Big Circumstance:Earth’s early history and why our planet is unique
How It All Began …Or At Least How We Think It Began
…O.k. it’s a good guess
Universe Originated as a Singularity
The Big Bang splattered radiation in all directions
Expansion and cooling; atomic particles formed through conversion of energy to mass.E = mc2 (energy = mass x speed of light 2 )
Simple elements (hydrogen, then helium) fused to form first stars
Heavier elements produced within giant pressure cookers (stars)
Evidence for Big Bang
1. Background radiation(excess radiation picked up by radio telescopes cannot be
accounted for if it is assumed that the universe is static).
2. Red shift in light spectrum galaxies
Light of an object moving toward an observer is shifted to blue (shorter wavelength, higher frequency)
Light from an object moving away from observer is shifted to red (longer wavelength, lower frequency)
High frequency,Short wavelength
Low frequency,Long wavelength
Light from galaxies tend to be shifted to red end of spectrum
An Analogy: Doppler Effect in Sound
Observer hears an increase in pitch when the car approaches(sound waves get scrunched together)Analogous to blue shift in light
Observer hears an decrease in pitch as the car moves away(sound waves go further apart)Analogous to red shift in light
If a galaxy is getting close to us, it should be blue shiftedIf a galaxy is moving away from us, it should be red shifted
The red shift observed in light of distant galaxies suggests that the universe is expanding (everything is moving away from everything else) and that this expansion must have resulted from an incredible event, involving an incredible amount of energy
An Expanding Universe
Formation of Stars and Galaxies
Stars and galaxies condensed out of the matter produced by the Big Bang and continued to move away from the initial singularity (sort of a point of explosion). This is still occurring.
Redistribution of heavy elements
Elements heavier than hydrogen are produced within stars
Dispersion of heavy elements into space results from explosion (supernova) of stars
Later stars are formed from the material of these exploded stars
Clumps of gas and dust accumulated, forming large, irregular, nebulae “clouds.”
Our solar system is believed to have originated in one such cloud.
Dust and gases settled gravitationally toward mid-plane of slowly rotating disc.
After some of the matter had collected in centre of disc, nuclear reactions began, forming the Sun
Remaining gas and dust, moving in circular bands around Sun collided and accreted to form planets.
Solar Nebula Hypothesis
Solar Nebula and Formation of Solar System
The Nine Eight Planets
Mercury
VenusEarth
Mars
Jupiter
Saturn
Uranus
NeptunePluto
terrestrial planets
Jovianplanets
Heating, partial melting of Earth due to:Impacting of extraterrestrial objects (meteorites)Radioactive decay of unstable elements Gravitational migration (sinking) of heavy elements
Early Evolution of Earth
Evidence of Planetary Bombardment by Other Objects
Obliquity of Axis
Venus “overturned” Uranus tipped on its side
All planets have at least some tilt
Jovian Planet Interior: Jupiter
Comparison of Atmospheric Components:Jovian vs. Terrestrial Planets
Jupiter
Major: Hydrogen (81 %) Helium (18 %)
Minor: Methane and other hydrocarbonsAmmoniaPhosphorusWater Vapour
Venus
Major: Carbon Dioxide (96.5 %)Nitrogen (3.5 %)
Minor: Sulphur Dioxide (0.015 %)WaterArgonCarbon MonoxideHeliumOxygen
Earth
Major: Nitrogen (78 %)Oxygen (21 %)Argon (0.9 %)Water Vapour (0.05 to 2 %)
Minor: Carbon Dioxide (0.03 %)Methane,OzoneRare Inert Gases
Venus
Major: Carbon Dioxide (96.5 %)Nitrogen (3.5 %)
Minor: Sulphur Dioxide (0.015 %)WaterArgonCarbon MonoxideHeliumOxygen
Comparison of Atmospheric Components: Venus vs. Earth
Evolution of Earth’s Atmosphere
1. Initial atmosphere much like Jupiter (rich in Hydrogen and Helium derived from solar nebula)- burned off by Solar Wind
2. Second atmosphere much like Venus(dominated by Carbon Dioxide from Earth’s interior)- “The Big Burp”
3. Third and present atmosphere (rich in Oxygen)- modified from second atmosphere due to
rise of anaerobic organisms
Important Implications:
Earth’s overall composition reflects that of the original “stuff” of the Solar System but has been modified through time due to:
1. Earth’s position relative to the Sun2. Size of the Earth3. Dynamic internal processes of Earth and resulting processes at the
surface (e.g. movement of tectonic plates) 4. Biological processes (e.g. photosynthesis)
Earth is rather unique in its composition – the diversity and distribution of gaseous, liquid and solid components have important implications to the influence of Earth materials on human health and the use of Earth materials in forensic studies
Also Remember: Earth As A Closed System
Material cycles within the system with no overall loss or gain(note implications for global environmental change)
And: The Earth’s Four Spheres
Interchange of matter among all subcomponents of the Earth system
Note:Humans are part of the biosphere and are affected by, and connected to:
the geospherethe hydrospherethe atmosphere
END OF LECTURE
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