Nangong American immigrants

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 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".

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 has not only vertical movement, but also 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 the two plates sank at the same time, which led to the abyss of the seabed. 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 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 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.

plate

Le Pixiong divided the global crust into six plates in 1968. Pacific plate, Asia-Europe plate, Africa plate, America plate, India plate (including Australia) and South plate. Except for the Pacific plate, which is almost entirely ocean, the other five plates have both continents and oceans.

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.

Global ecology has once again entered the red alert state ahead of schedule.

Overuse of earth resources in developed countries is the main reason.

The New Economy Foundation, a British think tank, released a report on June 6 10, saying that the world has entered an ecological red alert state from now on, that is, the world has entered an ecological debt state caused by excessive consumption, which means that in the rest of this year, human life is increasing the burden on the environment. Since the human beings began to overdraw the environment for the first time in 1980s, the annual "Ecological Debt Day" has been quietly advanced, and this year's "Ecological Debt Day" is three days earlier than last year. Ecological overdraft means that the demand and consumption of human resources on the earth is greater than the supply capacity that the earth can bear.

Excessive consumption exhausts resources.

The latest data available show that it is the richest countries that overuse the earth's resources. For example, if everyone in the world lives like Americans, human beings need 5.3 earths to ensure the supply of resources; If we live like France and Britain, we need 3. 1 planet. This figure is 3 compared with Spain, 2.5 in Germany and 2.4 in Japan.

The report shows that the demand of western countries for basic products in other parts of the world, such as food and energy, is still increasing. Although the public is more concerned about climate change, the lifestyle of western countries has also increased the resource consumption load of land, forests, rivers, oceans and mines in other parts of the world. Due to the profligacy of environmental resources in western countries, they have accelerated the ecological debt and deprived millions of people around the world who lack land, food and clean water of the opportunity to meet their needs. At the same time, it also leads to the danger of life supply mechanism on earth. Research shows that a high-quality life is equally easy to achieve even at a very low consumption level, and we must realize that pursuing a high-consumption lifestyle will destroy the well-being of the whole world. The report calls for the urgent need to form a wise and positive interdependence model among developed countries, other parts of the world and the life support system of the earth.

Abnormal transactions add fuel to the fire.

The report pointed out that while global warming is becoming more and more irreversible and ecological debt is getting heavier and heavier, the current ecological waste trade is still dominant. In the face of global challenges such as climate warming, it is obvious that if the British economy is to achieve sustainable development in the future, Britain must change its current trade dependence model with other countries.

Last year, Britain imported 6.5438+0.4 million tons of chocolate waffles from its trading partners, while exporting 6.5438+0.5 million tons. All the sweets imported from Italy and exported to Italy are 600 tons. The import and export volume of beer in Britain and Spain is basically the same. The report questioned why we should export 20 tons of mineral water to Australia and then bring back 2 1 ton of mineral water from there. The report said that the policy of focusing on short-term interests and self-interest in the 20th century made us lose the opportunity to face the negative impact of climate change and globalization.

Thieves shout to catch thieves and pass on pollution.

The report reveals that in order to support their high-consumption lifestyle, western countries are increasingly dependent on other regions, especially on imported products from developing countries. The report points out that developing countries are attacked by western countries because of increasingly serious pollution, but people seem to ignore two important issues: first, the per capita greenhouse gas emissions of developing countries only account for a small part of Europe and America. Secondly, carefully observing the trade flow, a large part of the increase in emissions of developing countries should be attributed to the dependence of other countries and regions in the world on the export products of developing countries. In addition, there is a fact that those countries that look glamorous and richer have just transferred a lot of heavy industry to developing countries. Major retailers in western countries swept the world with the cheapest production cost advantage in the world. Therefore, every time people buy a product, more greenhouse gases will be released into the atmosphere. Therefore, the carbon dioxide emissions of developing countries reflect the high consumption level of western countries.

Cooperate with each other to ensure interdependence.

The report reveals the positive and negative effects brought by the closer and more complex international economic system interwoven among countries in the world. In order to strive for a better future, the report suggests that western governments must shift from the economic competition policy of "all-round victory" to cooperation, which is the requirement of world interdependence. As the minimum commitment to form a positive global interdependence, the report calls on: the British government should set a timetable to ensure that policies and resources are fair and that the global ecological resources are occupied per capita; Committed to reversing the downward trend of food self-sufficiency rate in Britain; Commit to reduce greenhouse gas emissions year by year, and ensure at least 80% reduction by 2050. By taking major measures such as reducing demand, improving energy efficiency and using renewable energy, we will ensure energy security and independence. According to the report, the prosperity of countries with interdependent cultures in the world is something to celebrate. Western countries must be soberly and objectively aware that since the "ecological debt day", western countries must rely on the use of resources from other parts of the world to survive.

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 has not only vertical movement, but also 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 the two plates sank at the same time, which led to the abyss of the seabed. 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.