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Essentials of Physical Geology

5th EditionReed Wicander | James S. Monroe

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

Organisms break down rockinto soil. People alter thelandscape. Plate movementaffects evolution anddistribution of Earth’s biota.

Plate movement affects size,shape, and distribution ofocean basins. Running waterand glaciers erode rock andsculpt landscapes.

Hydrosphere Biosphere

Fig. 1-1, p. 5

Evaporation, condensation,and precipitation transferwater between atmosphereand hydrosphere, influencingweather and climate anddistribution of water.

Plant, animal, and humanactivity affect composition ofatmospheric gases.Atmospheric temperature andprecipitation help to determinedistribution of Earth’s biota.

Atmosphere

Atmospheric gases andprecipitation contribute toweathering of rocks.

Plants absorb and transpire water.Water is used by people for domestic,agricultural, and industrial uses.

Water helps determine abundance,diversity, and distribution oforganisms.

Heat reflected from land surface affectstemperature of atmosphere. Distributionof mountains affects weather patterns.

Convection cells within mantle contribute to movement of plates (lithosphere) and recycling of lithospheric material.

Core

Supplies heatfor convection

in mantle

Mantle

Plate

Stepped Art

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 factsformulating hypotheses to explain the phenomenontesting the hypothesesand 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 EventsEconomics and PoliticsOur Role as Decision

MakersConsumers and CitizensSustainable Development

Figure 1.3, p. 8

Fig. 1-3, p. 8

629 kgCopper

9203 kgClays

774,000 kgStone, sand,and gravel

311,034 lPetroleum

348 kgZinc

14,359 kgSalt

410 kgLead

>30,615 kgOther minerals

and metals

159,880 m3

Natural gas

14,694 kgIron ore

33,771 kgCement

2438 kgBauxite

(Aluminum)

260,530 kgCoal 8301 kg

Phosphate rock44 gGold

Stepped Art

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

Fig. 1-4, p. 9Stepped Art

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 atmospherictemperatures, which leads to global warming.

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 UniverseHow 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 SystemIts 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

EarthIts 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.

As the earth differentiated, 3 concentric layers formed.

CoreMantleCrust.


Fig. 1.10, p. 18

The core consists of

a small, solid inner region

a larger, liquid, outer portion

Composed of iron and a small amount of nickel.

The Core


Fig. 1.10, p. 18


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.

The Mantle

Fig. 1-10, p. 18


The outermost layer, the crust, is divided into:

thick continental crust

thin oceanic crust

The Crust

Fig. 1.10, p. 18


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 PlanetThe 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 PlanetPlate 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

Fig. 1-11, p. 18

Convectioncell

Innercore

MantleOutercore

Upwelling Hot

Cold

Continentallithosphere

TrenchMid-oceanic ridge

OceanSubduction

Oceaniclithosphere

Stepped Art


Plate Tectonic Theory

Fig. 1.12, p. 19


Plate Tectonic Theory

Volcanoes and earthquakes occur at the boundaries between the plates. Fig. 1.13, p. 19


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 IgneousSedimentaryMetamorphic

Fig. 1.14, p. 21

The Rock CycleIgneous Rocks form from the crystallization

of magma as it cools or the consolidation of volcanic ejecta.

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.

GraniteIntrusive Igneous Rock

BasaltExtrusive Igneous Rock Fig. 1.15 a-b, p. 22

The Rock CycleSedimentary Rocks are typically deposited

in layers formed from:

rock/mineral fragments precipitation of minerals from solution the compaction of plant and animal remains.

LimestonePrecipitation from seawater

ConglomerateForms from river gravels

Fig. 1.15 c-d, p. 22

The Rock CycleMetamorphic Rocks form from alteration of

other rocks, usually by:

Heat PressureChemically active fluids

GneissFig. 1.15 e-f, p. 22

Quartzite

The Rock CycleThe 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 CycleHow 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 andhave 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

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