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The Material Earth
Solar System Accretion Theory
Accreted components
Chondrite –composition
roughly equal to that of the
Earth. This is a slab of NWA
2089 (LL3)
Anatomy of a chondrite
www.arizonaskiesmeteorites.com
CAI’s: Calcium Aluminum-rich inclusions, varying size of
material that condensed at T> 1100ºC
Chondrules: rounded grains rich in silicon, condensed
between 400-900 ºC.
Matrix: low temperature silicon and carbon rich phases,
condensed below 175 ºC.
Chondrites become attracted
and attach
Growth continues with impacts
- heating, rounding with size
When a body is larger than 100
km diameter and hot, iron and
other heavy compounds sink
towards center, silicon-oxygen
compounds float towards
surface.
Hot Earth
Initial bombardment
formation of Earth;
impact energy
transferred into heat
Contraction due to
increasing gravitational
force; compression
increases heat
Radioactive decay of
elements produces
energies that heat
surroundings
The earth’s heat results from kinetic (movement) energy:
the energy of large (impactors) and small
(electromagnetic photons and atomic particles) objects.
But space is cold - we are losing this heat
You should know:
•It’s built from
chondrites.
•Center half is largely
made of iron.
•Only the outer core is
mostly liquid
•Outer half is largely
made of oxygen and
silicon.
•Our knowledge
diminishes as we
move into the planet.
How do we learn of
our planet’s interior?
Journey to the Center?
KTB
Kola
Photo by Hans-Joachim Kümpel
Heat release moves crustalupper mantle masses.
Surface includes once deeply
buried rocks
The Adirondacks
Old rocks from the
middle continental
crust
Volcanoes - heat and mass
breach the surface
Mantle
fragment
diamond
Mid Ocean
ridge
Our understanding of the
earth falls off with depth.
6,378 km
Piston Cylinder
Solid Media Pressure Apparatus
Faking it - reproducing
conditions within a lab
setting.
Near isostatic pressure
and elevated
temperatures
Earthquake (seismic)
waves are the result of
energy transfer through
matter
An earthquake releases
the energy
accumulated from
stress in the crust of
the earth
Seismic shadow
Figure 19.16
19-378
The speed of the
waves changes with
depth
This is a function of
material behavior
reflecting changes in
three things:
•Temperature
•Pressure
•Composition
The major plates of the
lithosphere
Source:After W. Hamilton, U.S. Geological Survey
Cold Lithosphere will sink. Slab drags plate downward.
Volcanism and rupturing at weak points builds new
oceanic crust
A deeper mechanism driving it all?
Subduction: Continental Arcs
Example: the Cascades
Trenches are the deepest
part of the oceans
Divergent Boundary - Continental Rift
Example: the East African
Rift
NASA Digital Tectonic Activity Map
Magmas
generated by
mantle melting
can make their
way to the
surface. They
also may induce
partial melting in
the crust.
NASA STS32
Continental collision
Example: the Himalaya
Arbuckle Mountains, Oklahoma
Rattlesnake Mountain, Wyoming
The hydrologic cycle
2-458
Water appears to be the most crucial
compound to life on Earth
It merits a closer look:
H-O bonds are bent towards
each other. Hydrogen atoms
near one end lend a positive
charge.
Examples of very porous rocks
Rocks like these are responsible for
storage and transports of large
reservoirs of potable water.
Sandstones, white area are grains of
quartz (SiO2), blue area is a dye to
show pore space in rock)
The path of groundwater
•4.56 billion year old chondrite-derived planet
•Differentiation has resulted in an iron core, a
rocky mantle and crust, a hydrosphere, and an
atmosphere.
•Heat loss from its formation drives interior and
surface modification through plate tectonics.
•Heat gain from Sun’s fusion reaction drives
surface modification through hydrologic cycles.
•The change of these energies results in very
complicated systems.