The Earth As A Dynamic Planet: Continental Drift, Crustal Recycling And Earthquake

The Earth is a dynamic planet by the lithosphere’s drifting. The lithosphere is a solid plate that cover the earth. The result shows that plates change at a speed of 1 cm to 10 cm per year (Hamilton, Rosanna L, 1995). According to the theory, the lithosphere can be divided into six plates, which are Pacific Plate, Asia-Europe Plate, Africa Plate, America Plate, Indian Ocean Plate and Antarctica Plate. And there is an asthenosphere under these plates, which is a high denser layer. The plates can float above the asthenosphere. At the same time, since there the difference in density and temperature inside the asthenosphere, its leads to the convection of the material inside, which drives the plate’s movement. The plates can drift on the asthenosphere, they will move and hit with each other. It’s also led to the rise and fold of the layer, and this is the source of the mountains as well. The lithosphere’s drifting may create mountain ranges, oceans and lots of new life. As we know, The Himalayan mountain range is created by the collision between the Indian plate and the Asian plate. ( National Geographic, 1996-2020).

At the end of the 16th century, The cartographer from Belgian, Otelius discovered that the contours of the coastline on both sides of the Atlantic Ocean could be matched. Everyone slowly realized that perhaps on the earliest earth, the continents at that time were gathered together. German meteorologist Wegener put forward the theory of ‘continental drift’ in 1912. All continents on the earth used to be unified huge land blocks, called pan-continents; since the Mesozoic, the pan-continent split and drifted, so each continent Gradually reach the present position. This essay will state that lithospheric plate motions and associated phenomena, such as continental drift, crustal recycling, earthquakes and tsunamis.

Continental drift

The continental plate can drift under the thermal drive. This movement process is based on the fact that the continental plate first cracked and the cracks generated, and then the magma upwelled. The power is the upwelling of magma caused by the oceanic crust sliding away from the continental plate, and the magma is rushing behind the land block. Therefore, the huge thermal power will push the plate forward. At the beginning, the continental drift was consistent with the seafloor expansion, but because the magma ejected from the ocean will soon be extinguished by the seawater, the seafloor expansion cannot be sustained (1969). However, after the continental plate drifted, magma continuously poured out behind it and was continuously extinguished by the seawater. This process of thermal propulsion continued to push the continental plate forward (Livermore R, 2018).

Someone once questioned, has the continental drift really happened? Alfred Wegener proposed that mountain ranges provide evidence for continental drift theory. There is a mountain range in South Africa that can be docked with a mountain in Argentina, and coal fields corresponding to coal fields in Europe can be found in North America. Alfred Wegener believes that the climatic characteristics of each latitude on the earth are fixed, but only the position of the continent is constantly changing. Its climate will be warmer when the mainland drifts towards the equator; conversely, its climate will become colder when it drifts towards the polar regions. Spitsbergen Island is now located in the polar climate in the northern Arctic Ocean. The island is covered with snow all year round, but fossils of tropical plants have been found there (www.nasa.gov/ ). These are all strong evidences that the continental drift phenomenon has occurred.

Why is the Indian plate’s drifting faster than other plates? The German scientist Rainer Kind (2007) believes that the Indian plate drifts faster than other plates since the Indian plate is thinner than other plates. When the Indian plate was part of the Gondwana continent, it was located in the hottest area of the asthenosphere, which caused its deeper areas to be melted and become thinner, so the Indian plate slipped more easily in the mantle. The Indian plate drifted for a long time in the upwelling zone of the crustal flow formed by the African plate. The upwelling of the crustal flow formed a stronger thermal power, just like surfing, which made the Indian plate drift faster.

Crustal recycling

The earth has a deformable and mobile outer crust, which is also the main reason why the Earth is a dynamic planet. First, if it were not for the Earth’s mantle to absorb and release water molecules, there might not be an ocean on Earth. Secondly, if there is no plate to promote the formation of the coastline and tides, the ocean may become barren, and many nutrients in the ocean will be buried forever in the bottom of the sea. Eventually, the seafloor will become cold if the plate structure does not force the plates to collide with each other. Therefore, many chemical components will not be discovered and studied, which means that life may never appear on the earth. Some studies believe that if there is no plate movement, life may not cease to evolve and evolve into today’s vibrant earth. Australia’s planetary scientist Craig O’Neill pointed out that the earth was formed about 4.54 billion years ago and was originally a hot lava ball. At least 1 billion years after the formation of the Earth, it may not have any recognizable plate structure, mainly because the planet is too hot (John T, Layne G, Haase K, & Barnes J, 2010). At that time, just like now, the convection inside the earth makes the heat and rocks move constantly. The rock is heated and squeezed inside the earth, then rises to the surface, becomes denser after cooling, and then sinks and restarts the process. The earth 3 billion years ago may have temporary plate tectonic activities in some areas, but it is not extensive. This will weaken the surrounding crust, because the colder part of the crust will sink. When this happens repeatedly, this weakened area gradually degenerates into the boundary of the plate.

From the perspective of the formation and evolution of the earth, the motive forces of crustal movement can be divided into tension, squeezing force, and gravity. The first is the tension of crustal movement, which stems from the state changes of the oceanic and continental crusts during the formation of the earth, that is, the volume of the mantle continues to increase (Rolf T, Coltice N, & Tackley P, 2012). The increase in the volume of the mantle will crack the crust. However, the rocks in the continental crust are horizontal and difficult to pull apart, so vertical ocean crusts are produced. As the volume of the mantle increases, the volume of the Earth also becomes larger, because the oceanic crust is in the expansion stage. Regarding the squeezing force of crustal movement, it comes from the reduction in the volume of the mantle, which is due to the discharge of liquid materials inside the earth, such as volcanic eruptions and the movement of magma. Finally, the gravity of the crustal movement comes from the change in the floating mass of the crustal itself. In fact, the generation of gravity is the result of the mutual adjustment of the volume, area and mass of the moving body. When the earth’s crust is squeezed, the area decreases and the volume and mass per unit area will increase.

