-~

t
t
........ ..
.....
---- ~
. ~

7
, , r
-!:' ~
,.
.J . .

W,1.
~ ,'.
/ .......
...
'
~ -..
,

~,;. " 'fTF-;i~1:::< ,,.

1{d:J.:_:-\'.J1i1!i'.{- t ·. ·· ·~r-' · :, 'i~
.· · · Setting the Stag~
:" for Learning about
j

the Earth

This sunset over the red cliffs of the Grand Canyon on the Colorado River in Arizona, shows
the Earth System at a glance-air, water, and rock all interacting to produce this stunning
landscape.
r
LEARNIN G 1.1 Thinkin g Like a Geologist
OBJECTI VES
■ Understand challenges 1.1.1 Introduction
geologists face when studying ts
Learning about the Earth is like training to become a detective. Both geologiS and
a body as large and complex as
the Earth
detectives need keen powers of observation, curiosity about slight differences, broadth
scientific understandin g, and instruments to analyze samples. And both ask e
■ Practice basic geologic
same questions: What happened? How? When? Why? Much of the logi~al thinking
reasoning and strategies
• Understand the concept of is the same, but there are big differences between the work of a detecuve and th_att
the Earth System and begin of a geologist. A detective's "cold" case may be 30 years old, but "old" to a geologiS
to learn how energy and means hundreds of millions or billions of years. To a detective, a "body" is a human
matter are connected through body, but to a geologist, a "body" may be a mountain range or a continent. Eyewit-
geologic cycles nesses can help detectives, but for most of Earth history there weren't any humans
• Use concepts of dimension, to witness geologic events. To study the Earth, geologists must therefore develop t
scale, and order of magnitude strategies different from those of other kinds of investigators . The overall goal of this
to describe the Earth
manual is to help you look at the Earth and think about its mysteries like a geologist.
■ Review the materials and
To help you begin thinking like a geologist, let's start with a typical geologic
forces you will encounter while
studying the Earth mystery. Almost 300 years ago, settlers along the coast of Maine built piers (like the
(
modern pier shown in FIG. 1.1) to load and unload ships. Some of these piers are
■ Learn how geologists discuss
the ages of geologic materials now submerged to a depth of 1 meter (39 inches) below sea level.
and events and how we
measure the rates of geologic ·
processes FIGURE 1.1 Subsidence along the coast of Maine.

■ Become familiar with the types

of diagrams and images used
by geologists

MATERIA LS
NEEDED
■ Triple-beam or electronic
balance
■ 500-ml graduated cylinder
■ Clear plastic ruler with
divisions in tenths of an inch
and millimeters (included in
the Geo Tools section at the
back of this manual)
■ Calculator
■ Compass

To~rists might not think twice about this phenomen on before heading for a lob-
ster dmner at the local restaurant, but a geologist would want to know what caused
the submerge~ ce an_d how rapidly the pier was submerged . How would a geologist
go about tacklmg this problem? Exercise 1.1 outlines the problem and shows some
of the basic geologic reasoning needed to get answers to the questions raised above.
At the same time, this exercise will be your first of many opportunit ies to see that
geologists solve real-world problems affecting real people.

CHAPTER 1 SETTING THE STAGE FOR LEARNING ABOUT THE EARTH

 EXERC ISE 1.1 Submergence Rate along the Maine Coast

Name: Section: _ _ _ __
Course-:-:----------------------- Date: _ _ _ _ __

1715

ocean's surface today. Because we weren't

The figure on the left illustrates a pier whose walkway sits 1 meter below the
logists often do this to make estimate s. So
there when it was built 300 years ago, we have to make some assumpt ions-geo
high tide, as many are built today (illustrated
let's assume that the pier's walkway was originally built 1 m above sea level at
With these assumpt ions, calculating the rate
in the figure on the right), and that submerg ence occurred at a constan t rate.
of submerg ence for the past 300 years become s simple arithmetic.
_ _ _ _ m) divided by the total
(a) The rate of submerg ence is the total change in the elevation of the pier(_ _
cm/yr. (Remem ber, 1 m = 100 cm.)
amount of time involved (_ _ _ _ _ years) and is therefore
Now conside r a problem this equation might solve:
is 50 cm above the high-wa ter
(b) A local restaura nt owner is considering the purchase of a pier, whose walkway
walkways less than 30 cm above the
mark, for use in outdoor events. The owner has been advised that piers with
and very high tides. If submerg ence
high-wa ter mark should be avoided because they can be flooded by storms
ter mark is less than 30 cm from
continu es at the rate you calculate d, how many yea.rs wi ll pass before the high-wa
the base of the walkway? ____ __ yea:·s

? What Do You Think Now it's time to try really thinking like a geolo-
E gist. Given your answers to question s (a) and ( b), wou ld you recomm end that
sheet
the restaura nt owner purchas e this pier? In a sentenc e or two, on a separate
should
of paper, explain why. Then describe another issue that you think the owner
investig ate before making a decision .

Congra tulation s! You've just tackled your first problem as a geologist-in-training.

sub-
A veteran geologist, however, would also want to explain why the piers were
try to come up
merged . When faced with a problem like this, geologists typically
explana-
with as many explana tions as possible. For example, which of the following
tions could accoun t for the submer gence?
D Sea level has risen.
□ The land has sunk.
□ Both sea level and land have risen, but sea level has risen more.
□ Both sea level and land have sunk, but the land has sunk more.
-
If you think all four choices might be'"right _(~<?filctly!), you realize that explain
cated than it seemed at
ing submer gence along the Maine coast may be more compli
ements .
first. To find the answer, you need more data-m ore observa tions or measur 3
 rgenc e is restric ted to Mai
One way to obtain more data would be to see if subme neb-,
s world wide. As it turns out ,SU
or to the east coast of North Ameri ca, or if it occur
the first choice above (sea-le vel
merge nce is observ ed world wide, sugge sting that
necess arily the only one.
rise) is the most proba ble expla natio n-but not
as: "Whe n did the subme r-
With even more data, we could answe r questi ons such
rate?" Maybe all the subme rgenc e
gence happe n?" "Did sea level rise at a consta nt
and then stopp ed. Or perha ps
occur red in the first 100 years after the pier was built
ly, we may not be able to answe r
it began slowly and then accele rated. Unfor tunate
detect ives who always get the bad
all of these questi ons becau se, unlike televis ion
must often live with uncert ainty.
guys, geolog ists don't always have enoug h data and
the Earth .
We still do not have answe rs to many questi ons about

