Rotation and revolution
1543, Copernicus first put forward the concepts of the earth's rotation and revolution in his book "On the Operation of Celestial Bodies". Since then, many observations and experiments have proved that the earth rotates from west to east and revolves around the sun at the same time. 185 1 year, the French physicist Foucault successfully conducted a famous experiment (Foucault pendulum experiment) in Paris, which proved the rotation of the earth. The earth's rotation period is about 23: 56 minutes and 4 seconds. When the sun is flat, the orbit of the earth's revolution is elliptical. The half-length diameter of the track is 149597870 km, and the track eccentricity is 0.0 167. Period of revolution is a sidereal year with an average revolution speed of 29.79 kilometers per second, and the intersection angle between the ecliptic and the equator (the intersection angle between the ecliptic and the equator) is 23 27'. The combination of the earth's rotation and revolution has produced the alternation of day and night, the change of four seasons and the distinction of five zones (tropical zone, north-south temperate zone and north-south frigid zone). The speed of the earth's rotation is uneven, with long-term change, seasonal change and irregular change. At the same time, due to the gravitational effects of the sun, the moon and the planets, as well as the various effects of the atmosphere, the ocean and the materials inside the earth, the earth's rotation axis will change in space and the direction of the earth itself, that is, precession nutation, polar shift and angle change.
Shape and size
The concept that the earth is spherical can be traced back to the fifth and sixth centuries BC. At that time, the Pythagorean philosophers in Greece only produced this concept from the most beautiful sphere concept. Aristotle scientifically demonstrated that the earth is a sphere for the first time according to the fact that the shadow on the moon is round during the eclipse. China As early as the Warring States Period, the philosopher Hui Shi put forward the view that the earth is spherical.
In the 3rd century BC, the ancient Greek geographer Eratosthenes successfully measured the meridian length between Aswan and Alexandria by triangulation. During the Tang Dynasty in China, the survey team led by Nangong Shuo, under the guidance of a delegation, conducted the earliest arc survey in the northern and southern plains of the Yellow River in Henan Province, and calculated that the difference in the horizontal height of the North Pole was one degree, which was equivalent to the difference in the ground distance between the north and the south of 0, about 3565438+80 steps (the length unit of the Tang Dynasty was 5 feet = 1 step and 300 steps = 1 mile), which was similar to that of Arabs. In modern times, in addition to geodetic methods; Gravity measurement can also be used to determine the equilibrium shape of the earth. After the launch of the artificial earth satellite, the geodynamic geodesy method has made great progress. The combination of various methods greatly improves the accuracy of determining the shape and size of the earth. In the astronomical constant system of 1976 international astronomical union, the equatorial radius α of the earth is 6378 140m, and the oblateness factor of the earth is 1/f is 298.257. The earth is not a right sphere, but a flat sphere, or more like a pear-shaped rotating body. The observation results of artificial earth satellites show that the equator of the earth is also an ellipse, so the earth can be considered as a triaxial ellipsoid. The inertial centrifugal force of the earth's rotation makes the spherical earth gradually expand from the poles to the equator, becoming a slightly flat rotating ellipsoid, and the radius of the polar pole is about 2 1 km shorter than the radius of the equator. The inhomogeneity of material distribution in the earth further causes the irregularity of the surface shape of the earth. In geodesy, the so-called shape of the earth refers to the shape of the geoid, on which the gravity potential is the same everywhere, which is an equipotential surface. The gravitational force of the sun and the moon on the earth makes the ocean and atmosphere on the earth tidal, and also makes the solid earth (to some extent, an elastic body) elastically deformed, which is called "solid tide".
Mass and gravitational acceleration
The mass of the earth is 5.976×l0^27 grams, which is determined according to the law of universal gravitation. The determination of the mass of the earth provides a basis for determining the mass of other celestial bodies. From the mass of the earth, it can be concluded that the average density of the earth is 5.52g/cm3. Any particle on the earth is affected by gravity and inertial centrifugal force, and their resultant force is gravity. Gravity decreases with the increase of height and changes with the change of latitude. The acceleration of gravity at the equator is 978.gal (cm/s 2), and at both poles it is 983.2 gal. Gravity anomalies will occur in some places, reflecting the uneven distribution of materials in the earth. Gravity anomalies are related to geological structures and deposits. Due to the tidal force of the sun and the moon, the acceleration of the earth's gravity also varies slightly periodically, up to several tenths of milligal. The gravity constant of the earth is 9.8N/kg, which is six times that of the moon.
