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FOSSILS- Evidence 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.

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fossils found in sedimentary rocks
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.
slide5

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?

absolute radioactive dating of fossils using the half life of elements
Absolute (Radioactive) Dating of Fossils using the half- life of elements
  • Half Lives for Radioactive Elements

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
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

slide12

1/2 C-14

1/4 C-14

1/8 C-14

12.5% C-14

25%

C-14

87.5% N-14

100%

C-14

50%

C-14

50%

N-14

75%

N-14

5730

years

5730

years

5730

years

C-14 Decay

PARENT = C-14

DAUGHTER = N-14

molds
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
Examples of Molds

Lobster

Fish

Trilobite

casts
Casts
  • Three-dimensional trace of organism
  • Protrudes out of surface of rock
examples of casts
Examples of Casts

Insect

Trilobite

Eurobrontes (dinosaur footprints)

imprints
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
body parts
Body Parts
  • Actual parts of an organism left behind from the past
  • Example: bones, organisms preserved in amber or ice
examples of body parts
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 WashD.C.