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.

E XAMPLES OF S EDIMENTARY R OCKS

D IFFERENT R OCK L AYERS OF THE E ARTH

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 Elements Radioactive Parent Stable Daughter Half life Potassium 40Argon billion yrs Rubidium 87Strontium billion yrs Thorium 232Lead billion years Uranium 235Lead million years Uranium 238Lead billion years Carbon 14Nitrogen 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 % C % N years 5730 years 5730 years 1/2 C-141/4 C-141/8 C-14 PARENT = C-14 DAUGHTER = N-14 C-14 Decay

M OLDS Are trace fossils Are not the organisms themselves, but is evidence that the organism has been there Depressions in a surface Smurf Mold

E XAMPLES OF M OLDS Lobster Fish Trilobite

C ASTS Three-dimensional trace of organism Protrudes out of surface of rock

E XAMPLES OF C ASTS Insect Trilobite Eurobrontes (dinosaur footprints)

I MPRINTS Different from moldsare not indented or depressed into its surface Different from castsdo not protrude from surface Thin layer of carbon which forms from where the organism was

E XAMPLES OF I MPRINTS Leaf Fish

B ODY P ARTS Actual parts of an organism left behind from the past Example: bones, organisms preserved in amber or ice

E XAMPLES OF B ODY P ARTS 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. A baby mammoth has been uncovered in the permafrost of north-west Siberia. Approx. 9,000 years old.

Gradualism- pg439

Punctuated Equilibrium-pg439