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The Layers of Earth
• Earth is over 1200 km thick and has four distinct layers:
1. Crust – outer solid rock layer (granite on land, basalt in oceans)
2. Mantle – thickest layer, mostly solid except for upper mantle being able to flow like “thick toothpaste”
3. Outer core – composed of liquid iron and nickel4. Inner core – mostly solid iron, at tremendous
temperature and pressure
The Upper Mantle....
• We know the “Lithosphere” contains the Earth’s crust and the uppermost part of the upper mantle.
• Just below this is the “Asthenosphere”– A partly MOLTEN layer
of the upper mantle
Plate Motion• The plates move because of convection currents
arising in the hot magma of the upper mantle in the Asthenosphere....
2 Q’s: What makes this layer HOT?
What causes the “currents”?
What Makes the Layer HOT!• Partly the upper mantle is hot
because of Earth’s hot core.... • The temp of the upper mantle varies
throughout• Large amount of RADIOACTIVE
elements (ex: Uranium) occur in certain spots –When these decay...they release HEAT!
What Causes the “Currents”Just like in air masses.....HEAT RISES!
Hot (less dense) material rises…cools….sinks….reheats
The Driving Force...• This “mantle convection” is the driving force
behind the movement of tectonic plates!
Tectonic Plates can PUSH or PULL
“Spreading Centers” are areas of the Earth’s surface where magma rises up....
(common) (less common)
IN OCEAN....“Spreading Ridge”
On LAND....“Rift Valley”
“Out with the OLD, In with the NEW”
• When magma rises and cools it forms new rock.• This new rock PUSHES old rock ASIDE
“RIDGE PUSH”
SUBDUCTION• When plates “bump” into each other, they
may subduct....
Consider a “heavy, dense” oceanic plate bumping into a lighter continental plate....
SLAB PULL• When a plate subducts deep into the
mantle....it PULLS the rest of the plate too
“SLAB PULL”
Action in the Subduction
Zones!• SUBDUCTION
ZONES experience more
– EARTHQUAKES
– VOLCANIC ERRUPTIONS!
• YouTube - Continental Drift & Plate Tectonics (clip)
Plate Interactions
• A plate boundary is an area where two plates are in contact.Divergent plate boundaries – areas where plates are
spreading apartConvergent plate boundaries – areas where plates
meet• Oceanic-continental• Oceanic-oceanic• Continental-continental
Transform plate boundaries – areas where plates move past each other
Divergent Plate Boundaries
1. Divergent plate boundaries are areas where plates are spreading apart.– Ocean ridges and continental rifts are examples.– The Mid-Atlantic Ridge is the longest mountain range on
Earth.
Convergent Plate Boundaries
2. Convergent plate boundaries are areas where plates collide.A. Oceanic-continental plate convergence• The oceanic plate subducts under the continental plate,
forming a trench.• Cone-shaped volcanoes can form from magma seeping to
the surface.• This is how the volcanic belt of North America’s west coast
has formed.• Mountain ranges like the Coast Mountain
range also formed from the collision.• Earthquakes can occur when subduction,
ridge push, and slab pull stall.
Oceanic-Oceanic Convergence
B. Oceanic-oceanic plate convergence– The cooler, denser plate will subduct
under the less dense plate.– Convergence may produce a volcanic island arc,
such as those found in Japan, Indonesia, and Alaska’s Aleutian islands.
Continental-Continental Convergence
C. Continental-continental plate convergence– Since both are continental plates,
their densities are similar.– As they collide, their edges fold and
crumple, forming mountain ranges.– The Himalayas are the world’s youngest (and tallest)
mountain range, formed as Asia and Africa plates collided 40 million years ago. They are still growing taller today.
Transform Plate Boundaries3. Transform plate boundaries are where plates move past
each other.– Usually are found near ocean ridges– Since rock slides past rock, no mountains
or volcanoes form.– Earthquakes and faults are very common.