Page 43 - The Restless Earth Fossils

42 Fossils

and at a great expense, and showed and admired with as much
pleasure as a child’s rattle or a hobby-horse is shown and admired
by himself and his playfellows, because it is pretty; and this has
been done by thousands who have never paid the least regard to
that wonderful order and regularity with which Nature has dis-
posed of these singular productions, and assigned to each class its
particular stratum.”
Smith became obsessed with an idea: He would create a
map that would show in complete detail the inner structure of
England. In essence, it would be a geological road map that would
reveal details like those that had so impressed Hutton. Smith’s
project would take nearly twenty years to complete. It would cost
him dearly both in money and good health. But in the end, he
created an enormous 8-foot-by-6-foot (2.4 m by 1.8 m) detailed,
full-color map that would change the way people thought about
the world. He provided a book whose layered pages of rock and
stone contained “letters” of distinctive fossils that spoke about
past times and vast mineral and energy treasures to those who
could read them. And although his map only outlined the geo-
logical “innards” of England, other scientists found the same
layers—and some of the same fossils—all over the world. Fossils
especially useful for marking distinct points in geological time are
called index fossils.

What MaKes a good index Fossil?
Index fossils should: (1) be easy to find, but unique to particular
layers of rock; and (2) change gradually over time with a well-
defined sequence of forms. The shells of various invertebrate
animals often make good index fossils because they belong to
relatively small creatures that reproduce in large numbers, fos-
silize readily, and possess ridges, pores, spines, and other distinc-
tive markings. Some examples include ammonites and baculites:
squidlike mollusks that floated in ancient seas and preyed on fish,
clams, worms, and trilobites. Ammonites possessed coiled shells
and baculites created straight shells not unlike skinny ice cream

RE_Fossils2print.indd 42 3/17/09 8:59:30 AM