Transcript Earth Systems & Resources

Earth Systems & Resources
APES: Chapter 8
Formation of Earth & Solar System
Approx. 5 billion years ago gas & dust from an exploded star converged
under the force of gravity into a spinning disc called a planetary nebula.
Earth formed in a process called accretion where materials clumped
together to form larger masses (increasing gravity of that mass).
Earth is 4.6 billion years old
and is a rocky inner planet.
High melting point
materials coalesced near
the sun (i.e. rock & metal).
Low melting point
materials (gas & ice)
coalesced far from the sun.
Earth’s surface was molten
due to heat from asteroid
bombardment and nuclear
fission of radioactive
elements.
Most dense materials sank to
the center of the molten Earth:
Fe, Ni, U, Pu (metals). These
layers are the inner & outer
core.
Least dense materials make up
the top layers: O, Si, Al, Ca, Mg
(rock). These layers are the
mantle & the crust.
Inner core is solid due to intense
pressure & heat. Heat in Earth’s
interior is from the decay of
radioactive elements.
Earth’s Structure
• Crust:
• Two types – oceanic &
continental
• Mantle:
• Two layers – upper
(asthenosphere) & lower
• Outer Core:
• Liquid Fe & Ni
• Inner Core:
• Solid Fe & Ni
• Very Hot!!
Earth’s Structure
• Lithosphere “plates”
• Crust + Solid upper mantle
• Rigid, broken into plates
• Asthenosphere
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•
•
•
Magma originates
Slowly deforming solid (ductile)
Convection
Fe, Mg Silicates (SiO2)
• Lower Mantle
• Solid
• Fe, Mg Silicates (SiO2)
Earth’s Structure
How do we know?
• Indirect Evidence
• Seismic Wave Studies
• Density measurements
• Heat Flow Measurements
• Lava Analyses
• Meteorite Composition
Minerals vs Rocks
• Minerals:
• Composed of
elements
• Form crystals
• Most common is SiO2
(aka quartz) &
Feldspar
• Unevenly distributed
around the Earth
• Can be a native
element like gold or a
compound like quartz.
• Rocks:
• Composed of minerals
• Three types – igneous,
sedimentary &
metamorphic
• Molten form inside
the Earth is magma;
surface of the Earth is
called lava
• Igneous rocks are the
most common.
• Make up the crust
Minerals
Rocks
Granite Rock
Types of Crust
Ocean Crust
• More dense
• Made of Basalt rock
• High in Iron
• Less Silica
• Thin
• Sinks
• Major Elements in the Crust:
• Oxygen, Silicon,
Aluminum, Iron,
Calcium, Sodium,
Magnesium, Potassium
Continental Crust
• Less dense
• Made of Granite Rock
• High in silica
• Less Iron
• Thick
• Floats
• Major Minerals/Elements
Mined:
• Copper, tungsten, iron
ore, diamonds (precious
stones), gypsum, gold
(precious metals),
aggregate (sand, gravel)
Convection & Hot Spots
• Radioactive decay in the core releases heat . . . Heat causes plumes
of hot magma in the mantle to well upward . . . . Plumes produce
hot spots. A hot spot is where molten material reaches the
lithosphere (crust).
Convection & Hot Spots
Hot spots are found all over the Earth. There are two hot spots in the
US. One in Hawaii and the other in Yellowstone National Park. Hot
spots are stationary (they don’t move) and produce volcanic activity on
the Earth’s surface.
Theory of Plate Tectonics
• Earth’s geological cycle consists of three major
processes:
• Tectonic Cycle – opening and closing of ocean basins
over time. Lithospheric plates are in constant motion.
• Rock Cycle – Recycling of the Earth’s crust through
erosion, uplift, and volcanism.
• Soil Formation – result of the physical and chemical
weathering of rock and the accumulation of detritus
from the biosphere.
Theory of Plate Tectonics
• Timeline:
• 1912 – Alfred Wegener proposed “Theory of Continental
Drift” based on continental evidence. Defined Pangaea.
