Page 12 - Laboratory Manual in Physical Geology

Measurement Units
People in different parts of the world have historically used different systems of measurement. For example, people in the United
States have historically used the English system of measurement based on units such as inches, feet, miles, acres, pounds, gallons,
and degrees Fahrenheit. However, for more than a century, most other nations of the world have used the metric system of meas-
urement. In 1975, the U.S. Congress recognized that global communication, science, technology, and commerce were aided by
use of a common system of measurement, and they made the metric system the official measurement system of the United States.
This conversion is not yet complete, so most Americans currently use both English and metric systems of measurement.

The International System (SI)
The International System of Units (SI) is a modern version of the metric system adopted by most nations of the world,
including the United States. Each kind of metric unit can be divided or multiplied by 10 and its powers to form the smaller
or larger units of the metric system. Therefore, the metric system is also known as a “base-10” or “decimal” system. The
International System of Units (SI) is the official system of symbols, numbers, base-10 numerals, powers of 10, and prefixes in
the modern metric system.

SYMBOL NUMBER NUMERAL POWER OF 10 PREFIX
12
T one trillion 1,000,000,000,000 10 tera-
9
G one billion 1,000,000,000 10 giga-
6
M one million 1,000,000 10 mega-
3
k one thousand 1000 10 kilo-
2
h one hundred 100 10 hecto-
1
da ten 10 10 deka-
0
one 1 10
–1
d one-tenth 0.1 10 deci-
–2
c one-hundredth 0.01 10 centi-
–3
m one-thousandth 0.001 10 milli-
–6
μ one-millionth 0.000001 10 micro-
–9
n one-billionth 0.000000001 10 nano-
–12
p one-trillionth 0.000000000001 10 pico-
Examples
1 meter (1 m) = 0.001 kilometers (0.001 km), 10 decimeters (10 dm), 100 centimeters (100 cm), or 1000 millimeters
(1000 mm)
1 kilometer (1 km) = 1000 meters (1000 m)
1 micrometer (1 μ m) = 0.000,001 meter (.000001 m) or 0.001 millimeters (0.001 mm)
1 kilogram (kg) = 1000 grams (1000 g)
1 gram (1 g) = 0.001 kilograms (0.001 kg)
1 metric ton (1 t) = 1000 kilograms (1000 kg)
1 liter (1 L) = 1000 milliliters (1000 mL)
1 milliliter (1 mL or 1 ml) = 0.001 liter (0.001 L)

Abbreviations for Measures of Time
A number of abbreviations are used in the geological literature to refer to time. Abbreviations for “years old” or “years ago” generally
use SI prefixes and “a” (Latin for year ). Abbreviations for intervals or durations of time generally combine SI symbols with “y” or “yr”
( years ). For example, the boundaries of the Paleozoic Erathem are 542 Ma and 251 Ma, so the Paleozoic Era lasted 291 m.y.

ka = kiloannum—thousand years old, ago, or before present
Ma = megannum—million years old, ago, or before present
Ga = gigannum—billion years old, ago, or before present
yr (or y) = year or years
Kyr or k.a. = thousand years
Myr or m.y. = million years
Gyr (or Byr or b.y) = gigayear—billion years

Preface ■ xi