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Earth as a system
• The Earth system is powered by energy from the
sun that drives the external processes in the
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Atmosphere
Hydrosphere
Biosphere
Geosphere (lithosphere)
• Earth system is also powered by internal processes
driven by heat flow within earth. What are some
sources of heat?
Figure 1.4
Was this rock formation the result of internal or external processes?
What had to occur for this arch to form?
• Can you think of one or more internal
processes that are of interest to
geologists?
• Can these processes be explained?
Two views of Pakistan
Charakusa Valley, Karakorum Range
Muzzaffarabad
Natural Hazards
• One important reason to study geology
and be able to predict processes is to
prevent threats to humans
• A natural hazard is just that – natural
process. It only becomes a hazard
when humans put themselves in harm’s
way.
The Science of Geology
• Geology - the science that pursues an
understanding of planet Earth
• GEO=earth OLOGY = study of
• Physical geology - examines the materials
composing Earth and seeks to understand
the many processes that operate beneath
and upon its surface
• Historical geology - seeks an
understanding of the origin of Earth and
its development through time
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
James Hutton: Theory of
the Earth Late 1700s –
birth of modern Geology
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
The nature of
scientific inquiry
• How or why things happen is 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
Box 1.2 Do glaciers move? (pg. 11)
Rhone Glacier, Switzerland, 1874-1882
credit: L. Agassiz
The nature of
scientific inquiry
• 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
Solar Nebular
Hypothesis
Is this hypothesis
created
by direct or indirect
observation?
How do you think this
model was made?
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)
Early evolution of Earth
• Origin of planet Earth
• Most researchers believe that Earth and the
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
Figure 1.9A
How did the moon form? Do scientists agree?
Speaking of models…how did this diagram
become a model of earth?
Early evolution of Earth
• Formation of Earth’s layered structure
• 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
Earth’s internal structure
• Layers defined by composition
• Crust
• Mantle
• Core
• Layers defined by physical properties
• Lithosphere
• Asthenosphere
• Mesosphere
• Inner and Outer Core
Figure 1.16
Earth’s
Layered
structure
Figure 2.29
Figure 1.5
Concept of Geologic Time
 The second frame of reference for geologic time is
absolute dating
– Absolute dating results in specific dates for rock units or
events
expressed in years before the present
 Radiometric dating is the most common method of
obtaining absolute ages
– Such dates are calculated from the natural rates of decay
of various natural radioactive elements present in trace
amounts in some rocks