chapter 1 an introduction to geology
TRANSCRIPT
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CHAPTER 1
AN INTRODUCTION TO GEOLOGY
ECIV 3302
Engineering Geology
Associate Professor Mazen AbualtayefCivil and Environmental Engineering Department
Islamic University of Gaza, PalestineThe materials are mostly adapted from the presentation of Stan & Cindy Hatfield
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Nisqually Glacier, Mt. Rainier, an
volcano in the Cascade Range, WA.
Learning about geology will provide students with a greater appreciation
and understanding of the natural features that shape the earth.
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Learning about geology could save your life. Many geologic processes,
such as landslides may pose significant hazards to the citizens who live
in proximity, such as in Oso, Washington (March 22, 2014).
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Learning about geology could save your life. Many geologic processes, such as
volcanic eruptions may pose significant hazards to the citizens that live in their
proximity, such as Mt. Pinatubo, Phillipines (1992).
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The Science of Geology
• Geology - “Geo” Earth; “ology” study of
• Geology - the science that pursues an
understanding of planet eartho Physical geology - examines the materials
composing earth and seeks to understand the
many processes that operate beneath and upon
its surface
o Historical geology - seeks an understanding of
the origin of earth and its development through
time
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• Geology, people, and the environment
oMany important relationships exist between people
and the natural environment
oProblems and issues addressed by geology include:
Natural hazards,
Resources,
World population growth, and
Environmental issues
The Science of Geology
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The Science of Geology
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Rocks
Igneous
Sedimentary
Metamorphic
Volcanoes
Intrusions
Weathering
SoilsErosion
Water
Underground Surface
Oceans
Wind
Glaciers
Fossils
Earth History
Earth’s Interior
Earthquakes
Mountains
Plate Tectonics
Other Planets
Mineral Resources
What is Physical Geology?
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Geology and other Sciences
Geology
Physics
•Geophysics
•Seismology
Chemistry
•Mineralogy
•Petrology
•Geochemistry
Biology
•Paleontology
•Paleo????ology
Astronomy
•Planetary Geology
•Helioseismology •Economic Geology
•Hydrology
•Engineering Geology
•Historical Geology
•Geomorphology
•Oceanography
•Structural Geology
•Volcanology
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Some Geologic Rates
Cutting of Grand Canyon• 2 km/3 M.y. = 1 cm/15 yr
Uplift of Alps• 5 km/10 M.y. = 1 cm/20 yr.
Opening of Atlantic• 5000 km/180 M.y. = 2.8 cm/yr.
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Some Geologic Rates
Movement of San Andreas Fault
• 5 cm/yr = 7 m/140 yr.
Growth of Mt. St. Helens
• 3 km/30,000 yr = 10 cm/yr.
Deposition of Niagara Dolomite
• 100 m/ 1 M.y.? = 1 cm/100 yr.
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The Science of Geology
• Some historical notes about geology
oThe nature of earth has been a focus of study for
centuries
oCatastrophism, “features such as mountains were
produced by sudden worldwide disasters.”
oUniformitarianism and the birth of modern geology
“the present is the key of the past”
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Geologic Time
• Geologists are now able to assign fairly
accurate dates to events in earth history
• Relative dating: means that dates are placed
in their proper sequence or order without
knowing their age in years
• Absolute dating
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• The magnitude of geologic time involves vast times – millions or billions of years
• An appreciation for the magnitude of geologic time is important because many processes are very gradual
• The big difference between geology and other sciences: TIME (geologically speaking, not much happens in a human lifetime!)
