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Obj. 1. Name and describe the layers of the Earth.
2. Explain transform, divergent and convergent
boundaries.
3. Define faults and describe three fault types.
II.
Earth Composition and Movement
a) Crust – the Earth’s solid and rocky outer layer,
including both land surface (continental crust), and
ocean floor (oceanic crust). The crust averages 32 km
thick and is composed of O2, Si, Al, Ca, Fe, Na, K, and
Mg.
b) Mantle – the layer below the crust comprised of the
lithosphere (upper mantle) and asthenosphere (lower
mantle). The lithosphere (lithos = stone) is a rigid layer
that floats on the soft, plastic-like, slow flowing
asthenosphere (asthenes = weak). The mantle is
approximately 2,900 km thick, 870-2100 o C and is
composed of Si, O2, Fe and Mg.
c) Core – after the mantle, comes the 2 parts of the Earth’s
core. The first is the liquid outer core (a layer of molten
metal outside the inner core). Then is the solid inner
core (a dense ball of metal). The inner core is under
such immense pressure that the atoms cannot spread
out to become liquid. The outer core is approximately
2,250 km thick, 2000 – 5,000 o C and is composed of
Fe and Ni. The inner core is approximately 1,200 km
thick, about 5,000 o C, and is also composed of Fe and
Ni.,
d) Plate Boundaries – are the point where two tectonic
plates meet and are divided into three types –
convergent, divergent, and transform. Plates are
classified into one of the three types based on the
movement that they have. Remember: convection
currents are the engines that drive plate movement. As
hot plumes of the asthenosphere rise at an ocean ridge,
the weight of the uplifted ridge pushes the oceanic plate
into a subduction zone. Then as the asthenosphere
cools and sinks, the weight of the subducting ocean
plate pulls lithosphere into the subduction zone.
1. Convergent boundary – are the boundaries (edges)
that move toward each other or together. When
convergent plate boundaries run into each other, three
things can occur: 1. the plate edges are forced up
(creates mountains), 2. one plate goes
under the other (subduction)
(creates
earthquakes or volcanoes), 3. the plate edges are forced
down
(creates trenches).
2. Divergent boundary – are the boundaries that move
away from each other. The plate edges are pulled apart
which causes: 1. rift valley – the crust reaches elastic
limit and breaks creating two new edges which move
away, causing the middle portion to fall, 2. depression
– the crust stretches but does not reach elastic limit
and break, 3. ocean ridges – from seafloor spreading.
3. Transform boundary – the edges of the plates move
side by side or back and forth to each other. The
moving plates cause the crust to break creating friction
that makes the rock melt and rock formations to
deform which causes: 1. volcanoes, and 2. earthquakes.
e) Faults are the surface along which rocks break and
move, rocks on either side of a fault move in different
directions relative to the fault surface creating different
types of faults.
1. Reverse faults – are caused by convergent
plate boundaries and compression forces. The
land/plate moves in opposite directions together and
gets pushed past its elastic limit causing two things to
occur: 1. folding-the rocks fold without breaking, 2. the
rocks break and slide under each other.
2. Normal faults – are caused by divergent plate
boundaries and tension forces. The land/plate gets
pulled past its elastic limit causing two things to occur:
1. rocks break to create a rift valley, 2. bends the rocks
without breaking to create a depression.
3. Strike-slip faults are caused by transform plate
boundaries. The land/plate slips and slides past each
other in opposite directions creating friction and
vibrations. This fault creates many earthquakes in the
crust.