Download Geologic History

Formation of Earth
Earth forms 4.65 Byrs ago through accretion process
Molten rock/metal leads to differentiation
Structure of Earth
Crust (3 g/cm3) - made of continental (granites) and oceanic (basalts)
Mantle (3 - 5 g/cm3) - 2900 km thick layer; location of lithosphere
& asthenosphere
Core (10.5 g/cm3) - liquid Fe/Ni shell surrounding solid Fe/Ni center
Hadean Eon
Leftover planetesimals crash into Earth regularly for the first
500 million years (Heavy Bombardment Period)
Origin of Atmosphere/Oceans
Atmospheric gases produced through outgassing during volcanic
eruptions and impact events
Early atmosphere dominated by CO2
Today: Nitrogen (78 %), Oxygen (21 %), trace CO2 (< 0.1 %)
Origin of Atmosphere/Oceans
Water vapor condenses and rains collect to form the oceans
Water source still unclear; suspect a combination of outgassing and
vaporized comets
Formation of Life
After .5 Byrs, chemical reactions produce self-replicating molecules
Miller-Urey Experiment
Miller
Panspermia
Life on Earth appeared such a short time (500 Myrs) after Earth’s
formation that it might make more sense that it came from elsewhere.
But where?
Impact Sterilizations
Heavy Bombardment Period of Earth makes for impact sterilization
Impactors with D = 350 - 400 km will raise surface temperature to
2000 °C
Origin of Continents
All rock is originally basaltic; some is remelted through plate
tectonics and low density granites form continents
Types of Rocks
Igneous Rocks: made from molten rock that cools underground
(intrusive) or above ground (extrusive)
Extrusive rock (lava) will form dark, dense basalts at plate
boundaries or above hot spots
Santiago Island, Galapagos
Queen’s Bath, Kaua’i
Types of Rocks
Intrusive rock (magma) will form low density, granites that form
the basis of mountains
Granite with minerals of quartz & feldspar
Types of Rocks
Sedimentary Rocks: formed by gradual compression of sediments
- Covers 75% of the land area
- Fossils are most commonly found in sedimentary rocks
Clastic rock forms from sediments that are the result of weathering
and erosion
Breccia
Types of Rocks
Organic sedimentary rock is formed by gradual compression of organic
material
Coal
Types of Rocks
Metamorphic Rocks: igneous/sedimentary rocks that have been
transformed under intense heat and/or pressure
Schist
Slate
Minerals are the crystals found in rocks that tell what the rock is
made of
Geologic Activity
Convergent boundary: continental vs. continental
Geologic Activity
Mt. Everest
Convergent boundary: continental vs. continental
Geologic Activity
Convergent boundary: continental vs. oceanic
Geologic Activity
Mt. St. Helens (1980)
Mt. St. Helens (1982)
Convergent boundary: continental vs. oceanic
Geologic Activity
Divergent boundary: seafloor spreading (ridge)
Mid-Atlantic Ridge
Continental Drift
Over time, plate motions cause continents to drift apart and come
together (forming super continents, like Pangaea)
Surface Features
Mantle plumes: isolated pockets of hot magma in the mantle that
give rise to volcanic island chains and geysers
Hawaiian Islands
Climate Regulation
Without an atmosphere, the global average temperature would
be -17 °C; the greenhouse effect raises that temperature to 15 °C
Greenhouse gases (CO2, CH4) slow the release of IR back into space
Initial CO2 levels were 170,000 times present levels and raised global surface
temperature to 85 °C
Hydrosphere
The collective mass of water on any world (oceans, rivers, ice caps, clouds)
~ 70% of Earth’s surface covered by water
Climate Regulation
The CO2 Cycle
- Atmospheric CO2 dissolves into rain water, ends up in oceans
- Silicate rocks are eroded and sediments end up in the oceans
- Minerals from rocks mix with CO2 in ocean to form carbonate minerals
- Carbonate minerals sink to ocean floor to make carbonate rock
- Plate tectonics force carbonate rock into mantle along subduction zones
- Carbonate rock melts & CO2 is released through outgassing
Climate Regulation
The CO2 Cycle as a Thermostat
If the global average temperature increases, ocean H2O evaporation increases
Increases cloud formation & rainfall
Increases weathering of silicates & more CO2 dissolved out of atmosphere
CO2 in oceans forms carbonate rocks faster
More CO2 able to be stored in oceans
Global average temperature lowers
Ice Ages
When the global average temperature is a few degrees cooler than normal,
snowfall reaches lower latitudes.
Most recent ice age peaked about 10,000 years ago
Other Influences on Climate
The Sun’s brightness has slowly increased since its formation
Rotation period of Earth has slowed down due to tidal forces of the Moon
Precession & nutation of Earth’s rotational axis