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POPS Earth Science Unit 2: Geology – Teacher Notes
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How and When Did The Earth Form?
o Protoplanet Theory
 Currently accepted theory
 Gas in nebulas condenses onto dust particles
 Cloud collapses under self-gravity
 Sun forms before planets
 Small planetesimals aggregate into planets.
 Asteroids, comets, and meteoroids remain.
o Estimated Age of Earth
 Radiometric dating indicates:
 Oldest rocks on Earth between 3.96 and 3.8 billion years old
 Oldest meteorites between 4.5 and 4.7 billion years old
 Oldest moon rocks are 4.6 billion years old
 Scientists agree age of earth is ~4.6 billion years.
How Do We Organize the Earth’s Systems?
o Energy drives the cycling of matter within and between systems
 Atmosphere
 Gas layer
 Hydrosphere
 Oceans
 Lithosphere
 Solid Earth
o Atmosphere
 Considerable volcanic activity on early earth
 Lava, water vapor, carbon dioxide, nitrogen, carbon monoxide
 Oxygen NOT common
 Ancient cyanobacteria used photosynthesis to produce essential nutrients
 Oxygen is a waste product
 Nearly all oxygen ever breathed is from photosynthesis
 Currently
 78% Nitrogen
 21% Oxygen
 1% all other elements
o Hydrosphere
 Considerable volcanic activity on early earth
 Major component is water vapor
 Surface of earth cooled, vapor condensed, produced rain
o Rainwater dissolved soluble minerals exposed at Earth’s surface.
 Some water released from small comets hitting Earth
 Significant portion of Earth’s surface water might be extraterrestrial!
o Lithosphere
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Less dense materials float on more-dense materials.
 Density of minerals decreases toward the crust.
 Differentiation
 Continents began to form about
3.8 billion years ago
 Currently:
 hot, but solid inner core
 liquid outer core
 solid mantle and crust.
How Was the Earth Originally Heated?
o Asteroid/Meteorite Bombardment
(friction)
 Meteoroids
 Small asteroids or
fragments of asteroids
o Called meteorites when fall to
earth.
 Generate tremendous heat upon impact
 Bombardment common in early earth
o Gravitational Contraction
 Due to meteor bombardment, mass of earth
increased.
 Gravity acts on mass
 Generates heat
o Radioactivity
 Radioactive isotopes more abundant in early earth
 Hadn’t decayed yet.
 Radioactive decay generates energy
 Heat
Does Earth’s Internal Heat Affect its Landscape?
o Plate Tectonics
 Earth's surface covered by crustal plates.
 Ocean floors are continually moving on thin slice of mantle
 asthenosphere
 Plates are continually regenerated
 spreading from center
 sinking at edges
o What Causes Plates to Move?
 Convection currents move plates
 Radioactivity deep in Earth’s mantle drives
convection currents
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How Do Plate Tectonics Affect Earth’s Landscape?
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Types of Plate Boundaries
 Divergent Plate Boundaries
 Plates move apart
o Sea Floor Spreading
 Usually form volcanoes
o Example: Mid-Atlantic Ridge
 Convergent Plate boundaries
 Thick, buoyant continental plates behave differently from thin, dense oceanic plates
 Three types of Convergent Plate Boundaries:
o Oceanic/continental
 Denser oceanic plate is pulled into asthenosphere
 Forms subduction zone
o Deep trench
 Subducted plate melts
 Volcanic mountain ranges form to release pressure.
o Oceanic/oceanic
 Older plate sinks
 colder, therefore more dense
 Subduction
 Underwater volcanoes form island arcs.
o Continental/ Continental
 Neither can sink
 Similar plates, similar density
 Forms highest mountains in the world
 Transform Plate Boundaries
 Plate boundaries grind past each other side by side
 Responsible for many of California’s earthquakes.
o Example: San Andreas fault
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