1.1.2 The Scientific Met hod

Like all scient ists (and most peopl e trying to find
identi fied), geolog ists follow a logica l proce ss that
answe rs to probl e m s th ey have
you are proba bly fa m ifo, r with:
•
in Exerc ise 1. 1 and will d o :;o m a ny
the scientific metho d. You did so instinc tively
d begin s with o bse rvati o m of
times throu ghout this course . The scient ific metho
1. 1, the obser vation that a colo nial
Earth featur es or proce sses-s uch as, in Exerc ise
the scient ific metho d are illus-
pier is now below sea level. The steps that const itute
trated schem atical ly in FIGURE 1.2 .

FIGU RE 1. 2 The scientific method.

1.0bse rve
Begin by looking at an
Earth feature or process.

2. Recognize
that a problem or question
exists.

3. Collect data to make

sure that the
observation is valid.

4. Hypothesis
Propose a tentati ve answer or
answers.

Sa. Design test of

hypothesis;
predict result.

6a. Test does not support

hypot hesis
Revise the hypoth esis to fit
new data or propos e a new
Sb. Test the hypot hesis
Perform a test, experim ent, or
I
6b. Test supports one o-;-i

Don~; ~;~i~~ :~~~~ ~onal j

tests to be sure that you have
the answer.
hypothesis. more observ ations and
measu remen ts.
"--- ----.--

4 CHAPTER 1 THE EART H

SETTING THE STAGE FOR LEAR NING ABOU T
STEP 1 Observ E th c
e an ar 1eature or process (e.g., the submerged pier).
STEP 2 Reco . th . .
~ize at a problem eXJsts and define the problem by asking questions
about it. Usually the problem is that we don't understand how what we've ob-
served came to be: Why was the pier in Exercise 1.1 submerged? By how much
· b een submerged? How fast did submergence take place? Was the
has th e pier
rate of submergence constant or sporadic? We respond with the steps that follow.
STEP
3 ~ollect more data to (a) confirm that the observation is valid and (b) shed
hght on what is going on. In Exercise 1.1, for instance, we determined that it
isn't just one pier being submerged, but many along the Maine coast.
STEP 4 Propose tentative answers to our questions, called hypotheses (singular,
hypothesis). Some versions of the scientific method suggest proposing a single
hypothesis, but when we first look at problems, we usually find that more than
one hypothesis can explain our observations. We therefore come up with as
many hypotheses as we can-a practice called multipl.e working hypotheses.
STEP 5 Test the hypotheses by getting more data. The new information may support
some hypotheses, rule out others, and possibly lead to new ones. Some of
this testing can be done in a classic laboratory experiment, but there are also
other types of tests, such as field trips to gain additional information, detailed
measuremen ts where there had been only eyeball estimates, and so forth .
STEP 6 Based on the new information, reject or modify those hypotheses that don't
fit, continue testing those that do, and propose new ones as needed to in-
corporate all the information. If your test supports a hypothesis, continue to
perform additional tests to further verify your result.

Continue cycling through steps 4, 5, and 6 as needed until a single hypothesis

remains. Then, to be sure, continue testing it. If this hypothesis survives years of fur-
ther testing, it is considered to be a theory. Nonscientists often don't understand the
difference between hypothesis and theory; when they say, "Oh, that's just a theory,"
they really mean, "That's just a hypothesis"- a possibl,e explanation that has not yet
been proved. A theory has been tested and proved. Some theories with which you
may be familiar are the theory of evolution. the germ theory of disease, and Einstein's
theory of relativity. And during this course you wil i bi~cmne very familiar with plate
tectonics theory, which explains how the Earth 's major foat;:,res fo rm and change.

1.2 An Introduction to the Earth System

Now that you know how geologists study things, let's look at what.we study. The
Earth is a dynamic planet. Unlike the airless, oceanless Moon, which has remained
virtually unchanged for billions of years, the Earth has gases in its atmosphere and
water on its surface that are in constant motion and cause the solid planet beneath
them to change rapidly (in relation to geologic time, that is). Modem scientists
envisage an Earth System that includes all of the Earth's materials-g ases, liquids,
solids, and life forms-and the energy that drives their activity. The first step in
understand ing the Earth System is to understand the nature of its matter and energy
and how they interact with each other.

1.2.1 The Nature of Matter

Matter is the "stuff' of which the Universe is made; we use the term to refer to any
material on or in the Earth, within its atmosphere , or within the broader Universe
in which the Earth resides. Geologists, chemists, and physicists have shown that
matter consists of ninety-two naturally occurring elements and that some of these

1.2 AN INTRODUCTION TO THE EARTH SYSTEM

 TABLE 1.1 Basic definiti ons
lly into other
• An element is a substanc e that cannot be broken down chemica
substances.
that element is
• The smallest piece of an element that still has all the propertie s of
an atom .
the smallest
• Atoms combine with one another chemica lly to form compounds;
possible piece of a compoun d is called a molecule . f
• Atoms in compoun ds are held together by chemical bonds.
a compou nd.
• A simple chemical formula describes the combina tion of atoms in
For example, the formula H O shows that a molecule of water contains two atoms 4
2
of hydrogen and one of oxygen.

elemen ts are much more abunda nt than others. Keep the definiti ons in
TA S~E 1.1

in mind as you read further about the compos ition of matter.

