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