Record in the Rock

1. Record in the Rock What Processes Shape our Earth?

2. Earth Science- the study of earth and space Importance of Earth Science: • Contributes to our knowledge of the world • Understanding forces that shape our earth can better forecast potential disasters • Provides valuable resources • Makes life better through application of technology

5. Layers of the Earth • Characterized by a gradual increase in temperature, pressure, and density with depth • Inner Core: solid; composed mainly of nickel and iron • Outer Core: hot liquid made of nickel and iron • Mantle: thick layer; plasma; denser than crust • Crust: thin layer of silicates; two kinds of crusts- • Oceanic Crust: Older, thicker, less dense, granite • Continental Crust: Thin, younger, denser, basalt

7. Lithosphere: crust and upper part of the mantle (plate) Asthenosphere: part of mantle; less rigid than the lithosphere; convection currents flow here

8. Age of the Earth • Kelvin Method: • Assumed earth was hot molten rock • he measured rate of earth’s cooling to present • Took into account heat coming from the sun and from within the earth • Problem: was not aware of radioactivity • Measured radioactive decay of Uranium 238  Lead 206 • Estimated Earth as 4.6 Billion Years old

9. Henri Bequerel discovered the radioactive element Radioactive Decay: when elements break down Radiometric Dating: rate at which radioactive decay takes place Based on half-life (time to take ½ of element to decay) Radioactive decay rates don’t change! Examples: Nonliving: 3.9 billion year old rock of Uranium 238  Lead 206 Living: Carbon 14  Carbon 12 Radiometric Dating

10. Radioactive Half-Life (t1/2 ): • The time for half of the radioactive substances in a given sample to undergo decay. • After one half life there is 1/2 of original sample left. • After two half-lives, there will be 1/2 of the 1/2 = 1/4 the original sample.

11. Example 1 You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years. • How many grams are left after one half-life? • Answer:50 g • How many grams are left after two half-lives?

12. Example 2 • The half-life of iodine-131 is 8 days. • If you start with 36 grams of I-131, how much will be left after 24 days? • 36 g  1 half-life  8 days  18 g • 18 g  2 half-lives  16 days  9 g • 9 g  3 half-lives  24 days  4.5 g

13. Relative Dating: Finding the age of something compared to something else Law of Superposition- the bottom layer of an undisturbed section is older than the top Types of Relative Dating

14. 2. Original Horizontality- soil is deposited horizontally (fall to bottom) then form rock layers

15. 3. Lateral Continuity- layers of sediment extend in all directions when they form

16. 4. Law of Cross-Cutting Relationships- Folds and faults are younger than the layers that they cut across

17. 5. Inclusions- the inclusions (rock pieces) are older than the surrounding rock

18. 6. Faunal Succession- fossils can be used to identify relative age of layers of rock

19. -Index Fossil- 1. lived in a certain time span in many places 2. lived in great numbers 3. distinct features to identify -Correlation- matching rocks by Index Fossil in different places

21. Alfred Wegener • Believed in the theory called “continental drift” • The supercontinent (Pangea) split into pieces, then moved to different positions

22. Support • a system of under water mountain chains or mid-ocean ridges, rise thousands of meters above the ocean floor. • Youngest ocean floor rocks-near the mid-ocean ridge. • Oldest near the edges of the ocean basins • When the seafloor reaches a continental boundary, it is forced downward beneath the continent called the seafloor trench old young continent continent old Seafloor & trench Mid-ocean ridge

23. Plate Tectonics • Plates- crust that extends into the upper part of the mantle. • Upper part of the mantle is called the lithosphere. • The bottom part of the lithosphere that is a plastic like zone is called the asthenosphere. Mid-ocean ridge Continental Crust Continental Crust Ocean Crust Ocean Crust lithosphere Convection Current

24. Plate Tectonics Theory A relatively recent theory that the Earth's crust is composed of rigid plates that move relative to one another. Plate movements are on the order of a few centimeters/year - about the same rate as your fingernails grow! There are 3 types of plate boundaries: 1. divergent 2. convergent 3. transform

25. -Earth has 6 major plates and many small ones. 1. Eurasian 4. North American 2. Pacific 5. South American 3. African 6. Antarctic

26. Plate Boundaries • Divergent- two plates move apart. • Example- seafloor spreading at the Mid-ocean ridge. (6 cm per year)

27. Plate Boundaries 2. Transform- plates move past one another in opposite directions or in the same direction at different speeds Example- San Andreas fault

28. Plate Boundaries 3. Convergent- two plates collide -There are 3 types of plate boundaries

29. Convergent Plates • Two ocean plates collide- the edge of one is bent downwards. • Regions where the plates descend are called subduction zone • May form volcanoes or islands (island arc)

30. Convergent Plates b. Oceanic and continental plates collide- the denser oceanic plate descends into the athenosphere. - may form chain of volcanic mountains - Earthquakes are common

31. Convergent Plates c. Two continental plates collide- the continental rocks buckle and rise. - mountain chains form - earthquakes are common - very little volcanic activity -continental motion occurs (1-5 cm per year)

33. Convection Currents

34. HOT Spots • Stationary plumes of hot material that initiate at the core/mantle interface • Hawaii: the plume is beneath oceanic crust

35. Hot Spots • Yellowstone is associated with a hot spot under continental crust

36. Hot Spots