Page 18 - Laboratory Manual in Physical Geology

Your instructor will not accept simple yes or no Spatial Scales of Observation and
answers to questions. He or she will expect your answers Measurement
to be complete inferences justified with data and an
explanation of your critical thinking (in your own words). Geologists study all of Earth’s materials, from the spatial
Show your work whenever you use mathematics to solve a scale of atoms (atomic scale) to the scale of our entire planet
problem so your method of thinking is obvious. (global scale). At each spatial scale of observation, they
identify materials and characterize relationships. Each scale
is also related to the others. You should familiarize yourself
ACTIVITY with these spatial scales of observation as they are sum-
marized in FIGURE 1.2 and the tables of quantitative units of

1.1 Geologic Inquiry measurement, symbols, abbreviations, and conversions on
pages xi and xii at the front of this manual . Terms such as
THINK | How and why do geologists observe regional, local, hand sample, and microscopic are hierarchi-
About It Earth materials at different scales cal levels of scale , not measurements. When making mea-
(orders of magnitude)? surements, geologists use these kinds of scales:
■ Bar scale —A bar scale is a small ruler printed on an
OBJECTIVE Analyze and describe Earth materials at image or map. You use it to measure distances on

different scales of observation, then infer how they are the image or map. For example, all of the images in
related to you and thinking about geology.
FIGURE 1.1 are accompanied by bar scales so you can
PROCEDURES make exact measurements of features within them. If
a bar scale is given in one unit of measurement, like
1. Before you begin , do not look up defi nitions
and information. Just focus on FIGURE 1.1 . Use miles, and you want to know distances in kilometers,

your current knowledge to start thinking like a then you must convert the measurement using the

geologist, and complete the worksheet with your table on page xii at the front of the manual.
current level of ability. Also, this is what you will ■ Magnification scale —This scale tells you how
need to do the activity: many times larger or smaller an object is in a picture
____ Activity 1.1 Worksheets (pp. 25 – 26 ) and compared to its actual size in real life. Magnification
pencil with eraser scale can be expressed as a percentage or a multiplication
factor. For example, if you take a picture of a rock and
2. Answer every question on the worksheets in a
way that makes sense to you and be prepared to enlarge it to twice its actual (normal) size, then you
compare your ideas with others. should note a scale of 200%, 2x, or x2 on the picture.
If you reduce the picture of the rock so it appears only
3. After you complete the worksheets , read below half of its actual size, then you should note a scale of
about scales of observation and direct and remote 50%, 0.5x, or x1/2 on the picture. It does not matter
observation of geology. Be prepared to discuss which units of measurement you magnify (multiply).
your observations and inferences with others.
For example, if you measure a distance of 6 millimeters
on the image that has a scale of 200% or x2, then the
distance is actually 12 millimeters in real life.
Scales of Earth Observation ■ Fractional scale —A fractional scale is used to indicate
how much smaller something is than its actual size.
The most widely known geologic feature in the United It is like the magnification scale, but expressed as a
States is undoubtedly the Grand Canyon. This canyon cuts a fraction. Therefore, if a picture shows a rock at only
mile deep, through millions of rock layers that are like pages half of its actual size, then you can use a fractional
of an immense stone book of geologic history called the scale of ½ scale to indicate it. It does not matter which
geologic record . The layers vary in thickness from millime- units of measure you use, the actual size would still be

ters to meters. Each one has distinguishing features—some half of what you measure in any units.
as tiny as microscopic fossils or grains of sand and some as
large as fossil trees, dinosaur skeletons, or ancient stream ■ Ratio scale —A ratio scale is commonly used when
channels. Yet when one measures and describes the layers, making models. The scale represents the proportional
it can be done at the scale of a single page or at the scale of ratio of a linear dimension of the model to the same
many pages, much the same as one might describe a single feature in real life. If a toy car is 20 centimeters long
tree or the entire forest in which the tree is found. Each suc- and the actual car was 800 centimeters long, then the
cessive layer also represents a specific event (formation of the ratio scale of model to actual car is 20:800, which
layer), which occurred at a specific time in Earth’s long geo- reduces to 1:40. (Note: this is the same as a fractional
logic history. Therefore, geologists are concerned with scales scale of 1/40.) Ratio scales are commonly provided on
of observation and measurement in both space and time. maps, as well as three-dimensional models.

Thinking Like a Geologist ■ 3