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