EESA module 2 PPT PDF

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The PPT for doing Module 2...

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How Earth Works The Earth is a spheroid of concentric layers with different physical and chemical properties. We live on the thin outermost shell called the lithosphere and have to overcome great challenges in order to understand the workings of the Earth’s interior. In this module, we try to understand how the Earth works from the inside out.

Chemical and Mechanical Layers of the Earth. The Earth is differentiated into layers based both on its mechanical properties ( liquid vs. solid vs. plastic) and its chemical or compositional properties. The Earth’s “crust” is defined based on its composition and refers to the relatively silica-rich low-density rocks that form the thin outer rind of the Earth. There are two types of crust: oceanic crust and continental crust with slightly different compositions and densities. The crust, together with the rigid uppermost layer of the mantle makes up the “lithosphere”.

The Crust and the Lithosphere The Earth’s “Crust” refers to the relatively silica-rich low-density rocks that form the thin outer rind of the Earth. The Earth’s “Crust” is defined based on its composition and refers to the relatively silica-rich low-density rocks that form the thin outer rind of the Earth There are two types of the crust: oceanic crust and continental crust with slightly different compositions and densities. The crust, together with the rigid uppermost layer of the mantle makes up the “lithosphere”.

Investigating the crust: Geology Geology is primarily concerned with studying rocks exposed at or near the surface. Some geologists work in the field and travel all over the world in order to describe and map rocks. Others work in the laboratory performing experimental work or in the office creating models and maps. Geologists often deal with practical matters like finding natural resources (petroleum, natural gas, groundwater and metals), and to predicting natural hazards (earthquakes, volcanic eruption etc.). Despite modern technology, we still know very little about the Earth and Geologists are forever trying to learn more about the subsurface. Drilling into the Earth’s crust can provide geologists with samples, but even the deepest drilling project on Earth, the Kola Superdeep Borehole, only extended 12.3 km into the crust, a tiny fraction of Earth’s around 6300km radius.

Investigating the crust: Geodesy Geodesy ( or geodetics) is the science of location. The Earth isn’t actually a sphere, but a slightly irregular ellipsoid that bulges out at the equator. Figuring out where a given feature is on that irregular ellipsoid (or “geoid”) is important because the Earth’s surface is constantly changing. Nowadays, satellite-based trading system are extremely popular. Most of us have used the Global Position System (GPS) for example in our cars and phones to get around, but it can also be used to track very small movements of tectonic plates. GPS receivers calculate their position from the time it tales for a signal to be transmitted from three satellites of known position to the receiver.

Investigating the crust: Geophysics Geologists are often interested in what lies beneath the Earth's surface, but it is very difficult to directly sample rocks from great depths. Geophysics is a branch of geology that uses a wide variety of physical methods such as seismic, gravitational, and magnetic properties to discover more about the subsurface. Seismic reflection surveys, for example, are a technique where a pulse of energy (like a sound or an explosion) created on the surface is reflected and refracted back to a set of receivers. Energy travels at different speeds through different types of materials, thus the speed at which waves are returned can create an image of the subsurface.

Investigating the crust: Gravimetry Gravimetry is the measurement of the strength of the gravitational field and uses an instrument called a gravimeter. The strength of the gravitational field varies by about +/- 0.5% due to heterogeneities below Earth's surface. Most gravimeters are effectively a weight on a spring, and they can be mounted on vehicles, aircrafts, and ships. Gravitational anomalies can be used to determine if a region is in isostatic equilibrium, to indicate unusually dense or light regions underground, and to quantify atmospheric mass variations, tides, groundwater level variations, and soil moisture variations.

