Page 51 - The Restless Earth Fossils

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Marking Turning

Points in Evolution

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THE EARTH CREATES ONLY A MISERLY HANDFUL OF FOSSILS—OFTEN ALL
that remains is a creature’s mineralized framework of bone or
shell. But every now and then paleontologists discover rich depos-
its of fossils in such great numbers or that are so well preserved
that an instant of deep time flickers into view in great detail.
Such rich seams of fossil life help paleontologists flag the geologi-
cal time scale with significant events in the history of life, just
as humans mark birthdays, graduations, and marriages during
their own much shorter lifetimes. This chapter will note some
spectacular fossil sites, look at a few in more depth, and highlight
some of life’s major evolutionary achievements on the long road
from microorganisms to mankind.

huManizing the geological tiMe scale
If the geological timeline shown at the end of Chapter 3 seems
like just a list of weird names and big numbers, it can be made
more real by using the human body to illustrate. Stretch out your
arms and let the middle finger of your left hand represent Earth’s

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