Introduction
This task is about the structure of the earth, seismic waves, plate tectonics, Australia and people’s how living near plate boundaries affects. I will clean writing about those.
1.Structure of the Earth
1.1(introduction about the layers of the Earth)
The Layers of the Earth are the crust, the mantle, the outer core, and the inner core. There are also sections of the mantle, which are the lithosphere, the asthenosphere, and the lower mantle.
(Crust)
The upper crust for granite layer (magmatic rocks), mainly by silicon-aluminum oxide form; the lower for basalt layer (magmatic rocks), mainly by silicon magnesium oxide-form. The theory is that through the earth's crust in temperature and pressure increase with depth, every 100 meters deep temperature 1 ℃. The drilling results show that in recent years, were three kilometers or more in every 100 meters deep temperature of 2.5 ℃, 11 kilometers to the depths of up to 200 ℃ temperature.
(Inner Core)
An extremely hot, solid sphere of mostly iron and nickel at the center of the earth. It is 3200 to 3960 miles (5150 to 6378 km) below the surface and about 750 miles (1200 km) in diameter.
(Outer Core)
The outer core is the only liquid layer of the earth-a sea mostly iron and nickel (2890 to 5150 km) below the surface and about 1400 miles (2300km) thick.
(Mantle)
Subdivided into two regions, upper and lower, this dense layer made of hot, semisolid rock is located directly below the crust and is about 1800miles(2900 km) thick.
(Mantle-Lithosphere)
Made up of the crust and a tiny bit of the upper mantle, this layer is divided into several constantly (very slowly) moving plates of solid rock that hold the continents and oceans
(Mantle-Asthenosphere)
The plates of the lithosphere move (or float) on this hot, malleable semiliquid zone in the upper mantle, directly underneath the lithosphere.
1.2 (Explain their influence on the Earth)
(Molten)
Even if the causes of the phenomenon remain still difficult to determine, scientists agree in saying that the planet's magnetic pole is in continual movement.Its drift is most likely caused by the Earth's always moving molten, influenced by the fluctuations in solar radiation.Not corresponding to the position of the geographic pole, the magnetic pole moves at a rate of about 40 kilometers a year. Its drift across the North Pole is, each and every year, closely monitored by the Geologic Survey of Canada.
(Partially Molten)
The microstructure of partially molten rocks plays a key role in determining their physical properties. The area fraction of intergranular contact, contiguity, governs the establishment of a skeletal framework of solid grains and controls the effective elastic moduli of the aggregate. This work presents a theoretical calculation of steady state grain shape, contiguity, effective elastic moduli, and S and P wave velocities for a partially molten aggregate containing an approximate melt volume fraction of 0.09. The steady state microstructure is controlled by surface tension gradients arising from interaction among adjacent grains in a close-packed aggregate. The ratio of viscosity between the grains and the melt, as well as the capillary number, strongly influence the contiguity
(Solid)
The earth formed approximately 4.6 billion years ago from a nebular cloud of dust and gas that surrounded the sun. As the gas cooled, more solids formed. The dusty material accreted to the nebular midplane where it formed progressively larger clumps. Eventually, bodies of several kilometers in diameter formed; these are known as planetesimals. The largest planetesimals grew fastest, at the expense of the smaller ones. This process continued until an earth-sized planet had formed.
Early in its formation, the earth must have been completely molten. The main source of heat at that time was probably the decay of naturally-occurring radioactive elements. As the earth cooled, density differences between the forming minerals caused the interior to become differentiated into three concentric zones: the crust, mantle and core. The crust extends downward from the surface to an average depth of 35 km where the mantle begins. The mantle extends down to a depth of 2900 km where the core begins. The core extends down to the center of the earth, a depth of about 6400 km from the surface.
1.3 (Explain differences between compositional and mechanical boundaries)
(Compositional layers)
There are two major types of crust: crust that makes up the ocean floors and crust that makes up the continents. Oceanic crust is composed entirely of basalt extruded at mid-ocean ridges, resulting in a thin (~ 5 km), relatively dense crust (~3.0 g/cm3). Continental crust, on the other hand, is made primarily of less dense rock such as granite (~2.7 g/cm3). It is much thicker than oceanic crust, ranging from 15 to 70 km. At the base of the crust is the Moho, below which is the mantle, which contains rocks made of a denser material called peridotite (~3.4 g/cm3). This compositional change is predicted by the behavior of seismic waves and it is confirmed in the few samples of rocks from the mantle that we do have.