Geotechnical building
The earth can be regarded as a series of concentric layers. There are core, mantle and crust structures in the earth. Outside the earth, there are hydrosphere, atmosphere and magnetosphere, forming a coat around the solid earth. The magnetosphere and atmosphere block the direct bombardment of the ground by ultraviolet rays, X-rays, high-energy particles and countless meteors from space.
More than seven-tenths of the earth's surface is covered by blue oceans, and lakes and rivers account for only a small part of the earth's surface waters. The liquid water layer on the earth's surface, called hydrosphere, has been formed for at least 3 billion years. The earth's surface is composed of various rocks and soils, and the ground is rugged, and low-lying areas flood into oceans and lakes; There are plains and mountains on the land above the water. The total vertical fluctuation of the earth's solid surface is about 20km, which is the height difference between the top of Mount Qomolangma (the elevation of Mount Qomolangma is 8844.43m as determined by the China mountaineering team) and the deepest part of the ocean (the depth of Mariana Trench is about 1 1km), which is more than half of the average thickness of the continental crust. The seabed is as uneven and unstable as land. The rocks on the seabed are much younger than those on land. Most rocks on land are less than 2 billion years old. Sedimentary rocks can be seen everywhere on the land, indicating that these places may be oceans in ancient times. Although there are several craters on the earth's surface, it is difficult to find as many craters as the moon, Mars and Mercury. This is because the earth's surface is constantly weathered, eroded and disintegrated by external forces (water and atmosphere) and internal forces (earthquakes and volcanoes).
For a long time, it has been thought that the crustal tectonic movement is mainly characterized by the uplift and subsidence of the ground, with vertical movement as the main movement and horizontal movement as the supplement. In recent ten years, more and more scientists believe that the upper part of the earth not only has vertical movement, but also has greater horizontal movement, and the relative position of the ocean and the mainland also changes during geological periods. Wei Gena put forward the hypothesis of continental drift. Since then, some geologists believe that there are two ancient continents on the earth-Gondwana in the southern hemisphere and Lauya in the northern hemisphere. However, for a long time, many scientists refused to admit the hypothesis of continental drift, because it was hard to believe that there was such a great force to tear apart the original continental block and let the debris drift gradually to its present position. In the early 1960s, Hess and Dietz put forward the hypothesis of submarine expansion, arguing that global tectonics is the direct result of submarine expansion. It is precisely because of the development of the hypothesis of seafloor spreading and the theory of plate movement that the theory of continental drift has been paid attention to again.
The top layer of the earth, about tens of kilometers thick, is the lithosphere with great strength, and the bottom layer, hundreds of kilometers thick, is the asthenosphere with low strength. The material in this layer is plastic under long-term stress. The lithosphere floats on the asthenosphere. When the energy (primary heat and radioactive heat) in the earth is released, the uneven distribution of temperature and density in the earth causes the convection movement of mantle materials. Mantle convection material moves to both sides along the cracks in the mid-ocean ridge of the ocean floor, and constantly forms a new ocean floor. In addition, the old ocean floor continues to expand outward, and when it approaches the continental margin, it is inserted under the continental crust under the traction of mantle convection, resulting in a series of tectonic movements in the lithosphere. This convection can make the whole seabed renew once every 300 million years. The lithosphere is separated by some active tectonic belts and divided into several discontinuous units called continental plates. Rebichon divides the global lithosphere into six plates: Eurasia plate, America plate, Africa plate, Pacific plate, Australia plate and Antarctic plate. The expansion of the seabed led to the movement of continental plates. The mutual compression of plates has created a huge mountain system, from the Alps through Turkey, the Caucasus to the Himalayas. In some places, the rocks of two plates sank at the same time, which led to the abyss of the sea floor. In addition, plate movement also triggered volcanoes and earthquakes. At present, the theory of plate motion is still developing, and there are also many controversial issues.
