Download Types of Fossils - Parkway C-2

FOSSILSEvidence from
Once-living
Organisms
Fossils found in SEDIMENTARY ROCKS
The lower the sediment layer is, the older the
fossils of the layer will be.- Law of Superposition
 As time elapses, more and more sediment layers
form to create the layers of sedimentary rocks.

EXAMPLES OF SEDIMENTARY ROCKS
DIFFERENT ROCK LAYERS OF THE EARTH
Relative dating places rocks in their proper sequence of formation, e.g. which
formed first, second etc.
Although relative dating cannot give us numeric dates for events that took place, it
does provide useful information on what event followed or preceded another event.
Relative dating is still very valuable to scientists and still widely used.
The discovery of radioactive dating has supplemented relative dating techniques.
Oldest?
Youngest?
Can you put
the events in
order?
Relative Dating combined with Radioactive Dating
Absolute (Radioactive) Dating of Fossils using the half- life of elements
oHalf Lives for Radioactive Elements
Radioactive
Parent
Stable
Daughter
Half life
Potassium 40
Argon 40
1.3 billion yrs
Rubidium 87
Strontium 87
48.8 billion yrs
Thorium 232
Lead 208
14 billion years
Uranium 235
Lead 207
704 million years
Uranium 238
Lead 206
4.5 billion years
Carbon 14
Nitrogen 14
5730 years
Half-Life of an
element is the TIME
it takes for HALF of
the atoms present to
RADIOACTIVELY
decay into a stable
element.
Types of Radioactive Decay
-100x more penetrating than alpha
-Neutron changes to one proton, one
electron
-Electron is emitted from nucleus
-2 protons, 2 neutrons
-Helium atom
-Emitted from the nucleus
-no charge or mass
-results in only lost energy
-Emitted in Photons
-most dangerous form
C-14 Decay
1/2 C-14
100%
C-14
50%
C-14
5730
years
1/4 C-14
1/8 C-14
12.5%
C-14
25%
C-14
50%
N-14
75%
N-14
5730
years
PARENT = C-14
DAUGHTER = N-14
87.5%
N-14
5730
years
MOLDS
Are “trace fossils”
 Are not the organisms themselves, but is
evidence that the organism has been there
 Depressions in a surface

Smurf Mold
EXAMPLES OF MOLDS
Lobster
Fish
Trilobite
CASTS
Three-dimensional trace of organism
 Protrudes out of surface of rock

EXAMPLES OF CASTS
Insect
Trilobite
Eurobrontes (dinosaur
footprints)
IMPRINTS
Different from molds—are not indented or
depressed into its surface
 Different from casts—do not protrude from
surface
 Thin layer of carbon which forms from where the
organism was

EXAMPLES OF IMPRINTS
Fish
Leaf
BODY PARTS
Actual parts of an organism left behind from the past
 Example: bones, organisms preserved in amber or ice

EXAMPLES OF BODY PARTS
A baby mammoth has been uncovered in
the permafrost of north-west Siberia.
Approx. 9,000 years old.
Skull of horned and
hornless deer
From the Dominican Republic,
Miocene epoch (23.8 to 5.3 mya)
The 67-million-year-old Tyrannosaurus rex skeleton
known as Sue stands on display at Union Station in
Wash D.C.
Gradualism- pg439
Punctuated Equilibrium-pg439