Earth Earth
One of the eight planets in the solar system, the third one is in the order of near and far from the sun. It is the planet where humans are. It has a natural satellite - the moon, which forms a celestial system - Earth-Moon System .
The earth has about 4.6 billion years of history. Whether it is the whole of the earth, or its atmosphere, ocean, crust or interior, it has been constantly changing and moving since its formation. During a series of evolutionary stages, it maintains a dynamic equilibrium state.
. Rotation and Revolution
1543, N. Copernicus first fully proposed the concept of earth's rotation and revolution in his book "On the Operation of Celestial Bodies". Since then, a large number of observations and experiments have proved that the earth rotates from west to east and revolves around the sun.
1851, French physicist Fuke successfully conducted a famous experiment (Fuke pendulum test) in Paris to prove the rotation of the earth.
The earth's rotation period is about 23:56:4 seconds to level the sun (stellar day). The orbit of the earth's revolution is elliptical, the length of the orbit is 149597870 kilometers (1 astronomical unit ), the orbital eccentricity is 0.0167, the revolution period is 1 stellar year (365.25 flat sun days), and the average revolution velocity is 29.79 kilometers per second, the intersection angle between the ecliptic and the equator (yellow-red intersection angle) is 23°20′.
The combination of earth's rotation and revolutionary movement produces the distinction between day and night alternation, four seasons and the five zones (tropical, north-south temperate and north-south cold zones) on the earth.
The speed of the earth's rotation is uneven, with long-term changes, seasonal changes and irregular changes. At the same time, due to the gravitational action of the sun, moon, and planets, as well as the various effects of matter inside the atmosphere, ocean and the earth, the direction of the earth's rotation axis in space and in the earth's body changes, namely, precession and movement, extreme movement and yellow Red intersection angle changes.
. Shape and size
Greek Philosopher Aristotle (384 BC-322 BC) According to the moon's shadow on the moon, it was a circle. It was scientifically proved for the first time that the earth should be a spherical shape.
Another Greek geographer Elatoseni (about 276 BC to about 194 BC) successfully used triangulation to determine the length of the meridian between Aswan and Alexandria.
Chinese Tang Dynasty Nangong said that in 724, 13 locations on the same meridian were selected in Henan Province for geodetic measurements. After calculation by astronomers (683-727), the length of the meridian was found.
Now, according to a comprehensive study of geodesy, gravity measurement, geodynamic measurement and space measurement, in the astronomical constant system released by International Astronomical Federation , the earth's equatorial radius is 6378 kilometers and the flatness is 1/298.
The earth is not a regular sphere but a triaxial ellipsoid, and the equatorial radius is about 21 kilometers longer than the pole radius. The uneven distribution of matter inside the earth causes the shape of the earth's surface to be uneven.
The earth's mass (including the atmosphere, etc.) is kilograms, the earth's volume is cubic meters, and the average density is 5.52 grams/cubic centimeter.
. Distribution and evolution of sea and land
The shape of the earth's surface is complex, with mountains, vast sea basins and structures of various scales. The highest point on the continent is Mount Everest, with an altitude of 8844.43 meters, the lowest point is the Dead Sea, the lake surface is 416 meters lower than sea level; the Mariana Trench at the deepest bottom of the sea, with a depth of 11,034 meters.
The total surface area of the earth is square kilometers, of which the continental area is about square kilometers, accounting for about 29% of the total surface area.
Earth is the only star in the solar system where liquid water exists on the surface and deep. The ocean area is about square kilometers, accounting for about 71%. Below the sea, the continent has a steep edge.
is based on average sea level. There are two sets of altitude statistics on the earth's surface that are the most widely distributed: one is between 0 and 1000 meters above sea level, accounting for more than 21% of the earth's total area; the other is below sea level Between 4000 and 5000 meters, accounting for more than 22%.
The total amount of water on the earth's surface is about cubic kilometers, of which fresh water is cubic kilometers, accounting for only 2.5% of the total water volume.