Matter occurs on the Earth in three states: solid, liquid, and gas. Atoms in
solids,
al bonds. As a result,
such as mineral s and rocks, are held in place by strong chemic
ough that
solids retain their shape over long periods . Bonds in liquids are weak en
of their
atoms or molecu les move easily, and as a result, liquids adopt the shape
togethe r at all, so a gas
contain ers. Atoms or molecu les in gases are barely held
one state to
expand s to fill whatev er contain er it is placed in. Matter change s from
to produc e
anothe r in many geologi c process es, as when the Sun evapor ates water
or when lava freezes to become
water vapor, or when water freezes to form ice,
solid rock.
and the
We describ e the amoun t of matter in an object by indicat ing its mass
. The more mass packed into
amoun t of space it occupie s by specify ing its volume
density
a given volume of matter, the greater the density of the matter. You notice
of rock of
differen ces every day: it's easier to lift a large box of popcor n than a piece
mass packed into
the same size because the rock is much dense r-it has much more
the same volume and therefo re weighs much more.

1.2.2 Distribution of Matter in the Earth System

(FIG. 1.3a).
Matter is stored in the Earth System in five major realms, or reservo irs
sed of about
Most gases are in the atmosp here, a semi-tr anspare nt blanke t compo
water vapor
78% nitroge n (N 2 ) and 21 % oxygen ( 0 2), as well as minor amoun ts of
all liquids
(H 20), carbon dioxide (CO 2), ozone (0 3), and methan e (CH 4). Nearly
rivers, lakes, and ground wa-
occur as water in the hydros phere- the Earth's oceans ,
makes up
ter, which is found in cracks and pores beneat h the surface . Frozen water
surface s of lakes or
the cryosph ere, which include s snow, thin layers of ice on the
oceans , and huge masses of ice in glacier s and the polar ice caps.
tric layers
Geolog ists divide the solid Earth, called the geosph ere, into concen
is relative ly
like those in a hard-bo iled egg (FIG. 1.3b). The outer layer, the crust,
e about
thin, like an eggshe ll, and consist s mostly of rock. We say mostly becaus
2% of the crust and mantle has melted to produc e liquid materi al called magma
the mantle ,
(known as lava when it erupts on the surface ) . Below the crust is
of the Earth's
which also consist s mostly of differe nt kinds ofrock ; it contain s most
central part
volume , just as an egg white contain s most of an egg's volume . The
core consist s
of the Earth, compa rable to the egg yolk, is the core. The outer
iron-ni ckel
mostly of a liquid alloy of iron and nickel, and the inner core is a solid
, you will
alloy. Human s have never drilled throug h the crust; during this course

CD 1 l= ARNIN r, AA() I JT T l-I I= I= AR TI-I

FIGU RE 1.3 The Earth System.
The a1n10 splwn, : Earlh' s
Cryos plwn•: C:onlinl'nlal
gaseo us l'll\'l'lo pl·
and n1ou111ain g:laciC'rs.
polar ,ea ic-c

\' .... ' ~

• ' • • •
I
. .

,..,. , ~ 1' ~-.'ftt,,J- ,_ .::·.:, e ~ •

' •»"\~v'.:~ :.,~ --~ ~ , •

. •;..--+• ;;.I • 'li.~lf o " -
,...,,_ "'"·~ *
•• <. ~-- ... ,(i
'.~~~~: ~•-:,:
Hydro sphen ':
Ocean s. rivers~ ~- -~ ~~ __ Biosph l're:
lakes. 11ndl'rgro11nd wall·r· All li\'ing lhings
the hard-boiled egg
(a) The Earth's major reservoirs of matter. (b) A simple image of the Earth's internal layering and
analogy for its pattern of layers.

ed, how thick those layers are, and

learn how we figur ed out that our plane t is layer
what they are made of.
low-density rocks , make up abou t
Cont inent s, which are comp osed of relatively
crust is covered by the oceans. Oce-
30 % of the crust. The rema ining 70% of the
nenta l crust. Thre e types of solids
anic crust is both thinn er and dens er than conti
aggregate of minerals and rocks
are foun d at the Earth 's surface: bedrock, a solid
d mineral grains such as bould ers,
attac hed to the Earth 's crust ; sediment, unatt ache
fied by interactions with the atmos-
sand , and clay; and soil, sedim ent and rock modi
ort plant life.
pher e, hydr osph ere, and organisms that can supp
nism s-ext ends from a few kilometers
The bios pher e-th e realm of living orga
above. Geologists have learn ed that
below the Earth 's surfa ce to a few kilometers
rtant parts of the Earth System
orga nism s, from bacte ria to mammals, are impo
sses by exch angin g gases with the
beca use they contr ibute to many geologic proce
ing rock into sedim ent, and play-
atmo sphe re, abso rbing and releasing water, break
to soil.
ing majo r roles in conv ertin g sedim ent and rock
to anot her is called a flux. Fluxes
The mov emen t of materials from one reservoir
rain is a flux in which water moves
happ en in many geologic processes. For example,
of flux depe nd on the materials, the
from the atmo sphe re to the hydr osph ere. Rates
cases , a material moves amon g sev-
reser voirs , and the processes involved. In some
We call such a path a geologic cycle .
eral reservoirs but even tually retur ns to the first.
s, inclu ding the rock cycle (the
In this class you will learn abou t several geologic cycle
her) and the hydrologic cycle (the
mov emen t of atom s from ·one rock type to anot
from the othe r reservoirs) . Exercises
mov emen t of wate r in the hydr osph ere to and
ibuti on and fluxes of matter.
1.2 and 1.3 will help you unde rstan d the distr

1.2.3 Energy in the Earth System

of how dyna mic the Earth is: rivers
Natu ral disas ters in the head lines remi nd us
nic ash bury villages; earth quak es
flood cities and fields; muds lides , lava, and volca
al regio ns. How ever, many geolo gic
topp le build ings; and hurri cane s ravage coast
s, such as the mov emen t of ocea n
proc esses are muc h slower and less dang erou

SYSTEM
1.2 AN INTRODUCTION TO THE EARTH
 EXERC ISE 1.3
Selecte d Fluxes Involving the Hydrologic Cycle (continued)
Name: Section: _ _ _ __
Course,-::---------------------- Date· _ _ __

