To determine the chemical composition inside the Earth indirect measurements are used. One way to determine composition is to measure how the density of rock changes with depth below the Earth’s surface. We can do this by measuring the speeds, because they move more quickly through dense rocks than through less dense rocks. From such measurements we know that density increases with depth, but not evenly. Knowing these different densities, we can estimate what the composition of the different layers must be. The layers of different chemical composition outward from the centre of the Earth are as follows: core, mantle, and crust.

1. Soran University
Faculty of Engineering
Petroleum engineering department
Geology
Prepared by: Raboon Redar Supervised by: Mr. Arkan
Mansur Nidhal
2019

2. Exercise 1
Chemical and Physical Properties of Earth
 Layers of Differing Chemical Composition
To determine the chemical composition inside the Earth indirect measurements
are used. One way to determine composition is to measure how the density of
rock changes with depth below the Earth’s surface. Wecan do this by measuring
the speeds, becausethey move morequickly through denserocks than through
less dense rocks. Fromsuch measurements weknow that density increases with
depth, but not evenly. Knowing these differentdensities, we can estimate what
the composition of the different layers must be. The layers of different chemical
composition outward fromthe centre of the Earth are as follows: core, mantle,
and crust.
The Core
At the Centre is the densestof the three layers, the core. It is mostly metallic iron
with small amounts of nickel and other elements.
The Mantle
The thick shell of the rocky matter that surrounds thecore is called the mantle.
The mantle consists of iron-magnesium-silicates and it is less dense than the core
but denser than the outermostcompositional layer, which also consists of rocky
matter.

3. The Crust
The outermost compositionalunit is the crust. While the core and the mantle
have nearly constant thicknesses, thethickness of the crustis different in
different places. The continental crust(30-70) is much morethicker than the
oceanic crust(8km). The oceanic crustis basalt while the continental crusthas a
granitic composition.
 Layers of Differing Physical Properties
In addition to compositional layering, other changes occur within the earth. Most
important, there are changes in physicalproperties such as rock strength and
solid versus liquid. The layers of different physicalproperties outward fromthe
centre of the Earth areas follows: inner core, outer core, mesosphere,
asthenosphere, and lithosphere.
The Inner and Outer Core
Within the core an inner region exists where pressures areso greatthat iron is
solid despite its high temperature. The solid centre of the Earth is in the inner
core. Surrounding the inner core is the outer core, a zonewhere temperature and
pressureareso balanced that the iron is molten and exists as a liquid. The
difference between the inner and outer cores is not one of the composition (the
compositions are believed to be the same). Instead, thedifference lies in the
physicalstates of the two: one is a solid, the other is a liquid

4. The Mesosphere
The strength of a solid is controlled by both temperature and pressure. When a
solid is heated, it loses strength. When it is compressed, it gains strength.
Differences in temperature and pressuredividethe mantle and crustinto three
strength regions. In the lower part of the mantle, the rock is so highly compressed
that it has considerablestrength even though the temperature is very high. Thus,
a solid region of high temperature but also relatively high strength exists within
the mantle from the core-mantle boundary (lower mantle) which is called
Mesosphere.
The Asthenosphere
Within the upper mantle bellow the earth's surface. is a region called the
asthenosphere("weak sphere"), wherethebalance between temperature and
pressureis such that rocks havelittle strength. Instead of being strong, like the
rocks in the mesosphere, rocks in the asthenosphereareweak and easily
deformed, like butter or warmtar. As far as geologists can tell, the compositions
of the mesosphereand the asthenosphereare the same. The difference between
them is one of physicalproperties; in this casethe property that changes is
strength.
The Lithosphere
Abovethe asthenosphereis the outermoststrength zone, a region where rocks
are cooler, stronger, and morerigid than those in the plastic asthenosphere. This
hard outer region, which includes the uppermostmantle and all of the crust, is
called the lithosphere ("rock sphere"). Itis importantto remember that despite