Origin and evolution
The systematic scientific research on the origin and evolution of the earth began in the middle of the eighteenth century, and many theories have been put forward so far. The popular view now is that the earth, as a planet, originated from the primitive solar nebula 4.6 billion years ago. Like other planets, it has experienced some similar physical evolution processes such as accretion and collision. At the beginning of embryo formation, the temperature was low and there was no layered structure. It is only because of the bombardment, radioactive decay and gravitational contraction of the original earth that the temperature of the earth gradually rises. With the increase of temperature, the materials in the earth become more and more plastic, and local melting occurs. At this time, under the action of gravity, material differentiation begins, heavier materials outside the earth gradually sink, lighter materials inside the earth gradually rise, and some heavy elements (such as liquid iron) sink to the center of the earth, forming a dense core (seismic wave observation shows that the outer core of the earth is liquid). The convection of matter was accompanied by large-scale chemical separation, and finally the earth gradually formed the present crust, mantle and core.
In the early stage of the earth's evolution, the primitive atmosphere completely escaped. With the recombination and differentiation of matter, various gases in the earth rose to the surface through volcanic eruption to become the second generation atmosphere, and later, due to the photosynthesis of green plants, it further developed into a modern atmosphere. On the other hand, the internal temperature of the earth rises, which makes the internal crystal water vaporize. With the gradual decrease of surface temperature, gaseous water condenses and falls to the ground to form hydrosphere. About three or four billion years ago, single-celled organisms began to appear on the earth, and then gradually evolved into various organisms until advanced organisms like humans formed a biosphere.
Earth data
Orbit long radius (astronomical distance unit) 1.000
Track long radius (million kilometers) 149.6
Rotating Stellar Time (Japan) 365.26
Revolution rendezvous period (days)
Track eccentricity 0.0 167
Track inclination (degree) 0.0
Longitude of ascending intersection (degree) 0.0
Longitude (degrees) of perihelion 102.3
Average track speed (km) 29.79
Equatorial radius (km) 637 1 (this data is the latest, and the previous data is 6378).
Polar radius (km) 6350 (this data is the latest, the previous data is 6357).
Earth circumference (km) 40030
Flat rate 0.0034
Mass (Earth mass = 1) 1.000
Density (g/cm3) 5.52
Equatorial gravity (Earth = 1) 1.00
Escape speed (km/s) 1 1.2
Rotation period (days) 0.9973
The intersection of yellow and red (degree) is 23.44.
Albedo 0.30
Maximum brightness-
Satellite (confirmed) 1
plate
At present, there are eight main departments in the world:
Eurasia plate-the eastern half of the North Atlantic, Europe and Asia (except India); Eurasia plate-the eastern half of the North Atlantic, Europe and Asia (except India);
Africa plate-Africa, the eastern half of the South Atlantic and the western side of the Indian Ocean; Africa plate-Africa, the eastern half of the South Atlantic and the western side of the Indian Ocean;
India-Australia plate-India, Australia, New Zealand and most of the Indian Ocean; India-Australia plate-India, Australia, New Zealand and most of the Indian Ocean;
Pacific plate-most of the Pacific Ocean (including the coast of Southern California); Pacific plate-most of the Pacific Ocean (including the coast of Southern California);
Nazca plate-the east side of the Pacific Ocean, next to South America; Nazca plate-the east side of the Pacific Ocean, next to South America;
North American plate-North America, the western half of the North Atlantic and Greenland; North American plate-North America, the western half of the North Atlantic and Greenland;
South American plate-South America and the western half of the South Atlantic; South American plate-South America and the western half of the South Atlantic;
Antarctic Plate-Antarctica and Southern Ocean. Antarctic Plate-Antarctica and Southern Ocean.
In addition, there are at least twenty small plates, such as Arabian Plate, Cox Plate and Philippine Sea Plate. In addition, there are at least twenty small plates, such as Arabian Plate, Cox Plate and Philippine Sea Plate. Earthquakes occur frequently at the plate boundary. It is obvious where the plate boundary is when the epicenters are pointed out one by one.
29% of the earth is land, and 7 1% is ocean. The global land can be divided into seven continents: Asia, Africa, Europe, Oceania, South America, North America and Antarctica. The global ocean can be divided into four oceans; Pacific Ocean, Atlantic Ocean, Indian Ocean and Arctic Ocean.
name
Earth is the only name that doesn't come from Greece or Rome. The word earth comes from old English and Germanic. Of course, there are many other languages. In Roman mythology, the goddess of the earth is called Tellus-fertile land (Greek: Gaia, mother of the earth).
