely distributed strata. A set of strata is like a history book, open this history book, we can reveal the formation of strata and changes in the environment, we can also imagine the evolutionary history of the earth's "vicissitudes".
Stratigraphy is a general term for the various layered rocks formed during the development of the Earth's crust. The main rock composition of the formation is sedimentary rocks, but also metamorphic and volcanically occurring rocks. Although sedimentary rocks account for only 5% of the total lithosphere, they are distributed on 75% of the land area, and the bottom of the ocean is almost entirely covered by sedimentary rocks or sediments.
Under the conditions of the surface of the earth's crust, the weathered clastic sediments of the parent rock are transported by flowing water or wind, and then sedimentation and diagenesis, and finally the sedimentary rock is formed. Normally, sedimentary rocks are produced horizontally at the beginning of their formation, and are deposited from bottom to top over time, which is called sedimentary formations. Sedimentary rocks are relatively stable and continuously distributed within a certain range, and the biggest feature is that the lower strata are old and the upper strata are new.
However, the morphology of the strata is intricate. They either tilt or even bend the original horizontal state due to tectonic movement, or disconnect or stagger the original continuous formation due to seismic activity, or the stratum is defoliated due to crustal movement, or the formation morphology and appearance are completely changed due to metamorphism. They are like an old book that has been bent and destroyed, and the page order must be re-examined, sorted out, and studied in chapters and sections. Therefore, when studying strata in the field, geologists often choose standard profiles with complete stratigraphic exposure, normal order, clear contact relationship, and good fossil preservation, which can be divided and compared.
Mountains and rivers, vicissitudes and mulberry fields, changes in the earth's environment and the evolutionary history of organisms can be analyzed and reconstructed through the information of strata in different eras. Geologists have found that sedimentary rocks differ significantly in lithology, paleontological (fossil) composition, and geochemical characteristics during different sedimentary environments and diagenesis processes. At the same time, non-integration in the contact relationship between strata can reflect major changes in the geographical environment, such as the upward and downward movement of the earth's crust or fold deformation.
The lithology of sedimentary rocks includes material composition, particle size, roundness, color, rock type, and structure and structure of sedimentary formations. The characteristics of lithology can reflect the sedimentary environment in which the sedimentary rock was formed from the side. For example, particle size and roundness reflect the strength of the carrying force and the distance of the handling distance, the color marks the redox conditions at the time of formation, and the structure of the layer theory and waves reflects the hydrodynamic conditions in the sedimentation process.
Fossils are biological remains (e.g., animal bones, hard shells) and remains (animal footprints, wormholes, eggs, feces) preserved in geological periods in strata. Strata of different ages often contain different kinds of paleontology or paleontological groups, such as the representative marine organisms of the Cambrian Period, such as trilobites and odd shrimps, the representative marine organisms of the Silurian Period as penstones, the Devonian Period as the "Fish Age", and the dominant players of the ocean during the Jurassic Period were ichthyosaurs and plesiosaurs. Biological fossils can therefore be used to estimate the approximate age of strata and to compare strata.
According to the lithology, paleontological and tectonic movement characteristics in a regional strata, the relationship between the old and new stratigraphics and the chronological order of the regional stratigraphy can be established. After a wider range of row stratigraphic comparisons, it is also possible to establish a large regional or even global stratigraphic chronology.
The fossils, lithology and geochemical characteristics of the formation contain various information about the environment in the geological period, and scientists interpret the environmental characteristics of the time by deciphering this information, such as the direction of the ancient water flow or the direction of the paleogeography, the redox of the seawater and the movement of the structure, etc., and finally restore the long history of the earth.
The course of life on Earth
Our earth is a blue planet that nurtures life. The earth is now 4.6 billion years old, and it is in a very active period of young and middle-aged people. But the moon evolved very "anxious", evolving for about 3.3 billion years to exhaust energy, lose its vitality, and become a dead planet. Mars is on the verge of wood, the surface is full of gravel, the average surface temperature is only -65 ° C, and the atmosphere is thin and cold.
Earth, like everything, has life, and eventually runs out of energy, dying, as quiet as the moon, but without exploding. Scientists predict that it will take more than 4 billion years for the Earth to be completely depleted of energy and become a planet that dies like the moon. Depending on the right amount of water and oxygen, the Earth can sustain life for more than 1 billion years. Some scientists have predicted that the deterioration of the ecological environment caused by increased human activities may make the earth more rapidly detrimental to the survival of life.
