1. Fossils & The Geologic Time Scale

2. Fossils Preserved remains or traces of an organism that lived in the past. Fossils are formed when organisms die and are buried in sediment. Eventually the sediment builds up and hardens to become sedimentary rock. law of superposition – oldest layer is at the bottom and each higher layer is younger than the layers belowsuperposition

3. Kinds of fossils Petrified - when minerals replace the remains and they become rock Mold - when the shell remains and the contents dissolve (hollow) Cast - when the mold becomes filled with minerals that are not a part of the original organism

4. PETRIFIEDMOLD CAST

5. Sometimes whole animals become preserved intact, but this is very rare. If an organism is surrounded by ice or tar they might be discovered looking much the same as they did when they died. AETOSAUR FOUND IN THE NATIONAL PETRIFIED FOREST

6. Relative Dating Relative dating: looks at where the fossil is located to determine its age relative to other fossils. This only works if the area has been undisturbed.

7. Absolute Dating Uses radioactive elements near the fossils to determine the actual age of the fossils. By determining the age of the radioactive element, scientists can calculate the age of the fossil buried nearby. The absolute age of fossils is estimated by dating associated igneous rock and lava flows.

8. Radioactive dating Radiometric dating or radioactive dating is a technique used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they formed

9. Index Fossils Index fossils (also known as guide fossils, indicator fossils or zone fossils) are fossils used to define and identify geologic periods (or faunal stages). Help geologist match rocks layers and represent a type of organism that existed only briefly

10. Fossil Record The dating of all fossils is included in the Geological Time Scale. This scale divides the time that the earth has existed into 4 eras. Eras are then divided into periods based on common events in that time period.

11. The Geologic Timeline a record of the life forms and geologic events in Earth’s history

12. Pre- Cambrian Began with the formation of the Earth 4.6 billion years ago. Bacteria appeared 3.5 billion years ago, followed by algae and fungi.

13. Paleozoic Era Divided into 5 periods: Cambrian period - Sponges, snails, clams and worms evolve Ordovician period - First fishes evolved and other species become extinct Silurian period - Land plants, insects and spiders appear

14. Devonian period - Amphibians evolve and cone-bearing plants start to appear. Carbonferous period - Tropical forests appear and reptiles evolve. Permian period - Seed plants become common and insects and retiles become widespread. Sea animals and some amphibians begin to disappear.

15. Mesozoic Era Divided into 3 periods: Triassic period - Turtles and crocodiles evolve and dinosaurs appear. Jurassic period - Large dinosaurs roam the world. First mammals and birds appear. Cretaceous period - Flowering plants appear, mammals become more common, dinosaurs become extinct.

16. Mesozoic began about 245 million years ago and lasted about 180 million years; the Age of the Dinosaurs and mammals began to evolve; “meso-“ means middle

17. Cenozoic Era Divided into 2 periods: Tertiary period - First primates appear and flowering plants become the most common. Quaternary period - Humans evolve and large mammals like woolly mammoths become extinct.

18. Cenozoic most recent era; began about 65 million years ago and continues to present day; the Age of Mammals; “ceno-“ means recent 3.Periods – these are subdivided eras and are characterized by what life existed worldwide 4.Epochs – further subdivided periods of the Cenozoic Era because the fossil record of this era is more complete and there are a lot more events to place in sequence.