The rocks at the bottom of the ocean are less than 200 million years old, much younger than land. sedimentary rocks can be found everywhere on land, indicating that these places may be oceans during the geological period.
1912 A.Wegener proposed the continental drift theory, believing that the relative position of the ocean and the continent changes during the geological period.
In the early 1960s, H.H. Hess and R.S. Dietz proposed the theory of seabed expansion, believing that global ocean basin evolution is the result of ocean floor expansion.
The subsequent plate tectonic theory further explains the movement of the earth. The split of the plate causes the formation of the ocean, and the entire ocean floor renews every 200 million years; the plate squeezing movement forms huge mountain systems, such as the Alps, Himalayas, etc.
. Structure and composition
Earth is a living planet. It is composed of a circle composed of different matter and different states of matter, that is, consisting of a solid earth, a surface water circle, an atmosphere and a biosphere.
With the development of science, they have become the main research objects of solid geophysics, geology, marine science, atmospheric science and biology respectively.
.1. Internal structure of the earth
According to the results of seismic wave velocity observation, it was found that there are global velocity sections inside the earth (such as the Moho interface, Gutenberg interface and Lehman interface, etc.). These sections can divide the earth into different circles.
In the 1980s, research on seismic tomography found that the internal structure of the earth had great lateral inhomogeneity, but was generally radially stratified. It is mainly divided into three circles: crust, mantle and core.
① Crust. The uppermost part of the solid earth has a bottom interface of Moho . The continental crust and the oceanic crust are significantly different, and the thickness of the continental crust in different regions varies greatly, from more than 20 kilometers to more than 70 kilometers; the oceanic crust is only a few kilometers. The earth's crust can be further divided into different layers, and the lateral changes are also very large.
② Mantle. The part under the earth's crust is between the Moho face and the Gutenberg face. The mantle can be further divided into many layers. The current global section has a 410 kilometers section, which is the phase transition from olivine to β spinel; the 660 kilometers section is the phase from spinel to perovskite and magnesium iron ore It is transformed and the 660 kilometers section is the interface between the upper and lower mantle.
③ The core of the ground. The part between the earth's center and Gutenberg interface can be divided into two parts: the outer core and the inner core. The interface between them is the Lehman interface with a depth of 5149.5 kilometers. The core of the ground is mainly composed of iron, nickel and a small amount of silicon and sulfur. The outer core is liquid and the inner core is solid.
.2. The composition of matter inside the earth
seismic wave velocity and material density distribution provide constraints for studying the composition of matter inside the earth. About 90% of the core is composed of iron-nickel alloy. But it also contains about 10% to 20% of the lighter substance, which may be sulfur or oxygen (but some people think that the core contains 21% silicon, 11% sulfur, and 7% oxygen).
The main minerals in the upper mantle are peridot , pyroxene and garnet . At a depth of 410 kilometers, the peridot phase changes into spinel structures, while the pyroxene phase changes into garnet. At a depth of 520 kilometers, β spinel becomes spinel, and pyroxene decomposes into spinel and super quartz . At a depth of 660 kilometers, these minerals are decomposed into perovskites and oxide structures.
In the lower mantle, there is no obvious change in mineral composition, but in the lowest 200 kilometers of the mantle, the density of matter increased significantly. Whether this area is enriched with iron is still a controversial question.
The rock minerals in the earth's crust are made from the differentiation of mantle matter.
.3. The overall composition of the earth
can be obtained through two ways. One is to estimate the approximate estimates based on the density, mass distribution of each circle of the earth and the basic assumptions of mantle and core components. The other is based on the theory of the origin of the earth and the results of comparative research on meteorites, and the components of specific types of meteorites are selected as the basis for establishing the overall model of the earth.
Since the atmosphere and oceans only account for 0.03% of the earth's total mass and the earth's crust accounts for less than 1% of the total mass, the overall composition of the earth is basically determined by the mantle and the core.
