UNIT 6 AND 7. THE EARTH´S INTERNAL ENERGY 1. GEOTHERMAL ENERGY Geothermal energy is the energy that comes from within the Earth. It is produced by two sources: a) the radioactive elements (uranium, thorium and potassium) that emit radioactive energy. b) the heat left over from the process of forming of Earth. This energy is responsible for the internal geological processes such as: - Movements of the continents. - Volcanoes. - Earthquakes. - Faulting, folding, the formation of some types of rocks, etc.. 2. CONTINENTAL DRIFT THEORY OF WEGENER Alfred Wegener explained this theory in 1912. He said that all the continents had once been united and these formed a super continent which he called PANGEA. To demonstrate this, he proposed three experiments: - Geographical evidence: This is to unite the coastlines of the continents on a map. We can see that continents, like Africa and South America, fit together perfectly. - Geological evidence: this is to study the situation of mineral deposits, such as diamond deposits in the Congo and Brazil. Both deposits were forming an only deposit, and this was fractured after. - Paleontological evidence: this is based on the study dinosaur fossils, as Mesosaurus, a terrestrial dinosaur that lived on both continents (Africa y South America) which are separated by 20,000 km. The scientific community did not accept Wegener's theory because he could not explain what the movement of continents was caused by.
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UNIT 6 AND 7. THEEARTH´S INTERNAL
ENERGY1. GEOTHERMAL ENERGY
Geothermal energy is the energy that comes from within the Earth.It is produced by two sources:a) the radioactive elements (uranium, thorium and potassium) that emit radioactive energy.b) the heat left over from the process of forming of Earth. This energy is responsible for the internal geological processes such as: - Movements of the continents. - Volcanoes. - Earthquakes. - Faulting, folding, the formation of some types of rocks, etc..
2. CONTINENTAL DRIFT THEORY OF WEGENER
Alfred Wegener explained this theory in 1912. He said that all the continents had once been united and these formed a super continent which he called PANGEA.To demonstrate this, he proposed three experiments: - Geographical evidence: This is to unite the coastlines of the continents on a map. We can see that continents, like Africa and South America, fit together perfectly. - Geological evidence: this is to study the situation of mineral deposits, such as diamond deposits in the Congo and Brazil. Both deposits were forming an only deposit, and this was fractured after. - Paleontological evidence: this is based on the study dinosaur fossils, as Mesosaurus, a terrestrial dinosaur that lived on both continents (Africa y South America) which are separated by 20,000 km.The scientific community did not accept Wegener's theory because he could not explain what the movement of continents was caused by.
3. THEORY OF PLATE TECTONICS:In 1960, scientists formulated a new theory, based on Wegener’s
theory, called “Plate Tectonics”. It says that: Earth’s surface consists of large blocks called tectonic plates. They
fit perfectly with each other, like a puzzle. These plates move each other,because they are floating on a semi-fluid mantle layer called theasthenosphere. The movement of the plates is due to the formation ofconvection currents. These are formed when the hottest materials in theasthenosphere rise. These materials strike the plates and cause theirmovements.
This theory does not speak of continents but of tectonic or lithosphere plates. The lithosphere is the layer of Earth’s surface formed by the crust and the first kilometers of the mantle.
3.1 TYPES OF TECTONIC PLATESLimits of tectonic plates are delimited by the sites where earthquakes or volcanoes are produced. The tectonic plates can be of three types: a) continental plates: they have continental crust on the surface. For example, the Arabian plate. b) oceanic plates: they have oceanic crust on the surface. For example, the Pacific Plate. c) Mixed Plate: they have oceanic crust and continental crust on the surface. For example, the North American Plate, the Eurasian Plate, African Plate, the indoaustraliana plate, etc.
3.2. TYPES OF MOVEMENTS OF TECTONIC PLATESThe plates can perform three movements:a) Movements of convergence: the two plates move towards each other, so that the end of one plate is subducted beneath the other, in a large depression known as trench. This creates:
◦ enormous earthquakes (Turkey, El Salvador), ◦ the formation of huge mountain ranges parallel to the
coastline (Andes) ◦ the formation of island arcs (Japan).◦ When all the oceanic plate subducted beneath other, two
continents can collide because both continents have the same density. This collision forms super mountain ranges as The Himalaya.
b) Movements of divergence: the two plates are separating from each other. For this reason, materials come from inside the Earth with large volcanic eruptions. Eruptions usually occur in the deep ocean and materials make up submarine elevations known as RIDGES. The slit through which these materials arise is called RIFT. The ridges provoke theseafloor spreading.
c) Shear movements: the two plates slide past each other. This causes the plates to crash into each other called transform faults. These cause major earthquakes, such as the San Andreas Fault in San Francisco in 1906.
4. VOLCANOES
Volcanoes are cracks in the earth's surface where there are materials that are composed mainly of molten rocks at temperatures between 400ºC and
800 ° C, called magma.Materials that a volcano can eject can be:a) Lava: material formed by magma without gases because these are released to atmosphere.b) gases, mainly water vapor, carbon dioxide and hydrogen sulfide.c) pyroclastics, are solids that are classified by size:ash: smaller than 2 mm.Lapillis: size between 2 and 64 mm.Volcanic bombs: larger than 64 mm.
