CHAPTER 1
Understanding Earth:
A Dynamic and Evolving Planet
Introduction
●
Geology is a complex, integrated
system of related parts,
components, or sub-systems.
●
These interact in an organized
fashion, affecting one another in
various ways. The principal
subsystems of the earth are the:
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○
○
○
○
○
Atmosphere
Biosphere
Hydrosphere
Lithosphere
Mantle
Core
Figure 1.1, p. 5
Atmosphere
Evaporation, condensation,
and precipitation transfer
water between atmosphere
and hydrosphere, influencing
weather and climate and
distribution of water.
Hydrosphere
Atmospheric gases and
precipitation contribute to
weathering of rocks.
Plants absorb and transpire water.
Water is used by people for domestic,
agricultural, and industrial uses.
Plant, animal, and human
activity affect composition of
atmospheric gases.
Atmospheric temperature and
precipitation help to determine
distribution of Earth’s biota.
Biosphere
Water helps determine abundance,
diversity, and distribution of
organisms.
Plate movement affects size,
shape, and distribution of
ocean basins. Running water
and glaciers erode rock and
sculpt landscapes.
Heat reflected from land surface affects
temperature of atmosphere. Distribution
of mountains affects weather patterns.
Organisms break down rock
into soil. People alter the
landscape. Plate movement
affects evolution and
distribution of Earth’s biota.
Convection cells within mantle
contribute to movement of plates
(lithosphere) and recycling of
lithospheric material.
Plate
Mantle
Core
Supplies heat
for convection
in mantle
Fig. 1-1,
What is Geology?
●
Geology is the study of the Earth,
other planets and their moons.
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○
Physical geology is concerned with the materials
and processes which compose and operate on the
surface of, and within, Earth.
Historical geology is concerned with the origin
and evolution of Earth's continents, oceans,
atmosphere, and life.
What is geology?
Geologists are employed in diverse
occupations.
●
Principle occupations include:
○ Mineral and energy resource exploration
○ Solving environmental problems
○ Predicting natural disasters
Geology and the Formulation of
Theories
●
○
What is a theory?
Derived from the scientific method, which involves:
gathering and analyzing facts
● formulating hypotheses to explain the
phenomenon
● testing the hypotheses
● and finally proposing a theory.
●
○
Science makes no claim about the existence or
nonexistence of the supernatural.
Geology and the Formulation of
Theories
In science, a theory is NOT a hunch or
guess, but a reliable explanation
supported by a large amount of
evidence.
In geology, plate tectonics is an
important theory.
Geology and the Formulation of
Theories
●
What is a theory?
○
The hypotheses is a tentative explanation.
○
A scientific theory is a testable explanation for
some natural phenomenon, that is supported
by a large body of evidence.
How Does Geology Relate to the Human
Experience?
●
Geology pervades our
everyday lives and is a part
of many aspects of human
experience, including the
arts and literature.
●
The range of environmental
problems, resources,
military tactics, and other
issues of concern to society
require a basic
understanding of geology.
Figure 1.2, p. 6
How does geology affect our daily
lives?
● Natural Disasters
● Economics and Politics
● Our Role as Decision Makers
● Consumers and Citizens
● Sustainable Development
Figure 1.3, p.
7
9203 kg
Clays
348 kg
Zinc
774,000 kg
Stone, sand,
and gravel
311,034 l
Petroleum
14,359 kg
Salt
159,880 m3
Natural gas
33,771 kg
Cement
>30,615 kg
Other minerals
and metals
14,694 kg
Iron ore
410 kg
Lead
2438 kg
Bauxite
(Aluminum
)
260,530 kg
Coal
629 kg
Copper
44 g
Gold
8301 kg
Phosphate rock
Stepped Art
Fig. 1-3, p.
Global Geologic and Environmental Issues Facing
Humankind
●
Most scientists would argue that
overpopulation is the greatest problem facing
the world today.
●
7 billion in 2011, perhaps 9
billion by 2045.
●
Increasingly large numbers
of people must be fed,
housed, and clothed, with a
minimal impact on the
environment.