1982 R.G. Mason assumes that the iron-nickel alloy of the core has the average iron and nickel component of the chondrite metal phase, and the metal phase of the core accounts for 27.10% of the earth's total mass; according to the chondrite metal phase, the metal phase also contains a certain component. For meteorite sulfide, it is calculated that the total amount of FeS contained in the earth's core is 5.3% of the total mass of the earth.
The composition of the mantle plus crust is the same as the average chemical content of the chondria silicate phase (silicate plus a small amount of phosphate and oxide), and its mass is 67.60% of the total mass of the earth. Based on this, Mason calculated the composition of the earth, which is shown in Table 2. Although the data on the overall average chemical composition of the earth in Table 2 is not accurate enough, some important issues have been explained.
90% of the earth's mass is composed of four elements: Fe, O, Si and Mg. The other elements with a content of more than 1% are Ni, Ca, AI and the other 7 elements Na, K, Cr, Co, P, Mn and Ti. The content is between 0.1 and 1%.
From this we can know some characteristics of the earth's matter. First, due to the different affinity of elements and oxygen (according to the free energy of the oxide generation), magnesium oxide , silica , aluminum trioxide , sodium oxide and calcium oxide precede the ferrous oxide of It is formed by . Under the condition of insufficient oxygen, most of the iron and nickel will exist in a metal state. Various oxides will bind to silicates, such as magnesium oxide and silica combine to form (pyroxene), or to form (peridot).
When a certain gravity equilibrium state is reached, most of the dense matter is concentrated towards the center of the earth and undergoes a layering effect, forming a dense metal core and a small density of silicate mantle.
Elements with low abundance are restricted by various geochemical effects and are distributed between the various earth circles. For example, platinum, gold, etc. tend to combine with metal iron and concentrate on the core, while oxygen-friendly elements, uranium, etc. are also lighter. The silicate combination is concentrated in the upper part of the earth.
Secondly, it can be reasonably conceived that the earth has been heated to reach a state of full or partial melting, and the low melting point volatile components (water, carbon dioxide, , nitrogen, argon) escape to form an atmospheric circle.
The mantle is rich in silica, aluminum trioxide, sodium and potassium oxide. The fusible and lighter substances that rise to the surface such as the earth's crust.
Therefore, the early Earth was separated into stratigraphic structures such as the core, mantle, crust, ocean and atmosphere. Existing evidence shows that the earth was close to its current layered structure about 4 billion years ago.
.4. Water Circle
The general term for the water body on the surface of the earth free water on the surface forms an ocean, and another 2.1% consolidates at the poles in the state of ice. The rest exists in the form of rivers, lakes and groundwater.
The existence of a large amount of liquid water is a major feature of the earth.
The average dissolved salts in seawater account for about 0.35% of the total seawater mass, mainly sodium chloride , which is weakly alkaline. There are not many dissolved substances in rainwater and river water, most of which are calcium bicarbonate , and are slightly acidic. Rainwater can obtain sulfur dioxide from industrial waste gas and become acid rain. River water can take away 100 tons of material per square kilometer in its basin every year, of which about 20% is in solution.
The water circle overlaps greatly with the upper part of the earth's crust. Groundwater can circulate to a depth of thousands of meters in the earth's crust, be heated and react with the rocks before returning to the ground. Hot springs and other geothermal phenomena are often found in volcanic active areas on land. There is similar hot water activity in the ocean ridges, where the temperature can reach 300°C at the black chimneys that spew metal sulfides, and there are biotas in this environment.
.5. Atmosphere
gas encapsulation layer outside the earth. It interacts with the hydrosphere.
The heat energy of the sun causes seawater to evaporate, condense into clouds, and form precipitation. Precipitation on land forms runoff and returns to the ocean from the ground or underground.
The atmosphere from the ground to a height of about 15 kilometers is troposphere , and the atmosphere from the height of 50 kilometers is the stratosphere from the top of the stratosphere to 80 to 85 kilometers is the intermediate layer. The height is , and the height is . The height above 500 kilometers is the outer layer.
