Earth’s Interior

1. Earth’s Interior Tectonics, earthquakes & volcanoes

2. Interior structure • The Earth is divided into several layers based on similar temperatures, materials, pressure, and depth

3. Interior Structure The materials that make up the Earth separated as the Earth cooled. The lighter materials rose to the surface and the heavier materials sunk to the center. Movement of heavy metals in the liquid outer core is responsible for the Earth’s magnetic field.

4. Interior Structure The mantle of the Earth is made of a mixture of hard, rigid rocks in the lower mantle and plastic, more flexible rocks in the upper mantle. The differences in temperature between the upper and lower portions of the mantle plus the flexibility of the upper mantle cause currents of material that move the crust above the mantle. HOT MATERIAL RISES, COOL MATERIAL SINKS

5. Interior structure The crust of the Earth is broken up into sections called tectonic plates made up of the lithosphere.

6. Interior Structure Oceanic crust is heavier and more dense so it sinks and stays below the water. Continental crust is lighter and less dense so it rises above the water.

7. Plate Tectonics • Geologist have known that the Earth’s landmasses have not remained in the same place throughout time • Early mapmakers first considered the idea that the continents have moved because of the similarity of coastlines between certain continents.

8. Plate Tectonics • History of plate movement based on current evidence.

9. Plate Tectonics History of Discoveries • 1500’s Abraham Ortelius(Dutch) noticed the fit of the continents surrounding the Atlantic Ocean and proposed (incorrectly) that the continents became separated by a series of earthquakes and floods • 1800’s Eduard Suess(Austrian) proposed that the Southern continents had once been joined in a single landmass

10. Plate tectonics • 1900’s Alfred Wegener(German) hypothesized that all the landmasses fit together in a supercontinent called Pangea in his 1912 publication • He reasoned that as the supercontinent broke apart the geologic structures fractured leaving small gaps along what would otherwise be matching coastlines • He found evidence on the modern continents to support his theory of an ancient supercontinent

11. Plate Tectonics Continental Drift Hypothesis: states that the continents had once been joined to form a single supercontinent (Pangaea)andbegan to break apart 200 million years ago to form the present landmasses Evidence to support the hypothesis: • Continent shapes • Fossils • Geologic Patterns • Climate Patterns

12. Plate tectonics Continent Shapes: • Scientists have studied the shorelines of continents to see how they may have fit together • The most obvious connection lies between Africa and South America

13. Plate Tectonics Fossils: • The same fossil groups have been found on separate continents with distances too great for organisms to travel if the continents were in the same places.

14. Plate tectonics Geologic Patterns: - Similarities in mountain ranges show that the mountains on separate continents may have been formed when they were joined together NOW THEN

15. PLATE TECTONICS Climate Patterns: - Glacier evidence on all of the modern day continents suggest that the continents all fit together and were located around the area of modern day Antartica

16. Plate tectonics Wegener’s Missing Pieces • Explanation of WHAT caused the continents to move • Explanation of HOW the continents continued to move He was never able to answer these two questions in his lifetime. He froze to death on an expedition to Greenland still investigating evidence to support his hypothesis.

17. Plate Tectonics • After Wegener’s death in 1930 scientists continued to search for the mechanisms behind his continental drift hypothesis • Shortly after his death Arthur Holmes proposed that mantle convection was the driving force behind the movements of the continental landmasses. His theory was proven correct but not until years after his initial proposal. Arthur Holmes 1890 - 1965

18. Plate Tectonics • Until the 1900’s the belief was that the ocean floor was completely flat and unchanging • During WWII submarine warfare and the use of SONAR began to prove this belief to be false when underwater mountains and valleys were mapped to help guide the submarines across the Atlantic Ocean

19. Plate Tectonics • The maps of the ocean surface, sediment cores and magnetic readings after WWII confirmed that the ocean floor is constantly changing and shows evidence of the tectonic activity proposed by Arthur Holmes.

20. Plate Tectonics Theory of Plate Tectonics: theory that helps explain the formation and movement of the tectonics plates which make up the Earth’s crust This led to the formation of the modern day landmasses and their current locations.