A lake freezes

Plant roots absorb water from the soil

Clouds form in the sky

Steam erupts from a volcano

by
current s and the almost undetec table creep of soil downhill. All are caused
energy, which acts on matter to change its charact er, move it, or split it apart.
which
Energy for the Earth System comes from (1) the Earth's internal heat,
is left over
melts rock, causes earthqu akes, and builds mounta ins (some of this heat
d today by radioac tive
from the formati on of the Earth, but most is being produce
on the
decay); (2) externa l energy from the Sun, wh ich warm:.; air, rocks, and water
h 'f, gi:aYity. Heat and gravity, working
Earth's surface; and (3) the pull of the Ear~
indepen dently or in combin ation, drive mos t geologi c p;-occss es.
-
Heat energy is a measur e of the d egree to whid1 atoms or molecu les in matter
in an oven, for exam-
includi ng those in solids- vibrate . When you h eat someth ing
energy
ple, the atoms in the materia l vibrate faster and move farther apart. Heat
flux of matter from
drives the change of matter from one state to another and the
ice causes
one reservo ir of the Earth System to another. For exampl e, heating of
heating of water causes
melting (solid ➔ liquid; cryosph ere ➔ hydrosp here) and
vibra-
evaporation (liquid ➔ gas; hydrosp here ➔ atmosp here). Cooling slows the
or freezing
tion, causing condensation (gas ➔ liquid, atmosphere ➔ hydrosp here)
e for the
(liquid ➔ solid, hydrosp here ➔ cryosph ere). Exercis e 1.4 explore s evidenc
sources of the heat energy involve d in geologi c process es.
force
Gravity, as Isaac Newton showed more than three centuri es ago , is the
of this force
of attracti on that every object exerts on other objects. The strengt h
the objects are to one
depend s on the amoun t of mass in each object and how close
anothe r, as express ed by the equatio n
m1 X m2
G= k - - -
d2

1.2 AN INTRODUCTION TO THE EARTH SYSTEM

r EXER CISE 1.4 Sources of Heat for Geologic Processes

Name: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Course:
_ _ _ _ __
-- -- -- -- -- -- -- -- -- -- --
.
Some of t h e heat t h at aff ects geologic
Section: _ _ _ __
Date: _ _ _ _ _ __
proces ses comes from the Sun and some comes from •insi·d the Earth What role ..
••
does each of these heat source s play in Earth processes? e ·

(a) If you take off your shoes on a beach and walk on it on

a hot, sunny day, is the sand hot or cold? Why?

(b) Now, dig down in the sand just a few inches . What
do you feel now, and why?
..
(c) What do these observ ations sugges t about the depth
to which heat from the Sun can penetr ate the Ear th ?

••
••
(d) Based on this conclu sion, is the Sun's energy or the
Earth's internal heat the cause of melting of rock wi th in th
Earth? Explain. e

•
where G = force of gravity; k = a gravitational const ant;
two objects; and d = the distance betwe en them.
The great er the masses of the objec ts and the close r
m1 and m2 = the masse s of

they are, the stron ger the

•
j
'-
'4ii
gravit ationa l attrac tion betwe en them. The small er the
masse s of the objec ts and ■
the farthe r apart th ey are, the weake r the attrac tion.
The Sun's enorm ous mass
produ ces a force of gravil ) ntfa:in:,i to hold the Earth
and the other plane ts of C
the Solar System in thei r orbits . T he Earth 's gravi tation
al force is far less than
the Sun's , but it is stron g enoug h to hold the Moon
in its orbit, hold you on the
Earth 's surfac e, cause rain or volca nic ash to fall, and
enabl e rivers and glacie rs
to flow.
The pull of the Earth 's gravity produ ces a force called
press ure. For exam -
ple, the pull of gravity on the atmo spher e creat es
a press ure of 1.03 kg/ cm2
(14.7 lb/in 2) at sea level. This mean s that every squar
e centi mete r of surfa ce of
the ocean , the land, or your body is affec ted by a
press ure of 1.03 kg. We call
this amou nt of press ure 1 atmo spher e (atm) . Scien
tists comm only speci fy pres-
sures using a unit called the bar (from the Gree k barros
, mean ing weig ht), wher e
1 bar= 1 atm.
Two kinds of press ure play impo rtant roles in the hydro
spher e and geosp here,
respectively. Hydrostatic pressure, press ure cause d by
the weigh t of overl ying water ,
increa ses with depth in the ocean and can crush
a subm arine at great depth s.
Lithostatic press ure, press ure cause d by the weigh
t of overl ying rock, incre ases
with depth in the geosp here and is great enou gh in
the uppe r mant le to chan ge
the graph ite in a penci l into diam ond. Rock s weigh
a lot more than air or water ,
so the pull of gravity cause s lithos tatic press ure to
incre ase much faster with dis-
tance than eithe r atmo spher ic or hydro static press
ure-s o much so that the stan-
dard meas ure of lithos tatic press ure is the kilobar (kbar
), equiv alent to 1,000 times
atmo spher ic press ure.

10 CHAP TER 1 SETTING THE STAGE FOR LEARNING ABOUT THE

EARTH
12
· -4 Tempera tures and Pressures in the Earth's Crust
th
Bo temperatur e and lithostatic pressure increase with depth in the Earth, and
th
e temperatur e in the core is estimated to be about 5,000°C. The increase in
temperatur e with depth, called the geothermal gradient, ranges from 15°C to
S0°C per kilometer in the upper 10 km of the crust, with an average beneath
th e continents of about 25°C/km. The increase in pressure with depth, called
th e geobaric gradient, is about 1 kbar for every 3.3 km of the crust. Exercise 1.5
explores conditions at varying depths in the crust based on the geothermal and
geobaric gradients.