The temperature height of the atmosphere varies, and the temperature in the troposphere decreases with the altitude. The temperature increases again from 20 to 50 kilometers upwards. The temperature in the intermediate layer decreases with the increase of height, and can reach a minimum of -100°C. The temperature in the thermal layer increases with the increase of height. exola is isothermal.
The main components of the atmosphere are nitrogen, oxygen, argon, carbon dioxide, water vapor, etc. The composition is stable within 100 kilometers at the bottom. The atmosphere density is about 1.2 kg/cubic meter on the ground, and it is reduced to kg/cubic meter at a height of 100 kilometers. 10 to 50 kilometers from the surface is the ozone layer . Although ozone in this layer is a secondary component, it can absorb most of the ultraviolet radiation from the sun.
According to the characteristics of atmospheric ionization , the atmosphere can be divided into neutral layer, ionosphere and magnetosphere.
is a neutral layer to about 60 kilometers on the surface of the ground, composed of neutral gas, and generally there are few charged ions.
is an ionosphere within a height range of 60 to 500 kilometers (or 1000 kilometers) in the atmospheric circle. Due to ionization, some atoms and molecules are charged, forming a state in which ions and free electrons coexist. The electron concentration of the ionosphere starts roughly from the stratosphere, and to the intermediate layer increases with the increase of height, reaching the maximum value when the thermal layer reaches its maximum, and then overlaps with the exogenous layer outward.
is outside the ionosphere, which is the outermost part affected by the Earth's magnetic field , with a height of 1,000 kilometers to thousands of kilometers from the ground. The ionization of the magnetosphere is the most complete, resulting in the formation of plasma and is affected by the earth's magnetic field. The charged particles captured by the geomagnetic field at a height of 3000 kilometers and 1500 kilometers have extremely high intensity, forming the van Allen radiation belt . It, along with other characteristics of the magnetic layer, is a new discovery since artificial satellites were used in space exploration .
.6. Biosphere
There are special circles of life on the earth. It includes the lower part of the atmosphere, the upper part of the lithosphere and the entire hydrosphere.
The most important characteristics of the composition, structure, dynamics and spatial distribution of the biosphere are determined by the activities of living organisms. There is a large amount of liquid water here, with sufficient energy from the sun, and an interface between the liquid, solid and gaseous states of matter.
Here, organisms and the environment interact with each other, exchanging matter, energy and information, and the earth's matter undergoes a biogeochemical cycle, thus forming a continuous development process of the movement of matter in the biosphere.
. Earth gravity field
Space for Earth gravity. The gravity acting on the Earth's surface is the result of the combined action of gravity generated by Earth's mass and the inertial centrifugal force generated by Earth's rotation.
The impact of centrifugal force on gravity changes regularly with different latitudes, and is the strongest at the equator. At the same time, due to the uneven density distribution of different parts of the earth, gravity changes and abnormalities will also occur. Therefore, gravity anomalies can provide information on the density changes of different parts of the earth.
. The Earth's magnetic field and magnetic layer
The Earth is magnetic, and the magnetic field around it is like the magnetic field generated by a magnetic rod (magnetic dipole) located at the center of the earth. This magnetic field in the space range from the center of the earth to the boundary of the magnetosphere is called the geomagnetic field.
The geomagnetic field is a very weak magnetic field, and its strength is the strongest near the two poles on the ground, less than 1 Gauss; the weakest near the equator is usually regarded as a dipole magnetic field, and the axis connecting the north and south poles is called the magnetic axis , the intersection angle between the magnetic axis and the ground axis is about 11°. The intersection point between the magnetic axis and the ground is called the geomagnetic pole. The position of the magnetic pole has long-term changes. Currently, the coordinates of the north magnetic pole are near 78.5° north latitude and 69.0° west longitude.
