Transcript Earth Structure

Earth Structure
Can you describe or draw a cross section
through the Earth and label the relevant layers?
Try?
Earth Structure
The specification states that you need to know about:
1) Layers: Compositions, depths and physical states of:
i) Continental and oceanic crust
ii) Mantle
iii) Inner and outer Core
2) Lithosphere and asthenosphere; Describe the nature of the
Lithosphere (rigid), Asthenosphere (rheid), Low Velocity Zone,
3) Discontinuities: Depth and nature of discontinuities: Inner
core, outer core, mantle, continental crust and oceanic crust.
4) Direct evidence: Such as deep mines, surface rocks,
volcanic vents and ophiolites.
5) Indirect evidence: Such as seismic wave velocities, shadow
zones, whole earth and rock density and meteorites.
Turn to page 11 of
Chernicoff and
look at the diagram
showing the
structure of the
Earth.
Earth Structure
Crust: the upper layer which
is solid (divided into 2
types).
Lithosphere: the crust plus
the upper part of the mantle
(solid).
Mantle:
Upper part is solid and is part
of the lithosphere.
Below this is the
asthenosphere which is partly
molten and can flow.
Rest of mantle is solid.
Outer Core: Liquid.
Inner Core: Solid.
What are (lithospheric) plates?
Lithospheric plates
comprise of 2
parts:
An upper part
which is crust.
A lower part which
is a solid part of the
upper mantle.
This makes a
lithospheric plate.
2 Types of Lithospheric Plate.
Continental.
Oceanic.
Classification of Igneous Rocks.
They can be classified based on their SiO2
content:
Acid: > 66%
Intermediate 52 – 66 %
Basic 44 – 52%
Ultrabasic < 44%
Oceanic Crust
Typically made of basic
igneous rocks (basalt).
7 - 10 km thick.
Density of 3.0 g/cm3
Will sink at subduction
zones.
Forms at Mid Ocean
Ridges and is saturated
in water.
Young Jurassic to
present.
Continental Crust
On average has
Acid/Intermediate
composition.
On average 30 km thick
but can be up to 90km
thick in mountain ranges.
Density of 2.7 g/cm3
Will not sink at
subduction zones.
Old: 4 billion
(Precambrian) to Present
MANTLE
Made of an olivine rich
ultrabasic rock called:
Peridotite.
Higher density than crust
(3.3g/cm3)
Upper mantle area - solid
peridotite (part of the
Lithosphere).
Low Velocity Zone - (50 250). The LVZ is also called
the asthenosphere (weak
sphere) or rheosphere
(flowing sphere).
MANTLE
In this zone a very slow
movement or creep is
possible due to convection
currents being present.
The convection currents
drive plate tectonics.
This area is 5% partially
molten peridotite.
Upper Mantle - (250 - 400).
Solid peridotite again.
Transition Zone - (400 - 1050).
Solid again and covers much
of the Upper mantle. This is a
transition from low-density
form of peridotite to a higher
density peridotite.
MANTLE
Lower Mantle (1050 - 2900).
Contains a higher
density version of
Peridotite (5.4
g/cm3).
CORE
OUTER CORE
Liquid
Ni, Fe, S, K, Si
(9.9g/cm3)
INNER CORE:
Solid
Ni, Fe alloy
(13.5g/cm3).
The Driving Force
Convection Currents
Very slow convection
currents flow in this
asthenosphere.
These currents provide
horizontal forces on the
plates of the lithosphere
much as convection in a
pan of boiling soup (must
be Heinz tomato) causes a
crouton on the surface of
the water to be pushed
sideways.
The Driving Force 2
The convection
currents are driven by
heat generated within
the earth.
This emanates
primarily from the core
and is transferred to
the surface by the
convection currents.