EXERCISE 1.5 Temperature-Pressure Conditions in the Crust

Section: _ _ _ __
Name:
----- ----- ----- ----- --- Date: _ _ _ _ __
Course:---------- ------------

(a) Draw lines representing the minimum (15°C/km), maximum (50°C/km), and average (25°Cfkm) geothermal
gradients on the diagram below, using a different color for each. Assume for this exercise that the temperature at the
Earth's surface is 0°C.
Pressure (kbar)
.-...,..........:;3-r--.--.--4r-~,---,---,
0 o;..._-.---,-........._;..----.--,,--.,....-..;:2___,_,

10 .___,__.. ....__,___ _._~~-~- ~~~~---- -~~-~-~~ ~

0 so 100 150 200 250 300 350 400 450 500
Temperature (°C)

(b) The deepest mine on the Earth penetrates to a depth of about 2 km. Using the geothermal gradients you just drew,
the
what range of temperatures would you expect halfway down the mine shaft? _ _ _ _ _ At the bottom of
mine? _ _ _ __
an
(c) Using the pressure scale at the top of the diagram, draw the average geobaric gradient in a fourth color, with
increase of 1 kbar per 3.3 km.

(d) What will the pressure be at the lowest level of the mine? _ _ _ _ _ kbar
(e) What will the pressure be 8 km below the surface? _ _ _ _ _ kbar
(f) What will temperature and pressure conditions be at
• 5 km, assuming an average geothermal gradient? _ _ _ __
• 4 km, assuming the minimum geothermal gradient? _ _ _ _ _ The maximum geothermal gradient? _ _ _ _ __

1.2 AN INTRODUCTION TO THE EARTH SYSTEM 11

 1.3 Units for Geologic Measurem ent
Beiore we b egm • to examine the components of the Ear th sYstem scientifically,
.
it is
. We
imp orta nt to b e familiar with the units of measurement use d to quantify them.
1 • · f: when studymg th e
can t 1 en examine the challenges of scale that geologi sts ace
Earth and the atoms of which it is made.

1.3.1 Units of Length and Distance

· m
Peop Ie h ave struggled for thousands of years to descri b e size · a precise wa·y with
nd
widely accepted standard units of measurement. Scientists everywhere a people
in nearly all countries except the United States use the metric ~tern to mea~-
ure length and distance. The largest metric unit of length is the kilometer (kr:r1; ,
which is divided into smaller units: 1 km = 1,000 meters (m); 1 m = 100 centim-
eters (cm); 1 cm = 10 millimeters (mm). Metric units differ from each other by
a factor of 10, making it very easy to convert one unit into another. For example,
5 km = 5,000 m = 500,000 cm = 5,000,000 mm. Similarly, 5 mm = 0.5 cm = 0.005
m = 0.000005 km .
The United States uses the U.S. customary system (called the English system
until Great Britain adopted the metric system) to describe distance . Distances
are given in miles (mi) , yards (yd), feet (ft) , and inches (in), where 1 mile =
5,280 feet; I yard = 3 feet; and I foot = 12 inches. A.J3 scientists, we use metric
units in this book, but when appropriate, U.S. customary equivalents are also
given (in parentheses).
Appendix I.I, at the end of this chapter, provides basic conversions between U.S.
customary and metric units.

1.3.2 Other Dimensions, Other Units

Length and distance are just two of the dimensions of the Earth that you will
examine during this course. Other units are used to describe other aspects of the
Earth, its history, and its materials: units of time, velocity, temperature, mass, and
density.
Time is usually measured in seconds (s), minutes (min) , hours (h), days (d),
years (yr), centuries (hundreds of years), and millennia (thousands of years). A
year is the amount of time it takes for the Earth to complete one orbit around
the Sun. Because the Earth is very old, geologists have to use larger units of
time: a thousand years ago (abbreviated Ka, for kilo-annum), a million years ago
(Ma, for mega-annum), and a billion years ago (Ga, for giga-annum). The for-
mation of the Earth 4,560,000,000 years ago can thus be expressed as 4.56 Ga,
or 4,560 Ma.
Velocity, or the rate of change of the position of an object, is described by units
of distance divided by units of time, such as meters per second (m/ s) , feet per sec-
ond (ft/ s), kilometers per hour (km/ h), or miles per hour (mph). You will learn
later that the velocity at which geologic materials move ranges from extremely slow
(mm/ yr) to extremely fast (km/ s).
Temperature is a measure of how hot an object is relative to a standard. It
is measured in degrees Celsius (°C) in the metric system and degrees Fahren-
heit (°F) in the U.S. customary system. The reference standards in both systems
are the freezing and boiling points of water: 0°C and l00°C or 32°F and 212°F,
respectively. Note that there are 180 Fahrenheit degrees between freezing and
boiling, but only 100 Celsius degrees. A change of 1°C is thus 1.8 times larger

12 CHAPTER 1 SETTING TH E STAG E FOR LEARNING ABOUT THE EA RTH

 th
t an a change of 1 °F (180° /100°). To convert Fahrenheit to Celsius or vice versa,
see Appendix 1.1 .
. Mass refers to the amount of matter in an object, and weight refers to the force
With which O ne O b.~ect 1s· attracted to another. The weight of an object on the Ear th
therefore
. depe n d s not onIy on its ·
· mass, but also on the strength of the Earth' s gravi-
tat:J.onal field. Objects that have more mass than others also weigh more than others
on_th e Earth because of the force of the Earth's gravity. But whereas the mass of an
object remains the same whether it is on the Earth or on the Moon, the object weighs
less on the Moon because of the Moon's weaker gravity.
Grams and kilograms (1 kg = 1,000 g) are the units of mass in the metric sys-
tem; the U.S. customary system uses pounds and ounce~ (I lb= 16 oz). For those
who don't read the metric equivalents on food packages, I kg = 2.2046 lb and
1 g = 0.0353 oz.
We saw earlier that the density (8) ofa material is a measure of how much mass
is packed into each unit of volume. Density, a property useful in studying minerals
3
and rocks, is generally expressed in units of grams per cubic centimeter (g/ cm ) •
We instinctively distinguish unusually low-density materials such as Styrofoam and
feathers from low-density materials such as water (8 = I g/cm 3) and high-density
materials such as steel (8 = ~7 g/ cm 3) because the very low-density materials feel
very light for their sizes and the high-density materials feel unusually heavy for their
sizes (FIG. 1.4).

