Earth&PlateTectonics_Butler_ERBmod.ppt
- 3. PLATE TECTONICS • The theory that the Earth’s outermost layer is fragmented into a dozen or more large and small plates that move relative to one another as they ride on top of hotter, more mobile material.
- 4. PLATE TECTONIC • The Earth’s crust is divided into 12 major plates which are moved in various directions. • This plate motion causes them to collide, pull apart, or scrape against each other. • Each type of interaction causes a characteristic set of Earth structures or “tectonic” features. • The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.
- 5. • At the beginning of the 20th century, many scientists explained the physical attributes of the Earth using the Raisin Theory.
- 6. WHAT IS THE RAISIN THEORY? • known as the "Geosynclinical Theory" or "Geosyncline Hypothesis", • According to this principle, the level of the Earth’s crust is determined by its density; lighter material rises, forming continents, mountains, and plateaus, and heavier material sinks, forming basins and ocean floors. Clarence Edward Dutton
- 8. Convection is like a boiling pot. Heated soup rises to the surface, spreads and begins to cool, and then sinks back to the bottom of the pot where it is reheated and rises again. Plate tectonics • Plates are driven by cooling of Earth (convection) • Gravity provides additional force to move plates. Modified from USGS Graphics ? ? ?
- 9. What are the tectonic plates? AKA: Lithospheric plate • The ~100-km-thick surface of the Earth; • Contains crust and part of the upper mantle; • It is rigid and brittle; • Fractures to produce earthquakes.
- 10. What is the asthenosphere? Asthenosphere: • Is the hotter upper mantle below the lithospheric plate; • Can flow like silly putty; and • Is a viscoelastic solid, NOT liquid!! USGS Graphics
- 11. Three Basic Types of Plate Boundaries Divergent Convergent Transform USGS Graphics Using hands to show relative motion
- 12. Three Basic Types of Plate Boundaries Divergent Convergent Transform USGS Graphics
- 13. There are a dozen large lithospheric plates (smaller plates not shown). Some plates have continents; some don’t. All are in motion. Question: What evidence is there for these plate boundaries? Tectonic Plates
- 14. There are thousands of small earthquakes every day “Strong” earthquakes (~M7) occur once a month. >M8 occur about once/year. Earthquakes Where are the deepest earthquakes? For earthquakes of the past 2 weeks, go to http://www.iris.edu/seismon/
- 15. Notice that the earthquakes coincide with plate boundaries, and the deepest quakes (blue) are in subduction zones. Question: Where would you expect to see volcanoes? Modified from USGS Graphics Earthquakes & Plate Boundaries Create your own maps at http://www.iris.edu/quakes/maps.htm
- 16. Modified from USGS Graphics This map shows that locations of volcanoes (ones above sea level) also tend to occur along the plate boundaries Volcanoes & Plate Boundaries
- 17. How fast are the plates moving? Plates move 1-10 centimeters per year (≈ rate of fingernail growth). Tectonic Plates Modified from USGS Graphics Fingernail growth plotted: http://jclahr.com/science/earth_science/thumbnail/index.html
- 18. How fast are the plates moving? Plates move 1-10 centimeters per year (≈ rate of fingernail growth). Continental Drift Source: http://www.tectonics.caltech.edu/outreach/animations/index.html
- 19. •CONTINENTAL DRIFT •Alfred Wegner was one of several people who thought the continents looked like they fit together, so he proposed the continental drift theory in 1912. Wegner was a meteorologist and astronomer so needless to say other scientists thought he was out of his field of study.
- 20. •His studies concluded that at one time all the continents were joined together in one land mass called Pangaea. • 1. Laurasia was the name given to the northern part of Pangaea •2. Gondwanaland was the name given to the southern part of Pangaea
- 21. Scientists thought this theory was outrageous because even though Wegner had evidence of one large land mass, he didn’t have the answers to what force (engine) “floated the plates”. He was laughed at and did not live to see his theory accepted. •This animation begins with the continents in their present location, and then moving back in time to form PANGAEA. The circles represent fossil evidence that Wegner used to prove his Continental Drift Theory. •PANGAEA means “all land”
- 22. • WHERE’S THE EVIDENCE • Wegner had 5 pieces of evidence to prove his continental drift theory: 1. PUZZLE PIECES: • The continents, especially South America and Africa, seemed to fit together like a puzzle.
- 23. 2. FOSSIL EVIDENCE: • Wegner noticed that plant and animal fossils were found on different continents. Do you think they swam all the way across the oceans? NO! This would lead people to believe that the continents were once joined. •Glossopteris…seed much to large to be windblown •Mesosaurus…lived in fresh water and could not have lived in salt water
- 25. •3. ROCK EVIDENCE: •Huge belts of rocks found in Africa and South America were identical. Not only were they the same, but they would match up (age, thickness, types) if the continents were put together. •Matching Mountains •The Appalachian Mountains that disappear off the coast of Newfoundland match mountains in the British Isles and Scandinavia which are comparable in age and structure.
- 26. •4. GLACIER EVIDENCE: •There is proof that glaciers moved from Africa, through the Atlantic Ocean, and then on towards South America. This would be much easier if the Atlantic Ocean were not there
- 27. •Glacial Striations…Scratches glaciers leave •on rocks as they travel
- 28. •5. CLIMATE EVIDENCE: •Warm weather plants have been found in the Arctic… but it’s not warm there! •Glacier deposits have been discovered in tropical and desert locations…it’s not cold there, either! •The continents had to have been at different locations in the geological past. •DVD on Continental Drift
- 29. •?????????? ONE QUESTION REMAINED ?????????? •WHAT FORCE WAS MAKING THE CONTINENTS MOVE •TOMORROW •FIND OUT •WHAT FINALLY PROVED THAT WEGNER’S •CONTINENTAL DRIFT THEORY •WAS RIGHT?
- 30. • AMAZING EARTH SCIENCE FACTS 1. The 4 pieces of evidence that support Continental Drift are •______________ fit together like puzzle pieces •__________ showing the same types of life existed •on the now separated land masses •___________________________match up along •coastlines of once joined continents •____________ evidence in temperate and hot •climates •Continents •Fossils •Rock layers & mountains •Glacial
- 32. Collision of ‘Drifting’ India with Eurasia Source: http://www.tectonics.caltech.edu/outreach/animations/index.html Side view of subduction, ‘drifting’ India, volcanoes, & mountain-building
- 33. Note on Source: First 8 slides are modified from a slide show prepared by Dr. Robert Butler, University of Portland, and Jenda Johnson, …the full source of which can be found at: http://www.iris.edu/hq/programs/education_and_outreach/videos#B