Global Geologic and Environmental Issues Facing
Humankind
●
Problems associated with overpopulation
●
●
●
●
●
Increased risks from
earthquakes, tsunami,
floods and volcanoes
More pollution
Wildlife threatened
Shortages of resources
Poverty
Global Geologic and Environmental Issues Facing
Humankind
Greenhouse effect: Retention of heat in the atmosphere.
● Humanity has been adding to the greenhouse.
● This results in an increase in the temperature of Earth’s
surface and atmosphere, thus producing global warming.
Figure 1.4, p. 8
Greenhouse
Effect
a) Short-wavelength
radiation from the Sun that
is not reflected back into
space penetrates the
atmosphere and warms
Earth’s surface.
b) Earth’s surface radiates heat in the
form of long–wavelength radiation
back into the atmosphere, where
some of it escapes into space. The
rest is absorbed by greenhouse
gases and water vapor and
reradiated back toward Earth.
c) Increased concentrations of
greenhouse gases trap more
heat near Earth’s surface,
causing a general increase in
surface and atmospheric
temperatures, which leads to
global warming.
Stepped Art
Fig. 1-4, p.
Origin of the Universe
●
Did it begin with a Big Bang?
○
In the Big Bang theory, the universe began approximately
○
An extremely dense, hot body of matter expanded and cooled
14 billion years ago.
Origin of the Universe
● How do we know? Evidence for the Big Bang:
○
the universe is expanding from a
central point.
○
The entire universe has a
pervasive and constant
background radiation, thought to
be the faint afterglow of the Big
Bang.
Fig. 1.7, p. 10
Origin of the Universe
●
Evidence for the Big Bang: Expansion of the
Universe
○
Objects farther from the Earth are moving
faster away from us.
○
Confirmed with the Doppler Effect.
Fig. 1.6, p. 10
Our Solar System
●
●
●
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Sun: a star
8 planets (Pluto no longer considered a planet)
Numerous moons, asteroids and comets
About 4.6 billion years old
Figure 1.8, p. 11
Our Solar System: Its Origin and
Evolution
●
●
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Formed from a rotating cloud (nebula) of matter about
4.6 billion years ago.
The cloud condensed, collapsed from gravity and
flattened into a rotating disk.
The Sun, planets, and moons formed within this disk.
Figure 1.9, p. 12
Earth: Its Place in Our Solar
System
●
Earth condensed as a solid body from the solar
nebula about 4.6 billion years ago.
●
Soon after internal heat differentiated the Earth
into a layered planet.
Fig. 1.10, p.
Why Earth is a Dynamic and
Evolving Planet
Earth has continuously changed during its 4.6 billion year existence as a result of
interactions between its various subsystems and cycles.
Why Earth is a Dynamic and
Evolving Planet
● As the earth differentiated, 3 concentric layers formed.
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Crust
Mantle
Core.
Fig. 1.11, p. 13
Why Earth is a Dynamic and Evolving Planet
●
The Core
The core consists of
●
a small, solid inner region
●
a larger, liquid, outer portion
Composed of iron and a small amount of nickel.
Fig. 1.11, p.
13
Why Earth is a Dynamic and Evolving
Planet
●
The Mantle
The mantle surrounds the core and
is divided into:
○
a solid lower mantle
○
a partially molten asthenosphere that
overall behaves plastically and flows
slowly
○
a solid upper mantle.
Composed primarily of peridotite, an
igneous rock made of olivine.
Fig. 1-11, p.
13
Why Earth is a Dynamic and Evolving
Planet
●
The Crust
The outermost layer, the
crust,
is divided into:
●
thick continental crust
●
thin oceanic crust
Fig. 1.11, p.
13
Why Earth is a Dynamic and Evolving
Planet
●
The Asthenosphere
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Surrounds the lower mantle
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Behaves plastically and slowly
flows
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Partial melting in the
asthenosphere generates magma
(molten rock) that rises to the
earth’s surface.
Fig. 1.11, p.
13
Why Earth is a Dynamic and Evolving
Planet
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The Lithosphere
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The crust and upper mantle make
up the lithosphere which forms
the solid outer layers of the Earth.
Fig. 1.11, p.
