Please enable JavaScript.
Coggle requires JavaScript to display documents.
A2 Oceanic Lithosphere (Part 1) (Formation of the Earth (4.6 billion years…
A2 Oceanic Lithosphere (Part 1)
Formation of the Earth
4.6 billion years ago, the Earth was a cloud of gas and dust known as a solar nebula
gravity collapsed the material in on itself and it began to spin, forming a sun at the centre
the remaining material began to clump. The small particles drew together into larger particles
the solar wind swept away lighter elements e.g hydrogen and helium leaving only heavy, rocky materials to form smaller terrestrial worlds like earth
further away the winds had less impact on the lighter elements allowing them to form gas giants
earth was formed by the collision of countless meteorites and asteroids
the impact ensured the earth remained a molten state
the heavier elements sank to form the core and the lighter elements formed the crust
evidence:
1) rocky planets- exoplanets have been discovered around stars in distant planets. According to NASA, core accretion implies that small rocky worlds should be more common than more giant gas clouds
2) the bulk chemistry of the Earth is similar to the bulk chemistry of chrondities
Layers of the Earth
upper continental crust
depth- 0-20km
temp- 0-300
density- 2.6gcm-3
p-wave- 4.0kms-1
rock types- all rock
deformation- top- cold, brittle failure, faults
deformation- bottom- warm- ductile- flexural
lower continental crust
depth- 0-100km
temp- 0-700
density- 2.8gcm-3
p-wave- 5.0kms-1
rock types- schist, gneiss, granite, migmatite
deformation- hot, plastic, flow folds
oceanic crust
depth- 5.0km
temp- 0-100
density- 3.1gcm-3
p-wave- 6.0kms-1
rock types- sediment ooze, pillowed basalt, sheeted dyke dolerite, gabbro, layered peridotite
deformation- cold, brittle failure, faults
upper mantle
depth- 150km
temp- 100-1300
density- 3.4gcm-3
p-wave- 8.0kms-1
rock type- solid peridotite, garnet peridotite
deformation- ductile/plastic, flow folds
Body Waves
primary
compressional/ longitudinal
more incompressible = speed up
higher density = slow down
6.0km/s density in the crust
travel through solids, liquids and gas
secondary
shear/ transverse
more rigidity = speed up
higher density = slow down
3.0km/s density in the crust
travel through solids and semi-solids
seismic waves crossing boundaries
crust to upper mantle
P and S waves speed up because the mantle is more incompressible and more rigid
angle of refraction is bigger than the angle of incidence
crust
p-wave- 6
s-wave- 3
upper mantle
p-waves- 8
s-waves- 4
mantle to asthenosphere
slow down as less incompressible and more rigid
asthenosphere
p-waves- 7.5
s-waves- 3.8
asthenosphere to lower mantle
speed up as more incompressible and more rigid
lower mantle
p-wave- 8.5
s-wave- 4.6
the presence of volcanoes and hot springs demonstrates that temperatures inside the Earth are significantly higher than at the surface. Heat comes from:
1) Radioactive decay of unstable isotopes (90%)
2) heat generated by tectonic and lithostatic pressure
3) 10-20% is residual heat in the core left over from the early molten phase of the Earth
CONDUCTION- heat always moves from hot to cold e.g baked margins
CONVECTION- colder more dense sinks and hot less dense rises
RADIATION- heat transfer via electromagnetic waves