Earthquake

The lithospheric motion can also trigger earthquakes, which is known by people well. It is easy to think of Earth as a solid ball, but it is not solid. One of the reasons earthquakes happen is that the outer shell of Earth is broken up into separate sections called tectonic plates (Frisch W, 2011). When an earthquake occurred, the most recent phenomenon is continuous vibration of the ground, the main feature is the obvious shaking. People in the earthquake zone feel the ups and downs before feeling the big shaking. This is because seismic waves are transmitted from the core to the surface, and the longitudinal waves first arrive. The share wave then generates large horizontal sway, which is the main cause of the earthquake disaster. When Chile took place an earthquake in 1960 which is super large, the shaking keeps almost 3 minutes.

The disaster cause by the earthquake is the first to destroy houses and buildings, such as the earthquake which took place in China Hebei Tangshan in 1976, about 70% to 80% of buildings collapsed, and lots of people get injured and even dead. The earthquake also have a great impact on the natural landscape. The main consequence is the occurrence of faults and seismic cracks on the ground. Surface faults in major earthquakes often stretch for ten to hundreds of kilometers, often have more obvious vertical offset and horizontal offset, which can reflect the characteristics of tectonic changes at the source. But not all surface faults are directly related to the movement of the source, they may also be due to secondary effects by seismic waves. Especially in areas with thick surface sediments, cracks often occur on the edges of slopes, riverbanks and roads, this is often due to topographical factors, and the topsoil is loosened and cracked without shaking on one side.

The shaking of the earthquake caused the topsoil to sink, shallow groundwater will squeeze and rise to the surface along the ground fissures, forming a sandblast. Large earthquakes can improve local terrain, or uplift, or subsidence. Split urban and rural roads, bend rails, and break bridges. In modern cities, water cuts, power outages, and communications are blocked due to broken underground pipes and cut cables. Gas, toxic gases, and radioactive materials can cause secondary disasters such as fire, poisons, and radioactive pollution. Earthquakes in mountain areas can also cause landslides, which can trigger tragedies to bury villages. Collapsed rocks clog rivers and form earthquake lakes upstream. And in 1923, a huge earthquake took place in Japan in a village, which causes a landslide till 5 kilometers (www.nasa.gov/ ).

However, scientists make classifications on those earthquakes. The first type is called a tectonic earthquake. Due to the rupture of the rock deeply underground, the movement quickly released the energy which has been accumulated for a long time, it spreads in all directions in the form of seismic waves, and the shaking caused by the ground is called an earthquake. These types of earthquakes occur most frequently and have the greatest destructive power, accounting for more than 90% of earthquakes worldwide. It is characterized by frequent activities, long duration, the widest range of influence, and the most destructiveness. Therefore, it is the main object of seismic research.

And the second type is called “scaquake”, which took place at the middle of the ocean. Ocean earthquakes can cause seafloor faults and cause tsunamis, but in many cases, they do not produce tsunamis. And what is good is that, there are signs before tsunamis. People who live near sea say that before the tsunami, they cannot catch the fishes which they usually can easily get, and some people say that they see some small islands floating on the ocean.

The third type is volcanic. It happens very few, just 7% of the total earthquakes. The source of the earthquake is often limited to volcanic activity. Generally, shallow source earthquakes with a depth of no more than 10 kilometers have a large magnitude but a small impact range. And there are three types of volcanic. The first one is called active volcano, which means that those volcanoes are still alive or have periodic activity. The second type is called extinct volcano, which means that it happens before, but then till now, it did not happen anymore. The third type called dormant volcano, which means that it happens before, but till now, did not happen too many times.

The last one is called collapse earthquake, which is formed by collapsed rocks. It usually occurs at those limestones area. It is because the stones are eroded by the underground water, and the cave roof collapses (Chester R. 2008). All of those phenomena are caused by the plate motion.

The lithospheric motion can also trigger the tsunami. When an earthquake occurs under the deep sea, the seafloor formation will rupture and some formations will suddenly rise or sink, which will cause strong fluctuations in the entire water layer from the bottom to the surface. This is a sudden change of the entire water body from the bottom to the surface of the sea, which contains huge energy. The three causes of the tsunami were earthquakes, seafloor collapse, and the influence of cosmic objects. Among them, earthquakes are the most important reason. When an earthquake occurs on the bottom of the deep sea or near the ocean, the crustal movement causes slippage between the plates, resulting in deformation of the bottom plate. Which will cause a large amount of seawater to reverse current and trigger the seawater to start a large-scale movement, and then form a tsunami. As a natural disaster, a tsunami is extremely destructive.

Conclusion

The earth is a dynamic planet by the lithosphere’s drifting, and the movement of the lithosphere plates and its phenomena fully prove this point. The continental drift causes the lithosphere to be divided into six plates, which is the result of a strong and continuous movement of the earth. The crustal movement keeps the earth constantly exploring new living nutrients from the ocean, mountains, oceans and diverse climates. As one of the points that motions among the essay, if there is no crustal movement, there may not be life on Earth. Although earthquakes and tsunamis are natural disasters, it also happens to show the strong vitality of the earth in the triggering of plate motion. The movement of plates in the lithosphere created life and vitality made the earth more colorful, and opened up infinite possibilities in the future.