The long history of the earth has gradually evolved and developed, which can be divided into different stages. In order to engrave this long history, geologists have established a set of geological chronology systems to represent different stages, and these units are called zeus, generation, era, epoch, and period from large to small. Among them, the Zeus is the largest geological chronology unit, with the Pluto, The Archaic, Proterozoic and Ephemeral. Each zeus can be further divided into generations, such as the Ezoozoic geological era can be divided into three generations, namely the Paleozoic, Mesozoic and Cenozoic. Each generation lasts for hundreds of millions of years. The Age is a further subdivision of each generation, such as the Paleozoic is divided into Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Mesozoic is divided into Triassic, Jurassic and Cretaceous, and Cenozoic is divided into Paleogene, Neogene and Quaternary. Each epoch has a different natural environment and unique paleontological species, and is the most commonly used unit of first-degree geological epoch, such as cambrian trilobites, Carboniferous ferns, Jurassic and Cretaceous dinosaurs, etc.
Each stage has a different evolutionary history.
The Pluto (4 billion years ago) was the initial formation of crustal rocks on Earth, most of which have not been preserved, if not all. Rocks are made up of minerals, and some of the minerals that are easy to retain, such as zircon, are preserved. By comparing it to the Moon, which still retains the rocky crust of the Pluto, we can imagine the Earth in the Pluto stage.
The Archean Dynasty (4 billion to 2.5 billion years ago) was the stage of the formation of stable continents. Stable continent, we call it Craton. The oldest preserved rock in the world is the gneiss of Akasta in northern Canada, at 4.04 billion years old. This age marks the beginning of the Archean Age. The oldest remaining crust on Earth is 3.8 billion to 3.3 billion years old, preserved in Greenland, an area equivalent to the size of three Hebei provinces.
The Proterozoic (2.5 billion to 541 million years ago) was an important stage in the evolution of the atmosphere, and the late Proterozoic was the stage of the "Great Explosion of Life". About 2.3 billion years ago, the earth's surface air was thin and the oxygen concentration was very low, and the concentration of gases such as methane (CH4) and hydrogen sulfide (H2S) in the air was probably greater than the concentration of oxygen. In 2.3 billion to 2 billion years, oxygen on the Earth's surface underwent a process of sudden increase in concentration, called the "Great Oxidation Event."
The Ezoogens (541 million years ago to the present) were the stage of prosperity in life. The Eminentinocene was further divided into three epochs: the Paleozoic, the Mesozoic, and the Cenozoic. Humans emerged in the Cenozoic Era.
This article is excerpted from "Motion: The Code of Life on Earth" (edited by Zhai Mingguo), and the title has been adjusted. Science creates the future, and humanities warm the world. In the era of science and technology leading development, we will pay attention to the history of science and technology, the philosophy of science and technology, the frontier of science and technology and the dissemination of science, and the sustainable development of human society. Sciences Humanities Online, create valuable reading! Welcome to follow, like, leave a message, forward, participate in the book donation activities, contact email: [email protected].
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Synopsis
The Earth is passionate and vibrant from the moment it was born. From the inside to the outside, from small to large, on various time and space scales, the earth never stops moving, interpreting its extraordinary life in a unique way. This book takes us to explore: how can human beings understand the internal structure of the earth step by step? What kind of violent birth process did the earth go through? How do rocks record the history of the ancient Earth? How did the vicissitudes evolve? How do fiery magma and ubiquitous fluids form rich minerals? As you read, you will gradually decipher Earth's "code of life." The whole book brilliantly shows the process from the unknown, doubt to scientific exploration, there are confusions, surprises, and fascinating. Hopefully, the younger generation will take up the challenge and continue to explore the unsolved mysteries of the earth.
This book integrates science, knowledge, and interest, which is beneficial to cultivating scientific interest, broadening horizons, and tapping inner potential, and is suitable for public readers who are interested in science, nature and the future.
About the author
Zhai Mingguo is an academician of the Chinese Academy of Sciences, an academician of the Academy of Sciences of Developing Countries, a senior chair professor of the University of Chinese Academy of Sciences, and a researcher of the Institute of Geology and Geophysics of the Chinese Academy of Sciences. His main research areas are Precambrian geology and metamorphic geology, petrology and mineral deposits, and his research direction is early continental evolution and continental mineralization. Systematic innovations have been made in the formation and growth of the early continental crust, the heterogeneous core scientific problems of precambrian and Proteozoic metamorphic action and dynamic mechanism, and the enrichment mechanism of continental evolutionary history and mineral resources. He has won two second prizes of the National Natural Science Award, one first prize and two second prizes of the Natural Science Award of the Chinese Academy of Sciences, one first prize of the Land Resources Science and Technology Award, one first prize of the Natural Science Award of the Ministry of Education, as well as the Ho Leung Ho Lee Foundation Science and Technology Progress Award, the Korean Geological Special Contribution Award, etc.
(This article is edited by Zhu Pingping)
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