Earth Science

1. Earth Science

2. Structure of the earth

4. Tectonics

5. Continental Drift Wegener’s Continental Drift Hypothesis (1912) stated that the continents had once been joined to form a single supercontinent (Pangaea). Wegener proposed that Pangaeabegan to break apart 200 million years ago and formed the present landmasses.

6. Continental Drift

8. Continental Drift Evidence • The Continental “Puzzle” • Matching Fossils • Rock Types and Structures • Ancient Climates

9. Matching Mountain Ranges

10. Glacier Evidence

11. Continental Drift Wegener could not provide an explanation of what made the continents move. New technology led to findings which then led to a new theory called plate tectonics

12. Plate Tectonics • According to the plate tectonics theory, the uppermost mantle, along with the crust, behaves as a strong, rigid layer (lithosphere) • A plateis one of numerous rigid sections of the lithosphere that move as a unit over the “softer” asthenosphere

16. Plate Boundaries • Divergent boundaries (spreading centers) are the place where two plates move apart • Convergent boundaries form where two plates move together • Transform fault boundaries are margins where two plates grind past each other without the production or destruction of the lithosphere

17. Plate Boundaries

18. Divergent Boundaries • Oceanic ridges are continuous elevated zones on the floor of all major ocean basins. • Rift valleys are deep faulted structures found along the axes of divergent plate boundaries. They can develop on the seafloor or on land • Seafloor spreading produces new oceanic lithosphere

19. Divergent Boundaries

21. Continental Rifts

22. Convergent Boundaries A subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate Oceanic-Continental: • Denser oceanic slab sinks into the asthenosphere; Pockets of magma develop and rise • Continental volcanic arcs form; Andes, Cascades

23. Convergent Boundaries

24. Convergent Boundaries Oceanic-Oceanic • Two oceanic slabs converge and one descends beneath the other • Volcanic island arcs form as volcanoes emerge from the sea • Examples include the Aleutian, Mariana, and Tonga islands

25. Convergent Boundaries

26. Convergent Boundaries Continental-Continental • When both subducting plates contain continental material • This kind of boundary can produce new mountain ranges, such as the Himalayas

27. Convergent Boundaries

28. Transform Fault Boundaries • Plates grind past each other without destroying the lithosphere • Most join two segments of a mid-ocean ridge • At the time of formation, they roughly parallel the direction of plate movement • They aid the movement of oceanic crustal material

29. Transform Fault Boundaries

31. Summary of Plate Boundaries

32. Evidence for Plate Tectonics Paleomagnetism is the natural remnant magnetism in rock bodies; is permanent • This can be used to determine the location of the magnetic poles at the time the rock became magnetized Normal polarity— rocks show the same magnetism as the present magnetic field

33. Evidence for Plate Tectonics Reverse polarity— rocks show the opposite magnetism as the present magnetic field • The discovery of strips of alternating polarity across the ocean ridges, is among the strongest evidence of seafloor spreading

34. Evidence for Plate Tectonics

35. Evidence for Plate Tectonics Hot Spots • A hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface; • Hot spots occur in the middle of a plate • The Pacific plate moves over a hot spot, producing the Hawaiian Islands • Hot spot evidence supports that the plates move

36. Evidence for Plate Tectonics

37. Convection: The Force Behind Tectonics

38. Earth's Tectonic Future