GL 107 Earth Systems Science
K. Hannula
Answers to discussion questions for 9/10/07
divergent plate boundary - Plate boundary at which plates move apart from one another.
mid-ocean ridge - Feature formed at divergent plate boundaries; place where oceanic crust is formed.
convergent plate boundary - Place where two place move towards one another.
subduction zone - Type of convergent plate boundary (ocean-ocean or ocean-continent convergent boundary), at which an oceanic plate dives into the asthenosphere beneath another plate.
volcanic arc - Chain of volcanoes formed on the overriding plate at a subduction zone.
transform plate boundary - Plate boundary at which plates slide horizontally past one another.
2. Describe the motion that occurs at each type of plate boundary (divergent, convergent, and transform).
Divergent: plates move apart
Convergent: plates move toward one another
Transform: plates slide horizontally past one another.
3. How are the crust, the mantle, and the core different from one another:
Crust: similar to granite or gabbro
Mantle: peridotite
Core: liquid or solid iron
Crust: more Si, K, Na, Ca
Mantle: more Fe, Mg than crust, but still a lot of Si so that most minerals are silicates
Core: mostly Fe (iron), some nickel, sulfur
Crust: outermost layer, extending to 5 to 70 km depth
Mantle: middle layer, extending from the base of the crust to a depth of about 2700 km
Core: innermost layer, filling the center of the earth
4. How are continental and oceanic crust different from one another:
Continental: thicker (20 to 70 km; average 35 km)
Oceanic: thinner (5 to 10 km; average 7 km)
Continental: approximately granite
Oceanic: gabbro
5. How are lithosphere and asthenosphere different from one another:
Lithosphere: rigid
Asthenosphere: ductile, though mostly solid
Lithosphere: crust plus uppermost mantle; extends to a depth of about 100 km
Asthenosphere: found below the lithosphere
Lithosphere: forms the rigid tectonic plates
Asthenosphere: forms the soft, easily-deformed layer on which plates are able to move
6. How are the lithosphere and asthenosphere related to the crust and the mantle?
The lithosphere includes all of the crust plus the uppermost part of the mantle.
The asthenosphere is entirely contained within the mantle.