Bimodal Altitude Distribution — definition?
Two distinct peaks: oceanic (-4500 m) and continental (+300 m).
Crust composition — continental rocks?
Primarily granite, silica-rich, coarse-grained, ~2.7 density.
Crust composition — oceanic rocks?
Mainly basalt and gabbro, mafic, denser (~2.9), fine- to coarse-grained.
Moho discontinuity — role?
Separates crust from mantle, marked by seismic velocity increase.
Gutenberg discontinuity — depth?
Approximately 2900 km, separates mantle from outer core.
Lehmann discontinuity — significance?
Divides outer liquid core from inner solid core at ~5100 km.
Seismic wave — types?
P-waves (compressional) and S-waves (shear).
Discontinuity — seismic signature?
Velocity jumps, reflections, refractions at layer boundaries.
Low Velocity Zone — location?
100-200 km depth, marks lithosphere-asthenosphere boundary.
Thermal gradient — typical value?
Approximately 30°C/km in lithosphere, ~0.3°C/km in mantle.
Heat transfer mode — dominant in mantle?
Convection, large-scale material movement.
Conduction — primary in?
Earth's crust, especially in rigid lithosphere.
Thermal anomaly — example?
Hot spots (positive), subduction zones (negative).
Mantle plume — effect?
Creates localized positive thermal anomalies, volcanic activity.
Seismic wave refraction — indicates?
Changes in wave speed at layer boundaries.
Discontinuity of Moho — depth variation?
7 km under oceans, up to 30 km under continents.
Gabbro — texture?
Coarse-grained (grenue), intrusive mafic rock.
Basalt — texture?
Fine-grained (microlitique), volcanic mafic rock.
PREM model — purpose?
Describes Earth's layered internal structure from seismic data.
Seismic shadow zone — caused by?
Refraction in the outer core, absence of S-waves.
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1. What does the bimodal altitude distribution of Earth's surface represent?
2. What are the main rocks that compose the oceanic crust?
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