6. Time

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6. Time

• Earth From Creation to Its Present State

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A Brief History of the Earth
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A Brief History of the Earth
pg. 271 24 hour clock of Earths history
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How do we know how old things are?
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Determining the Age of the Earth

• Radiometric dating (pg. 260)
• Use decay of isotope to measure time
• Ratio of parent to daughter isotopes
• Carbon-14 half-life 5,730 years
• Uranium-238 half-life 4.5 billion years

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Early History of the Earth
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Determining Earths Age
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Determining Earths Age
Age of Earth based on age of meteors that
originate in our solar system
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Early History of the Earth
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Earths Magma Ocean
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Earths Magma Ocean

• Heavy asteroid/meteor bombardment
• Internal heat from radioactive decay
• Molten rocks ? Magma ocean
• Heavier elements sank to the core
• Iron catastrophe
• Liquid iron core

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Early History of the Earth
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Iron CoreProtection Against the Solar Wind
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Iron CoreElectro-magnetic Shield

• Solar wind (radiation)
• Spinning Iron core gives Earth protection via
  magnetic shield
• Space travel (no protection)
• Mars
• No liquid iron core
• No magnetic shield
• No atmosphere

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Early History of the Earth
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Formation of the Moon
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The Moon

• Collision between Earth and a Mars-sized planet
• Moon formed from debris
• Effects of the collision
• Tilting of the Earths axis
• Earth-Moon moving apart
• Stabilizes Earths rotation
• Tides
• Seasons

Galileo Project, JPL, NASA
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Early History of the Earth
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Earths Crust and Water
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Earths Crust and Oceans

• Formed 150 million years after Earth itself
• Evidence Age of Zircon crystals
• Some Zircons only form in water
• Earths oceans from
• Volcanic activities
• Comets

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Early Life
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Hydrothermal Vent Communities
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Cold Seep Communities
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First Life on Earth

• Chemosynthesis
• Extracting chemical energy
• Hydrogen sulfide
• Methane
• Hydrothermal vent communities (pg. 620)
• Very hot, high pressure environments
• bacteria extract energy from sulfide
• eaten or share energy with other organism
• tube worms, crabs, mussels, fish
• Cold Seeps
• bacteria extract energy from methane gas
• used by other organisms

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Categories of life

• Prokaryotes
• first life
• no membranes around cellular organelles
• energy production via anaerobic respiration
• Eukaryotes
• came later
• membranes surround organelles
• aerobic respiration

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Early Life
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Evolution of Photosynthesis
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Photosynthesis

• Primitive photosynthetic organisms
• Cyanobacteria form Stromatolites
• Oxygenation of the atmosphere
• Oxidation (rusting) of the planet (iron ore)

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Early Life
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Oxygen and Complex Life Forms
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Evolution of Complex Life Forms
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Summary
History of the Earth has made life
possible Magnetic shield Moon Water Early life
derived energy from chemicals Development of
photosynthesis enabled other life to
evolve Complex life is a very recent development
on Earth
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Next time Origins Read section 1.3 15.1