continental drift Flashcards
(14 cards)
what are the 4 types of PLATE BOUNDARY?
- CONVERGENT- move towards each other; subduction zones
- DIVERGENT- moving away from each other- new land created
- COLLISION- two continental plates moving towards each other- creates fold mountain ranges (nothing subducts, both are pushed up)
- CONSERVATIVE- plates move alongside each other; get stuck/ snag, builds pressure, released as earthquakes
what are the two types of VOLCANO formed at eruptions?
- COMPOSITE CONE STRATO VOLCANO-viscous lava
- SHIELD VOLCANO- low viscosity, basaltic lava
what is the difference between a NATURAL HAZARD and a NATURAL DISASTER?
a NATURAL HAZARD has potential to harm life and cause damage; a NATURAL DISASTER actually does result in loss of life and damage (10 people killed/ 100 people effected)
summary of the layers of the earth
INNER CORE- solid iron and nickel
OUTER CORE- semi- molten iron+ nickel
MANTLE- semi-molten; three sections: MESOSPHERE, ASTHENOSPHERE, LITHOSPHERE
MOHO- divide between crust+ mantle
CRUST- solid rock; two types: OCEANIC (denser, 7-10km thick), CONTINENTAL (less dense, 30-70km thick)h
what do TECTONIC PLATES consist of?
the LITHOSPHERE which includes the CRUST and the RIGID UPPER LAYER OF THE MANTLE
they sit on top of the semi- molten asthenosphere where convection currents allow the plates to move/ drift
what are the differences between OCEANIC and CONTINENTAL crust?
OCEANIC
* 7-10km thick (thinner)
* more dense, so SUBDUCTS
* basaltic
CONTINENTAL
* 30-70km thick (thicker/ taller)
* less dense
* granitic
explain CONVECTION CURRENTS
RADIOACTVE DECAY in CORE+ MANTLE generates a lot of heat
lower parts of ASTHENOSPHERE heat up, become less dense, and rise
cool down as rise, become more dense, and sink
CIRCULAR MOVEMENTS of semi- molten rock called CONVECTION CURRENTS
these convection currents create DRAG on the base of the plates, causing them to move
who created the theory of CONTINENTAL DRIFT?
ALFRED WEGENER
what evidence did ALFRED WEGENER collect to support his theory of CONTINENTAL DRIFT?
GEOLOGICAL:
* APPARENT FIT of continents (e.g. south America + Africa on either side of the Atlantic)
* GLACIAL STRIATIONS- in south Africa, south America and Australia indicate they were once joined near the south pole
* MOUNTAIN RANGES+ ROCK SEQUENCES on either side of oceans with SAME ROCK TYPE (e.g. Canada+ Scotland)
BIOLOGICAL:
* FOSSIL COROLLATION (same animal fossils in separate continent coastlines e.g. MESOSAURUS which could not swim or fly)
* SIMILAR FOSSIL BRONCHIOPODS (marine shellfish) found in Australian+ Indian limestones
how did WEGENER say the continents had moved?
250 mil years ago: supercontinent PANGEA
split into the continents: LAURASIA+ GONDWANDALAND
currently: 7 continents
what is a weakness of Wegener’s theory of continental drift?
no explanation as to WHY THEY MOVED/ no mechanism to explain the movement
explain PALEOMAGNETISM
DIVERGENT boundaries- plates move away from each other, allowing magma to rise from asthenosphere to fill the gap; cools as rises- contains IRON PARTICLES which are locked into rock when cools.
the particles face MAGNETIC NORTH; POLARITY REVERSES every 400,000 years
(alternately aligned iron particles on either side of boundary)
supporting theory of SEA FLOOR SPREADING
explain OCEAN DRILLING
cores extracted up to 7000m deep- revealed SPACIAL PATTERN of sediments supporting theory of SEA FLOOR SPREADING; thickest+ oldest sediments found nearest continents
oldest rock found were 200 million years old- must be constantly recycled
what did NUCLEAR TESTS in the 1960’s reveal?
SEISMIC DATA which showed most earthquakes (esp. high magnitude) were concentrated in narrow bands (rigid lithosphere+ crust divided into plates)
