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Changing Earth
Exploring Geology and Evolution
5th Edition
James S. Monroe | Reed Wicander
academic.cengage/com/earthsci
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:
 Atmosphere
 Biosphere
 Hydrosphere
 Lithosphere
 Mantle
 Core
Figure 1.1, p. 5
Evaporation, condensation,
and precipitation transfer
water between atmosphere
and hydrosphere, influencing
weather and climate and
distribution of water.
Plant, animal, and human
activity affect composition of
atmospheric gases.
Atmospheric temperature and
precipitation help to determine
distribution of Earth’s biota.
Atmosphere
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.
Hydrosphere
Plate movement affects size,
shape, and distribution of
ocean basins. Running water
and glaciers erode rock and
sculpt landscapes.
Biosphere
Water helps determine abundance,
diversity, and distribution of
organisms.
Heat reflected from land surface affects
temperature of atmosphere. Distribution
of mountains affects weather patterns.
Plate
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.
Mantle
Supplies heat
for convection
in mantle
Core
Stepped Art
Fig. 1-1, p. 5
Introduction
 The interaction of these subsystems has resulted in
a dynamically changing planet in which matter and
energy are continuously recycled into different forms.
Table 1.1, p. 6
What is Geology?
Geology is the study of the Earth.
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
Table 1.2, p. 6
Geology and the Formulation of Theories
What is a theory?
It is arrived at through the scientific method, which
involves
gathering and analyzing facts
formulating hypotheses to explain the phenomenon
testing the hypotheses
and finally proposing 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
and issues of concern to society
require a basic understanding of
geology.
Figure 1.2, p. 7
How does geology affect our daily lives?
Natural Events
Economics and Politics
Our Role as Decision
Makers
Consumers and Citizens
Sustainable Development
Figure 1.3, p. 8
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. 8
Global Geologic and Environmental
Issues Facing Humankind
 Most scientists would argue that overpopulation is
the greatest problem facing the world today.
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
 The greenhouse effect is the retention of heat
in the atmosphere.
 Mankind 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. 9
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. 9
Origin of the Universe
Did it begin with a Big Bang?
In the Big Bang theory, the universe began
approximately 15 billion years ago.
An extremely dense, hot body of matter
expanded and cooled
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. 1.8c, p. 16
Our Solar System
Its Origin and Evolution
The Solar System formed from a rotating cloud of
interstellar matter about 4.6 billion years ago.
This cloud, upon condensing, collapsed under the
influence of gravity and flattened into a rotating disk.
The sun, planets, and moons formed within this disk.
Figure 1.7, p. 16
Earth
Its Place in Our Solar System
Earth formed from a swirling eddy of nebular
material 4.6 billion years ago, accreting as a solid
body and soon thereafter differentiated into a
layered planet during a period of internal heating.
Fig. 1.9, p. 17
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.
Core
Mantle
Crust.
Fig. 1.10, p. 18
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. 1.10, p. 18
Why Earth is a Dynamic and
Evolving Planet
The Mantle
The mantle surrounds the core and
is divided into:
 a solid lower mantle
 an asthenosphere that behaves
plastically and flows slowly
 a solid upper mantle.
Composed primarily of peridotite, an igneous rock
made of olivine.
Fig. 1-10, p. 18
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. 1.10, p. 18
Why Earth is a Dynamic and
Evolving Planet
The Asthenosphere
 Surrounds the lower mantle
 Behaves plastically and slowly
flows
 Partial melting in the
asthenosphere generates magma
(molten rock) that rises to the
earth’s surface.
Fig. 1.10, p. 18
Why Earth is a Dynamic and
Evolving Planet
The Lithosphere
 The crust and upper mantle make
up the lithosphere which forms the
solid outer layers of the Earth.
Fig. 1.10, p. 18
Why Earth is a Dynamic and
Evolving Planet
Plate Tectonic Theory
 The lithosphere is composed of rigid plates that
diverge, converge, or slide sideways past one
another as they move over the asthenosphere
Fig. 1.11, p. 18
Mid-oceanic ridge
Trench
Ocean
Subduction
Oceanic
lithosphere
Continental
lithosphere
Convection
cell
Cold
Upwelling
Outer
core
Hot
Mantle
Inner
core
Stepped Art
Fig. 1-11, p. 18
Why Earth is a Dynamic and
Evolving Planet
Plate Tectonic Theory
Fig. 1.12, p. 19
Why Earth is a Dynamic and
Evolving Planet
Plate Tectonic Theory
 Volcanoes and earthquakes occur at the
boundaries between the plates.
Fig. 1.13, p. 19
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
 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.
There are three major groups of rocks
Igneous
Sedimentary
Metamorphic
Fig. 1.14, p. 21
The Rock Cycle
Igneous Rocks form from the crystallization
of magma as it cools or the consolidation of
volcanic ejecta.
Granite
Intrusive Igneous Rock
Basalt
Extrusive Igneous Rock
Intrusive igneous rock
crystallizes beneath the
earth’s surface.
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. 1.15 a-b, p. 22
The Rock Cycle
Sedimentary Rocks are typically deposited
in layers formed from:
 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. 1.15 c-d, p. 22
The Rock Cycle
Metamorphic Rocks form from alteration of
other rocks, usually by:
Heat
Pressure
Chemically active fluids
Gneiss
Quartzite
Fig. 1.15 e-f, p. 22
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. 1.14, p. 21
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. 1.16, p. 23
Organic Evolution and the
History of Life
The theory of organic evolution states:
that all living things are related and
have descended with modification from organisms
living in the past.
 Charles Darwin proposed that the mechanism of
natural selection results in survival reproductive age
of those organisms best suited to their environment.
 Fossils, the remains of once-living organisms provide
the 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
 An appreciation of the immensity of geologic time is
central to understanding the evolution of the Earth
and its’ life.
 Geologic time differs from the human
perspective of time
 Earth goes through cycles of much
longer duration than the human
perspective of time
 The immense span of time
encompassed by the Earth's
existence and geological processes
sets geology apart
 The geologic time scale is the
calendar that geologists use to date
past events in Earth’s history.
Fig. 1.17, p. 24
Geologic Time and
Uniformitarianism
 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.
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