21. Plate tectonics Modern day plate sizes and locations:

22. Plate movement • Plates meet at locations called plate boundaries. • Where these plates meet movement causes activities like earthquakes, volcanoes, and mountain building

23. Plate movement Divergent Boundaries: places where the tectonic plates are moving apart Examples: mid-ocean ridges, rift valleys

24. Plate movement Divergent Boundaries Seafloor spreading: as oceanic plates move apart new ocean floor is built by cooling lava

25. Plate movement Divergent Boundaries Continental Rift Valleys: places in the middle of a continental plate where spreading is occurring

26. Plate movement Convergent Boundaries: plate boundaries where two plates are moving together - Types of convergent boundaries rely on the type of crust that is being moved together

27. Plate movement Convergent Boundaries Oceanic vs. Continental -forms where a piece of oceanic crust is subducted(pulled under)beneath a section of continental crust Subduction zone: Ocean plate slides under continental plate and forms a deep-ocean trench and continental volcanic arc

28. Plate movement Convergent Boundaries Oceanic vs. Oceanic - Forms when one oceanic plate is subducted under another oceanic plate. - Creates a deep ocean trench and a volcanic island arc

29. Plate movement Convergent Boundaries Continental vs. Continental - Forms when two continental plates collide and form mountain ridges

30. Plate movement India and Eurasia Collision

31. Plate Movement Transform Fault Boundary: plate boundary where two plates move past each other along a fault (break in the crust) - High numbers of earthquakes occur in these areas Example: San Andreas Fault

32. Plate movement What causes this movement? Isostasy: the idea that the upper mantle of the Earth is elastic and will adjust to the weight of the plates above it ISOSTASY ANIMATION

33. Plate movement What causes this movement? Convection currents: circulation of molten rock within the mantle. As hot magma rises and cool rock sinks plates begin to move

34. Evidence of plate tectonics The Earth supplies evidence for plate tectonics on a daily basis because it is constantly changing. - Tectonic activity like seafloor spreading, earthquakes and volcanoes are the best source of evidence to prove the plate tectonics theory Map of worldwide earthquake and volcano activity.

35. Evidence of plate tectonics Earthquake: shaking and trembling that results from sudden movement of part of the Earth’s crust Reasons Why Earthquakes Occur: - Volcanic eruption -collapse of a cavern -impact of meteor -major cause: stress that builds up and causes faulting

36. Tectonic Changes Tension Stress: a force acting on a material Tension: stress that pulls apart Compression: stress that pushes together Shear: stress that twists Compression Shear

37. Tectonic CHanges Stress: the force that acts on a material Strain: a weakening or change in a material CAUSES STRESS STRAIN

38. Tectonic CHanges 2 types of Strain • Elastic – material deforms and then goes back to its original shape after the stress is removed • Like a rubber band • Ductile – material deforms and stays deformed after the stress is removed • Like play-doh

39. Tectonic Changes Fault – a fracture or break in rock that happens when stress is applied too quickly or strain is too great • Faults are often concentrated around plate boundaries • When stress is relieved around a fault it causes an earthquake

40. Tectonic CHanges Normal Fault: tensional stress pulls plates apart and stretches the Earth’s crust

41. Tectonic Changes Reverse fault: compression stress pushes the plates together and squeezes the crust

42. Tectonic Changes Strike-Slip fault: shear stress forces plates to move past each other

43. Earthquakes When the stress becomes too much the plates experience a sudden shift and release of energy. Elastic Rebound Theory: theory that explains how rocks that are strained past a certain point will fracture and spring back to their original shape

44. earthquakes • Earthquake Anatomy Epicenter: point on Earth’s surface directly above the focus Focus: point beneath the Earth’s surface where the rocks break or move apart

45. earthquakes Earthquake Wave Motion P Waves: -move fastest -move through solid, liquid or gas -push-pull waves

46. Earthquakes Earthquake Wave Motion S Waves: -travel slower -move side to side -travel through solids

47. Earthquakes Earthquake Wave Motion L Waves: -move slowest -move like ripples on a pond -move only through the crust

48. Earthquakes Earthquake Wave Motion Earthquake information is picked up by seismic recording stations around the world. Seismograph: instrument that detects and measures seismic waves

49. Earthquakes P waves travel faster so they arrive first followed later by S waves. The further the distance from the epicenter the longer the time between earthquake waves. Blue lines = primary waves Red lines = secondary waves

50. Earthquakes Seismogram: seismograph’s record of waves; shows vibration lines from the shaking motion of the earthquake waves The amount of time between the P and S waves indicate how far from the epicenter the recording station is.