Presentation on theme: "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."— Presentation transcript:
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.
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 40 1.3 billion yrs Rubidium 87Strontium 8748.8 billion yrs Thorium 232Lead 20814 billion years Uranium 235Lead 207704 million years Uranium 238Lead 2064.5 billion years Carbon 14Nitrogen 145730 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
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.