At the core-mantle boundary, composition changes again. Seismic waves suggest this material is of a very high density (10-13 g/cm3), which can only correspond to a composition of metals rather than rock. The presence of a magnetic field around the earth also indicates a molten metallic core. Unlike the crust and the mantle, we don’t have any samples of the core to look at, and thus there is some controversy about its exact composition. Most scientists, however, believe that iron is the main constituent.
(Mechanical layers)
The compositional divisions of the earth were understood decades before the development of the theory of plate tectonics - the idea that the earth’s surface consists of large plates that move .By the 1970s, however, geologists began to realize that the plates had to be thicker than just the crust, or they would break apart as they moved. In fact, plates consist of the crust acting together with the uppermost part of the mantle; this rigid layer is called the lithosphere and it ranges in thickness from about 10 to 200 km. Rigid lithospheric plates "float" on a partially molten layer called the aesthenosphere that flows like a very viscous fluid, like Silly Putty®. It is important to note that although the asthenosphere can flow, it is not a liquid, and thus both S- and P-waves can travel through it. At a depth of 660 km, pressure becomes so great that the mantle can no longer flow, and this solid part of the mantle is called the mesosphere. The lithospheric mantle, asthenosphere, and mesosphere all share the same composition (that of peridotite), but their mechanical properties are significantly different. Geologists often refer to the asthenosphere as the jelly in between two pieces of bread: the lithosphere and mesosphere.
The core is also subdivided into an inner and outer core. The outer core is liquid molten metal while the inner core is solid. The distinction between the inner and outer core was made in 1936 by Inge Lehmann, a Danish seismologist, after improvements in seismographs in the 1920s made it possible to “see” previously undetectable seismic waves within the P-wave shadow zone. These faint waves indicated that they had been refracted again within the core when they hit the boundary between the inner and outer core.
2. Seismic waves
2.1 (What are seismic waves?)
Seismic waves travel faster in the ,mantle than they do in the crust, because it is composed of denser material.Occurs in the source and in the surface of the earth and the spread of internal elastic wave called seismic waves. Seismic waves generated by earthquakes is also the elastic wave.
2.2 (What type of seismic waves do we have?)
(body -P Waves )
Primary waves (or P waves) are the fastest moving waves, traveling at 1 to 5 miles per second (1.6 to 8 kilometers per second). They can pass through solids, liquids and gases easily. As they travel through rock, the waves move tiny rock particles back and forth -- pushing them apart and then back together -- in line with the direction the wave is traveling. These waves typically arrive at the surface as an abrupt thud.
(body -S Waves)
Secondary waves (also called shear waves, or S waves) are another type of body wave. They move a little more slowly than P waves, and can only pass through solids. As S waves move, they displace rock particles outward, pushing them perpendicular to the path of the waves. This results in the first period of rolling associated with earthquakes. Unlike P waves, S waves don't move straight through the earth They only travel through solid material, and so are stopped at the liquid layer in the Earth's core.
(surface-L Waves)
Unlike body waves, surface waves (also known as long waves, or simply L waves) move along the surface of the Earth. Surface waves are to blame for most of an earthquake's carnage. They move up and down the surface of the Earth, rocking the foundations of man-made structures. Surface waves are the slowest moving of all waves, which means they arrive the last. So the most intense shaking usually comes at the end of an earthquake.
2.3 (How do they move through the earth's surface?)
P waves-compression
-can travel solids
S waves-ripple waves
-can't thought the solids
L waves-Rayleigh waves-ground roll
-travel ur ripple
-love waves-Arular shoring
2.4(Explain how analysing these waves scientists are able to determine what is inside the Earth）
Knowledge of the Earth's interior is based on the reactions of seismic waves from earthquakes to the density and state of materials that they encounter. Seismic waves travel at differing speeds through different materials (and also, at different speeds through material of different states, i.e., liquid or solid). Because we know the size of the Earth, by measuring how long it takes to pick up on seismic activity on opposite sides of the Earth, we can gauge about how much of the Earth is solid, liquid, made of a certain materia.
