Full Course notes for GEO1009. Includes a summarized version of all notes and PowerPoints on all three sections in the first semester course (Geology, Archaeology, EGS) . Relevant diagrams included to further enforce understanding. These notes will help you achieve great results in Tests and the Ex...
GEO1009F Complete Syllabus
Earth and Plate Tectonics - Week 1.5
Topic 1: What is Earth and Geology
What is Earth
A complex, dynamic chemical system driven by physical processes with an evolutionary history
spanning about 4500 million years.
How do we study Earth:
• Observe = systematically describe and carefully measure natural phenomena
• Analyse = apply fundamental concepts (laws) from Physics, Maths and Chemistry
• Synthesise = combine all available knowledge to solve geo-problems
• Interpret = deduce the meaning of the observed phenomena
• Signify = predict (forecast) the near and distant future of our planet (e.g., natural disasters,
location of renewable and non-renewable natural resources)
The ultimate goal of Earth scientists
To reconstruct the history of the Earth, to understand how it works now and how it may behave in
the future.
What is Geology:
The scienti c study of the solid Earth and the plethora of the processes shaping it.
Why is Geology important?
“Civilisation exists by geological consent, subject to change without notice
What does a Geologist study?
Geology is more than just the study of rocks. It is the study of Earth systems
Two sides of Geology
• Extract resources needed for energy and commodities
• Clean up and protect land from the destructive forms of resource extraction
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,Scale:
• Atomic (e.g., arrangements of atoms in crystals/minerals)
• Global (e.g., plate tectonics - natural phenomena that operates on several thousands of km’s in
length & depth)
Topic 2: Earth from the Inside and Outside
OUR SOLAR SYSTEM
The four terrestrial planets (left) are much smaller than the four gas-giant planets.
The planets, in the decreasing order of their size, are
• Jupiter has faint rings in the horizontal plane
• Saturn has rings in a tilted plane
• Uranus has rings in the vertical plane
An asteroid belt is between Mars and Jupiter. All the planets are in the same plane.
, Our Earths position
• Our Solar System lies on the outer edge of the Milky Way Galaxy, which contains about 300
billion stars.
• The red shift of light from distant galaxies indicates that galaxies are moving away from the
Earth. This observation supports the expanding Universe theory.
• This expansion began after the Big Bang that occurred about 13.8 billion years ago.
The Big Bang
• The start of the Universe ~13.8 Ga ago (GA = billion years)
• The Big Bang Theory (BBT) proposes that all matter and energy in the Universe started out as a
single in nitesimally small point.
• It exploded and has been expanding since.
EVIDENCE FOR BBT:
• Distant galaxies in every direction are going away from us with speeds proportional to their
distance
• Cosmic radiation (the glow left over from the explosion itself)
~13.8 to ~4.6 Ga is the Formation of the Solar System
Nebular theory of planet formation
About 4.6 Ga ago, nebular cloud of gas and debris combined from older stars.
The nebula condenses into a nebular disk with a bright centre
Over time, the dust particles orbit around the proto Sun in distinct rings, where the dust combined
to form planetesimals
Gravity pulling together combining gas, dust and ice to form “lumpy planetoids” that eventually
joined together to form the present-day eight planets of the solar system
The formation of the Earth
• The formation of the Earth from a lumpy
planetoid (= irregularly shaped proto-Earth)
• Progressively, the interior heated up to the
point of melting, the proto-Earth became
spherical and separated into core and
mantle.
Terrestrial planets built collisions of little
planets by gravitational pull
Gas Giants grew by gas accretion
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, Separation of the Earth’s interior
• The Earth started out as a ball of very, very hot liquid.
• This liquid was mostly made of two elements called oxygen and silicon. But there were small
amounts of other elements too.
• In fact, it was a mixture of almost every element in existence.
• This all happened around 4.6 billion years ago.
• Over time, Earth began to cool down.
• The heavier elements, like iron and nickel, sank into the centre of the planet (the core).
• The Earth’s core is as hot as the surface of the sun
• The core is full of iron, because Earth acts like a giant magnet, drawing some elements to it.
• This magnetic core is very useful: it means we can use a compass
All terrestrial planets went through the same process of separating layers. The thickness of
these layers vary according to the planet
Earths History
• In the rst ONE billion years there was No solid land or water and was very hot
• Continually bombarded by metors (meteorites, after landing) which gave clues about Earth’s
interior.
• Stony meteorites and iron meteorites are thought to be fragments of planetesimals that had
di erentiated into mantle and core.
The formation of the Moon
• The formation of the Moon ~4.4 Ga ago
• After separation of the earths layers, a Mars-sized planetoid collided with Earth blasting out a
large part of its mantle.
