Uncovering Earth's Past: Fossil Formation and Preservation

1. Chapter 13 Clues to Earth’s Past

2. 1. How do we know they existed?2. Where can we find fossils?3. What process eventually exposes the fossil at the surface?

3. FOSSILS • Nearly all fossils are found in sedimentary rock

4. 4. What are fossils?

5. Fossils • Remains, imprints, or traces of prehistoric organisms • Prehistoric – before history was written • Tells when, where, and how organisms lived

6. 5. What is the name for scientists who study fossils?

7. Paleontologist • Scientists who study fossils

8. 6. What conditions are needed for fossils to form?

9. Conditions Needed For Fossils to Form: • Organisms must quickly be covered by sediment to keep scavengers away & bacteria from causing decay (bananas) • Organisms with hard parts have a better chance of fossilization b/c they decay slower

10. 7. What are the 7 types of preservation of fossils?

11. Answer to 7: permineralized remains, carbon films,coal, molds and casts, original remains, trace fossils, trails and burrows

12. 8. What are permineralized remains?

13. 7 Types of Preservation/Fossils: • Permineralized Remains • 1. when minerals fill small holes in hard parts like bone, teeth, & shells • Bones have small holes that are usually filled w/ blood cells, nerves, etc. When org. die, soft tissue decays leaving holes for minerals to fill • In some permineralized remains (fossils in which spaces are filled w/ minerals) can encase original genetic material • 2. water flows over buried fossil, dissolves fossil and fills space w/ minerals in water

14. 9. What are carbon films?

15. Types of Preservation • Carbon Films • Thin film of carbon residue that forms a silhouette of the organism • Sediment buries the dead org., as sediment piles up heat and pressure force liquids out leaving carbon behind

16. 10. What type of fossil preservation has accumulated plant matter that is buried and carbonized?

17. Types of Preservation • Coal • Plant matter accumulated & buried then carbonized forming coal • Since plant structure is usually lost there is not much revealed about the plant

18. 11. What type of fossil preservation has rock with pore space which allows water to flow through decaying the organism and leaving behind a cavity in the shape of the organism?12. Mineral-rich water flows through answer to #11 and fills cavity producing a copy of the organism is called _____________.

19. Types of Preservation • Molds and Casts • Hard parts of organisms are covered by sediment • sediment is compacted, cemented and turns to rock • Rock has pore space & allows water to flow through decaying the organism & leaving behind a cavity in the shape of the org. = mold • Mineral-rich water flows through mold & fills cavity producing a copy of the org. = cast

21. 13.What type of fossil preservation has organisms original remains preserved in amber, ice, or tar?

22. Type of Preservation • Original Remains • Original soft parts can be preserved in – • Amber – sticky tree resin • Ice • tar

23. 14. What type of fossil preservation has fossilized tracks and other evidence of organisms activity?

24. Types of Preservation • Trace Fossils • Fossilized tracks & other evidence of org. activity • Can tell size, weight, age, social behavior • Ex. Texas tracks of Sauropod, small prints inside large on outside – What des this suggest about social behavior?

25. 15. What type of fossil preservation has tunnels left behind by burrowing organism?

26. Types of Preservation • Trails and Burrows • Tunnels left behind by burrowing org.

27. 16. ______ fossils are the remains of species that existed on Earth for relatively short periods of time, were abundant, and were widespread geographically.

28. Index Fossils • Existed for short periods of time • Were abundant (lots of them) • Widespread geographically (covered a broad area) • Used to identify ages of other rock layers • Fossil Range Chart 367

30. Fossils determine past climates • Organisms that are limited to certain habitats can be found in completely different habitats • Ex: Fossils of sea organisms found in deserts tells us that desert was once covered by water • Fossils in VA are found mainly in Coastal Plain, Valley & Ridge, and Appalachian Plateau • Most fossils found in VA are marine org. • Proves that large area of state covered by seawater

31. Relative Ages of Rocks Section 2

32. Principle of Superposition • Older rocks on bottom, younger on top • Sediments accumulate in horizontal layers

33. Relative age • Determine the age of a layer of rock in comparison to the layers around it. • Ex: layers of sedimentary rock that are offset by a fault • Which is older the fault or the sedimentary rock? D B C A

34. “Structures” • Intrusions and faults

35. Igneous intrusion – where magma has filled a gap between rock layers

36. Fossils can be used to determine the age of disturbed rock layers • What conclusion can you draw if a younger fossil is found on the bottom and older on top?

37. Unconformities • When layers of rock are missing creating a gap in geologic time • Develop when agents of erosion (water, glaciers) remove layers by washing or scraping away

38. Types of Unconformities • Angular unconformity • Horizontal layers of rock are tilted and uplifted • Erosion & weathering erode the tilted rock layers • Younger sediment is deposited on top

40. Types of Unconformities • Disconformity • layer of rock that is exposed to erosion w/ no new deposition • Top layer as well as others can erode • Deposition begins again which leaves a gap in time F GAP IN GEOLOGIC TIME D EROSION DEPOSITION E C B B B A A A

42. Types of Unconformities • Nonconformity • Igneous or metamorphic rock are uplifted and eroded • Sedimentary rocks are deposited on top Sediment/sedimentary rock Igneous/ Metamorphic rock Igneous/ Metamorphic rock

43. How can you match rock layers • Finding the same types of fossils in the same type of rock will prove the rock layers are the same age

44. Absolute Ages of Rocks Section 3

45. Absolute Age • The age in years of a rock or other object • Determined using atoms that make up the material • Gives a numerical age to an event

46. Difference between Relative Age and Absolute Age • Relative age is a comparison with surrounding rock layers (no definite year) • Absolute age tells age in years

47. Radioactive Decay • The process of isotopes breaking down & giving off energy • Used to determine the absolute age of a rock • # of neutron determines form of element or isotope • Protons (p+) – in nucleus • Neutrons (n˚) – in nucleus • Electrons (e-) – cloud surrounding nucleus • # of p+ determines the identity • # of n˚ determines form of the element or isotope • Some isotopes are unstable & break down • Unstable atom changes into a new atom (parent material/daughter material) • Cut paper demo

48. How atoms breakdown: • Alpha Decay – isotope gives off 2 protons & 2 neutrons = alpha particle • Beta Decay – n˚ breaks down to a p+ & an e-, e- leaves atom = beta particle • Nucleus has lost a n˚ but gained a p+, # of p+ has changed & new element has formed

49. Half-life • Parent isotopes undergo radioactive decay either alpha or beta producing a daughter product • Each element has a given amount of time for half of the parent isotope to decay into daughter material • That amount of time is an isotope’s half-life • After each time period only half of the remaining parent isotope has decayed

50. Radiometric Ages • Radiometric dating – process used to calculate the absolute age • Using ratio of parent isotope to daughter product in a mineral & knowing the half-life of the parent • w/ older rock scientist have to pick elements w/ longer half-lives • Ex. 50 yr old rock Would you use an isotope w/ a half-life of 2 months.