N: Geologic Time
1. Geologic History
a. Fossils
3. Geologic Time Scale
4. Geologic Belts
5. NC Geologic History
How do we know geologic
history?
Earth's History
•Earth's history spans over a
length of 4.5 billion years
•Geologists have divided that
time into units based on major
geologic events and life forms
Past Life Forms
We discovered that some organisms
only existed during certain time
units, so when geologists find the
remains, we know exactly which
time unit a rock is from.
Fossils are the clues
Fossils are the preserved
remains and traces of past life
forms. They are found in
sedimentary rocks.
Ordering the Grand Canyon’s History
Geologic Time Scale
•The time scale was created
to show the order of events
in Earth's history of 4.5
billion years
Divisions
From smallest to largest, the units of
geologic time are:
1. Epochs
2. Periods
3. Eras
4.Eons
Each unit of time is recognized by the
fossils it contains!
Examples:
1. Age of Coal Swamps 2.Age of Reptiles
3.Age of Mammals 4.Age of Fishes
M.Y.A = Million Years Ago
Each division is represented by millions
of years ago (mya)
Geologic Belts
Rocks with similar characteristics and history
are grouped together in units called GEOLOGIC BELTS
North Carolina's Geologic History
In North Carolina, there are 11
different belts of igneous,
sedimentary, and metamorphic
rocks that have similar geologic
history.
North Carolina's Geologic History
•We know that Wilmington is in the Coastal
Plain Belt and some of the rocks here
formed 66 million years ago!
Let's find out more......
How and Why?
12.4 The Geologic Time Scale
Structure of the Time Scale
 Eons represent the greatest expanses of time. Eons are
divided into eras. Each era is subdivided into periods.
Finally, periods are divided into smaller units called epochs.
 There are three eras within the Phanerozoic eon: the
Paleozoic, which means “ancient life,” the Mesozoic, which
means “middle life,” and the Cenozoic, which means
“recent life.”
12.4 The Geologic Time Scale
Structure of the Time Scale
 Each period within an era is characterized by somewhat less
profound changes in life forms as compared with the
changes that occur during an era.
 The periods of the Cenozoic era are divided into still smaller
units called epochs, during which even less profound
changes in life forms occur.
12.4 The Geologic Time Scale
Precambrian Time
 During Precambrian time, there were fewer life forms. These
life forms are more difficult to identify and the rocks have
been disturbed often.