• Debris from the collision formed a ring around Earth.
• The Moon formed from the ring of debris and Earth’s axis of rotation is tilted 23 degrees giving
us SEASONS.
Earths layers
THE CORE
• Made of the : solid inner core + liquid outer core
• Made of Fe (Iron) & Ni (Nickel)
• Convection in the liquid outer core creates Earth’s magnetic eld
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,THE MANTLE
• The largest layer of the Earth Comprises:
lower mantle + upper mantle (+transition
zone)
• Made of O, Si, Mg & Fe
• Convection in the mantle transfers heat
from the Earth’s interior to the surface.
Lower Mantle
• Hot, squishy body of rock
• Has VERY SLOW currents that ow like
honey or any thick, sticky dark syrup.
• The slow currents push the plates of rigid
rock around
Upper mantle
• More rigid and rock like
• 150 to 660 km deep
• The Upper mantle and the Crust form the Lithosphere ( where tectonic plates move )
THE CRUST
• Thin and light
• Is roughly 10 - 70 km deep
• Early on in Earth’s history, minerals began to form. Lighter minerals oated up toward the
surface and formed a thin crust of rock around the outside of the planet
• The crust is mostly made of minerals such as quartz, feldspar and mica.
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, • These are the shiny crystals in granite rocks
• Over long periods of time these minerals and the rocks
they forms break down into small pieces* and are carried
around by winds, currents and waves
• These are cobbles, pebbles, sand and mud, and get
deposited in rivers, lakes, on the beach or inside the sea/
oceans
The Geothermal Gradient
• This is a measure of the increase in temperature (T) with
depth within the Earth.
• Di ering rates of change with depth re ect variation in
Earth’s layers.
• Note the rapid decrease in the rate of T change at the
base of the crust OR variation in the rate of T change
across the core-mantle boundary.
Topic 3: Plate Tectonics
Why Earth is unique
• Life
• Large body of water
• Active plate tectonics
Earths interior summary
• Crust: ~10–70 km thick, intermediate (felsic and basaltic) composition
• Mantle: ~2800 km thick, ma c composition
• Outer core: ~2200 km thick, liquid iron
• Inner core: ~1500 km thick, solid iron
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, Lithosphere
•the outermost 100–
150 km of Earth.
•Behaves rigidly, as
a non- owing
material
•Comprised of two
components: crust
and upper mantle.
•This is the material
that makes up
tectonic plates.
Asthenosphere
• Upper mantle below the lithosphere.
• Shallow under oceanic lithosphere; deeper under continental.
• Flows as a soft solid.
• The lithosphere rides on top of the asthenosphere
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,Evidence of the Super Continent
ROCK EVIDENCE
• Glacial deposits of the same age occur in the southern hemisphere continents.
• If southern hemisphere continents and India are untied, the glacial deposits combine into a
single entity, which could have formed when the combined continents lay over the South Pole
FOSSIL EVIDENCE
The distribution of fossils of land-dwelling and marine reptiles found in the southern hemisphere
continents and the certain plant fossils suggest that these continents were once joined together.
MAGMATIC EVIDENCE
Earthquakes
• Sudden movement in the crust from vibration and shaking
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,• Produce seismic energy waves
• As they travel across the Earth, undergo velocity changes with depth depending on the density/
composition of the materials(Layers of earth) they encounter.
• Evidence for showing that the Earth’s interior is layered.
Fault: fracture plane that facilities the movement of rock bodies past other
• This is called a normal fault.
• Forms during extension of the crust.
• Faults come at all scales
Tsunami
Wave energy during tsunamis is enormous, it creates LONG wavelength and increases the wave
base far below the wave base of fair weather conditions.
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, VOLCANOES
• Not randomly distributed.
• Just like earthquakes, most of them form belts devastating zones of geological activities
• Volcanoes (igneous activity) NOT only tracks tectonic plate boundaries, but when occurs within
the plates can tell direction and rate of movement.
Sea oor mapping shows that most of the underground volcanoes & earthquakes are
associated with the Earth’s longest mountain chain called: The mid ocean ridge system
(MORS)
MAGNETIC EVIDENCE
• Electromagnetic currents are generated by the convection in the uid outer core and from the
di erent rotation speeds of outer liquid core and mantle material
• Earth’s magnetic eld – capable of magnetising materials that contain iron-bearing minerals
(e.g., magnetite minerals)
• Magnetisation of sediment grains results in the magnetised iron-bearing mineral grains become
aligned with Earth’s magnetic eld & point toward the magnetic poles that existed at the time of
deposition
•Bands of normal and reversed polarity
are mirrored across the mid-ocean ridge
(MOR) axis
•Black is normal polarity and the gaps are
reversed polarity
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