FIGURE 1. 4 Weights of materials with different densities.

High density Low density Very low density
(Steel) (Y-/ater) (Feathers)

To measure the density of a material, we need to know its mass and volume.
Mass is measured with a balance or scale, and the volumes of regular geomet-
ric shapes such as cubes, bricks, spheres, or cylinders can be calculated from
simple formulas. For example, to calculate the volume of a bar of gold, you
would multiply its length times its width times its height (FIG. 1.Sa). But rocks
rarely have regular geometric shapes; more typically, they are irregular chunks.
To measure the volume of a rock (or another irregular object), submerge it in
a graduated cylinder partly filled with water (FIG. 1.Sb) . Measure the volume of
the water before the rock is added and then with the rock in the cylinder. The
rock displaces a volume of water equivalent to its own volume, so simply subtract
the initial volume of the water from that of the water plus the rock to obtain the
volume of the rock. The density of a rock can then be calculated simply from the
definition of density: density = mass -;-- volume. Exercise 1.6 provides practice
in determining density.

1.3 UNITS FOR GEOLOGIC MEASUREMENT

 FIGURE 1.5 Measuring the volume of materials.

Second reading

Len
THeight
j_

rdth
~
f h lid is the volume of
(a) For a rectangular solid, volume = length x width x height. ( b'1 For an irregular solid, the volume O t e so h d'ff
d 1· d which is t e I erence
the liquid it displaces in a graduate cy in er,
between the first and second readings.

EXERCISE 1.6 Measuring the Density of Earth Materials

Name: Section: _ _ _ __
-----------------------
Course: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Date: _ _ _ _ __

(a) Determine the density of a liquid provided by your instructor using a balance, a graduated cylinder, and a container
of the liquid. Consider how to go about this, and then do it. Make sure to provide the proper units with your answer.
The density of the liquid is _ _ _ __

(b) Your instructor will give you samples of granite, a light-colored rock that makes up a large part of the continental
crust, and basalt, a dark-colored rock that makes up most oceanic crust and the lower part of the continental crust.
Determine their densities, and record your answers with units included.
• What is the density of granite? _ _ _ __
• What is the density of basalt? _ _ _ __
• If the volume of continental crust is half granite and half basalt, what is its density? _ _ _ _ __

(c) Modern ships are made of steel, which has a density of about 7.85 g/cm 3-much greater than the density of water
that you just calculated. So how can these ships float?

1.3.3 Some of the Earth's "Vital Statistics"

Now that you are familiar with some of the units used to measure the Earth, we can
look at some of the planet's "vital statistics."

■ Place in the Solar System: Among the eight Solar System planets, the Earth is the
third from the. Sun. It is one of four. terrestrial planets , along wi· th Mercury, ·uvenus,
and Mars, whICh are made ofrock, m contrast to thejovian planets Uup1·ter, Saturn,
Uranus, and Neptune), which are mostly made of methane and a mmon1a · m• e1t. h er
gaseous or frozen forms.
■ The Earth's orbit: The Earth takes 1 year (365. 25 days , or 3 •15 x 101 secon d s ) to
complete one orbit around the Sun.

14 CHAPTER 1 SETTING THE STAGE FOR LEARNING ABOUT THE EA RTH

 • Rotation - Th e Eart h rotates about its axis in 1 day (24 hours or 86,400
·
seconds) .
• Shape· The E h is · l
d .· art a most, but not quite, a sphere. The Earth's rotation pro-
uces a~shght bulge t h O ") ·
2I km . a t e equator: its equatorial radius of 6,400 km ( ~4,00 m1 1s
( 15 mi) longer than its polar radius.
• Temperature: The Earth's average surface temperat ure is l5°C (59°F) ; its core
tempera ture is about 5,000oC ( ~9,000oF).
• Highest mountain : The peak of Mt. Everest is the Earth's highest point, at 8,850 m
29
< ,o 35 ft) above sea level (and is still rising!).
• Average ocean depth: 4,500 m (14,700 ft).
. • Deepest part ofocean floor:The bottom of the Mariana Trench in the Pacific Ocean
is the deepest point on the ocean floor, at 11,033 m (35,198 ft) below sea level.

1.4 The Challenges of Studying an Entire Planet

Problem s such as submerg ence along the Maine coast pose challenges to the geolo-
gists who are trying to solve them and the students who are trying to learn about the
Earth. These challenge s require us to
■ understa nd the many kinds of materials that make up the Earth and how
they behave.
■ be aware of how energy causes changes at the Earth's surface and beneath
it.
■ consider features at a wide range of sizes and scales-fr om the atoms that
make up rocks and minerals to the planet as a whole.
■ think in four dimensio ns, because geology involves not just the three
dimensio ns of space but also an enormou s span of time.
■ realize that some geologic processes occur in seconds but others take
millions or billions of years, and are so slow that we can detect them only
with very sensitive instrume nts.
The rest of this chapter examines these challenge s an d hc ,v geologists cope with
them. You will learn basic geologic terminol ogy and h ow to use: too1s of observat ion
and measure ment that will be useful througho ut you..- ge(,k1; ic studies. Some con-
cepts and terms may be familiar from previous science classes.