Investigating the crust: Heat Flow

Heat flow is the energy lost from one medium to another. The temperature gradient with depth, or 'geotherm', can be measured

directly near the Earth's surface in deep mines or boreholes. The normal geothermal gradient is about 25 degrees Celsius per kilometer near the surface. Continental crust tends to insulate the interior of the Earth, preventing heat in the core and mantle from reaching the surface, but heat is also produced in the continental crust by radioactive minerals releasing energy. Oceanic crust is primarily heated from the mantle below. The heat flow from Earth's interior to the surface through young oceanic crust ultimately drives many deep Earth processes (see figure, Davies and Davies, 2010). Investigating the crust: Geomagnetism Geomagnetism is the study of Earth’s magnetic field and uses a magnetometer to assess the strength and direction of anomalies in the magnetic field. Anomalies results from changes in the concentration of magnetic minerals buried deep underground. Because the magnetic field changes over time, geologists can also use fossilized magnetism to figure out where continents were located in the past.

Tectonic Plates The lithosphere is broken into about a dozen tectonic plates that slide over the plastic asthenosphere below and interact at plate boundaries. The motion of one lithospheric plate relative to another is called relative plate motion.At divergent boundaries, the plates are pulling away from each other, forcing new plate material to be created to fill that gap. At transform boundaries, plates slide past each other with no addition or destruction of either plate. At convergent margins, two plates collide, either resulting in the destruction of the denser plate at a subduction

zone, or the crumpling of the two plates into an orogeny (“mountain belt”). Tectonic plates also have an absolute plate motion, which is the motion of a plate relative to a stationary point. Stationary mantle plumes for example help us to track absolute plate motion because they leave behind chains of volcanic islands as the lithospheric plate above slides past. Some chains visible on the seafloor were created by mantle plumes that no longer exist. CON Divergent Boundary N.CO NUSA Transform Boundary SA NU

The Mantle The Earth’s mantle is made of ferromagnesian silicate minerals, and is therefore more rich in iron and magnesium than crustal rocks, but still contains silica, unlike the metallic core. We call these rocks “ultramafic” (compared to magic rocks in the crust) because they are so rich in magnesium and iron (Fe). It makes up 67% or Earth’s mass, and 84% of Earth’s volume. The mantle is solid rock, but it convects over very long time scales, giving rise to a number of important phenomenon at the surface of the Earth.

Mantle convection Though the mantle is solid rock, over very long time scales rock flows in large convection cells that bring heat from the interior to the surface. Hot rock close to the core tends to rise, while cold rock near the surface tends to sink. Mantle subduction is hugely important to plate tectonics. During subduction for example, cold slabs of lithosphere descend into the mantle, dragging relatively

cool upper mantle downwards. This process displaces hot water mantle rocks which can rise to the surface and cause volcanism either at mid ocean ridges, or within-plates.

The Core The earth’s core is largely composed of Nickel and Iron metals. It has two layers: the solid inner core and liquid outer core. Though the core is only about 15% of the Earth’s volume, it holds about 33% of the Earth’s mass. Although it is impossible to sample the core, geologists think that the composition is similar to metallic meteorites that fall on Earth’s surface, which could be the cores of other worlds.

Investigating the Interior: Seismology (I)

Seismology is the study of earthquakes and seismic waves. Seismograms record vibrations from the waves generated during earthquakes that travel along Earth's surface (surface waves) and also waves that travel through the Earth's (body waves). Seismologists can use seismograms generated from both natural and artificial earthquakes to learn about Earth's interior. Two types of body waves are used: P waves (primary waves) which are compressional like sound waves, and S waves (secondary waves) which have transverse motion. P waves travel faster than S waves, and can travel through liquids and solids while S waves can only move through solid rock.

Investigating the Interior: Seismology (II) P waves travel faster than S waves, and can travel through liquids and solids while S waves can only move through solid rock. By looking at patterns of seismic refraction, scientists were able to determine that the outer core is liquid and the inner core is solid.

Earth’s Magnetic Field The Earth’s magnetic field is a geodynamo generated by convection of molten iron and nickel in the fluid outer core. Grains of magnetite in lava flows on Earth’s surface often align with the magnetic field before solidifying, locking in the record of changes in the strength, directionality and polarity of the magnetic field. This property can be used to determine how continents have shifted over time....