Suggested that all the continents were once joined as one large land mass.
Think about the outward curve of South America and the inward curve of Africa – Could they fit together?
PANGAEA – name of the ‘Supercontinent’.
Theory accepted in 1930.
Notice how close the southern continents are to the South Pole.
Glaciers have left grooves/ridges in areas that are now tropical.
Not only did the continents drift apart, they shifted position away from the Pole.
Fossils of certain plants & animals have been found on different continents
This supports the theory that the land masses must have been connected at one time.
Rocks similar in age & structure have been found on different continents.
The Appalachian Mtns of the US match the Caledonian Mtns of Europe.
Rocks in Eastern South America match Western Africa.
What 3 pieces of evidence support continental drift?
1- similar climate
2- similar fossils
3- similar rocks
MORE HISTORICAL EVIDENCE…
Scientists found underwater Mountain ranges, Mid-Ocean Ridges, with rocks in the middle younger than rocks at the edges. (proven by Glomar Challenger )
Theory: Harry H ess (1960s) hot, less dense magma below Earth’s crust rises through ridges, flows side-ways, pushing older material with it.
Contracts as cools, is denser & sinks, forms ridge.
The Earth’s crust and part of the upper mantle are broken into sections, called Plates.
This portion is called the Lithosphere & it floats .
Beneath the Lithosphere is the plastic-like layer on which it floats, the Asthenosphere .
Combines the theories of Continental Drift & Seafloor Spreading.
Convection currents inside the Earth’s Mantle cause a cycle of heating, rising, cooling, & sinking down of material.
The transfer of heat inside the Earth provides the energy to move plates.
http://www.seismo.unr.edu/ftp/pub/louie/class/100/interior.html and http://www.seismology.harvard.edu/Projects.html Blue blobs show where colder, denser material is sinking into the mantle. Near the surface, most of the colder material is in the ancient roots of continents. Subducting slabs of oceanic lithosphere appear, recycled into the mantle from oceanic trenches.
http://www.seismo.unr.edu/ftp/pub/louie/class/100/interior.html and http://www.seismology.harvard.edu/Projects.html Red blobs are warmer plumes of less dense material, rising principally into the ocean- ridge spreading centers. A huge plume seems to be feeding spreading at the East Pacific Rise directly from the core. Most of the heat being released from the earth's interior emerges at the fast-spreading East Pacific Rise.
Session 1- (5 minutes)
What’s happening in your map?
Compare your map to your group members.
Do your maps have anything in common?
Use your blank map to mark on so you can see similarities easier.
What did your maps have in common?
Which map do you think is the “cause” and which map do you think is the “effect?”
Describing in your own words ….
List facts about…
15 major plates float on the Asthenosphere.
When plates move, they interact.
The results of movement are seen at the boundaries.
Notice the landmasses in relation to the plates & boundaries.
Two plates that are moving apart.
The Mid-Atlantic Ridge is an excellent example.
The Great Rift Valley in Eastern Africa is another example. It has yielded fabulous archaeological and geological information about the Earth.
AFRICA’S GREAT RIFT VALLEY
Oceanic & continental plates collide. Volcanoes form at or near boundary. 2 oceanic plates collide. Deep-sea trenches and/or volcanoes form at or near boundary.
2 plates collide.
Called Subduction when an oceanic plate is involved.
The area of the Mantle where this occurs is called the Subduction Zone .
The denser plate will sink under the less dense one; typically, oceanic under continental.
With water involved
2 continental plates collide. Mountain ranges, NOT VOLCANOES , form at or near boundary.
Such as the Himalayas & Appalachians .
Without water involved
Occurs when 2 plates slide past each other.
They can move in opposite directions OR in the same direction, but at different rates, causing earthquakes.
The San Andreas fault in California is the meeting point of the Pacific and North American plates. It is known as a Strike-Slip Fault.
Nearly 90% of all Earthquakes occur at Plate Boundaries.
Notice how the black dots in the picture on the left (which indicate earthquake activity) line up with the plate boundaries in the picture on the right.
World seismic hazard map
Volcano formation coincides with plate boundaries, especially along oceanic-continental boundaries.
The Pacific Ring of Fire is a particularly active volcanic region. It also matches the black dot (quake) region.
Hawaii is known as a hotspot.
Faults and Rift Valleys: Tension forces cause the Earth’s crust to stretch and pull apart. Examples: San Andreas Fault (Ca), Great Rift Valley (Africa), Mid-Atlantic Ridge (under the Atlantic Ocean).
Mountains: Formed when 2 continental plates collide , such as the Appalachians and the Himalayas.
Volcanoes: Formed when an oceanic plate collides with another plate, allowing magma to rise to the surface at the point of collision.
Faults: can occur when plate move in any direction
San Andreas Fault: sliding past each other (Transform fault)