Geology Reference
In-Depth Information
geologists view Earth history as a series of such short-term
or punctuated events. This view is certainly in keeping with
the modern principle of uniformitarianism.
Furthermore, uniformitarianism does not require that the
rates and intensities of geologic processes be constant through
time. We know that volcanic activity was more intense in
North America 5 to 10 million years ago than it is today, and
that glaciation has been more prevalent during the last several
million years than in the previous 300 million years.
What uniformitarianism means is that even though the
rates and intensities of geologic processes have varied during
the past, the physical and chemical laws of nature have
remained the same. Although Earth is in a dynamic state of
change and has been ever since it formed, the processes that
shaped it during the past are the same ones operating today.
Eon
Era
Period
Epoch
Recent or
Holocene
Pleistocene
0
0.01
Pliocene
1.8
Miocene
5
Oligocene
23
Eocene
34
Paleocene
56
Cretaceous
66
Jurassic
146
Triassic
200
Permian
251
BENEFIT US?
The most meaningful lesson to learn from the study of geol-
ogy is that Earth is an extremely complex planet in which
interactions are taking place between its various subsystems
and have been for the past 4.6 billion years. If we want to
ensure the survival of the human species, we must under-
stand how the various subsystems work and interact with
each other and, more importantly, how our actions affect
the delicate balance between these systems. We can do this,
in part, by studying what has happened in the past, particu-
larly on the global scale, and use that information to try to
determine how our actions might affect the delicate balance
between Earth's various subsystems in the future.
The study of geology goes beyond learning numerous
facts about Earth. In fact, we don't just study geology—we
live
it. Geology is an integral part of our lives. Our standard
of living depends directly on our consumption of natural
resources, resources that formed millions and billions of
years ago. However, the way we consume natural resources
and interact with the environment, as individuals and as a
society, also determines our ability to pass on this standard
of living to the next generation.
As you study the various topics covered in this topic,
keep in mind the themes discussed in this chapter and how,
like the parts of a system, they are interrelated and respon-
sible for the 4.6-billion-year history of Earth. View each
chapter's topic in the context of how it fi ts in the whole Earth
system, and remember that Earth's history is a continuum
and the result of interaction between its various subsystems.
By relating each chapter's topic to its place in the Earth sys-
tem, you will gain a greater appreciation of why geology is so
integral to our lives.
299
Pennsylvanian
318
Mississippian
Devonian
359
Silurian
416
Ordovician
444
Cambrian
488
542
2500
4600
◗
Figure 1.17
The Geologic Time Scale The numbers to the right
of the columns are ages in millions of years before the present.
Dates are from Gradstein, F., J. Ogg and A. Smith.
A Geologic Time
Scale 2004
(Cambridge, UK: Cambridge University Press, 2005),
Figure 1.2.
Uniformitarianism is a powerful principle that allows
us to use present-day processes as the basis for interpret-
ing the past and for predicting potential future events. We
should keep in mind, however, that uniformitarianism does
not exclude sudden or catastrophic events such as volca-
nic eruptions, earthquakes, tsunami, landslides, or floods.
These are processes that shape our modern world, and some
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