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 3,565,438+80 steps (the length unit of the Tang Dynasty was 5 feet = 1 step and 300 steps = 1 mile). This work 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".
3. The mass and acceleration of gravity
The mass of the earth is 5.976×l027, 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.
Fourth, the structure
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 of 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.
The Origin and Evolution of verb (the abbreviation of verb)
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 of meteorite materials, radioactive decay and gravitational contraction of the primitive 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 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 (ten million kilometers) 149.6
Rotating Stellar Time (Japan) 365.26
Revolution rendezvous period (days)
Track eccentricity 0.0 17
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) 6378
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 0.40
Maximum brightness-
Satellite (confirmed) 1