California
State University Long Beach
GEOL 300i; Earth Systems and Global Change
Lecture 2
Dr. Rick Behl
Cosmology:
Origin of the Universe, Solar System, & Earth
.
Lots of questions,
little direct evidence
.
The
Big Bang (13.7 billion years ago; Ga)
o
Violent explosion of
energy -> atomic matter from a single point
.
All matter expands
outward from a single point
.
Indicated by:
.
Red-shift of stars and
galaxies
.
Even distribution of
X-ray energy
.
Galaxies, stars, and interstellar "dark
matter"
.
(95%!,
invisible because cold and nonradiating)
o
The
Sun is one of ~100 billion stars in the Milky Way Galaxy, with many billions of
galaxies in the universe
Evolution of the Sun (or a similar mass
system)
.
First Stage: gravitational collapse of diffuse nebula
o
Triggered by a nearby
supernova
o
Increased heat,
pressure, and kinetic energy make a protostar
.
1000's of astronomical
units (AU) wide
.
Starts radiating when
>2500 degrees K
.
Second Stage: Lighting the furnace
o
Gravitational pressure
increases enough to initiate nuclear fusion of hydrogen
emperature in the core reaches 15 million degrees K and balances gravitational
collapse
o
Temperature at surface
~6000 degrees K
.
Third Stage: Stability to instability
.
This is the current
state of the Sun
o
As long as enough
hydrogen is present, star remains about the same size and temperature
o
Lighter elements
formed, heavier elements require a previous stellar lifetime
o
Collapse to white dwarf
when hydrogen supply decreases
Formation of the planets
.
Nebular
hypothesis
o
Originally ~ 1000
atoms/cm3
o
~4.6-4.7 Ga, As the
nebula collapsed towards center of mass
.
Rotating disk shape to
conserve angular momentum
o
Irregular patches or
eddies coalesce into km-size (and less) planetesimals.
.
Planetesimals attracted
each other and grew by accretion into protoplanets
.
Protoplanets continued
to grow by collision of other protoplanets and planetesimals
.
Moon formed by huge collision
.
Earth knocked off
kilter
.
Whole Earth mostly
assembled by ~4.0 Ga
The
Solar System
Planetary composition: The Nine Planets
.
Inner terrestrial
(Earth-like)planets
o
Compositional distribution
akin to a distillation-condensation sequence
Iron (Fe), Magnesium (Mg), Silicon (Si), & Oxygen (O) dominant
.
Mercury, Venus, Earth,
Mars
.
Outer Jovian Planets
(gas giants)
o
Hydrogen, helium, water
(plus small iron cores)
.
Saturn, Jupiter, Neptune,
Uranus
Differentiation of Earth
.
Originally a
homogeneous agglomeration
.
Fast generation of heat.
More than enough to melt rocks
o
Collision/impact
kinetic energy
o
Radioactive decay of:
.
Uranium (U)
.
Thorium (Th)
.
Potassium (K)
.
Many more radioactive
isotopes present in early history of Earth than at present
Two
times or ways to differentiate the Earth
.
Hot accretion (most
likely)
o
High energy of impacts
already melted & differentiated planetesimals
or
.
Cold accretion
o
Melting &
differentiation soon after accretion by radiogenic heat
.
Compositional Structure (layering)
o
Developed
because of density differences between compounds (not elements)
o
Core
.
Iron
melting (iron catastrophe) by 4.5 Ga!!
.
Fe
is ~1/3 mass of Earth
.
Sinking
of molten iron releases potential energy (additional 2000 degrees C of heat)
.
Formed
Fe/Ni (+ S) core
.
Density
= 11-12 g/cm3
o
Mantle
.
Silicates
(Si-O)
.
Enriched
in Fe, Mg
.
Density
= 5-7 g/cm3
o
Crust
.
Silicates
.
Ca,
Al, K, Na
.
Density
= 2.6-3.1 g/cm3
The Earth's structure
o
Radius=6370 km average
o
Oblate spheroid; 6378
km at equator, 6356 km at poles
.
Internal structure
o
Studied by indirect
methods only
o
Seismologic evidence
.
Velocity varies with
density (phase and composition)
o
Crust
.
Continental crust
o
30-70 km thick
o
Granitic composition;
2.7-2.8 g/cm3
.
Oceanic crust
o
6-9 km thick
o
Basaltic composition;
3.0-3.1 g/cm3
o
Mantle
.
~10-2900 km depth; 4.5
g/cm3
.
Mostly solid, but
plastic
o
Peridotite composition
.
Low Velocity Zone (LVL)
o
~100 km to 220 km depth
o
Partial melted,
lubricated
o
Core (from center to
2900 km depth)
.
i.e., ~3470 km thick
.
Inner core
o
Solid Fe-Ni-(S)
o
1270 km thick
.
Outer core
o
Liquid Fe-Ni-(S)
o
2200 km thick
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written by R. Behl.
Last changes: 1 Sept 2003