Chapter 17.1 Plate Tectonics

Plate Tectonics Overview Historical Development Continental Drift and Paleomagnetism

1) Overview-note major plates TECTONICS 1) Overview-note major plates

1) Overview-note associated volcano and earthquake activity PLATE TECTONICS 1) Overview-note associated volcano and earthquake activity

PLATE TECTONICS 1) Overview-note plate interactions that cause volcanoes, earthquakes, & trenches

2) Historical development PLATE TECTONICS 2) Historical development Note how some coastlines fit together like puzzle pieces

2) Historical development PLATE TECTONICS 2) Historical development 300 Million years ago Present

2) Historical development PLATE TECTONICS 2) Historical development 1915 Alfred Wegener published hypothesis of continental drift He hypothesized: existence of single “super-continent” Pangaea (“pan - G - uh”) ~ 200 million years ago Pangaea broke into smaller pieces, & “drifted” to present positions

P A N G A E A This is what Wegner hypothesized the world to be like 200 million years ago GONDWANALAND LAURASIA P A N G A E A

Below are maps of the movement Wegner hypothesized

2) Historical development PLATE TECTONICS 2) Historical development Fossil Evidence Several fossil organisms have been found in common on different continents -this supports the idea that these organisms lived on connected land masses Mesosaurus Lystrosaurus How can the same species evolve on widely separated continents??? Cynognathus Glossopteris

Note the location of identical fossil remains that are on continents which are now separated by oceans

Shown here are more examples of fossil remains and how the patterns of where they are found match to how the continents must have previously been arranged

More Fossil examples-observe how these support how the continents once fit together

2) Historical development PLATE TECTONICS 2) Historical development Rock evidence Mountain belts on one continent match up with another. Similar Mountainous structure and age of rocks: Appalachians (eastern US) Matches with British Isles and Scandanavia

Here is how the mountain belt patterns would have formed when the continents were once fit together

2) Historical development PLATE TECTONICS 2) Historical development Rock evidence Similar rock & mineral deposits are found on different continents – more evidence that the continents were once fit together.

2) Historical development PLATE TECTONICS 2) Historical development Paleoclimate evidence (ancient) Ice sheets covered big areas of southern hemisphere ~ 220-300 million years ago

2) Historical development PLATE TECTONICS 2) Historical development Paleoclimate evidence = fossilized evidence of climate situations Ice sheets covered big areas of southern hemisphere ~ 220-300 million years ago – left impressions in rock Glacial striations

Note where the ice sheet impressions are found and how this is evidence that these continents were once connected

2) Historical development PLATE TECTONICS 2) Historical development 1924 Wegener’s book was translated to English – more people read his ideas. His ideas were met with hostile criticism Main objection: In addition to some backlash from the religious community about the age of the Earth, Wegner had no way to explain the actual function that caused continental drift.

3) Continental drift and paleomagnetism PLATE TECTONICS Wegener’s idea died until 1950’s. Renewed interest from rock magnetism Paleomagnetism: ancient magnetic field of Earth recorded and frozen into rocks How? Need to know about 2 things: - Earth’s magnetic field - Magnetism in rocks

3) Continental drift and paleomagnetism PLATE TECTONICS Rock magnetism -Certain minerals are magnetic (e.g., magnetite, iron) -They loose magnetization when heated above Curie point (580oC for iron) -When cooled below Curie pt, magnetic grain aligns w/ Earth’s magnetic field so the direction of the field and the position of the rock where it was found in the Earth can be noted.

3) Continental drift and paleomagnetism PLATE TECTONICS Rock magnetism -Certain minerals are magnetic (e.g., magnetite, iron) -They loose magnetization when heated above Curie point (580oC for iron) -When cooled below Curie pt, magnetic grain aligns w/ Earth’s magnetic field - It is expected that the rocks will have magnetic alignment as shown below

“Polar wandering” 3) Continental drift and paleomagnetism PLATE TECTONICS “Polar wandering” A discovery in 1950’s showed that some rock formations were not aligned with what was expected. It was noted that what is the North Pole inferred from rock magnetization appears to have moved in past The conclusion is that either the North Pole has “wandered” or that the continents have drifted (The ones that were at the North Pole are now moved.)

This map shows the curves of polar migration (as per rock magnetic alignment). To overlay these 2 curves, North America needs to be moved uniting it with Europe on the ancient continent of Pangea.

Sea floor spreading 3) Continental drift and paleomagnetism PLATE TECTONICS Sea floor spreading Harry Hess, in the early 1960’s gave a proposal of a means by which continents could spread: As per observations of ocean ridges - he proposed these are above mantle upwellings, which cause seafloor to spread, like a conveyor belt Hess explained that an upwelling of magma replaces the gap in the seafloor as it moves away, becoming new oceanic crust This is supported by the observation of deep ocean trenches which are locations where oceanic crust has crevasses deep in planet

These illustrations show the convection movement of magma as it rises through the gap in the seafloor and pushes the crust outward.

3) Continental drift and paleomagnetism PLATE TECTONICS Geomagnetic reversals are also evidence that magma rises up and pushes the crust outward Earth’s magnetic field “reverses” approximately every 400,000 years The magnetic field is recorded rocks found in lava flows

Seafloor magnetic stripes have been observed and recorded 3) Continental drift and paleomagnetism PLATE TECTONICS Seafloor magnetic stripes have been observed and recorded 1963, Vine & Matthews connected seafloor spreading & continental drift, from magnetic field reversals recorded in cooling lavas of new seafloor symmetric patterns (“stripes”) on either side of spreading center (mid-ocean ridge) changes in width of a given stripe indicate changes in spreading rate.

This diagram shows the lava flows with the varying magnetic stripes recorded in the rock

In Conclusion: The Theory of Plate Tectonics is now well documented with significant evidence from fossil, mountain, and rock formations The Theory of Continental Drift is now well documented with significant evidence from sea floor spreading/magma upwellings and magnetic pole recordings in rock formations Scientists continue to collect evidence to further our understanding of how the surface of the Earth has changed over millions of years.