Overheads:
Geocentric Model of the Universe - the Earth is central. This model was developed by the ancient Greeks and accepted until the time of Copernicus and Galileo (~1580-1620).
The Heliocentric Model is the current Model of the Solar System.
Solar System Characteristics
(which any theory of formation must explain)
Almost all planets orbit the sun in a common plane
Planet all orbit in the same direction
Planetary orbits are almost circular
Planets display a regular progression in orbital period
The Sun has most of Solar System mass
Inner planets are 'rocky' and solid
Outer planets are mostly gaseous
Meteorites are similar to the 'rocky' planets in composition
Prevailing Theory for Solar System Formation
Initial spinning disk of dust and gas (about 5 Ga)
Gravity caused most mass to move toward center, increase spin,
and create turbulant eddies
Protosun formed from central densest eddy and became star when
high density started fusion reactions in core
Protoplanets developed from smaller eddies
Formation of the Earth - I
Protoplanet Earth swept its orbit clean of dust/gases; added
then to its mass
Continued gravitational collapse, radioactive decay, and impacts
cause increased heating of the planet interior
Heavier elements (Fe, Ni) migrated toward the Earth's center as
partial melting occurred
Formation of the Earth - II
Lighter elements (gases, Si, Al, Mg) migrated towards the
Earth's Surface
Planetary differentiation was complete by about 4.6 Ga
Oldest known rocks about 4.1 Ga
Structure of the Earth - 1
CORE (2900-6370 km deph)
composed mostly of iron
inner core solid; outer core liquid
Temperatures greater the 5000*K
MANTLE (~100-2900 km depth)
Composed on Fe and Mg rich silicates
Solid rock but ductile
Temperatures from ~5000*K-1000*K
Structure of the Earth - 2
CONTINENTAL CRUST
Al Silicates (Granite)
30-100 km thick
Makes up all continents and many large islands
Up to 3.5 Ga in age
Oceanic Crust
Fe, Mg Silicates (Garbbro. Basalt)
~20 km thick
underlies all major ocean basins
<200 Ma in age
Lithospheric Plates
Aesthenosphere lies 10-50 km below the crust within the uppermost
mantle
Aesthenosphere is a region or partially melted mantle
Uppermost mantle and crust above the Aesthenosphere is termed
lithosphere
The lithosphere can be considered to be 'floating' on the aesthenosphere
The Earth's Magnetic Field
The earth's magnetic field is generated by dynamo action in
the liquid-Fe outer core
The field at the Earth's surface look s like that of a bar magnet
(dipole) located at the Earth's center and aligned with the rotation
axis
The field at the Earth's surface generally points toward the North
Pole and points up or down depending on latitude
Paleomagnetism tells us that the dipole field has changed polarity
(bar magnet gets flipped) many times (last time was 780 ka
Initial Formation of the Earth's Outermost Fluid Layers
The Earth's oceans and atmosphere developed last
As the sun started to shine its solar wind blew most volitile
elements (gases) outward where the now make up most of 'Jovian'
planets
Gases and water on Earth came from 'Degassing' of the crust and
mantle after planetary differentation
Oceans and Atmosphere
The Oceans
Composed of water and dissolved solids
Makes up 71% of Earth's surface
Up to 10km thick
The Atmosphere
Now composed mostly of N (78%) and O (21%)
has several distinct layers
about 100km thick
Originally had no free oxygen - developed after origin of
photosynthesis