Layers of the Earth Using a laser pointer, briefly highlight and describe the layers of the earth’s interior. Also highlight the fact that the earth has oceanic and continental crust.

CRUST/LITHOSPHERE thinnest layer floating on mantle is cool and solid between 3 - 40 km thick floating on mantle Oceanic Crust: 3 - 8 km thick Continental Crust ~ 40 km thick

Mantle/Athenosphere average thickness is about 2880 km solid but very hot behaves like plastic, flowing and circulating slowly without breaking

Core radius ~ 3470 km half of the Earth’s diameter metallic - made of iron and nickel outer core - liquid inner core -solid

Supercontinent Pangea – all lands Similar Reptiles and insects Tropical forests coal deposits Discuss the theory of Pangea and show animation (click on link). Tens of Millions of years ago!

Pangaea Wegener revived the early idea of continental drift, contending that all of the present-day continents were connected, side-by-side, as long ago as the Carboniferous (~300 Myr). He called the supercontinental mass Pangaea, Greek for ‘all lands’.

Today’s Continents As soon as maps of the globe became available, people wondered about the arrangement of the continents and oceans. Hundreds of years later, valid explanations were constructed.

The crust and lithosphere are broken up into 25 Plates USGS

Movement of the Plates: Continental Drift Evidence How it works

Continental Drift: Fossil Evidence Mesosaurus: purely freshwater reptile Glossopteris: seeds too large to be effectively wind-transported

Continental Drift: Rock Ages Rock ages showed strong correlation across the Atlantic, as did mountain ranges of similar age

Continental Drift: Geometry evidence shape of the continents eg. the shape of the west coast of Africa and the east coast of South America are remarkably similar and were perhaps once joined

More Evidence:Mantle Convection Materials that can flow tend to lose thermal energy by the convection process. This explains circulation in a pot of water that is being heated from below in the same way it describes the convection currents in the Earth’s mantle.

Where convection rises sea floor spreading takes place. Mantle Convection Giant convection cells within the upper mantle drag the plates along laterally. Where convection rises sea floor spreading takes place. Where the convection cells descend they drag crust down, causing subduction

How does it work? Plates – pieces of the lithosphere Plates fit closely together along cracks called Plate Boundaries Convection Currents  movement Explain that the lithosphere is broken into pieces called plates. The place where the pieces fit together are the boundaries. Using a laser pointer, explain the theory that plate movement is caused by convection currents in the mantle.

Here is another version of the Rock Cycle http://www.volcanoworld.org/vwdocs/vwlessons/lessons/Metrocks/Metrocks2.html

Mechanisms of Plate Tectonics:

Mechanisms of Plate Tectonics: 2 Ridge-Push RIDGE 1 TRENCH MANTLE 3 drag convective flow of mantle

Sea Floor Spreading Hot material rose at the oceanic ridges, thus explaining the high heat flow and volcanic activity, and why the ocean floor is bulged up at the ridges. The logical next step is that where continent and ocean meet, at the trenches, ocean crust is being returned to the mantle at the same rate it is being generated at the ridges.

Types of Boundaries Divergent Convergent Sliding Define each term. Have the students as a class mimic the movement of divergent, convergent, and transform boundaries using their hands. Use the hyperlinks as visuals while discussing each type of plate boundary.

To summarize……

C Sliding B Convergent A Divergent plates are moving apart new crust is created Magma is coming to the surface plates are coming together crust is returning to the mantle plates are slipping past each other crust is not created or destroyed

C Sliding B Convergent A Divergent Plates move against each other Stress builds up Stress is released earthquake 2 continental plates  mountain range Continental crust  rift valley Oceanic crust  mid-ocean ridge C Sliding B Convergent A Divergent 2 oceanic plates or oceanic + continental subduction

DIVERGENCE: Sea Floor Spreading Sea floor spreading, leads to continental drift *This hypothesis makes a number of testable predictions.*

* Taking magnetic stratigraphy back in time is paleomagnetism. * Magnetic Reversals Interestingly, the polarity of the magnetic field shifts every 0.5 - 1.0 Myr. That means rocks formed over time will record either ‘normal’ magnetic orientation (like today), or ‘reversed’. This leads to alternating bands of normal and reversed magnetism. We are apparently headed into a polarity reversal, to be complete in ~3000 yr. * Taking magnetic stratigraphy back in time is paleomagnetism. *

Paleomagnetism and Sea Floor Spreading The magnetic stripes as products of steady creation of new ocean crust over geologic time.

Oceanic Ridges

The ridge is a Divergent Plate Margin and divergence takes place by Sea Floor Spreading. From http://www.uwsp.edu/geo/faculty/ritter/glossary/s_u/sea_flr_spread.html New crust is added from upwelling magma (molten rock) from the upper mantle. Older crust is pushed laterally away from the ridge axis – so that the sea floor spreads away from the ridge axis.

CONVERGENCE: Oceanic Crust – Continental Crust The denser oceanic crust descends beneath lighter continental crust. Coastal mountain chains develop due to compressive forces and volcanics (e.g., the Andes of South America). Magma material rises from descending slab and builds volcanoes in the rising mountains.

CONVERGENCE: Oceanic Crust-Oceanic Crust The oldest, densest crust normal descends beneath the younger crust. Volcanic islands develop at the surface of the over-riding crust (forming Island Arcs) - e.g. Hawaii

Continental Crust-Continental Crust CONVERGENCE: Continental Crust-Continental Crust Neither plate subducts (both too light). Compressive forces driving plates fold and thrust the continental margins forming an extensive mountain belt (e.g., the Himalayan Mountains).

SLIDING: Slip-Strike Faults Plate margins along which the plates slip by each other. Termed: Slip-Strike Faults/Transform Faults On either side of a fault plate motions are in opposite directions.

The Big Picture Remind students to look for their assigned boundaries and write down information to describe them.