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 = mc 2 (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 shifted If 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 Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto terrestrial planets Jovian planets

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 hydrocarbons Ammonia Phosphorus Water Vapour Venus Major: Carbon Dioxide (96.5 %) Nitrogen (3.5 %) Minor: Sulphur Dioxide (0.015 %) Water Argon Carbon Monoxide Helium Oxygen

Earth Major: Nitrogen (78 %) Oxygen (21 %) Argon (0.9 %) Water Vapour (0.05 to 2 %) Minor: Carbon Dioxide (0.03 %) Methane, Ozone Rare Inert Gases Venus Major: Carbon Dioxide (96.5 %) Nitrogen (3.5 %) Minor: Sulphur Dioxide (0.015 %) Water Argon Carbon Monoxide Helium Oxygen 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 Sun 2.Size of the Earth 3.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 geosphere the hydrosphere the atmosphere

END OF LECTURE