Transcript The History of Earth

The History of Earth
Chapter 6 Sections 1 and 2
Understanding the history
of Earth.
• The history of the Earth, it’s geological
formations and organisms that inhabit the
Earth, go hand in hand.
• Scientists study the remains of dead
organisms to understand the geologic
conditions in which they lived.
• Paleontology is the study of these long
dead organisms.
How do scientists know the
age of geologic formations
on Earth?
• Geologists rely on rocks and fossils to
help them understand what happened in
Earth’s past.
• Determining the age of an object or
event is called relative dating.
Dating Rock Layers
 First you have to get to know the rocks
before you can go on a date. Ha! Ha!
 Scientists know that rock layers can be
dated by where they are located.
 Rock layers near the bottom are older
than rock layers near the top.
 The principle that states that “younger
rocks are over older rocks” is called
SUPERPOSITION.
Superposition
• Using relative dating
principles and the
position of layers within
rock, it is possible to
reconstruct the
sequence of geologic
events that have
occurred at a site.
• In the image below, you
can see the different
layers that have been
deposited over
thousands of years.
1. Which is older--rock unit 2 or rock unit 3?
2. Which is older--rock unit 6 or rock unit 20?
3. Which is older--pluton 10 or rock unit 23?
4. Which is older--rock unit 4 or pluton 10?
5.Which episode happened earlier—
the folding of 3, 4, 5, and 6 or the intrusion of dike 11?
6.Are rock units 1 through 6 older or younger than
the episode of folding?
Geologic Column
• The arrangement of rock
layers in which the oldest
rocks are at the bottom
and the youngest at the
top is a geologic column.
• Scientists look at the
layers to determine what
has occurred in the
history of this particular
area.
• The layering that occurs
is called stratification.
What is a unconformity?
An unconformity is a missing
rock layer that creates gaps in
the rock sequence.
As you can see in the picture,
erosion has worn away rock
layers and then sediment was
deposited on top of the older
rocks.
As you can see in the picture,
layers are missing.
What process disturbed these rock
layers?
What process disturbed these rock
layers?