The earth is the third closest planet to the sun with an orbital radius of14960000 km (1.00au). With a diameter of 12756.3 km, it ranks fifth among the nine planets. The mass is 5.9736x 10 24 kg.
The composition of the earth
It was not until Copernicus in the 16th century that man realized that the earth was just another planet in the solar system. It was not until Copernicus in the 16th century that man realized that the earth was just another planet in the solar system.
Of course, we can know the earth without a space probe, but it was not until the twentieth century that we really outlined the whole picture of the earth. Of course, it is very important to get its image from space. The space image of the earth is very helpful for weather forecast, especially for typhoon (hurricane) forecast. The earth seen from space is really beautiful.
According to the chemical composition and seismic characteristics, the earth can be divided into several layers, and their names and ranges (depth in kilometers) are as follows:
0- 40 crust 40-2890 mantle 2890-5 150 outer core 5 150-6378 inner core.
The thickness of solid crust varies greatly, and the crust in marine areas is thin, with an average thickness of about 7 kilometers; The continental crust is much thicker, with an average thickness of about 40 kilometers; The mantle is also solid, but there is a very small partially melted area on it, called asthenosphere. The top of the mantle and the whole crust above it are called lithosphere. As for the outer core is liquid and the inner core is solid. These different layers are bounded by discontinuities, the most famous of which is the Mo Holovics discontinuity between the crust and mantle.
The mantle occupies the main part of the earth, while the core occupies the second place. As for the space where we live, it is only a tiny part of the whole earth (mass, unit is 10 to the 24th power kilogram: atmosphere = 0.000005 1, ocean = 0.00 14, crust = 0.026, mantle = 4.043).
The main component of the core is iron (or iron-nickel), but there may be some lighter substances. The core temperature is about 7,500K, which is higher than the surface temperature of the sun. The main components of the lower mantle may be silicon, magnesium and oxygen, plus some iron, calcium and aluminum; The main components of the upper mantle are olivine and pyroxene (iron magnesium silicate rocks), but there are also calcium and aluminum. All the above knowledge comes from seismic data. Although the material in the upper mantle is sometimes brought to the surface by lava from volcanoes, we still can't reach the main part of the solid earth, and the current seabed drilling operation has not even dug through the crust. The crust is mainly composed of silicate such as quartz (silica) and feldspar. Generally speaking, the geochemical components are: iron 34.6%, oxygen 29.5%, silicon 15.2%, magnesium 12.7%, nickel 2.4%, sulfur 1.9% and titanium 0.05%.
The earth is the main star with the highest average density.
Other terrestrial planets also have structures and compositions similar to those of the Earth, but there are some differences: the moon nucleus accounts for the smallest proportion; The proportion of mercury nuclei is the largest; The letters of Mars and the moon are thicker; There is no difference in chemical composition between the moon and mercury. The earth may be the only one that can be subdivided into an inner core and an outer core. However, please note that our understanding of the interior of the planet mainly comes from theoretical deduction, even for the earth.
Different from other terrestrial planets, the outermost layer of the earth (including the crust and the top of the upper mantle) is divided into several pieces and "floats" on the fiery mantle below, which is the famous theory of plate tectonic movement. This theory mainly describes two kinds of movements: extension and dive. The former occurred in the place where the two plates were far apart, and the magma below them spewed out to form a new crust; The latter occurs when two plates collide with each other, one of which dives under the other plate and finally disappears into the mantle. In addition, there are some plate boundaries that cross each other or two continental plates collide with each other.
The surface of the earth is very young, only about 500 million years old, which is really short from the astronomical point of view. Erosion and tectonic geological movements constantly destroy and rebuild most of the surface, thus almost completely destroying the early geological records of the surface, such as impact craters, so most of the early earth history has disappeared. The earth is about 4.5 billion to 4.6 billion years old, but the oldest known rocks are only about 4 billion years old, and rocks over 3 billion years old are very rare. The oldest biological fossils are no more than 3.9 billion years ago, and there is no record about the critical period of the origin of life.
