Download 12.2 The Geologic Time Scale

12.2 The Geologic Time Scale
KEY CONCEPT
The geologic time scale divides Earth’s history based
on major past events.
Tollund Man:
• Died about 2200 years ago in
what is now Denmark.
• Details such as his skin and
hair were preserved by the
bog in which he was found.
A bog is a type of wetland that
accumulates peat, the deposits of dead
plant material.
12.2 The Geologic Time Scale
Index fossils are another tool to determine the age of rock
layers.
• Index fossils can provide the relative age of a rock layer.
• Defined as:
– Fossils of organisms that existed only during specific
spans of time over large geographic areas.
• Characteristics:
– Common
– Easy to identify
– Found widely around the world
– Only existed for a relatively brief time
12.2 The Geologic Time Scale
12.2 The Geologic Time Scale
Index fossils are another tool to determine the age of rock
layers.
• Examples:
– Index fossils include fusulinids and trilobites.
• Non-example:
– Any fossil that is rare or only found in a certain region.
12.2 The Geologic Time Scale
The geologic time scale organizes Earth’s history.
• The history of Earth is
represented in the geologic time
scale.
100
250
550
1000
• Geologic Time Scale:
– Representation of the history of the
Earth that is organized by major
changes or events.
• Organized into Eons, Eras, Periods
and Epochs.
2000
PRECAMBRIAN TIME
This time span makes up the
vast majority of Earth’s history.
It includes the oldest known
rocks and fossils, the origin of
eukaryotes, and the oldest
animal fossils.
Cyanobacteria
12.2 The Geologic Time Scale
The geologic time scale organizes Earth’s history.
• Eons represent the greatest
expanses of time. There are 4
Eons: Hadean, Archean,
Proterozoic, and Phanerozoic.
100
250
550
1000
• The Hadean, Archean, and
Proterozoic are collectively
known as Precambrian Time,
from 4.56 billion years ago to
540 million years ago.
• Eons are divided into Eras.
2000
PRECAMBRIAN TIME
This time span makes up the
vast majority of Earth’s history.
It includes the oldest known
rocks and fossils, the origin of
eukaryotes, and the oldest
animal fossils.
Cyanobacteria
12.2 The Geologic Time Scale
The geologic time scale organizes Earth’s history.
• Eras: last from tens to hundreds
of millions of years and consist of
2 or more Periods.
• Periods: last for tens of millions
of years and are the most
commonly used units of time.
Associated with rock systems.
• Epochs: last for several millions
of years and are the smallest
units of time.
12.2 The Geologic Time Scale
• Eras last tens to hundreds of millions of years.
– consist of two or more periods
– three eras: Cenozoic, Mesozoic, Paleozoic
12.2 The Geologic Time Scale
Eras last for tens to hundreds of millions of years.
1) Cenozoic Era: Evolution of
primates, diversification of
mammals, flowering plants.
Continues today.
12.2 The Geologic Time Scale
Eras last for tens to hundreds of millions of years.
2) Mesozoic Era: Evolution and
extinction of dinosaurs, evolution of
ferns and cycads and mammals.
12.2 The Geologic Time Scale
Eras last for tens to hundreds of millions of years.
3) Paleozoic Era: All existing
animal phyla developed, earliest
land plants evolved.
Liverworts
Mosses