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.