1.4.1 The Challenge of Scale

Geologists deal routinely with objects as incredibly small as atoms and as incredibl y
large as the Appalac hian Mountai ns or the Pacific Ocean. Sometim es we have to
look at a feature at different scales, as in FIGURE 1.6, to understa nd it fully.
One of the challeng es we face in studying the Earth is a matter of perspec-
tive: to a flea, the dog on which it lives is its entire world, but to a parasite inside
the flea, the flea is its entire world. For most of our history, humans have had a
flea's-eye view of the Earth, unable for many centuries to recogniz e even the most
basic facts about our planet: that it is nearly spherical , not flat, and that it isn't the
center of the Universe , or even the Solar System. Nor that as we sit at a desk, we
are actually moving thousand s of miles per hour because of the Earth's rotation
and orbit around the Sun. Exercise 1. 7 provides some perspect ive on the matter
of perspect ive.
We must cope with enormou s ranges in scale involving size (atoms to sand grains
to planets) , tempera ture (below 0°C in the cryosphe re and upper atmosph ere to
more than l,000 °C in some lavas to millions of degrees Celsius in the Sun), and

1.4 THE CHALLENGES OF STUDYING AN ENTIRE PLANET 15

 Fl Gu RE 1.6 The white cliffs of Dover, England, seen at two differen
-.. -
t scales.

i
j

(a) The towering chalk cliffs of Dover, England stand up to (b) Microscopic view of th~ ~halk (plankton shells) that the
110 m (350 ft) above the sea. cliffs are made of. The eye of a needle gives an idea of the
th
minuscule sizes of the shells that make up e cliffs.

EXER CISE 1.7 The Challenge of Perspective and Visualizing Scale

Section: _ _ _ _ __

I Name: _ _ _ _ _ _ __
Course: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
The enormous differen ce in size between ourselves and our planet
·
and makes understanding major Earth processes challenging. To
Date: _ _ _ _ __

gives us a limited perspective on large-sc~le f~aturefs

h' h II nge, conside r the relative sizes o
appreci·ate t 1s c a e
familiar objects (use Append ix 1.1 for convers ions):

E
N

1mm

12.800 kr:,
lm

Relative sizes of a dog and a flea. Relative siz:Es of the Earth and a tall geologist.

(a) Assume that a flea is 1 mm long and that a dog is 1 m long.

how long is the flea in inches? _ _ _ _ _ _ inches
• To relate this to our U.S. custom ary system of measurement,
_
• How many times larger is the dog than the flea? _ _ _ _ _
_
• How long is the scale bar representing the flea? _ _ _ _ _
dog and the flea were shown at the same scale?
• How long would the bar representing the dog have to be if the

(b) Now, think about the relative dimensions of a geologist and the Earth.
_ __
• How many times larger than the geologist is the Earth? _ _
drawn at the same scale as the geologi st? Give you r
• How large would the drawing of the Earth have to be if it were
_ _ _ _ miles
answer in kilometers and in miles. ___ ___ km _ _
the Earth, does a flea have a better unders tand in of a
• Based on the relative sizes of flea and dog versus human and g
dog than a human has of the Earth? Or vice versa? Explain .

16 CHAPTER 1 SETTING THE STAGE FOR LEARNING ABOU T THE EARTH

 I I
velocity (conti ts .
nen movmg at 2 cm/ yr to tsunamis moving at hundreds of kilome-
ters ~er ~our to light traveling at 299,792 km/ s).
Sc1ent1sts som ti d . . . .
. e mes escnbe scale m approximate terms and somellmes more
precisely Fo
· r examp1e, the terms mega-seal£, meso--seak, and micro-seal£ denote enor-
mous mode t d .
' ra e, an llny features, respectively but don't tell exactly how large or
th
small ey are because they depend on a scientist's frame of reference. Thus, mega-
sea/,e to an astron omer m1g · ·
· distances,
· h t mean mtergalacllc · 1t
but to a geo1ogist · may
me~n the size of a continent or a mountain range. Micro-seal£ could refer to a sand
gram, a bacterium, or an atom. Geologists often express scale in terms that specify the
frame of reference, such as outcrop-seal£ for a feature in a single roadside exposure of
rock (an outcrop), or hand-specimen-scakfor a rock sample you can hold in your hand.
Scientists can describe objects more precisely as differing in scale by orders of
magnitude. A feature an order of magnitude larger than another is 10 times larger;
a feature one-tenth the size of another is an order of magnitude smaller. Something
100 times the size of another is two orders of magnitude larger, and so on. We also
use a system of scientific notation based on powers of 10 to describe incomprehen -
1
sibly large or small objects. In scientific notation, 1 is written as 10°, 10 as 10 , 100 as
2
10 , and so on. Numbers less than 1 are written with negative exponents: for exam-
ple, 1/ 10 = 10- 1, 1/ 100 = 10- 2 , 1/ 1,000 = 10- 3 .Apositivee xponenttells howmany
places to move the decimal point to the right of a number, and a negative exponent
how many places to the left. Therefore, 3.1 X 102 = 310; 3.1 X 10- = 0.031.
2

Scientific notation saves a lot of space in describing very large or very small
objects. For example, the 15O,OOO,OOO-km (93,OOO,OOO-mi) distance from the Earth
to the Sun becomes 1.5 X 108 km (9.3 X 107 mi) , and the diameter of a hydrogen
atom (0.0000000001 m) becomes 1.0 X 10- 10 m. The full range of dimensions that
scientists must consider spans an incomprehen sible 44 orders of magnitude, from
the diameter of the particles that make up an atom (about 10- m across) to the
18

radius of the observable Universe (an estimated 10 m) (TABLE 1.2).

26

TABLE 1.2 Orders of magnitude defining lengths in the Universe

(in meters)
- ,... . , .. ·-·· .. ~- .•. ·---------
-2 X 1026 Radius of the observable Universe
' -···-·- ---
2.1 X 1022
-•- - - ~~:,

Distance to the nearest galaxy (Andro~~c:_:fo;~ .

-

. -·- -· ·--- --
9.0 X 1020 Diameter of the Milky Way
---- ·- -------- - ·-- -------- -
1.5 X 1011 Diameter of the Earth's orbit

6.4 X 106 Radius of the Earth

5.1 X 106 East-west length of the United States

8.8 X 103 Height of Mt. Everest (the Earth's tallest mountain) above sea level

1.7 X 10° Average height of an adult human

1.0 X 10-3 Diameter of a pinhead

6.0 X 10- 4 Diameter of a living cell

2.0 X 10-6 Diameter of a virus

1.0 X 10-10 Diameter of a hydrogen atom (the smallest atom)

1.1 X 10-14 Diameter of a uranium atom's nucleus

1.6 X 10-is Diameter of a proton (a building block of an atomic nucleus)

-1 X 10- 18 Diameter of an electron (a smaller building block of an atom)

1.4 THE CHALLENGE S OF STUDYING AN ENTIRE PLANET 17

To help visualize th b.Ir
span to a .~ 1 ions of years of geologic time, it may help to compare its
. .
more fam1har one· 1.f II O f geologic .
each seco d · a Ume was condensed mto a single year,
n would represent 145 years.

