Erosion, weathering, mass wasting. Earth's Interior Geologic Time Scale - Assignment Example

? 9 November Earth Science 1 Erosion Erosion occurs when wind or water blow/wash away the topmost fertile layer of soil. As fertile land loses its fertility due to soil erosion, it is difficult to grow crops on eroded lands. Apart from affecting crops, erosion also weakens land, causing buildings to collapse. Soil erosion can be prevented by planting windbreaks. Windbreaks are lines of planted bushes and plants that hold soil firmly with their roots and prevent it from being washed away. Other methods include terracing, in which level plains are cut on hillsides and crops are grown on these plains. (wikipedia.org) 1. 2 Weathering Weathering is the process of decomposition or breakdown of soils and rocks when they come in direct contact with natural forces such as wind, rain and heat. Weathering is of two types, mechanical and chemical. Mechanical weathering involves the breakdown of rocks due to wind, heat, rain and ice. Sand that is carried by wind grinds down the surfaces of rocks, causing wind erosion/weathering. Higher temperatures cause cracks in rocks. This mostly occurs when sun rays heat up the surface of the rocks while the inside of the rock remains cool. When the surface of such rocks cools down at night, it contracts. Repeated contraction and expansion causes cracks in the rock, leading to its breakdown and weathering. Raindrops too cause weathering, either by wearing down the rocks or by causing chemical changes by mixing with minerals in the rocks. Ice glaciers running over rocks also lead to their breakdown. Chemical weathering occurs when environmental agents, such as CO2, react with rock minerals. (wikipedia.org) 1.3 Mass wasting Mass wasting is the process by which soil and rocks move down a slope due the action of gravity. This occurs when the gravitational forces acting on a soil layer on a slope exceeds the frictional force that is keeping the soil layer in place. The maximum angle of the slope at which the soil continues to stay in place without being pulled by gravity is called angle of repose. Mass wasting occurs when the slope’s angle exceeds the angle of repose. Landslides, mudflows and creeps are examples of mass wasting. It usually occurs due to change in slope angle, weathering of rocks, intensive increase or decrease in water content of the soil, and lack of vegetation to hold the soil together. (wikipedia.org) 2. Earth's lithosphere and plate tectonics The earth’s lithosphere is the solid outermost region of the earth, comprising of the crust and the upper mantle. Lithosphere is of two types, oceanic and continental. The oceanic lithosphere is the crust that exists beneath the oceans, and whose thickness is about 50-100 Km. Continental lithosphere is about 40-200 Km thick and is associated with the continental crust. The thickness of the oceanic lithosphere increases as it ages. Moreover, it always sinks beneath the continental lithosphere. The lithosphere is divided into plates called tectonic plates that are constantly in gradual motion. The theory of plate tectonics explains the large-scale motion of the earth’s tectonic plates. This theory builds up on other theories such as those of continental drift. The energy for motion of tectonic plates is derived from the dissipated heat from the earth’s mantle. While the mechanism underlying the motion of tectonic plate is still under debate, several reasonable explanations do exist. Apart from several minor plates, there are eight major tectonic plates – namely, Antarctic Plate, African Plate, Indian Plate, Australian Plate, Eurasian Plate, Pacific Plate, South American Plate, and the North American Plate. Below these plates, which comprise the lithosphere, the asthenosphere (hot, viscous fluid that is a part of the upper mantle) flows gradually. Convection currents generated in the asthenosphere transfer heat to the tectonic plates in the lithosphere, which are then separated by the action of magma. Movement of these tectonic plates gives rise to mountains, earthquakes, oceanic trenches and volcanic activity. Mountains and volcanoes form when tectonic plates move together or towards each other. In this case, the plate boundary is called collision boundary (e.g., the Andes mountain range in South America). Earthquakes and oceanic trenches occur when plates move away from one another. Here, the plate boundary is called spreading boundary (e.g., the Great Rift Valley in Africa). Earthquakes also occur when plates slide past each other at the “transform boundary” (e.g., San Andreas Fault in California). (wikipedia.org) 3. Geologic Time scale, major eras and what happened in those eras The geologic time scale is used by paleontologists and geologists to estimate the time of occurrence of events based on the study of rock layers. It is used to record the history of the earth, which is divided into several eras based on data obtained from rock layers. The largest unit of time is supereon that is divided into eons, which are further divided into eras, periods, epochs and ages. The major eras of geologic time scale and the events that occurred during these eras are described as follows: Cryptic: Formation of the earth and the moon, Zircon-the oldest known mineral formed Pre-Nectarian: First life forms appeared, oldest known rocks belong to this era, end of Late Heavy Bombardment on Earth, Napier Orogeny began in Antartica Nectarian: Great lunar basins such as the Nectaris Basin formed Early Imbrian: Evidence of photosynthesis, early life Eoarchean: Oldest single celled bacteria and archea existed Paleoarchean: First oxygen producing bacteria, oldest cratons (Pilbara Craton and Canadian shield) may have formed, Rayer Orogeny occured in Antarctica Mesoarchean: Stromatolites developed, Blake River Megacaldera Complex began to form, Humboldt Orogeny occurred in Antarctica Neoarchean: Abitibi greenstone belt began to form, the earth’s mantle may have overturned, most modern cratons stabilized Paleoproterozoic: Complex single celled life forms originated, atmosphere was oxygenated Mesoproterozoic: Green algal colonies formed in seas, Nimrod Orogeny began in Antarctica Neoproterozoic: “Snowball earth” period, Rodinia landmass began to break up Paleozoic: First vertebrates appeared, Rodinia broke up into smaller continents Mesozoic: High volcanic activity, tectonic motion, dinosaurs went extinct Cenozoic: End of glacial period, large mammals appeared, human civilization (wikipedia.org) Works Cited Wikipedia.org. “Erosion.” Wikipedia, 2011. Web. 9 Nov. 2011. . Wikipedia.org. “Weathering.” Wikipedia, 2011. Web. 9 Nov. 2011. http://simple.wikipedia.org/wiki/Weathering Wikipedia.org. “Mass weathering.” Wikipedia, 2011. Web. 9 Nov. 2011. http://en.wikipedia.org/wiki/Mass_wasting Wikipedia.org. “Lithosphere.” Wikipedia, 2011. Web. 9 Nov. 2011. http://simple.wikipedia.org/wiki/Lithosphere Wikipedia.org. “Plate tectonics.” Wikipedia, 2011. Web. 9 Nov. 2011. http://simple.wikipedia.org/wiki/Plate_tectonics Wikipedia.org. “Geologic time scale.” Wikipedia, 2011. Web. 9 Nov. 2011. http://en.wikipedia.org/wiki/Geologic_time_scale Read More