2.5(What is the Moho?)
The Mohorovicic discontinuity, usually referred to as the Moho, is the boundary between the Earth's crust and the mantle. The Moho serves to separate both oceanic crust and continental crust from underlying mantle. The Moho mostly lies entirely within the lithosphere; only beneath mid-ocean ridges does the Moho also define the lithosphere-asthenosphere boundary. The Mohorovicic discontinuity was first identified in 1909 by Andrija Mohorovicic, a Croatian seismologist, when he observed the abrupt increase in the velocity of earthquake waves (specifically P-waves) at this point.2.6(Explain how it was found?)
1909 A.Mohorovicic defined the frist magor bamdary between the crust and mantle. That is a depth where seismic waves changes in chemical where is a change in chemical composition.
3. plate tectonics
3.1(What are tectonic plates?)
Tectonic plates are large plates of rock that make up the foundation of the Earth's crust and the shape of the continents. The tectonic plates comprise the bottom of the crust and the top of the Earth's mantle.3.2(What the major plates on a world map?)
First the global lithosphere is divided into six parts, namely the Pacific plate, the Eurasian plate, the Indian Ocean plate, plate, America, Africa and Antarctica plate tectonic plates.
3.3(Explain the Wagener's theory 'continental drift'. What was the evidence that supported his theory? Why was it rejected at frist?)As evidence, he noted, as had others before him, of the geographic correlation in coastline perimeters of South America and Africa. This was the feature that led Wagener to investigate for other evidences. His investigations revealed that mountain ranges in South America and Africa, and strata and composition of coal fields in Europe and North America matched or lined up. Additionally, matching reptilian fossils were found on either side of the ocean, indicating that the continents were once joined together.
Because he had no physical mechanism to explain how his "islands" of rock could go freely sailing about where they wanted to through the solid rock of the ocean floor. That was how his theory was seen at the time.
3.4(What is the main difference between the Wagener's theory of continental drift and Theory of plate tectonics?）
Continental drift theory was proposed before the discovery of the mid-oceanic ridges, when it was hypothesized that the continents were actually plowing through the oceans. This theory was an attempt to explain the commonality of fossils on opposite sides of the Atlantic Ocean, and the observation on maps of the Earth that the North American and South American continents appeared to have been pulled apart from Europe and Africa. With the discovery of the mid-oceanic ridges, where new crustal plate is being created, and subduction zones, where plates are being destroyed, plate tectonic theory was born; that the crust of the earth is divided into many segments that are in constant motion, that the oceanic crust is constantly being recycled--all driven by heat from the Earth's interior.
3.5(Describe the evidence that Theory of the plate tectonics.)
To explain the phenomenon of continental drift developed a geological theory. The theory that the earth's lithosphere is a collage by plate; Global into six big plate (1968 years of French PiShun division), sea and land position is changing. According to this theory, the earth's internal structure of the outer divided into two parts: the outer layer of the lithosphere and inner circle of soft flow. This theory is based on two separate geological observation: the expansion and continental drift.
4. Australia
4.1（Which plate Australia be found? How does it move?）
Australia found in Indian Ocean plate.
Australia, which sits at the leading edge of the giant Indian-Australian Plate, moves in a northeasterly [right] direction. In so doing it collides with the western edge of the Philippine Plate. This collision pushes up the ocean floor above sea level, creating island chains, island arcs, and a twisted, tumultuous sea floor .
4.2(Use plate tectonic to explain why Australia is geologically old and stable.)
Because it's not on a tectonic plate margin, it has no active volcanoes and few earthquakes, unlike places closer to, or on plate margins like "Ring of Fire" countries such as Japan and NZ, and Australia plate is Independence.
5. （Describe how living near plate boundaries affects people's lives.）
If you live in the near of the plate, and have a lot of accidents will happen, such as earthquake, volcanic eruption that are often happen. So I would want to live in the plate center, that would at least be safer.
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