• 1940’s – WWII and the development on sonar/radar
revealed the shape of ocean floor (Harry Hess).
• 1960’s – Glomar Challenger (drill ship) collected oceanic
crust samples & dated them (radiometric dating
techniques).
• 1963 – J. Tuzo Wilson proposed “Theory of Sea Floor
Spreading” based on ocean floor evidence.
• 1965 – J. Tuzo Wilson & Harry Hess proposed “Theory of
Plate Tectonics”. Combined both Continental Drift &
Seafloor Spreading theories and their collective evidence.
Continental Evidence
• Alfred Wegener observed several lines of evidence that
supported that the continents were once joined as a
supercontinent called Pangaea.
• Puzzle fit of the continents (matching coastlines)
• Similar mountain ranges across an intervening ocean
• Climatic evidence –
• Glacier evidence in Africa & S. America near equator
• Coal deposits in Antarctica
• Fossil evidence –
• Identical species of freshwater fossils found in Africa & S. America
• Both plant and animal fossils discovered in all southern continents
(Gondwanaland).
Ocean-Base Evidence
Technology in the late 20th century allowed the
collection of ocean-based evidence:
• Sonar used in WWII discovered mid-ocean ridge and
deep-sea trenches.
• Deep-sea drill ships (ODP) collected ocean floor rocks –
• Sea floor rocks were volcanic
• Sea floor rocks were young in age (oldest 220 Ma)
• Sea floor rocks magnetism showed a pattern that was identical to
sea floor rock ages
• Earthquake data from seismometers showed patterns of
earthquakes that were associated with mid-ocean ridges &
deep-sea trenches.
• Volcanoes also were associated with mid-ocean ridges &
trenches.
Theory of Plate Tectonics
• States that the Earth’s lithosphere is divided into plates,
most of which are in constant motion. Tectonic plates
“float” on the convecting asthenosphere.
• There are three types of plate boundaries (areas where
two or more plates meet):
• Divergent Plate Boundary – plates moving away from each other.
Seafloor is being created @ this boundary
• Convergent Plate Boundary – plates moving towards each other.
Seafloor is being destroyed @ this boundary.
• Three types depends on crust involved
• Transform Plate Boundary – plates are moving past each other
(sliding). Ocean crust is neither created nor destroyed.
Divergent Plate Boundary
• Create mid ocean ridges
• Mid Atlantic Ridge
• Ocean crust is created @ MOR
• Long chains of submerged
volcanic mountains
• Igneous Rocks formed
• Basalt (pillow basalts)
• Minerals at hydrothermal vents
• Nicklel, chromium, asbestos,
copper, iron
Sea floor spreading – Red Sea
Deep sea vents/black smokers
Divergent Plate Boundary
Convergent Boundary – Subduction
• Volcanic Mountain chains
(continents or islands)
• Andes
• Philippines
• Igneous Rocks formed
• Andesite
• Minerals
• Cu, Pb, Ag, Au
Sea floor is destroyed
at subduction zones.
• Hazards
• Volcanoes, Earthquakes,
Tsunamis
Convergent Plate Boundary – Subduction
Zones
• Ocean to Ocean Subduction:
• Deep sea trenches mark subduction on the surface
• Two ocean crust colliding –
• Older, colder therefore more dense crust subducts (destroyed)
• Volcanic Island Arcs are formed
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•
•
•
Parallel the trench
Volcanoes at subduction zones are explosive
Earthquakes & Tsunami’s common
Most destructive EQ ever recorded on subduction zones
• Ocean to Continent Subduction:
• Deep sea trenches parallel continent
• Continental volcanic mountain chains form
• All other characteristics the same as Ocean to Ocean
Subduction Zones
Convergence of India – Collision Zone
• High (non volcanic) mountain
ranges
• Himalayas
• Metamorphic Rocks
• Minerals
• Same associated with
sunduction and spreading
centers
• Hazards
• Earthquakes
Transform Boundaries
• 2 Plates moving passed one
another
• San Andreas Fault
• Hazards
• earthquakes