Download 2015-2016 EARTHS HIST Chapter 15 Section 2

RELATIVE DATING:
WHICH CAME FIRST?
»
»
RELATIVE DATING is
any method of
determining whether
an object or event is
older or younger than
other objects and
events.
PRINCIPLE OF
SUPERPOSITION
states that younger
rocks lie above older
rocks in an
undisturbed sequence.
http://comp.uark.edu/~sboss/geol1113study04s09.htm
GEOLOGIC COLUMN
»
»
»
Is an IDEAL sequence of rock layers that
contains all of the rock layers and fossils
on Earth arranged from oldest to
youngest.
This information comes from geologic data
from all around the world.
Is used to interpret rock sequences and
identify layers in puzzling rock
sequences.
ROCK LAYERS
»
»
»
»
Are arranged from oldest to youngest
Are in horizontal layers
HOWEVER, sometimes rock layers are
disturbed by processes within the Earth
Geologists use the relationships
between rock layers and the disturbance
to determine the relative age of the
rock layers and the events that
disturbed them.
DISTURBED ROCK LAYERS
»
There are four types of disturbances:
Faults - breaks in the Earth’s crust.
Intrusions - molten rock flows into existing
rock.
Folding - layers bend due to pressure.
»
Tilting- internal forces slant the rock layer.
»
»
»
IN WHAT ORDER DID THE ROCK
LAYERS FORM?
WHICH CAME FIRST,
EARTHQUAKE OR INTRUSION?
UNCONFORMITIES
»
»
»
»
Are gaps in the geologic column.
Geologists find that certain rock layers you
expect to be present in a certain place are not
there.
Erosion: when an area is worn down by
water, wind, or other elements.
Erosion and nondeposition are the
major causes of unconformities.
TYPES OF UNCONFORMITIES
»
Disconformities- part of a parallel rock layer is
missing
»
»
»
Disconformities are the most common type of
unconformity!
Nonconformities- sedimentary rock layers lie
on top of an eroded igneous surface.
Angular unconformities-exists between
horizontal rock layers and layers that are tilted
and folded.
Types of Unconformities Animation