28 PART 1^ |^ EXPLORING THE SKY
scientists organize their ideas in logical arguments. Th roughout
this book, many chapter sections end with short reviews entitled
“Scientifi c Argument.” Th ese feature a review question, which is
then analyzed in a scientifi c argument. A second question gives
you a chance to build your own scientifi c argument on a related
topic. You can use these “Scientifi c Argument” features to review
chapter material, but also to practice thinking like a scientist.
The So-Called Scientifi c Method
How is a scientifi c argument different from
an advertisement? Advertisements sometimes
sound scientifi c, but they are fundamentally
different from scientifi c arguments. An adver-
tisement is designed to convince you to buy
a product. “Our shampoo promises 85 percent
shinier hair.” The statement may sound like
science, but it isn’t a complete, honest discus-
sion. “Shinier than what?” you might ask.
An advertiser’s only goal is a sale.
Scientists construct arguments because
they want to test their own ideas and give
an accurate explanation of some aspect of
nature. For example, in the 1960s, biologist
E. O. Wilson presented a scientifi c argument
to show that ants communicate by smells. The
argument included a description of his careful
observations and the ingenious experiments
he had conducted to test his theory. He also
considered other evidence and other theories
for ant communication. Scientists can include
any evidence or theory that supports their
claim, but they must observe one fundamental
rule of science: They must be totally honest—
they must include all of the evidence and all of
the theories.
Scientists publish their work in scientifi c
arguments, but they also think in scien-
tifi c arguments. If, in thinking through his
argument, Wilson had found a contradic-
tion, he would have known he was on the
wrong track. That is why scientifi c arguments
must be complete and honest. Scientists
who ignore inconvenient evidence or
brush aside other theories are only fooling
themselves.
A good scientifi c argument gives you all
the information you need to decide for your-
self whether the argument is correct. Wilson’s
study of ant communication is now widelyScientists have discovered that ants communicate
with a large vocabulary of smells.
(Eye of Science/Photo Researchers, Inc.)2-4 Scientifi c Arguments
understood and is being applied to other fi elds
such as pest control and telecommunications
networks.What Are We?
Along for the RideHuman civilization is spread over the surface of planet Earth
like a thin coat of paint. Great cities of skyscrapers and tangles
of superhighways may seem impressive, but if you use your
astronomical perspective, you can see that we humans are
confi ned to the surface of our world.
The rotation of Earth creates a cycle of day and night that
controls everything from TV schedules to the chemical workings
of our brains. We wake and sleep within that 24-hour cycle of
light and dark. Furthermore, Earth’s orbital motion around the
sun, combined with the inclination of its axis, creates a yearly
cycle of seasons, and we humans, along with every other living
thing on Earth, have evolved to survive within those extremes
of temperature. We protect ourselves from the largest extremes
and have spread over most of Earth, hunting, gathering, and
growing crops within the cycle of the seasons.
In recent times, we have begun to understand that condi-
tions on Earth’s surface are not entirely stable. Slow changes in
its motions produce a cycle of ice ages with irregular pulses of
glaciation. All of recorded history, including all of the cities and
superhighways that paint our globe, has occurred since the last
glacial retreat only 12,000 years ago, so we humans have no
recorded experience of Earth’s harshest climate. We have never
experienced our planet’s icy personality. We are along for the
ride and enjoying Earth’s good times.SCIENTIFIC ARGUMENT
Why was it critical in testing the Milankovitch hypothesis to determine
the ages of ocean sediment?
Ocean fl oors accumulate sediment year after year in thin layers.
Scientists can drill into the ocean fl oor and collect cores of those
sediment layers, and from chemical tests they can fi nd the tem-
perature of the seawater when each layer was deposited. Those
observations of temperature could be used as reality checks for
the climate temperatures predicted by the Milankovitch theory, but
that meant the ages of the sediment layers had to be determined
correctly. When a confl ict arose with evidence from Devil’s Hole
in Nevada, the age determinations of the samples were carefully
reexamined and found to be correct.
After reviewing all of the evidence, scientists concluded that the
ocean core samples do indeed support the Milankovitch hypothesis.
Now construct your own argument. What might the temperatures
recorded at Devil’s Hole represent?