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Transcript
Atoms The basis of all matter, they are made up of protons, neutrons, and electrons. Their size is approximately one tenth of a billionth of a metre. Banded iron ore Very ancient iron ore formed by alternating layers rich in ferrous oxide and layers of schist. 90% of the iron mined on Earth comes from banded iron ore. Continental plate A tectonic plate made up of continental crust. Most of the larger tectonic plates include continental and oceanic zones, although some are almost entirely continental, like the Arabian plate. Convection Movements in liquids or gases generated by differences in temperature and density. The liquid or gaseous masses that are hotter and denser tend to rise, while those that are colder and less dense go downward. The combination of these two tendencies causes the circular movement that is convection. Core The core is the centre of the Earth. It is made up of metals (mainly iron and nickel) and has a diameter of about 7000 km. The outer core is liquid and the inner core is solid. Glossary WebGeol.com 1 Erosion The wearing-down of matter by wind, rain, rivers, glaciers, etc. Erosion acts slowly but can flatten mountains in a few million years. Fault Line of separation between two moving walls of rock; they may be coming closer together or moving farther apart, or they may be sliding against each other. Faults can extend for thousands of kilometres, and in general, are related to tectonic movements. Geological time Chronological scale used to establish periods and date events since the beginning of the Earth’s history. Geothermics The transmission of the Earth’s warmth from its deep layers to the surface. By extension, the term geothermics also applies to the use of this energy to heat buildings or produce electricity. Hotspots Zones on the Earth’s surface where volcanic action is regular and long-lasting, due to abnormally hot areas under the Earth’s crust. These points can remain active for long periods; they are not connected to the tectonic plates, which move over them. Glossary WebGeol.com 2 Limestone Sedimentary rock mainly composed of calcium carbonate. Limestone is formed by sedimentary deposit and the piling-up of shells and skeletal fragments originating on the ocean floor. Magma Fusing rock containing dissolved gases. Magma is formed by fusion occurring in either the mantle or the crust. When it reaches the Earth’s surface, it loses its gases and becomes lava. Magnetic field The force that orients compass needles, acting like a magnet. It is created by movements in the Earth’s core and acts as a shield against solar winds, which carry particles harmful to living beings. Magnitude (seismology) The magnitude of an earthquake is the measurement of its intensity. In this scale, each unit designates ten times the intensity of the unit below it. Thus, a magnitude 6 earthquake is 100 times stronger than a magnitude 4 earthquake. Mantle The mantle is the part of the globe between the crust and the core. It is about 2900 km. thick and makes up 80% of the Earth’s volume. Glossary WebGeol.com 3 Mass extinction The rapid disappearance of a large number of animal and plant species on a global level, both on land and in the oceans. The most important known mass extinction to affect the Earth occurred at the end of the Permian era, when 95% of marine species and 75% of land species were wiped out. Obduction The thrusting of oceanic crust on top of continental crust. It is the contrary of subduction, in which oceanic crust pushes underneath continental crust, and is a much rarer phenomenon. Ocean ridges Long underwater mountain chains, varying between 1000 and 2000 kilometres in width and reaching heights over 2000 metres above the ocean floor. They occur at the converging boundaries of tectonic plates that are moving apart, producing oceanic crust which allows the oceans to expand. Oceanic plate A tectonic plate made up of oceanic crust. The majority of tectonic plates are composed of both continental and oceanic zones. Some, however, are exclusively oceanic, such as the Nazca and the Pacific plates. Pangea Former supercontinent that held together all the land masses of our planet, about 250 million years ago. Glossary WebGeol.com 4 Plate tectonics Theory explaining the overall phenomena involved in the displacement of continents, the formation of oceans, the distribution of earthquake zones over the Earth’s surface, etc. According to this theory, the movements of the tectonic plates are caused by convection occurring in the Earth’s mantle. San Andreas Fault Large fault that crosses through California. The San Andreas Fault corresponds to the meeting-point between the Pacific and the North-American plates. It triggers many earthquakes, including the one that destroyed San Francisco in 1906. Depth of focus The depth in kilometres of the hypocentre, the place in the Earth’s mantle where the tearing of a fault produces an earthquake. Radioactivity Natural physical phenomenon in which the nuclei of certain atoms disintegrate, releasing energy in the form of rays. Rift A zone in which the Earth’s crust is stretched thin. On continents, rifts form graduallywidening trenches which will eventually be filled by an ocean. An example is the rift of the Red Sea between North Africa and the Middle East. Glossary WebGeol.com 5 Sediment Debris carried by water, ice, or wind, sediment may be of mineral origin (particles of rock) or organic origin (fragments of the remains of living organisms). Sediment is mainly produced by erosion. Seismology The study of earthquakes and of the propagation of seismic waves through the ground. Seismometer Instrument that detects and measures ground vibrations, particularly those produced by earthquakes. Subduction The phenomenon that occurs when two tectonic plates converge and one slides under the other, sinking into the Earth’s mantle. The most common instance is when an oceanic plate pushes under a continental plate. Supercontinent A huge continent, past or present, that combines several large continental masses. Pangea and Gondwana are examples of supercontinents that existed in the past. Today, Eurasia is a supercontinent. Tectonic movement The movement of the tectonic plates on the Earth’s surface. Glossary WebGeol.com 6 Tectonic plates Hard, rigid plates that cover the surface of the Earth. The surface is not covered by a uniform layer of rock, but by some fifteen large plates and about 50 secondary plates, all of which are changing their positions with respect to the others. Traps Large plateaus of volcanic rock formed during a period of successive volcanic eruptions on a colossal scale, which spewed immense quantities of lava onto the Earth’s surface. Uranium A naturally radioactive, silvery-white metal. Minute quantities of uranium are found in rock, water, air, plants, and animals. Glossary WebGeol.com 7