In fact, the geomagnetic field is very complex and it has significant time changes. Changes can be divided into long-term and short-term. The long-term changes in the geomagnetic field come from the movement of matter inside the earth; the short-term changes come from the tidal movement of the ionosphere and the changes in solar activity.
The current system in the ionosphere can cause the daily changes in the geomagnetic field, and the atmosphere in the upper layer of the polar region is impacted by charged particles, resulting in aurora and magnetic storm . There are plasmas called solar winds between the sun and the earth.The Earth's magnetic field is compressed by the solar wind on the side facing the sun, and is stretched on the side facing the sun, so that the Earth's magnetic field is confined to a narrow area called a layer around the earth.
It can be seen from this that the magnetosphere is an area around the earth surrounded by solar wind and controlled by the geomagnetic field. The outer boundary of the magnetolayer is called the magnetolayer top boundary layer.
The intensity and direction of the magnetic field vary not only from place to place, but also from time to time. During the geological history period, the magnetic poles have been reversed many times.
The geomagnetic field mainly originates from the inside of the earth, and the components from space are less than 1% of the total amount. The origin of the Earth's magnetic field and its changes during the history of the earth are related to the current generated by the structure of the earth's core and the relative movement of the matter of .
The existence of the earth's magnetic field prevents the earth from the direct influence of the solar wind. The existence of the magnetosphere plays a significant role in the composition of the atmosphere and the ground climate, and thus affects the development of life on the earth.
. The temperature and energy of the earth are
The radiation energy received by the ground from the sun is about @%￥#￥…%￥ tsuke every year, but most of them radiate back to the space, and only a small part of them affects very shallow areas underground. The temperature gradient of the shallow underground layer is about 1℃ for every 30 meters increase in depth, but there are great differences between places. The heat flow can be calculated from the temperature gradient and the thermal conductivity of the rock. The total heat flowing out from the ground is tile.
Part of the energy inside the earth comes from radioisotope , which contains elements such as uranium, thorium, potassium, etc. in rocks. It is estimated that the Earth's current heat released by long-lived radioactive elements is about tiles, less than the loss of ground heat flow. The heat loss of radioactive heat generation is less than that of the Earth may tend to make the Earth gradually cool.
Another energy source is the gravitational potential energy when the earth is formed. Assuming that the earth is formed by the accumulation of diffuse matter in the solar system, this part of the energy is estimated to be focal, but during the accumulation process, a large part of the energy disappears into the space outside the earth, and a small part of the energy is about focal, due to the earth's adiabatic heat. Compressed and accumulated as elastic properties of earth's matter.
Assuming that the earth was formed was quite uniform at first, then it evolved into the current layered structure, which would release a portion of the gravitational potential energy, estimated to be about focal, which would cause the earth to heat up.
The earth is turning slowly and slowly. Since its formation, the loss of rotational energy is estimated to be about kog, and the energy released by volcanic eruptions and earthquakes, but its orders of magnitude are much smaller.
The temperature gradient near the ground cannot be extrapolated to a depth of tens of kilometers. The earth has its own heat source, so the deeper the underground, the more enthusiastic the heat transfer mechanism deep underground is extremely complicated.
In the rock layer, the main mechanism of heat transfer is heat conduction; while in the mantle and outer core, the main mechanism of heat transfer is thermal convection, and of course, this also includes other heat transfer mechanisms.
According to other geophysical phenomena, the temperature at certain depths inside the earth can be estimated: at a depth of 100 kilometers, the temperature is close to the melting point of the rock at this place, about 1100~1200℃; at 410 kilometers and 660 kilometers and 660 meters. At a depth of kilometer, the rock undergoes phase transition, and the temperature is about 1400℃ and 1700℃ each; at the boundary of the core mantle, the temperature is above the melting point of iron, but below the melting point of mantle matter, it is about 3400℃; at the outer core and At the core boundary, the temperature is about 4600℃, and the temperature in the center of the earth is about 4800℃.