13
Why Earth is a Dynamic and Evolving
Planet
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Plate Tectonic Theory
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The lithosphere is composed of rigid plates that diverge, converge,
or slide sideways past one another as they move over the
asthenosphere
Fig. 1.12, p.
16
Mid-oceanic ridge
Trench
Ocean
Subduction
Oceanic
lithosphere
Continental
lithosphere
Convection
cell
Cold
Upwelling
Outer
core
Hot
Mantle
Inner
core
Stepped Art
Fig. 1-12, p.
Why Earth is a Dynamic and Evolving
Planet
●
Plate Tectonic Theory: The Plates
Fig. 1.13, p.
16
Why Earth is a Dynamic and Evolving
Planet
●
Plate Tectonic Theory: Boundaries between Plates
●
Volcanoes and earthquakes occur at the
boundaries between the plates.
Fig. 1.14, p.
17
Why Earth is a Dynamic and Evolving
Planet
●
Plate Tectonics and Earth Systems
○
Plate tectonic theory is a unifying explanation for many geologic features and events,
helping us understand the composition and internal processes of Earth on a global scale.
The Rock Cycle
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A rock is a solid aggregate of one or more minerals, as
well as non-crystalline matter such as natural glass or
organic material like coal.
◻
Three major groups of
rocks:
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◻
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Igneous
Sedimentary
Metamorphic
Fig. 1.15, p.
18
The Rock Cycle
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Igneous Rocks form from the crystallization of
cooling magma or the consolidation of volcanic
ejecta.
○ Intrusive igneous rock crystallizes beneath the
Earth’s surface.
○
Granite
Intrusive Igneous Rock
Basalt
Extrusive Igneous Rock
Extrusive igneous rock crystallizes and cools at
the earth’s surface. At times it cools so fast that it
forms a glass or ash.
Fig. 1.16 a-b, p. 19
The Rock Cycle
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Sedimentary Rocks typically layered deposits formed
from:
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○
rock/mineral fragments
precipitation of minerals from solution
the compaction of plant and animal remains.
Conglomerate
Forms from river
gravels
Limestone
Precipitation from seawater
Fig. 1.16 c-d, p.
The Rock Cycle
● Metamorphic Rocks form from alteration of other rocks, usually by:
○
○
○
Heat
Pressure
Chemically active fluids
Gneis
s
Quartzit
e
Fig. 1.19 e-f, p.
The Rock Cycle
○
The rock cycle illustrates the interactions between Earth’s internal and external processes and how
the three rock groups are interrelated.
Fig. 1.15, p.
18
The Rock Cycle
● How are the rock cycle and
plate tectonics related?
●
Plate movement is the
driving mechanism of
the rock cycle. Plate
interaction determines,
to some extent, which
of the three rock
groups will form.
Fig. 1.17, p. 20
Organic Evolution and the History of Life
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The theory of organic evolution states:
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○
that all living things are related
have descended with modification from
organisms living in the past.
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Charles Darwin proposed that the mechanism
of natural selection results in survival to
reproductive age of organisms best suited to
their environment.
●
Fossils, the remains of once-living organisms
provide evidence for evolution and a history of
life before humans.
Organic Evolution and
Plate Tectonics
Together the theories of plate
tectonics and organic evolution have
changed the way we view our
planet.
Geologic Time
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An appreciation of the immensity of geologic time is central to understanding
the evolution of the Earth and its life.
○
Earth goes through cycles of
much longer duration than
the human perspective of
time
○
The geologic time scale is
the calendar that geologists
use to date past events in
Earth’s history.
Fig. 1.18, p.
22
Geologic Time and
Uniformitarianism
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Uniformitarianism forms a cornerstone of geology. It
is a fundamental tenet of geology.
○
This principle states that the laws of nature have remained unchanged through time and
thus, that the processes observed today have also operated in the past, though possibly at
different rates.
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Therefore, to understand and interpret geologic events from evidence preserved in rocks,
geologists must first understand present-day processes in rocks.
How does the study of
geology benefit us?
● Understanding how the Earth’s subsystems work will help ensure
the survival of the human species.
● It will help us to understand how our actions affect the delicate
balance between these systems.
End of
Chapter 1