An Introduction to Physical Geology
Chapter 1
Geology The science that pursues an
understanding of planet Earth Physical geology – examines Earth
materials and seeks to understand the many processes that operate on our planet
Historical geology - seeks an understanding of the origin of Earth and its development through time
Geology, People, and the Environment Many important relationships exist
between people and the natural environment
Problems and issues addressed by geology include
• Natural hazards, resources, world population growth, and environmental issues
Brief History of Geology The nature of the Earth has been a
focus of study for centuries. Aristotle:
Influential Greek philosopher from 300s BC.
Made arbitrary pronouncements about natural world
Beliefs held throughout Middle Ages
Dueling Theories—17th & 18th Centuries Catastrophism: Sudden world-wide
upheavals. Uniformitarianism: Processes occurring
today also occurred in the past at about the same rate. James Hutton said "The present is the key to
the past." Most widely accepted geologic theory today. Birth of modern geology as a science.
What Does it Mean to be a Science? 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
The Nature of Scientific Inquiry How or why things happen are
explained using: •Hypothesis – a tentative (or untested)
explanation •Theory – a well-tested and widely
accepted view that the scientific community agrees best explains certain observable facts
The Nature of Scientific Inquiry, cont’d Scientific method involves
• Gathering facts through observations• Formulation of hypotheses and theories
There is no fixed path that scientists follow that leads to scientific knowledge
Example of Transformation from Hypothesis to Theory Brief history of plate tectonics
Early 20th century-continents and oceans believed to be fixed features on the surface of the earth
“Continental drift” hypothesis was proposed and ridiculed
Over 50 years of research before hypothesis transformed into the theory of plate tectonics
Geologic Time Earth is approximately 4.6 billion years
old Oldest rock on earth: 4.4 byo Relative ages based on fossil record
Relative dating means that rocks are placed in their proper sequence or order without knowing their specific age
Absolute ages based on isotopic dating
Geologic Time
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
A View of Earth Earth is a planet that is small and
self-contained Earth’s four spheres
• Hydrosphere• Atmosphere• Biosphere• Geosphere
Earth as a System Earth is a dynamic planet with many
interacting parts or spheres Earth System Science
• Aims to study Earth as a system composed of numerous interacting parts or subsystems
• Employs an interdisciplinary approach to solve global environmental problems
Earth as a System, cont’d What is a system?
• Any size group of interacting parts that form a complex whole
• Open vs. closed systems
Feedback mechanisms• Negative feedback – maintains the status
quo• Positive feedback – enhances or drives
changes
Earth as a System, cont’d The Earth system is powered by the
Sun that drives external processes in the
• Atmosphere• Hydrosphere• At Earth’s surface
The Earth system is also powered by Earth’s interior
Earth’s Interior Layers defined by composition (density)
• Crust• Mantle• Core
Layers defined by physical properties (strength)
• Lithosphere• Asthenosphere• Mesosphere• Inner and outer core
Chemical Divisions of the Earth Crust
Uppermost surface of the Earth Thinnest layer Largest variety of rock types
Mantle Below the crust Composed of igneous and metamorphic rock
Core Below the mantle Composed dominantly of iron with some
nickel and other elements
Physical Divisions of the Earth Lithosphere
Crust and strong part of upper mantle Makes up the tectonic "plates" of plate tectonics
Asthenosphere Weak part of upper mantle Partially molten in some areas Lithosphere moves over this part of the mantle
Mesosphere Lower mantle Stronger than asthenosphere
Physical Divisions of the Earth, cont’d Outer Core
Liquid Composed of Fe with some Ni and other
elements Inner Core
Solid Same composition as outer core
The Face of Earth—the Crust Earth’s surface
Continents Oceans
Continents Mountain belts
• Most prominent feature of continents The stable interior
• Also called a craton – composed of shields and stable platforms
The Face of Earth, cont’d
Ocean basins consist of Continental margins Deep-ocean basins Ocean ridge system
Ocean Basins Continental margins
• Includes the continental shelf, continental slope, and the continental rise
Deep-ocean basins• Abyssal plains• Oceanic trenches • Seamounts
Oceanic ridge system• Most prominent topographic feature on Earth• Composed of igneous rock that has been fractured
and uplifted
Major Types of Rocks Igneous rocks
Sedimentary rocks
Metamorphic rocks
Igneous Rocks Cooling and solidification of magma
(molten rock) Examples include granite (intrusive)
and basalt (extrusive)
Sedimentary Rocks Accumulate in layers at Earth’s
surface Sediments are derived from
weathering of preexisting rocks Examples include sandstone and
limestone
Metamorphic Rocks Formed by “changing” preexisting
igneous, sedimentary, or other metamorphic rocks
Driving forces are heat and pressure Examples include gneiss and marble
The Rock Cycle The loop that involves the processes
by which one rock changes to another
Illustrates the various processes and paths as earth materials change both on the surface and inside the Earth
Demonstrate GEODe