Interpreting Geologic History

1. Interpreting Geologic History Introduction to Relative and Absolute Dating

2. The Solar System • The solar system is the sun and all objects that orbit the sun under its gravitational influence. • The solar system formed approximately 5 billion years ago (4.6 billion years ago).

3. Evolution of the Solar System • At first there was a gas dust cloud (nebula) that was released by the Big Bang Theory or by an explosion of stars. • Gravitation stemmed from a shock wave from an exploding star, caused the cloud to condense into one or more mass concentrations. • 99% of the nebula of our solar system makes our sun.

4. The Nebular Model of the Formation of the Solar System

5. Relative Dating of Rock Strata • Relative Dating is the determination of the age of a rock or event in relation to the age of other rocks or events. • The composition, structure, position and fossil content of Earth’s rocks provide information about Earth’s geologic history. • Evidence in Earth’s rocks dates back approximately 4 billion years.

6. Review of the Rock CycleSee p.6 in your reference table

7. Formation of Rock Strata • The rock strata below, originally formed from deposition (by water), compaction and cementation. • It was disturbed at some point in time by a magma extrusion.

8. Observing Rock Strata • How do we use rock strata for relative dating? • Always start at the bottom • The lowest layer is the oldest. • Pay attention to any disturbances A disturbance is anything that disrupts the layering of the parent rock. For example: look for faults folding or tilting metamorphism (both contact and regional) erosion

9. Look for the disturbances

10. Let’s Interpret Rock Strata • What are the order of events for the rock strata below?

11. Let’s Interpret Rock Strata What are the order of events for the rock strata below?

12. Lab Activity #1: Geologic Profiles • Please complete lab activity #1 titled: Geologic Profiles. • When finished, please complete the following: questions 1-7 on pages 280-281.

13. HW#1: July 11, 2011 • Regent review book, read pages 284-286. Answer questions for Regents practice pages 286-287 questions 21-36. Answer all questions in your workbook. • IF we did not get to it, please complete questions 1-7 on pages 280-281 and pages 283-284 #8-20 • Study for your quiz.

14. Correlation by Use of Index Fossils • Fossils are the remains or evidence of former living things. • Some examples of fossils are: • Bones • Footprints • Shells • Organic compounds (such as DNA)

15. Correlation by Use of Index Fossils • Index fossils are used to correlate rock layers. • An index fossil is an organism that lived • For a short period of time • Over a large geographic area

16. Index Fossils • With minor exceptions, fossils are found exclusively in sedimentary rock. • They are rarely found in igneous and metamorphic rock because fossils are usually destroyed by the melting of igneous rock and by the heat and pressure associated with the formation of metamorphic rocks.

17. How do we use index fossils to correlate rock layers? • Based on fossil evidence, determine the geologic period during which the unconformity formed. • Identify the coral index fossil that would most likely be found in the same layer as • the index fossil Ctenocrinus.

18. Lab Activity #2: Using Index Fossils to Correlate Rocks • Please complete lab activity #2. • When finished, please complete questions 8-15 on page 283 in your regent review book.

19. HW#2: July 12, 2011 • Answer questions for Regents practice pages 299-300 questions 45-47. Answer all questions in your workbook. • IF we did not get to it, please complete pages 283-284 #8-20 • Study for your quiz.

20. Interpreting Geologic Time • Pages 8 and 9 of your reference table shows the many geologic events and different forms of life that evolved over 4600 million years.

21. Reference Table page 8 • If you look at p. 8 it breaks down the 4600 million years into • Eons (the broadest time category) • Eras • Periods • Epochs (the simplest and most specific time category)

22. Reference Table p.9 • Time distribution of index fossils • Important Geologic Events in New York • Inferred Positions of Earth’s Landmasses

23. Lab Activity #3: Geologic Calendar • Please complete the Geologic Calendar Lab. • When finished, please complete questions 47-52 page 295 (if there is time). If not complete for homework.

24. HW#3: July 15, 2010 • Complete the handout about geologic history. • We will go over this worksheet at the beginning of tomorrow’s class (after your quiz). • Study for your quiz.

25. Radioactive Decay (Half Life) • The principle of superposition and methods of correlation help to determine the relative age of rock layers, but do not give their absolute age. • Absolute age is expressed in scientific units; such as years before the present.

26. Isotopes and Radioactive Decay • Isotopes are unstable forms of an element that differ from its parent element by its mass. • They emit particles and electromagnetic energy in a process called radioactive decay or nuclear decay thus changing into atoms of other isotopes and elements.

27. Radioactive Decay DataPage 1 of Reference Table

28. Half Life • The time required for half of the atoms in a given mass of an isotope to decay is called the half life of the isotope. • The half life of a radioactive isotope can be used along with the ratio between the amount of the original isotope and the amount of its decay product to estimate the absolute age of a rock sample. • This method is called radioactive (absolute)dating.

29. Lab Activity #4: The Half Life of M&M’s • Please complete lab activity #4. • When finished please answer questions 37-46 on p.290 in your regent review book. • If you do not get to this, please complete for homework.

30. HW#4, July 16, 2010 • Please complete questions 35-41 on pages 298-299 in your regent review book. • If not completed in class, please answer questions 37-46 on p.290 in your regent review book. • Study for your quiz. Have a great weekend.