Geology Reference
In-Depth Information
to the world's oceans. It is predicted that at the current rate
of glacial melting, sea level will rise 21 cm around 2050, thus
increasing the number of people at risk from flooding in
coastal areas by approximately 20 million!
We would be remiss, however, if we did not point out
that many other scientists are not convinced that the global
warming trend is the direct result of increased human activ-
ity related to industrialization. They point out that although
the level of greenhouse gases has increased, we are still
uncertain about their rate of generation and rate of removal,
and whether the rise in global temperatures during the past
century resulted from normal climatic variations through
time or from human activity. Furthermore, these scientists
point out that even if there is a general global warming dur-
ing the next hundred years, it is not certain that the dire pre-
dictions made by proponents of global warming will come
true.
by Einstein's theory of relativity, space and time are unalter-
ably linked to form a space-time continuum, that is, without
space, there can be no time.
How do we know that the Big Bang took place ap-
proximately 14 billion years ago? Why couldn't the universe
have always existed as we know it today? Two fundamental
phenomena indicate that the Big Bang occurred. First, the
universe is expanding, and second, it is permeated by back-
ground radiation.
When astronomers look beyond our own solar system,
they observe that everywhere in the universe galaxies are
moving away from each other at tremendous speeds. Edwin
Hubble fi rst recognized this phenomenon in 1929. By mea-
suring the optical spectra of distant galaxies, Hubble noted
that the velocity at which a galaxy moves away from Earth
increases proportionally to its distance from Earth. He
observed that the spectral lines (wavelengths of light) of the
galaxies are shifted toward the red end of the spectrum; that
is, the lines are shifted toward longer wavelengths. Galaxies
receding from each other at tremendous speeds would pro-
duce such a redshift. This is an example of the
Doppler effect,
which is a change in the frequency of a sound, light, or other
wave caused by movement of the wave's source relative to the
observer (
Earth, as we know, is a remarkably complex system, with
many feedback mechanisms and interconnections throughout
its various subsystems and cycles. It is very diffi cult to predict
all of the consequences that global warming would have for
atmospheric and oceanic circulation patterns and its ultimate
effect on Earth's biota.
Figure 1.5).
One way to envision how velocity increases with in-
creasing distance is by reference to the popular analogy of a
rising loaf of raisin bread in which the raisins are uniformly
distributed throughout the loaf (
◗
SOLAR SYSTEM, AND EARTH'S
PLACE IN THEM
How did the universe begin? What has been its history? What
is its eventual fate, or is it infi nite? These are just some of the
basic questions people have asked and wondered about since
they fi rst looked into the nighttime sky and saw the vastness
of the universe beyond Earth.
Figure 1.6). As the dough
rises, the raisins are uniformly pushed away from each other
at velocities directly proportional to the distance between
any two raisins. The farther away a given raisin is to begin
with, the farther it must move to maintain the regular spac-
ing during the expansion, and hence the greater its velocity
must be. In the same way that raisins move apart in a ris-
ing loaf of bread, galaxies are receding from each other at a
rate proportional to the distance between them, which is ex-
actly what astronomers see when they observe the universe.
By measuring this expansion rate, astronomers can calculate
how long ago the galaxies were all together at a single point,
which turns out to be about 14 billion years, the currently
accepted age of the universe.
◗
with a Big Bang?
Most scientists think that the universe originated about
14 billion years ago in what is popularly called the
Big Bang
.
The Big Bang is a model for the evolution of the universe
in which a dense, hot state was fol-
lowed by expansion, cooling, and
a less dense state.
According to modern
cos-
mology
(the study of the origin,
evolution, and nature of the uni-
verse), the universe has no edge
and therefore no center. Thus,
when the universe began, all mat-
ter and energy were compressed
into an infi nitely small high-tem-
perature and high-density state in
which both time and space were
set at zero. Therefore, there is no
“before the Big Bang,” only what
occurred after it. As demonstrated
Low
pitch
High
pitch
◗
Figure 1.5
The Doppler Effect The sound waves of an approaching whistle are slightly
compressed so that the individual hears a shorter-wavelength, higher-pitched sound. As the
whistle passes and recedes from the individual, the sound waves are slightly spread out, and a
longer-wavelength, lower-pitched sound is heard.
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