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Lecture 2

Environmental Science
Course Code
Nick Eyles

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Jan 16 2009
- }v]vvo](Wíõíî~tPvZWvP[
- Sea floor spreading 1960 (Hess)
- Polar wander paths for continents 1965
- Magnetic reversals and stripes 1965 (Vine)
- Mid-ocean ridges and hot spots
- Plate tectonics: 1967
- Oceanic vs. continental plates
- Collisional (obducting and subducting) margins and divergent (ridges)
Mid Ocean Ridges (MOR) and trenches
- Are actually volcanoes (shallow water) or ocean crust/floor
- Fractures divide mid ocean ridges into segments
- Trenches: very deep water
- A lot of volcanic and biological activity
- Zu}l[vu]vo}]
o t]v}vÁ]ZuPu]ZµZ[]lµ~ÀvP]vP}vvuo
in rocks as it rises up and cools on the ocean floor
o E.g. nickel, silver, copper, lead
o ,µPZ(}Ç[}(}vv]vPuo}vZ(o}}
o Important to driving ocean circulation
Harold Hess introduced idea of sea floor spreading (1962)
- ^(o}}DKZ[Ço]v}uvovvZ
- Oceanic crust spreads and pushes into subduction zones
- Basalt in crust gets melted and mixed to become magma
- Magma get less dense and will want to push up
- The younger the ocean, the hotter the basalt, oceans are shallowest at the middle portion
(ridge) as material is being recycled
- Older oceans have more dense rocks, so they are deeper
- Continental crust is the result of the subduction, melting of oceanic crust plus sea water
- The whiter (more silica) the lighter/less dense it is
- A lot of magnetic particles in the magma that are free to rotate but will point to the north pole
- Declination: orientation of magnetic particle with respect to magnetic north (e.g. if its pointing
south, its declination is 180degrees)
- Inclination: the dip of a particle affected by latitude (steeper dip closer to the poles)
- When magnetic particles become fixed in a rock, there is a record of where the land mass was
before it moved by measuring the inclination and declination µZv}Z}o}v[
- Magnetite: Acicular-shaped (needle-like)
- W]}]oUZZ[uPv](]o(o]~ÀoZ}µvÇ
o North becomes south, south becomes north
- Lava flow will show record of when the magnetic field reversed
- Magnetic stripes
o Magnetometer surveys of ocean floor identified patterns of anomalies on each side of
o Patterns matched pattern of magnetic reversals
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