5. the fact that the crustand mantle differ in composition, it is rock strength, not
rock composition, that differentiates the lithosphere fromthe asthenosphere.
Note: The difference in strength between rock in the lithosphereand rock in the
asthenosphereis a function of temperature and pressure. Ata temperature of
1300°C and the pressurereached at a depth of 100 km, rocks of all kinds lose
strength and become readily deformable.
Exercise 2
Why are plate tectonics important?
The process is actually very importantto life on Earth. Severalbillion years ago,
the surfaceof our Earth began forming into puzzlepieces called plates. Plates
cover the entire Earth, and their boundaries play an importantrole in geologic
happenings. Plates crash together to make mountains, such as the Himalayas.
They leave trenches whereone slips beneath the other. They make giant rift
valleys and ridges when going their separateways. This process trapped our
atmospheric carbon dioxide into rocks and stabilized our climate, making Earth
habitable.
 There are 3 main types of plate boundaries
1. Convergent boundaries - where two plates arecolliding.
Subduction zones occur when one or both of the tectonic plates are composed of
oceanic crust. The denser plate is subducted underneath the less dense plate. The
plate being forced under is eventually melted and destroyed. Thereare three
types of meetings.

6. • Whereoceanic crustmeets ocean crust
• Whereoceanic crustmeets continental crust
• Wherecontinental crustmeets continental crust
2. Divergent boundaries - where two plates are moving apart.
The space created can also fill with new crustalmaterial sourced frommolten
magma that forms below. Divergent boundaries can formwithin continents but
will eventually open up and become ocean basins.
• On land
• Under the sea
3. Transformboundaries - whereplates slide passed each other.
The relative motion of the plates is horizontal. They can occur underwater or on
land, and crustis neither destroyed nor created.
Because of friction, the plates cannot simply glide pasteach other. Rather, stress
builds up in both plates and when it exceeds the threshold of the rocks, the
energy is released causing earthquakes.

7. Exercise 3
 Natural DisastersCausedby Plate Tectonics
Plate tectonics are among the mostinfluential forces that shapeEarth. Mostof
the time, these plates moveslowly and only create changes over the courseof
millions of years. Sometimes, however, two plates move abruptly with respect to
each other. When that happens, the Earth’s surfaceis subjectto natural disasters.
Events such as earthquakes, volcanoes and seismic waves (tsunamis) allresult
because of plate tectonics.
Rocks that Roll: Earthquakes
Most earthquakes occur as the resultof the sudden movement along a fault line
between two adjacent tectonic plates. The famous San Andreas fault in California
marks the location where the North American plate and the Pacific plate slide
past each other. The two plates moveat a rate of about 6 cm per year, causing
hundreds of tiny earthquakes yearly and the occasional major earthquake.
Erupting Volcanoes
In general, volcanoes occur either along plate boundaries or over “hot spots.”
When a plate moves over the top of another plate, the energy and friction melt
the rock and push the magma upwards. Theworld's biggestvolcano, also an
enormous ocean volcano Mauna Loa is one of five volcanoes on the Big Island of
Hawaii. Its mostrecent eruption was in 1984, and Mauna Loa has spewed lava 33
times in the past 170 years.

8. Seismic SeaWaves
Plate tectonics indirectly causeseismic sea waves, better known as tsunamis.
When a major seismic tremor shifts the crustunderneath a body of water, the
energy from that tremor transfers into the surrounding liquid. The energy spreads
out fromits original site, traveling through the water in the form of a wave. The
devastating tsunami of December 2004, which killed more than 300,000 people
around the edges of the Indian Ocean, emanated froman extremely powerful
earthquake(magnitude, 9.2) on the ocean floor near Indonesia.
References
Anon.,2018. Lumen PhysicalGeography. [Online]
Available at:https://courses.lumenlearning.com/geophysical/chapter/the-composition-and-structure-
of-earth/
Brown,L., April 19, 2018. Sciencing. [Online]
Available at:https://sciencing.com/natural-disasters-caused-plate-tectonics-5516200.html
Duarte,J. C.,2016. Earth and SpaceScience News. [Online]
Available at:https://eos.org/editors-vox/plate-boundaries-and-natural-hazards
Duarte,J. C.,and W. P. Schellart(2016),Plate boundariesandnatural hazards,Eos,97