Geochronology, Dating, and Precambrian Time: The Beginning of the World As We Know It - ISBN:1615301259

Geochronology, Dating, and Precambrian Time: The Beginning of the World As We Know It

Date: 21 April 2011, 02:27

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Introduction
Planet Earth was formed roughly 4.6 billion years
ago. For human beings—used to measuring time in
terms of days, weeks, and months—such an enormous
span of time can be a difficult concept to grasp.
Geologists, scientists who study the Earth and the processes
that continue to shape it, have broken up this vast
expanse of “deep time” into major divisions based on
what they have learned from the study of ancient rocks
and fossils. The first of these divisions—from approximately
4.6 billion until 542 million years ago—is known
as the Precambrian, meaning everything that happened
before the Cambrian period. (Today some people prefer
to call this period the Cryptozoic, which means “hidden
life.”) Almost all of planet Earth’s history is Precambrian.
Until recently, however, it has remained the most unknown,
the strangest, and most perplexing period in all geologic
history—what some have referred to as the “Dark Ages”
of Earth’s existence.
For centuries, the Earth yielded no fossil record to
help humans envision Precambrian time. Discoveries of
rich caches of fossils from the Cambrian period enabled
scientists to assemble a vivid picture of the creatures that
inhabited the planet during that time, but the Precambrian
Earth remained largely unimaginable. What was known as
the “missing fossil record” of the Precambrian period
stood for more than a century as one of the great unsolved
mysteries of the natural sciences. This mystery perplexed
Charles Darwin and many other scientists who followed
in his footsteps. Humans had not yet developed the various
methods to accurately determine the age of rocks
formed during this interval of geologic time. They had not
yet identified and interpreted the remains of the microscopic
bacteria that formed in the earliest oceans. The
story scientists were beginning to piece together was full

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