With these temperature estimates at specific depths, the temperature distribution under the spherical symmetric earth model can be inferred based on the main heat transfer mechanism. The distribution of temperature inside the earth is extremely important for studying the evolution and movement of the earth and is an urgent problem to be solved.
. Earth Age
Based on the results of determining meteorites, moon and ancient rocks using various isotope chronology methods, it was found that the annual ridges formed by various celestial bodies in the solar system are relatively close, and the time interval between formation is about 100 million years, so various universes are therefore The age results of chronologically measured celestial matter can be compared with each other and improve its reliability.
Currently, the synthetic age of the solar system elements is 6.2 billion to 7.7 billion years, and the solar nebula condenses into various planets, including the Earth, which is 4.54 billion to 4.6 billion years.The application of isotope geochemical dating method also gives the precise time coordinates of various geological periods in the history of earth's evolution.
. Origin and development of life on Earth
Earth is the only planet in the solar system where life and human activities exist. The remains of primitive biological cyanobacteria and green algae on the earth have been discovered in rocks with an age of 3.5 billion years.
Although the problem of the origin of life on Earth has not been solved, it can be traced back to 4 billion years ago. The early atmospheric components of the Earth's early atmosphere consist mainly of water, carbon dioxide, carbon monoxide and nitrogen , as well as other gases erupting from mountain volcanoes. In this case, life must start from an oxygen-free environment, and oxygen entering the atmosphere is considered to be due to Results of biological activities.
Initially, the content of oxygen in the atmosphere could only increase slowly, and it was estimated that the content was about 1% of the current 2 billion years ago. When the oxygen in the atmosphere increases to the extent that a protective ozone layer can appear, organisms can live in relatively shallow water. The reproduction of organisms with photosynthesis promotes the development of animals that can breathe oxygen.
The initial traces of the multicellular organism are found in rocks about 1 billion years old. About 700 million years ago, complex animals such as jellyfish , worms and primitive scale animals have appeared.
has been around 570 million years ago, which is between the Procambrian and Cambrian periods. Animals with hard shells appeared in large numbers, allowing a large number of fossils to be preserved in rocks. During this period, marine life had sudden development.
Fish appeared in the Ordovician; Silurian in the late stage, vegetation was already covered on land. Amphibians appeared in the Carboniferous Sea. Reptiles and the original mammals appeared in the Triassic period, but they did not reproduce and spread in large quantities until the Cenozoic era. Although the development of organisms has a stable evolutionary process, the fossil record also shows that a large number of plant and animal species that have periodic conditions have disappeared roughly during the Phanerozoic period. The cause of this catastrophe has been discussed for a long time, and some scholars believe that it may be caused by the impact of meteorites or asteroids. However, some scholars have pointed out that not all living things are affected at the same time. This issue needs further research.
0. Space Detection Earth
1947 A small V-2 rocket obtained the first photo of looking down at the earth from space at an altitude of 160 kilometers, which became the beginning of Earth's space exploration.
1957 After artificial Earth satellites entered the sky, observing the earth from space has gradually become a conventional means of earth science.
Since the birth of the Earth about 4.6 billion years ago, the climate and environment have been changing continuously. The evolution of the sun, volcanic activities, crust movement, celestial meteorites, the formation and changes of the atmosphere and oceans, the emergence of life, etc., have made the Earth an active and Dynamic planets, space exploration helps to recognize, understand and predict the direction and prospects of Earth's evolution.
Recommended Bibliography
Fu Chengyi . Ten Lectures on Earth. Beijing: Science Press, 1976.
Frank Press and Raymond Siever, Earth. 4th ed. New York: W. H. Freeman and Company, 1986.
TARBVCK E J, LVTGENS F K. Earth Science, 8th ed, Upper Saddle River, N. L: Prentice Hall, c1997.
Excerpted from: "China Encyclopedia (2nd Edition)" Volume 5, China Encyclopedia Press, 2009
