SCIM1040 Lecture Notes - Lecture 9: Feldspar, Great Ocean Road, Uluru
5 Jun 2018
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SCIM1040- Lecture 9
The Crust
The Earth's Crust is very thin and cool in comparison to the other three layers. The crust is only
about 5-10 km thick under the oceans (oceanic crust) and about 32-50 km thick under the
continents (continental crust).
The crust is composed of two kinds of rocks.
1. The continental crust is mostly granite.
2. The oceanic crust is mainly basalt. Basalt is
much denser than the granite.
The Mantle
• The Mantle is the largest layer of the Earth.
• The mantle is composed of very hot dense rock that flows like asphalt under a heavy
weight. The movement of the mantle is the reason that the crustal plates of the Earth
move.
The Outer Core
• The core of the Earth is like a ball of very hot metals.
• The outer core is so hot that the metals in it are all in the liquid state.
• The outer core is composed of the melted metals of nickel and iron.
The Inner Core
• The inner core of the Earth has temperatures and pressures so great that the metals of
nickel and iron are squeezed together and are not able to move about like a liquid, but are
forced to vibrate in place like a solid.
• Is the hottest part of the Earth, possily as hot as the “us surfae.
Plate Tectonics
• The Earths surfae is ade up of a uer of large plates like pieces of a jigsaw puzzle)
that are in constant, slow motion pulling apart, colliding and grinding past each other.
This process is named plate tectonics.
• Convection currents in the mantle move the plates. The source of heat driving the
convection currents is radioactive decay which is happening deep in the Earth. The very
hot material at the deepest part of the mantle rises, cools and sinks again over and over.
• At the edges of plates (plate boundaries) earthquakes and volcanoes occur. Mountain
ranges and deep-sea trenches also form.
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• Earths ladasses hae ee pushed together ad ripped apart aout eery 500 illio
years in what is known as the tectonic supercycle.
The movement of plates has caused the formation and break-up of continents over time, including
the occasional formation of a supercontinent that contains most or all of the continents.
The supercontinent Rodinia is thought to have formed about 1 billion years ago and to have included
most or all of Earth's continents. It broke up into eight continents around 600 million years ago.
The eight continents later re-assembled into another supercontinent called Pangaea.
Pangaea broke up 225 million years ago into Laurasia (which became North America and Eurasia)
and Gondwana (which became the remaining continents).
Evidence for plate tectonics
There is evidence that these regions
were once very close or joined together.
1. Study of fossils
Similar fossils are found on different
continents.
2. Shapes of continents
Some continents fit together like a jigsaw.
3. Similar patterns of rock layers on different continents is evidence that the rocks were once close
together or joined.
The ultimate proof of plate movement
Laser beams are fired from Earth ground stations to satellites studded with glass reflectors able to
redirect the laser beams back to a second point on the ground. Scientists can then measure the
time difference and distance between the two points with great accuracy.
Three types of plate boundaries
. Divergent boundaries occur where two plates slide apart from each other. Mid-ocean ridges (e.g.,
Mid-Atlantic Ridge+Iceland) and Africa's Great Rift Valley are both examples of divergent
boundaries. Divergent zones create new crust.
2. Convergent boundaries occur where two plates slide towards each other forming either a
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a) continental collision (if the two plates contain continental crust) e.g., site of the
Himalayas. Convergent boundaries destroy crust OR
b) subduction zone (one plate moves underneath the other) causing a deep sea trench.
3. Transform boundaries occur where plates slide or grind past each other along a faults. E.g., San
Andreas Fault. There is no creation or destruction of crust at these boundaries.
The twisting and turning of New Zealand
• The lower-density continental crust of the North Island, which sits on the Australian plate,
is forcing the dense oceanic crust on the Pacific plate beneath it to be subducted and
destroyed.
• The South Island has continental crust on the Pacific plate so it is the Australian plate that
is being destroyed through subduction.
• In between, the continental crust lies on the Pacific and Australian plates causing sliding
past one another on South Island where crust is neither created nor destroyed.
Earthquakes
• Plates moving in any direction can cause earthquakes.
• At the boundaries between plates, friction causes them to stick together. When built up
energy causes them to break, earthquakes occur.
• Earthquakes are measured on the Richter Scale with 10 being the most destructive in an
area (none have been recorded yet).
• The origin of an earthquake within the crust is called the focus.
• The epietre is the poit o the Earths surfae ertially aoe the fous.
An earthquake that forms beneath an ocean can cause a tsunami to form, another very destructive
effect of earthquakes.
Tsunami
• A tsunami is a series of destructive waves.
• The sea often withdraws temporarily from the coast acting as a warning sign for an
approahig tsuai. Hoeer, ot all tsuai ause this disappearig sea effet.
• In the deep ocean, tsunami can travel unnoticed on the surface at speeds of up to
800km/hr.
• As the tsunami approaches the shore it slows down but as the depth of water decreases
the height of the wave increases by up to ten times .
Types of Rocks- Rocks tell the story of the earth
There are three main types of rocks:
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find more resources at oneclass.com
Document Summary
The earth"s crust is very thin and cool in comparison to the other three layers. The crust is only about 5-10 km thick under the oceans (oceanic crust) and about 32-50 km thick under the continents (continental crust). The crust is composed of two kinds of rocks: the continental crust is mostly granite, the oceanic crust is mainly basalt. The mantle is the largest layer of the earth. The mantle is composed of very hot dense rock that flows like asphalt under a heavy weight. The movement of the mantle is the reason that the crustal plates of the earth move. The core of the earth is like a ball of very hot metals. The outer core is so hot that the metals in it are all in the liquid state. The outer core is composed of the melted metals of nickel and iron. Is the hottest part of the earth, possi(cid:271)ly as hot as the u(cid:374)(cid:859)s surfa(cid:272)e.
