Download geologic history, fossils, & relative dating

GEOLOGIC HISTORY, FOSSILS,
& RELATIVE DATING
Geologic History
 Uniformitarianism
 The idea that the
same geologic
processes that are
shaping Earth today
have been at work
throughout Earth’s
history.
 Catastrophism
 The principle that
states that all
geologic change
occurs suddenly.
What kind of rocks
are these fossils in?
Which layer is
oldest?
Which layer is
youngest?
How do you know?
ROCKS TELL A STORY
 Rocks can tell where they
were made and when
 Sedimentary rocks can
have fossils in them
 Rocks can tell when mass
extinctions happened
PALEONTOLOGY
the study of fossils  remains of ancient life

Body fossils vs. trace fossils



Body = remain of organism, like bones;
Trace = evidence of organism, like footprints
Scientific dating


Absolute dating (gives age in years)
Radiometric / radioactive dating (isotopes)
Relative dating (gives age before, after, during) Observation of
rock layers
FOSSILS
Traces and preserved remains of ancient life
found within rock layers

Fossils show:





Biodiversity
How species have changed over time
Correlation between rock layers from around the world
Relative ages to particular strata
Evidence for the geological time scale
RELATIVE DATING & AGE
 Relative Dating: putting
rocks and geological
events in correct
chronological order
 Relative Age: how old
something is in
comparison to something
else
 Geologic Column: an ideal
sequence of rock layers
based on relative age with
the oldest on the bottom
HOW?
 Use of sedimentary rocks
 Use of fossils
 Study of strata
ABSOLUTE DATING
 Any method of
measuring the age
of an event or
object in years
 Examples of how
absolute dating is
used:
 Radioactive Decay
 Half-life: the time
that it takes for half
of the unstable
atoms in a sample to
decay
p.132
Using Half-Lives to Date Fossils – p. 132
INDEX FOSSIL
Fossil that defines and identifies geologic
periods; often in only one layer of rock
 Easily recognizable
 Short-lived (found only in a few layers of rock
worldwide)
 Wide distribution (geographic range)
Ex/ INDEX FOSSIL: AMMONITE

Ammonite fossils are
found worldwide, but
they existed for only a
very specific period of
time

this means ammonites
are found in very
specific layers of rock

when an index fossil is
found, the age of the
rocks it is preserved
can be determined
What kind of rocks
are these fossils in?
Which layer is
oldest?
Which layer is
youngest?
How do you know?
LAW OF SUPERPOSITION
For undisturbed rocks, the oldest layer is on
the bottom and the youngest is on top (Supai
is oldest)
LAW OF HORIZONTALITY
Sediments are originally deposited in horizontal
layers
 The Cross Cutting
Law:
 Folds or inclines:
layers must have
been formed after
they were
deposited.
LAW OF SUCCESSION
 Fossils are found in a predictable sequence
 Fossils in rock B are older then fossils in rock A
LAW OF INCLUSIONS
If a rock body (Rock B)
contained fragments
of another rock body
(Rock A),
then Rock B must be
younger than the
fragments of rock it
contained
GEOLOGIC TIME SCALE
a series of time
intervals that
divides Earth’s
history
•
Each layer of rock
represents specific interval
of time
•
Index fossils help
determine specific period
•
Time periods divided by
specific events like mass
extinctions