What is Geology
Earth knowledge"
-Scientific study of our planet
-Earth's history
-Earth's composition
-Earth's internal structure
-Earth's surface features
Sustainable Development
Earth is a "spaceship" with limited resources and a delicate life-support system.
"Sustainable Development": Current generation must ensure hospitable planet for future generations.
The Roles of Geologists
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The Scientific Method
A procedure used to discover how the universe works through systematic observations and experiments
Principle of Uniformitarianism
Processes that occur on modern Earth have worked in much the same way during the geologic past.
Earths layers
outer core, inner core, mantle, and crust
The Inner Core
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The outer Core
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The Mantle
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The Crust
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Earth as a System
-Open system: Exchange energy and mass
-Two primary sources of energy:
1. Solar
2. interior Earth
-Open and interacting geosystems
-Positive and negative feedbacks between the systems
Geodynamo System
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Plate Tectonic System
-Convection in the mantle drives the movement of Earth's surficial plates.
Note: Plates are composed of lithosphere, which is the crust and upper, rigid mantle.
Continental Drift
-Alfred Wegener (1915) proposed that all of the continents were once part of a large supercontinent - Pangaea.
Based on:
-Similarities in shorelines
-Terrestrial geologic evidence
-Distinctive fossil groups found in Africa and South America
Paleontological Evidence
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Pangaea
Early Jurassic, 195 Ma
Late Jurassic, 152 Ma
Late Cretaceous, Early Tertiary, 66 Ma
Problems with Continental Drift
-Wegener proposed a mechanism for drift:
a.Continents plowed through solid ocean floor,
b.Tidal forces drove the motion,
-Tidal forces are know to be too weak to move continents.
-However, the hypothesis was largely rejected due to an inadequate mechanism of continental movement.
Seafloor Spreading
-Original evidence for continental drift was from continental rocks.
-Technological advances in the 1940s, 1950s, and 1960s allowed investigation of the seafloor.
-New data provided intriguing new information!
Geology of the Ocean Floor
Bathymetry of the ocean basins:
-Sonar revealed ridge system in ocean basins.
-Ridge system is continuous around the entire globe.
-There is a central rift VALLEY within the ridge.
Seafloor Spreading: Testing the Hypothesis
Magnetic anomalies record symmetric patterns of magnetism on either side of mid-ocean ridges.
-Positive anomalies correspond with seafloor formed during times of NORMAL polarity.
-Negative anomalies correspond with seafloor formed during times of REVERSED polarity.
Plate Tectonic Theory
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Plate Tectonic
As plates move around the globe, their edges interact with one another at the boundaries.
There are three types of plate boundaries:
-Divergent boundaries
-Convergent boundaries
-Transform margins
Divergent Boundaries
Two varieties:
Oceanic plate separation
-Mature
Continental plate separation
-Juvenile
Divergent Boundaries (Oceanic)
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Divergent Boundaries (Continental)
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Convergent Boundaries
Three varieties:
Ocean - Ocean convergence
-Subduction
Ocean - Continent convergence
-Subduction
Continent - Continent convergence
-Collision
Convergent Boundaries (Ocean - Ocean)
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Convergent Boundaries (Ocean - Continent)
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Convergent Boundaries (Continent - Continent)
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Transform Fault Boundaries
Two varieties:
-Mid-ocean ridge transform fault
-Continental transform fault
Mid-ocean Ridge Transform
Due to the spherical nature of Earth, divergent boundaries are broken with a step-like pattern, resulting in transform motion.
Continental Transform
Plates slide against one another on land and lead to large earthquakes.
How Fast Do the Plates Move?
Typical relative plate velocities are between 5-150 mm/year.
How do we know this?
Velocity = Distance over Time
Method #1: Seafloor Ages
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Method #2: Mantle Plumes and Hotspots
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Method #3: Global Positioning System
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What Drives the Plates?
Internal heat and associated density differences drive plate motion through:
-Mantle convection
-Ridge push
-Slab pull
Reconstructing Plate Motion
-The assembly and break-up of Pangaea
-An introduction to the Wilson Cycle of supercontinents
a. Rodina, 1.1 billion old, broke up about 750 Ma
Elements: Building blocks of minerals
An atom is composed of protons, neutrons, and electrons.
Atomic number: Number of protons
-Defines an element.
Atomic mass: Sum of protons and neutrons
-Isotopes of an element have different atomic masses.
Chemical Bonding
Chemical reaction: interaction of atoms of chemical elements in fixed proportions to produce chemical compounds
Bonds: formed from electron transfer or sharing:
-In Ionic bonds the electrons transferred
-In Covalent bonds the electrons shared
Ionic Bonds
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Covalent Bonds
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Formation of Minerals
Crystallization is the process in which atoms of a gas or liquid join in a proper chemical proportion and crystalline arrangement to form a solid substance.
Forming Minerals
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Rock-Forming Minerals
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Silicate Minerals
-Most abundant group of minerals in Earth's crust
-Silicon-oxygen tetrahedron is the fundamental building block of all silicates.
ex. olivine, feldspar, pyroxene, Amphibolie, mica
Carbonate Minerals
-Carbonate ion is a basic building block.
-Common mineral formed at Earth's surface
example: calcite
Oxide Minerals
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Sulfide Minerals
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Sulfate Minerals
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Mineral ID with Physical Properties
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Hardness
-Ease with which a mineral surface can be scratched
-Hardness is related to the strength of chemical bonds.
-Geologists use Moh's Scale of Hardness.
(1)Talc to Diamond(10)
Cleavage
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Color and Streak
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Crystal Habit
Shape in which an individual crystal (or aggregate of such crystals) grows
ex. Selenite, Asbestos
Other Useful Physical Properties
-Fracture: Tendency for a crystal to break along irregular surfaces
-Luster: the way in which the surface of a mineral reflects light
-Density: mass per unit volume (g/cc)
Three Major Classes of Rocks
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Igneous Rocks
Form directly from cooling of magma or lava.
Example: granite (magma) and obsidian (lava)
Extrusive- lava erupts = fast cooling
Intrusive-magma =cools slowly= granite
Intrusive Igneous Rocks
rock formed from the cooling and solidification of magma beneath Earth's surface
Extrusive Igneous Rocks
Rock that forms from the cooling and solidification of lava at earth's surface
Sedimentary Rocks
Formed when particles of broken rock and organic materials are pressed and cemented together to form new rocks.
Sediments are mud, sand, pebbles, shells, bones, leaves, and stems.
Example- sandstone, limestone, and gypsum.
Metamorphic Rocks
Made when heat, pressure, or fluids change one type of rock into another type of rock
examples - hornfels and eclogite
The Rock Cycle
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The Rock Cycle Graph
Chapter 4 Slide 30
Mineral Resources
A number of minerals are valuable to society, either by themselves or by extracting important metals.
Atmosphere
Air
Hydrosphere
All the water at and near the surface of the earth, 97% of which is in oceans
biosphere
Consists of all life on Earth and all parts of the Earth in which life exists, including land, water, and the atmosphere.
cryosphere
A term referring to all water that is temporarily frozen in polar ice caps, snow, permafrost, and glaciers
lithosphere
A rigid layer made up of the uppermost part of the mantle and the crust.