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GLG101 Physical Geology Spring 2010 Thomas D. Hoisch
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NAU Geology Club Contact: Carmen Winn,
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The Science of Geology Geology, people, and the environment
Problems and issues addressed by geology include Natural hazards, resources, and environmental issues
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The Science of Geology Some historical notes about geology
The nature of Earth has been a focus of study for centuries Catastrophism Uniformitarianism and the birth of modern geology
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What is Geology? Geology vs. other sciences Physical Geology
What do geologists do?
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Table 1.1
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Figure 1.2
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Figure 1.7B
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Geologic time Absolute ages: Geologists are now able to determine fairly accurate dates for events in Earth history Relative ages: Relative dating means that dates are placed in their proper sequence or order without knowing their specific age
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Geologic time The magnitude of geologic time
Involves vast times – millions or billions of years Many processes are very gradual
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The nature of scientific inquiry
How or why things happen are explained using a Hypothesis – a tentative (or untested) explanation Theory – a well-tested and widely accepted view that the scientific community agrees best explains certain observable facts Paradigm - a theory with broad implications
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The nature of scientific inquiry
Scientific methods involves Gathering facts through observations Formulation of hypotheses and theories
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Science – a definition:
“Science is the acceptance of what works and the rejection of what does not” …Jacob Bronowski - mathematician
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Earth as a system *Hydrosphere Atmosphere Biosphere **Solid Earth
Outer space?
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Figure 1.5
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Early Earth Evolution Big Bang
According to NASA WMAP mission – occurred at 13.7 Ga First stars appears 200 m.y. later
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Early evolution of Earth
Origin of planet Earth Most researchers believe Earth and other planets formed at essentially the same time Nebular hypothesis Rotating cloud called the solar nebula Composed of hydrogen and helium Nebula began to contract about 5 billion years ago
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Early evolution of Earth
Origin of planet Earth Most researchers believe Earth and other planets formed at essentially the same time Nebular hypothesis Rotating cloud called the solar nebula Composed of hydrogen and helium Nebula began to contract about 5 billion years ago
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Early evolution of Earth
Origin of planet Earth Nebular hypothesis Assumes a flat, disk shape with the protosun (pre-Sun) at the center Inner planets begin to form from metallic and rocky substances Larger outer planets began forming from fragments of ices (H2O, CO2, and others)
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Early evolution of Earth
Formation of Earth’s layered structure: the “Great Catastrophe” Metals sank to the center Molten rock rose to produce a primitive crust Chemical segregation established the three basic divisions of Earth’s interior Primitive atmosphere evolved from gases in Earth’s interior
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Earth’s internal structure
Layers defined by composition Crust Mantle Core Layers defined by physical properties Lithosphere Asthenosphere Mesosphere Inner and Outer Core
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Earth’s Layered structure
Figure 1.16
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Figure 1.14A
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Figure 1.14B
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The face of Earth Earth’s surface Continents
Continents: average elevation 0.5 miles Oceans: average depth 2.4 miles Continents Mountain belts Most prominent feature of continents The stable interior Also called a craton – composed of shields and stable platforms
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Figure 1.16
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The face of Earth Ocean basins Continental margins Deep-ocean basins
Includes the continental shelf, continental slope, and the continental rise Deep-ocean basins Abyssal plains Oceanic trenches Seamounts
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The face of Earth Ocean basins Oceanic ridge system
Most prominent topographic feature on Earth Composed of igneous rock that has been fractured and uplifted
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Figure 1.15Left
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Figure 1.15Right
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Rocks and the rock cycle
Basic rock types Igneous rocks Cooling and solidification of magma (molten rock) Examples include granite and basalt Sedimentary rocks Accumulate in layers at Earth’s surface Sediments are derived from weathering of preexisting rocks
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Rocks and the rock cycle
Basic rock types Sedimentary rocks Examples include sandstone and limestone Metamorphic rocks Formed by “changing” preexisting igneous, sedimentary or other metamorphic rocks Driving forces are increased heat and pressure Examples include gneiss and marble
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Rocks and the rock cycle
The Rock Cycle: One of Earth’s subsystems One rock changes to another and back with time Materials change both on the surface and inside the Earth
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The Rock Cycle Figure 1.23
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End of Chapter 1
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