fossils- evidence from once-living organisms
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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.
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
o Half Lives for Radioactive ElementsRadioactive
ParentStable
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
-2 protons, 2 neutrons -Helium atom-Emitted from the nucleus
-100x more penetrating than alpha-Neutron changes to one proton, one electron -Electron is emitted from nucleus
-no charge or mass -results in only lost energy-Emitted in Photons-most dangerous form
100%C-14
50%C-14
50%N-14
25%C-14
75%N-14
12.5% C-
14
87.5% N-14
5730 years
5730 years
5730 years
1/2 C-14 1/4 C-14 1/8 C-14
PARENT = C-14DAUGHTER = N-14
C-14 Decay
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
BODY PARTS Actual parts of an organism left behind from the
past Example: bones, organisms preserved in amber or
ice
EXAMPLES OF BODY PARTS
Skull of horned andhornless 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.
A baby mammoth has been uncovered in the permafrost of north-west Siberia. Approx. 9,000 years old.
Gradualism- pg439
Punctuated Equilibrium-pg439
