Chapter 18 Fossils and Geologic Time

First birds
Extinction of dinosaurs
Earliest humans in Africa
End of Wisconsin Glacial Episode
Columbus sails to the Americas
GEOLOGIC HISTORY OF NEW YORK STATE 429
When the events have been plotted, divide your time line into Precambrian,
Paleozoic, Mesozoic, and Cenozoic eras. You may wish
to make each era a different color.
GEOLOGIC HISTORY OF NEW YORK STATE
Figure 18-7 on pages 430–431 is taken from pages 8 and 9
of the Earth Science Reference Tables. It is a chart of Earth’s
geologic history. Geologic events and fossils of New York State
are highlighted. You should be familiar with the information
in this chart and how to use it. Look at the figure and note
the following.
• The left page is primarily used to show the major
divisions geologic time and the absolute age of these
divisions in millions of years before the present. For
example, Precambrian time ended at the beginning of
the Paleozoic Era, 544 million years ago.
• The column labeled “Life on Earth” identifies important
changes in the evolution of life. This information expands
on the information given in the gray area on the left side
of the page.
• In the next column, thick, black, broken vertical lines
indicate the age of bedrock in New York State. The open
parts of the thick line represent intervals for which there
is no bedrock in New York. Notice that there are whole
geological periods missing. These incomplete parts of the
line represent major unconformities in New York bedrock.