T5 Fossils & the Rock Records

1. T5 Fossils & the Rock Records ...it’s as old as the hills. PowerPoint Notes created by S. Koziol Date : 12/1/2013 Revised : ?/?/??

2. Part 1 Objectives • Describe the geological time scale • Distinguish among the following time scale divisions: eon, era, period & epoch.

3. Time Scale The geologic time scale divides Earth’s history into units from its origin to the present. Time Scale – To be Completed

4. Blank Time Scale

5. Time Scale Continued

6. Recent period The most recent period is the Quaternary

7. Epoch On the geologic time scale, the smallest unit of time is called an epoch - longer than an age and shorter than a period.

8. Phanerozoic Eon The Phanerozoic Eon includes the Paleozoic, Mesozoic, and Cenozoic Eras

9. Eons The Archean and Proterozoic are examples of eons

10. End of the Precambrian The end of the Precambrian is marked by the appearance of organisms with hard parts. Cloudina, the earliest known calcium carbonate shell-bearing fossil.

11. Units of geologic time Units of geologic time in order from shortest to longest • epoch, period, era, eon

12. Periods Periods are defined by the abundance or extinction of life-forms.

13. Eras vs. Periods Both are units of time on the geologic time scale. Eras Periods are usually measured in terms of tens of millions of years to hundreds of millions of years. They are defined by the life-forms that were abundant or became extinct during the time in which specific rocks were deposited. are longer spans of time, measured in hundreds of millions to billions of years. They are defined by differences in life-forms found in rocks.

14. Part 2 Objectives • Apply the principles for determining relative age to interpret rock sequences. • Describe an unconformity and how it formed within the rock record.

15. Oldest rock layer The oldest rock layer in an undisturbed rock sequence occurs at the bottom of the sequence

16. The Principle of Superposition The principle of superposition states that, in an undisturbed sequence, the oldest rocks are at the bottom of the sequence and successive layers are younger than those below them.

17. Cross-cutting Relationships You can use the principle of cross-cutting relationships to infer that a fault or an intrusion is younger than the rock it cuts across.

18. Correlation The matching of rock layers from one geographic area with those of another area is known as correlation.

19. Inferences and rock layers

20. Uniformitarianism The principle of uniformitarianism states that the processes occurring today have been occurring on Earth since it formed. However, the rate, intensity, and scale with which these processes occur have changed.

21. Unconformity When part of the rock record is destroyed, the erosional gap that forms is an unconformity.

22. Angular Unconformity The gap in the rock record that occurs between folded or uplifted rock layers and a sedimentary rock layer on top of them is called an angular unconformity.

23. Nonconformity A buried erosional surface between a nonsedimentary rock and a sedimentary rock is called a nonconformity.

24. Part 3 Objectives • Explain the several different methods used by scientists to determine absolute age. • Describe how objects are dated by the use of certain radioactive elements. • Explain how annual tree rings and glacial varves are used to date geological events.

25. Half Lives for Radioactive Elements ½ Life The amount of time it takes for one-half of the original amount of an isotope to decay is known as its half-life. ½ Life Practice Sheet

26. Absolute dating Radiometric dating is used to determine the absolute age of a rock

27. Key Beds A key bed contains distinctive material that geologists can easily recognize in the rock record and use as a time marker.

28. Contrast relative-age dating and absolute-age dating. Relative-age dating Absolute-age dating In contrast, absolute-age dating determines the actual age of a rock, a fossil, or an object. This is done through radiometric dating, a process that determines the ratio of parent material to daughter product in a given sample of rock or fossil. Relative-age dating places the ages of rocks and the events that formed them in order, without exact dates. This is done by comparing one event with another or one rock with another rock.

29. Part 4 Objectives • Define fossil. • Explain several methods by which fossils can be preserved. • Describe the characteristics of an index fossil. • Discuss how fossils can be used to interpret Earth’s past physical and environmental history.

30. Fossils  Fossils are the remains or evidence of once-living plants or animals. They provide clues about Earth’s past environmental conditions and evolutionary changes in organisms over time. They also help to correlate rock layers from one area to another.

31. Fossils (continued) Fossil insects preserved in hardened tree sap are called amber.

32. Fossils (continued) Molds, casts, coprolites, and petrified wood are all example of fossils

33. Fossils - original preservation Mummified animals found in dry caves can be examples of fossils with original preservation.

34. Fossils - original preservation Fossil insects can be found imbedded in amber, the hardened sap of prehistoric trees. An insect imbedded in amber is an example of a fossil with original preservation.

35. Fossils (altered) An example of a fossil with altered hard parts includes petrified wood

36. Trace Fossils An example of a trace fossil includes worm trails.

37. Permineralization In the process of permineralization, pore spaces within an organism’s shell are filled in with mineral substances.

38. Fossils - casts A cast forms when the hollowed-out impression of a fossil organism becomes filled with minerals or sediment.

39. Fossils - molds When the original parts of an organism in a sedimentary rock are weathered and eroded, a hollowed-out impression called a mold forms.

40. Index fossils Index fossils are useful to geologists if the fossils have lived over a short period of time

41. Index vs. Trace Fossils  Both are similar in that they are types of fossils. Index fossils Trace fossils are not remains but indirect evidence of organisms, such as imprints, trails, and burrows. are the remains of organisms that can be used by geologists to correlate rock layers over large geographic areas or to date rock layers.

42. Evolution The adaptation of life-forms to changes in the environment is known as evolution. A process by which (generations of) organisms adapt to changes in their environments.