7 1% of the earth's surface is covered with water, and the earth is the only planet in the solar system that can have liquid water on its surface (liquid ethane or methane exists on Titan's surface, while liquid water may exist under Europa's surface, but it is still unique that liquid water exists on the earth's surface). Liquid water is an indispensable element in our known life forms; Because of the large specific heat of water, the thermal volume of the ocean has become a great contributor to keeping the earth's temperature constant; Liquid water is also the main force of erosion and weathering on land, and land is the only place in the solar system that has this effect (it may have had this effect in the early days of Mars, but it is no longer there).
In the composition of the earth's atmosphere, 77% is nitrogen, 265,438+0% is oxygen, followed by trace amounts of argon, carbon dioxide and water vapor. Most of the atmosphere at the beginning of the earth may be carbon dioxide, but most of it has been combined with carbonate rocks, and the rest is dissolved in the ocean and discharged by green plants; Nowadays, plate tectonic movement and biological action are the continuous masters of the growth and decline of carbon dioxide in the atmosphere. The greenhouse effect caused by moisture and trace carbon dioxide in the atmosphere is very important to maintain the surface temperature. The greenhouse effect increases the surface temperature by about 35℃, otherwise the average surface temperature will be extremely cold -2 1℃! Without water vapor and carbon dioxide, seawater would freeze and life forms as we know them would be impossible to develop. In addition, water vapor is an indispensable angle in the earth's water cycle and weather changes.
The existence of free oxygen is also a major feature of geochemical composition, because oxygen is a very active gas and should be easily combined with other elements in the atmosphere. Oxygen on the earth is produced and maintained entirely by biological action. Without life, there is no free oxygen.
The tidal force between the Earth and the Moon will increase the rotation period of the Earth by about 2 milliseconds every century. The latest research shows that 900 million years ago, there was only 18 hours a day, while there was 48 1 day a year. The earth has a moderate magnetic field, which should be caused by the current in the liquid outer core. Due to the interaction between the solar wind and the earth's magnetic field and the outer atmosphere, the aurora is produced. The imbalance of the above factors causes the magnetic poles to move on the surface. At present, the magnetic North Pole is located on the northern border of Canada. Due to the interaction between the solar wind and the earth's magnetic field and the outer atmosphere, the aurora is produced.
The earth's magnetic field and its interaction with the solar wind also cause the Van Allen radiation belt, which is a pair of annular belts around the earth, like doughnuts, composed of gas ions (plasma), and the outer circle extends from 19000km above sea level to 4 1000km. The elevation of the inner ring is between 13000-7600 km.
Satellites and seismic waves
There is a satellite on the earth, the moon, which is 384,000 kilometers away from the earth, with a radius of 1738 kilometers and a mass of 7.35 x 1022 kg. However, beyond that: thousands of small satellites are also orbiting the earth; The complex orbit of asteroid 3753 (1986 TO) is related to the earth. It is not a satellite of the earth, but is generally considered as a "companion star", which is more like the position of Saturn's Enceladus and Enceladus. During the period of 1846, someone claimed to have found a second moon, Lilith, which was later confirmed not to exist.
Seismic wave-the key to open the door to the center of the earth. At the beginning of the 20th century, Yugoslav seismologist Mohorovicic suddenly realized that seismic waves are "ultrasonic detectors" for us to explore the interior of the earth! Seismic wave is the seismic wave emitted during an earthquake. It has two kinds: shear wave and longitudinal wave. Shear waves can only pass through solid materials, while longitudinal waves can freely pass through any kind of materials, such as solids, liquids and gases. When the density of passing matter is high, the propagation speed of seismic wave is fast, and when the density of passing matter is low, the propagation speed is slow. Mohorovicic found that the propagation speed of seismic waves suddenly accelerated at 33 kilometers underground, which indicated that the density of materials here was very high and the composition of materials was different from that of the earth's surface. This depth inside the earth is called "Moho".
19 14 years, American seismologist Gutenberg found that at 2900 kilometers underground, the velocity of longitudinal waves suddenly slowed down and the shear waves disappeared. This shows that the density of matter here has become smaller, and there is no solid matter. The center of the earth is here, leaving only liquid and gas. This depth is called "Gutenberg surface".
The mystery of the center of the earth has finally been solved: from the outside to the inside, the earth is divided into three layers by Moho surface and Gutenberg surface, namely crust, mantle and core. The crust is mainly rock, the mantle is mainly peridotite containing magnesium, iron and silicon, the core, the real heart of the earth, mainly iron and nickel, and the temperature here is over 200 1 Celsius.
