Origin of the Universe
“ The Big Bang”
=> 14-20 billion years ago the universe began during a cataclysmic release
of energy from a point source of infinite mass.
• 10-43second -> matter/antimatter
- quark soup - inflation
- 3000 bill degrees K - hadrons
- 3 minutes - dueterium & He nucleii
- 300k - H & He - photons released = light
- first galaxies (~ 1 bill. Yrs.)
- continued expansion
How do we know the universe is expanding?
• Expansion is suggested by the “Red Shift” (Hubble, 1929)
• Red shift can be explained by the Doppler Effect
Origin of the Solar System => Nebular Hypothesis
• ~5 bill. yrs. ago - solar system began as large, slowly rotating cloud
of dust and gas - Solar Nebula
• => material from a supernova
Origin of the Solar System => Nebular Hypothesis
• Cooling and Gravity => from cloud to sphere.
• Velocity of rotation increases => sphere to disk.
• Most of mass near center of disk => proto-sun. Origin of the Solar
System => Nebular Hypothesis
• Sun turns on - H + H = He -> nuclear fusion
• Planets form by chemical condensation/accretion
Evidence - Nebular Hypothesis
• planets orbit in same plane
• planets rotate in same direction as they revolve around the sun
The Solar System
• Discuss the following question with the people next to you
• Were there any “leftovers” in the solar system following
the accretion of the sun and planets?
• What might they be?
• Have they had any impact on earth history?
ORIGIN OF EARTH
• Origin=> 4.6 b.y. ago => condensation/accretion
• Earth heats up
• Density Differentiation
ORIGIN OF EARTH
• How is Earth different from the other inner Planets?
• Size
– Retained some H
– Generates internal heat
• Distance from sun
– Abundant liquid water
The Interior of the Earth
How is it that we know so much about the Interior of the Earth?
* deepest wells ever drilled into the Earth only penetrate around 12 km (7.5
mi)
=> Seismic Waves behave in predictable ways as they pass through earth materials
=> and we can follow their path
The Interior of the Earth
• Discontinuities
• Moho
• Low velocity zone
• Outer and inner core
The Interior of the Earth
• The earth’s magnetic field
• Electric dynamo
• Confirmation of a iron and nickel core
• Very important
– Preserves the atmosphere
The Early Earth
• At least partially molten for differentiation
• Is the earth currently heating up, cooling off, or stable?
• Cooling - but insulated
The Early Earth
• Origin of the crust?
• Chemical differentiation of the mantle
• Partial melting = basalt
• Continental crust?
The Early Earth
• Origin of the Atmosphere
• Outgassing => “The Big Burp”=> the early Atmosphere
H, H2O (vapor), CH4, NH3
• Why is the current atmosphere different? - O2
• Plants and photosynthesis
• Photochemical dissociation
The Early Earth
• Origin of the Oceans
• Outgassing and condensation
• Water from comets?
The Early Earth
• Importance of the oceans and atmosphere
• Ocean - atmosphere interactions
• Chemical Cycles - Global Chemostat
• Limestones & CO2
The Early Earth
• Ocean - atmosphere interactions
• Climate
• Special properties of water + circulation
• Moderates global climate
Cryptozoic History
=> longest interval of Earth History = Precambrian
=> interval of time that is poorly known - PROBLEM:
(1) fossil record lacking or sparse
- dating must be done exclusively using radiometric methods
(2) radiometric and paleomagnetic records reset by later events
(3) very limited exposure
Where are Precambrian Rocks Exposed?
- Cratons - the oldest parts of continents
- Precambrian shields - parts of the cratons where Precambrian rocks are exposed
at the surface
=> oldest rocks = 4.2 b.y.
The Archean Earth
• Discuss the following question with the people next to you:
• Heat flow was very much higher in the Archean than it is today. What
was plate tectonics like?
The Archean Earth
High heat flow =
- thin crust
- smaller more mobile plates
- continents?
The Origin of Continents
• Forming Continental Crust - Felsic (granite)
a. island arcs
- subduction zones
b. hot spots
- partial melting - isostatic sinking - partial melting
Example: Iceland
The Origin of Continents
• Why Small Continents?
=> high heat flow and mobility
• The Oldest Continental Crust
=> 4.1 - 4.2 g.a.
Archean Rocks
• two basic rock groups:
a. granulites or gneiss belts: evidence for continental/granitic crust
b. greenstone belts: volcanic rocks (mafic and ultramafic) and sedimentary rocks
derived primarily from volcanics; remnants of oceans and volcanic arcs.
c. Other: sedimentary rocks - deeper water facies
The Modern Earth
- Proterozoic through Phanerozoic
- North America
- Craton
- Shield
- Platform
- Mountain Ranges
- Appalachians
- Cordilleran
- Coastal Plain
The Proterozoic
(2.5 billion - 600 million)
More like the Phanerozoic than the Archean
continents & plate tectonics
Evolution of the Atmosphere
Climate Change
Life
The Assembly of North America
Continental Accretion
micro/protocontinents form during Archean
sutured together during the proterozoic
North American Craton fully assembled between 1.9 and 1.8 ga
Shield + Platform
Geologic Provinces
The geologic provinces of the North American Craton
accreted microcontinents
Geology changes abruptly from one province to the next