• Therefore, geologists use millions of years as the standard unit of time
Geologic Time
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Age of Earth
• ~ 4,600 million years
• Radioactive minerals
oRadium, uranium, lead
• Salts in the oceans and its accumulation (not
accurate)
• Fro younger ages, deposits and C14
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The geologic
time scale
Figure 1.8
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The Nature of Scientific Inquiry
• Science assumes the natural world is
consistent and predictable
• Goal of science is to discover patterns in
nature and use the knowledge to make
predictions
• Scientists collect data through observation
and measurements
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The Nature of Scientific Inquiry
• How or why things happen is explained
using a
o Hypothesis – a tentative (or untested)
explanation
o Theory – a well-tested and widely accepted
view that the scientific community agrees
best explains certain observable facts
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The Nature of Scientific Inquiry
• Scientific method involves
o Gathering facts through observations
o Formulation of hypotheses and theories
• There is no fixed path that scientists follow
that leads to scientific knowledge
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A View of Earth
• Earth is a planet that is small and self-
contained
• Earth’s four spheres
oHydrosphere
oAtmosphere
oBiosphere
oSolid earth
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Earth as a System
• Earth is a dynamic planet with many
interacting parts or spheres
• Earth system science
oAims to study earth as a system composed of
numerous interacting parts or subsystems
oEmploys an interdisciplinary approach to solve
global environmental problems
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Earth as a System
• What is a systemoAny size group of interacting parts that form a
complex whole
oOpen vs. Closed systems
• Feedback mechanismsoNegative feedback – maintains the status quo
oPositive feedback – enhances or drives changes
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Earth as a System
• The earth system is powered by the sun that drives external processes in the o Atmosphere
o Hydrosphere
o At earth’s surface
• The earth system is also powered by earth’s interior
• External energy (sun)…. Wind, waves…
• Internal energy… Earthquake, volcanoes
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Rocks and the Rock Cycle
• Basic rock types
oIgneous rocks
Cooling and solidification of magma (molten rock)
Examples include granite and basalt
oSedimentary rocks
Accumulate in layers at earth’s surface
Sediments are derived from weathering of preexisting
rocks
Examples include sandstone and limestone
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Rocks and the Rock Cycle
• Basic rock types
oMetamorphic 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
oThe loop that involves the processes by which one
rock changes to another
oIllustrates the various processes and paths as earth
materials change both on the surface and inside
the earth
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Therockcycle
Figure 1.22
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Early Evolution of Earth
• Origin of planet Earth
oMost researchers believe that earth and the
other planets formed at essentially the same
time
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Early Evolution of Earth
• Origin of planet earth
oNebular hypothesis
Rotating cloud called the solar nebula
Composed of hydrogen and helium
Nebula began to contract about 5 billion years ago
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
oMetals sank to the center
oMolten rock rose to produce a primitive crust
oChemical segregation established the three
basic divisions of earth’s interior
oPrimitive atmosphere evolved from gases in
earth’s interior
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Evolution of the Solar System
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Evolution of the Solar System
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The Solar System
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Earth’s Internal Structure
• Layers defined by compositionoCrust
oMantle
oCore
• Layers defined by physical propertiesoLithosphere
oAsthenosphere
oMesosphere
oInner and outer core
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Earth’slayered
structure
Figure 1.26
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The Face of Earth
• Earth’s surface
oContinents
oOceans
a. Continents
1. Mountain belts
Most prominent feature of continents
2. The stable interior
Also called a craton – composed of shields and stable
platforms
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The Continents
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The Face of Earth
b. Ocean basins
1. Continental marginsIncludes the continental shelf, continental slope, and
the continental rise
2. Deep-ocean basins Abyssal plains
Oceanic trenches
Seamounts
3. Oceanic ridge system Most prominent topographic feature on earth
Composed of igneous rock that has been fractured and
uplifted
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The Face of Earth
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The Face of Earth
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Oceanic Ridge System
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Dynamic Earth
• The theory of plate tectonics
oInvolves understanding the workings of our
dynamic planet
oBegan in the early part of the twentieth century
with a proposal called continental drift – the
idea that continents moved about the face of the
planet
oTheory, called plate tectonics has now emerged
that provides geologists with the first
comprehensive model of earth’s internal
workings
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Tectonic Plates
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• Plate boundaries
All major interactions among individual plates occurs along their
boundaries
1. Divergent boundary – two plates move apart, resulting in
upwelling of material from the mantle to create new
seafloor
2. Convergent boundary – two plates move together with
subduction of oceanic plates or collision of two continental
plates3. Transform boundaries – located where plates grind past
each other without either generating new lithosphere or consuming old lithosphere
4. Changing boundaries – new plate boundaries are created in response to changes in the forces acting on the lithosphere
Dynamic Earth
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Dynamic Earth
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Iceland is being pulled apart as it sits
astride the Mid-Atlantic Ridge
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San Andreas Fault