The earth is the home of mankind. However, with the development of science and technology and the expansion of economic scale, the global environmental situation has been deteriorating in the past 30 years. According to some data, since meteorological instruments were observed in 1860, the global annual average temperature has increased by 0.6 degrees Celsius, and the warmest years in 13 all appeared after 1983. In the 1980s, the global average population affected by disasters was 65.438+0.47 billion, but in the 1990s, this figure rose to 265.438+0. 1 billion. At present, about 40% of the world's population is seriously short of water. If this trend is not contained, more than 55% of the world's population will face water shortage in 30 years. The deterioration of the natural environment also seriously threatens the wild species on the earth. Today, 0/2% of birds and a quarter of mammals in the world are on the verge of extinction, and overfishing has led to the depletion of one-third of fish resources.
1On April 22nd, 970, in the United States across the Pacific Ocean, in order to solve the problem of environmental pollution, people spontaneously launched a massive mass environmental protection movement. On this day, more than 20 million people took to the streets in 0/0000 primary and secondary schools, 2,000 colleges and universities, 2,000 communities and major groups in the United States. People hold high the polluted earth model, huge paintings and charts, shout the slogan of protecting the environment, hold demonstrations, assemblies and speeches, and call on the government to take measures to protect the environment. This event shocked the ruling and opposition parties, prompting the US government to pass the amendments to the Water Pollution Control Law and the Clean Air Law in the early 1970s, and set up the US Environmental Protection Agency. Since then, American NGOs have proposed to designate April 22nd as "Earth Day". With the development of environmental protection, its influence has expanded and surpassed the national boundaries of the United States, and it has received positive responses from many countries in the world.
In the 20 years since the birth of Earth Day, great progress has been made in environmental protection around the world. 1In June 1972, the United Nations held an epoch-making conference on human environment.1In June 1973, the United Nations Environment Programme was established. Many countries have established environmental protection management institutions and scientific research institutions, environmental protection has been put on the important agenda of many governments, and environmental problems have aroused widespread public concern. At many major international conferences, environmental protection has also become one of the important topics, such as the 44th General Assembly held in 1989, the Summit of Non-Aligned Countries, the Commonwealth Summit and the G-7 Summit. These meetings discussed environmental issues and adopted resolutions or declarations on environmental protection. This shows that environmental protection has become a "hot spot" in international politics and international relations. More and more politicians, scientists and people of insight are strongly aware that environmental pollution and ecological deterioration will greatly hinder the progress of social civilization.
As environmental protection has become a hot topic in international politics, the organizers of 1990 Earth Day decided to take 1990 Earth Day as the first international Earth Day to urge hundreds of millions of people all over the world to actively participate in environmental protection. Therefore, the organizers of Earth Day wrote to the leaders of China, the United Kingdom and the United Nations Secretary-General, calling for the convening of a high-level environmental conference with the target date of 65438+1April 22, 990, so as to lay the foundation for the conclusion of multilateral treaties. Call on all countries to take active measures and reach an agreement to stop and reverse the development of global environmental degradation. At the same time, we call on governments all over the world who are willing to protect the environment and carry out international cooperation to celebrate the 20th anniversary of Earth Day in their own countries.
The call to celebrate the 20th anniversary of Earth Day has been warmly responded and actively supported by countries and groups on five continents. US President George W. Bush declared April 22nd as the official Earth Day in the United States, and called on citizens to actively participate in actions to improve the environment. Dennis hayes, Chairman of the Coordination Committee of "Earth Day 1990", visited the activity groups in London, Paris, Rome, Bonn and Brussels in advance, and got a clear reply, agreeing to commemorate Earth Day 1990 as the International Earth Day. Many countries and regions in Asia, Africa and Latin America also responded positively and organized commemorative activities. Many international organizations, such as the International Student Union and the Youth Development and Cooperation Association, also expressed their strong support and active participation in the 20th anniversary of Earth Day. 1On April 22nd, 990, various environmental protection publicity activities were held in more than 0/00 countries around the world, with hundreds of millions of participants. From then on, "Earth Day" became international and became "Earth Day".
Earth Day aims to arouse people's awareness of caring for the earth and protecting their homes, and promote the coordinated development of resource exploitation and environmental protection. Since 1990s, China has held Earth Day on April 22nd every year.