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Guide
to Reading 
The last chapter dealt with how Earth’s history
has been worked out; this one deals with the story itself. It’s
presented in chronological order and in terms of the major divisions
of geologic time: the Precambrian (from Earth’s beginning 4.6
billion years ago up to 545 million years ago) and its subdivisions
(Hadean Eon, Archean Eon, and Proterozoic Eon) and the rest of all
time, the Phanerozoic, including its subdivisions (the Paleozoic
Era, including the Cambrian, Ordovician, Silurian, Devonian, Carboniferous,
and Permian Periods; the Mesozoic Era, including the Triassic, Jurassic,
and Cretaceous Periods; and the Cenozoic Era, with special attention
paid to the Pleistocene Ice Age of the Quaternary Period). That’s
a lot of names, but do learn them. They’re basic to any discussion
of Earth history.
Basically, Chapter 11 is narrating the highlights
of 4.6 billion years of change. This presents a problem. Even the
most concise summary of 4.6 billion of anything is going to be long.
What is essential to learn? The author has chosen major milestones
in Earth’s development that any well-informed general geologist
should know. This guide narrows the focus even further. Still, basic
literacy means different things to different students, to different
teachers, and in different situations. For example, the particular
facts required of you could depend on the location of your school.
If you’re in the Denver area, no doubt you’ll have to
know about the Ancestral Rockies, the Laramide Revolution, and the
Western Interior Seaway. If you’re located in Boston or Seattle,
other particulars may seem more important to you or to your teacher.
This chapter presents a wonderful opportunity to bring basic concepts
to life by indulging your curiosity about the history of your present
(or hometown) surroundings.
Whatever your goal, it’s easy to get mired
down in all the details and proper nouns. To avoid this, as you study,
try to picture our planet as it was in the past—a truly alien
world. It’s not dull stuff; it’s been the subject matter
for popular comics and blockbuster movies for decades. Who hasn’t
heard of the Flintstones or Jurassic Park? Asteroid encounters have
been exciting from Superman days up to Deep Impact. People everywhere
wonder why the dinosaurs became extinct; maybe after reading this
chapter you’ll also wonder why the trilobites became extinct.
As you read, remind yourself that this is not a fanciful movie plot;
it’s all based on scientific data and reasoning. Truth really
is stranger than fiction.
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Key Terms
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