Fundamentals of Geology (F4 Key Idea 1) Flashcards
What is the earth’s shape and size?
‘oblate spheroid’ - squashed sphere
~40,000km mean circumference
Which is denser, Oceanic or Continental crust?
Oceanic.
3.0g/cm^3 vs 2.7g/cm^3
What is the composition of Oceanic crust?
Sima.
Rich in iron and magnesium
What is the composition of Continental crust?
Granite rocks.
Rich in silicon and aluminium
Which is thicker, Oceanic or Continental crust?
Continental.
35-40km vs 6-7km
What are P-waves?
Longitudinal, and travel relatively quick, and can travel through solids and liquids.
What are S-waves?
Transverse, travel slower than P-waves and can only travel through solids
What is the Moho layer?
Boundary zone between Earth’s crust and mantle
What is the lithosphere?
Lithosphere: the strong, outer mechanical part of the upper mantle and overlying crust, forming a rigid outer shell with its base marked by the 1300°C isotherm.
• Crust
What is the Asthenosphere?
the mechanically weaker layer that underlies the lithosphere and over which it moves. This is evidenced by the seismic low velocity zone (LVZ) where temperatures near the melting point of mantle peridotite.
• Part of the upper mantle located below the crust.
• Flows like molten plastic
Earth structure: rock evidence?
• Meteorites - thought to share similarities with the Earth’s mantle and the Earth’s core.
• Xenoliths - mantle peridotites often brought up as xenoliths in lava.
• Density - the measured densities of rocks from the crust and upper mantle are lower than the mean density calculated for the whole Earth (5.5g/cm^3). Therefore cores density must be greater than the crust
What is Geomagnetism?
The Earth’s fluctuating magnetic field, roughly parallel to its axis, is consistent with that induced by a moving (liquid) nickel-iron core.
Evidence for earth’s structure?
• Geomagnetism
• Gravity
• Seismological evidence (P-waves and S-waves)