1·5 Rates of Geologic Processes

Some geologic pr ocesses h appen qmckly. . . . .
A meteorite impact takes a fracuon of a
·
second; most ea r th qua k es are over m •
. a few seconds; and a landslide or explosive
vo l can1c eruption can h appen m . . . , .
mmutes. But others occur so slowly that 1t s d1f-
fi cult to reco · h h .
gmze t at t ey are happenmg at all. It often takes decades before
anyone notices the slow downhill creep of soil; layers of mud only an inch thick
may require thousands of years to accumulate in the deep ocean; and satellite
~easureme nts show that continents are moving 1 to 15 cm/yr. The slow rates of
important geologic processes were the first clue that the Earth must be very old,
· understood this long before they were able to measure the ages of
and geo l ogists
rocks (see Chapter 12) .
Even small changes can have big results when they are repeated over enormous
expanses of time, as you will see in Exercise 1.9. And at the very slow rates at which
some of these processes take place, familiar materials may behave in unfamiliar
ways. For example, if you drop an ice cube on your kitchen floor, it shatters into
pieces. But given time and the weight resulting from centuries of ice accumulatio n,
the ice in a glacier can flow slowly, at tens of meters per year (FIG. 1.10a). Under
geologic conditions and over long enough periods, even layers of solid rock can be
bent into folds like those shown in FIGURE 1.10b.

FIGURE 1.10 Solid Earth materials behave in unexpected ways over long periods and
under appropriate conditions.

(a) Flowing ice in Athabasca Glacier, Alberta, Canada. (b) Folded sedimentary rocks in eastern Ireland.

You will learn later that mountains and oceans are not permanent landscape fea-
tures. Mountains form by uplift or intense folding, but as soon as land rises above
the sea, streams, ice, and wind begin to erode it away. When the forces that cause the
u lift cease, the mountains are gradually leveled by the forces of erosion. Oceans
a: also temporary features. They form when continents split and the pieces move
a art from one another, and they disappear when the continents on their margins
c~llide. Exercise 1.9 examines the rates at which these processes operate and gives
insight into the life spans of mountains and oceans.

1.5 RATES OF GEOLOGIC PROCESSES

 EXERCIS E 1.9 How Long Does It Take to Make an Ocean? To Erode a Mountain?

Name: Section: _ _ _ __
Course-:---------------------- Date: _ _ _ _ __

erosion
(a) Rates of uplift and erosion. The following questions will give you a sense of the rates at which uplift and
are fir st upl ifted,
take place. We will assume that upl ift and erosion do not occur at the same tim e-that mountains
and only then does erosion begin-whe reas the two processes actually operate simultaneou sly.
__ m
• If mountains rose by 1 mm/yr, how high would they be (in meters) after 1,000 years? _ _ _
10,000,000 years? _ _ _ _ _ m 50 million years? _ _ _ _ _ m
began about
• The Himalayas now reach an elevation of 8.8 km, and radiometric dating suggests that th ei r uplift
rise? _ _ _ _ _ km/yr
45 mi llion years ago. Assuming a constant rate of upl ift, how fast did the Himalayas
_ _ _ _ _ m/yr _ _ _ _ _ mm/yr
now eroded nearl y
• Evidence shows that there were once Himalaya-scale mountains in northern Canada, in an area
how fast would the rate of erosion have had to be
flat. If the Earth were only 6,000 years old, as was once believed,
in 6,000 years? _ _ _ _ _ m/yr _ _ _ _ _ mm/yr
for these mountains to be eroded to sea level
At th is rate, how
• Observations of modern mountain ranges suggest that they erode at rates of 2 mm per 10 years.
long would it take to erode the Himalayas down to sea level? _ _ _ _ _ years
At one
(b) Rates of seafloor spreading. Today the Atlantic Ocean is about 5,700 km wide at the latitude of Boston. st
northwest coa
t ime, however, there was no Atlantic Ocean because the east coast of the United States and the
to form "only" 185,000,00 0 years ago,
of Africa were joined in a huge supercontinent. The Atlantic Ocean started
as modern North America spl it from Africa and the two continents slowly drifted apart in a process called seafloor
spreading.
been moving away
• Assuming that the rate of seafloor spreading has been constant, at what rate has North America
from Africa? _ _ _ _ _ mm/yr _ _ _ _ _ km per million years

Scaling Geologic Time in the Grand Canyon

Name: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Section: _ _ _ __
Course: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Date: _ _ _ _ _ __

Exploring Geology Using Google Earth

1. Visit digital.ww norton.co m/geolab manual4
2. Go to the Geotours tile to download Google Earth Pro and the accompanying
Geotours exercises file.

Check and double-clic k the GeotourOl folder icon in Google Earth

•
i
to fly to the Grand Canyon of northern Arizona. Here, erosion by the 4
Colorado River treats visitors to one of the most spectacular exposures
of geologic history on the planet (ranging from~ 270-million -year-
old Kaibab Limestone capping the Grand Canyon's rim to the ~ 2000 4
million-yea r- old Vishnu Schist paving the Inner Gorge). Right- click on
the Bright Angel Trail (red path), and select Show Elevation Profile to
plot a graph of elevation change (y-axis) versus distance along the trail
(x-axis) . Please note that axisvalues can vary slightly depending on window
size, so students should use the numbers provided for their calculations.

(continued)

22 CHAPTER 1 SETTING THE STAGE FOR LEARNIN G ABOUT THE EARTH