5. TYPES OF VOLCANOESVolcanoes can be of three types: * Pelean Volcanoes have very dense magma rich in gas. When the magma comes out, there are violent explosions. The volcanic cones are steep and accumulate many pyroclastics. When the magma cools this results in clear-looking rocks. For example, pumice. * Hawaian volcanoes are made up of very fluid magma with few gases. The eruptions are quiet. The volcanic cones have shallow slopes and few pyroclasts accumulate. When the magma cools this results in dark looking rocks. For example, the basalts. * Intermediate volcanoes have characteristics in between the Pelean and Hawaiian. Most volcanoes are of this type.
6. VOLCANISM IN SPAIN
Volcanic processes in Spain are limited to the Canary Islands. These islands have a volcanic origin. On the island of Tenerife is Mount Teide, Spain's highest peak. And the volcano is still active.There are remnants of volcanic rocks in the Campo de Calatrava (Ciudad Real), Cabo de Gata (Almería) and Olot (Gerona) showing a volcanic origin of these areas. But these volcanoes are extinct.
7. EARTHQUAKESAn earthquake is a sudden shaking of the ground dues to the abrupt release of energy inside the Earth.The area inside the Earth where the earthquake originates is called the hypocenter.The place on the surface located vertically above the hypocenter, is calledthe epicenter.Seismic waves are transmitted in all directions and are responsible for the earthquake reaching distances far away.
8. SCALES OF MEASUREMENT OF EARTHQUAKES
To measure earthquakes, we can use two different scales:
MERCALLI SCALE: This scale measures the amount of general havoc that an earthquake, ie, its intensity. Measured from I to XII. I is a perceivedslight tremor XII destruction with deaths. It is an objective scale, since it depends on the materials the buildings are constructed with. Thus, in El Salvador, an earthquake can produce quite a lot of deaths, but in Japan noharm.
RICHTER SCALE: This scale measures the amount of energy released,ie the magnitude. Is measured from 0 to 9.5. This is an objective scale, since it speaks of the energy of the earthquake.
Builds in Tokyo (Japan) Adobe buildings (South America)
9. SEISMIC RISK IN SPAINIn Spain, the seismic risk is moderated, because we are not close to any rift or trench. But we are near a transform fault that crosses the Straits of Gibraltar and the peninsula shows a multitude of faults. These are particularly important in sub Betic Cordilleras and the lift area where failures are most important, and therefore, here there is more seismic risk.
10. GEODYNAMIC MODEL OF THE EARTH The manner in which seismic waves are transmitted into the interiorof the Earth, have allowed to deduce how the inner layers of our planet a.reSeismic waves can be of three types:* P or longitudinal waves: They are spread across all media, solids, liquids and gases, but are faster in solids. The particles vibrate in the same direction than the direction of wave propagation.* S or shear waves: It is transmitted only on solid media. The particles
vibrate in a direction perpendicular to the direction of wave propagation.* Surface waves: its are transmitted on surface. They are responsible for the destruction generated by earthquakes.
When an earthquake occurs, P and S waves are transmitted in depth, both increase its speed, because the materials become more compact. But when it reaches 70 km of depth, occurs a discontinuity in the speed of propagation of both waves, and these slow down. This area isknown as the Mohorovicic discontinuity situated between the crust and mantle.
The wave velocity increases gradually, reaching the 100 km depth where there is a slight decrease in velocity of both waves, which we translate as waves pass through an semi-fluid area known as asthenosphere.From here, P and S waves significantly increase the speed. To reach the 2900 km depth where there is a great disturbance in the waves. The S wave ceases to propagate and greatly decreases the P wave velocity. This means that the solid mantle passed to a liquid outer core. The area is known as the Gutenberg discontinuity.
In the outer core only spreads the P wave, which slowly recovers its speed to reach the 5200 km depth where there is a new discontinuity. It separates the liquid outer core and solid inner core is known as Lehman
discontinuity.From here the P-wave velocity increases substantially, reaching very
high speeds, and it is translated as the core is formed by an alloy of iron and nickel.
11. TYPES OF ROCKSRocks are classified, according to their origin, into three types: IGNEOUS OR MAGMATIC ROCKS: these are rocks formed by cooling and solidification of magma. Depending on how this cooling happens, we can speak of three types of magmatic rocks:a) Volcanic rocks: rocks that are formed when the cooling is very fast onthe outside of the volcano. Minerals do not have time to solidify into large crystals so the texture of the rock is called porphyritic texture, for example, basalts. It is also common for rocks to have pores due to its highcontent of gases (such as pumice), or when the cooling is very fast, forming glassy rocks like obsidian.
b) Plutonic rocks: rocks that form when the cooling is very slow within the magma chamber. Minerals have time to solidify into large crystals, thus the rock texture is called granuda texture, for example, granite. METAMORPHIC ROCKS: These are rocks formed from other rocks, which undergo increases in pressure and / or temperature and the new rock is totally different. For example, quartzite and slate are metamorphic rocks. Many times, when there is an increase of pressure, the initial minerals are redistributed and these are arranged into a position perpendicular to the direction of the pressure. This is how it is transformed into another different rock. For example, slate is formed from clay. SEDIMENTARY ROCKS: These are rocks formed from sediment. Sediment is transported to sedimentary basins, where it accumulates. This is followed by the digenesis process, comprising of:1º) Accumulation of sediments in the sedimentary basin.2º) Compaction of sediments under the weight of materials placed on top of them.3º) Cementing: The water charged with bicarbonate of calcium, passes through the remaining pores between the sediment and the evaporation isaccumulated in the form of carbonate, bicarbonate, cementing and bonding the grains of sediment.
The sedimentary rock can be classified into several types. The most important are conglomerates, breccias, sandstone, claystone, siltstone, limestone, dolomite, coal, oil (only liquid rock) etc...
