plate tectonics Flashcards
what are the three layers of the earth
concentric
core mantle crust
what is the core divided into
a liquid outer layer
solid inner layer
temperature and pressures are extremely hot and strong which cause the rock of the inner core to be solid
what does the core consist of
iron and nickel
describe the mantle (3)
very thick mantle which is mostly dense and solid
mixture of rock in the solid and molten state
upper part - asthenosphere made up of molten rock where the movement causes plate tectonics
what is the mantle rich in
magnesium and iron
describe the crust (2)
thin solid outer layer which is made of rocks
where all human activities take place
what are the two types of crust
continental and oceanic
describe continental (4)
comprised of silica and aluminum
called sial or granite rock
can be up to 40 km thick
less dense than oceanic crust
describe oceanic (4)
comprised of basalt which is silica and magnesium
called sima
between 6 and 10 km thick
much thinner than oceanic yet more dense
define plates
earth’s crust broken into several large sections
define plate tectonics
massive irregularly shaped slab of solid rock made up of earth’s crust floating above magma below in the mantle below
how do continents occur
when continental crust rests on top of oceanic crust
why do plates move (4)
convection currents flow due to heat source within the core
as semi molten rock from asthenosphere is heated it becomes less dense than surroundings and so rises
as it reaches the crust above, spreads out carrying plates above with it
when it cools, it gradually sinks back down to be reheated
explain the theory of pangea
initially one supercontinent called Pangea meaning all land
around 200 million years ago split and the pieces drifted apart over millions of years to form today’s continents
who suggested this theory of pangea
german geographer alfred wegener in 1915
list 5 evidences that support the theory of pangea
west coast of africa fitting closely with east coast of south america
matching fossils reptiles in africa and south america
presence of coal formed in warm wet conditions under antarctic ice cap
rocks of same age and geological structure formed in southwest africa and southeast brazil
presence of an identical fossil fern in all southern continents
define a plate margin or boundary
point where two plates meet
define convergent/destructive
two plates move towards each other
if one is made of dense oceanic crust, will dove down or subduct beneath other to form subduction zone
at the subduction zone there is immense heat and friction which melts and destroys the subduction plate thus forming new magma which is lighter or less dense than surrounding rock in the mantle
how are earthquakes formed as a result of convergent/destructive
when subducting, the movement is not smooth and sometimes the plates sticks and suddenly jerk releasing energy via seismic waves resulting in earthquakes — Haiti Earthquake 2010
how are volcanoes formed as a result of convergent/destructive plate boundaries
some of the magma may rise to surface along lines of weakness or cracks in crust forming volcanoes
what are other features formed as a result of convergent/destructive plate boundaries
ocean trenches - mariana trench located in western pacific ocean and the peru chile ocean trench
tsunamis 2004 indian ocean earthquake
earthquakes
define ocean trench
long narrow deep depressions along sea floor which mark the boundaries where the sea floor suddenly plunges to great depths – peru chile oceanic trench and mariana trench located in western pacific ocean
how are fold mountains created (4)
when two continental plates converge, there is no subduction zone due to the plates being of similar density so instead the sea floor crumples at the boundary which creates fold mountains – himalayan mountains in northern india of the indo australian plate and eurasian plate
tethys sea laid between 2 land masses and was pushed out of existence as they slowly moved together
rock strata on sea bed folded up to form himalayans where marine fossils found there proved it was once sea floor
india continues to push against eurasian plate by 5 cm a year forming mt everest approx 8848.86 m
define divergent and constructive plate boundary
2 plates moving away from each other
as they diverge, molten rock or magma rises in between the two crustal plates leading to the formation of new crust when magma cools and solidifies
if 2 oceanic plates move apart is called sea floor spreading resulting in formation of new crust such as the midatlantic ridge where north american plates diverges away from eurasion plate to form underwater mountain ridge in atlantic ocean
volcanoes are also common to form volcanic islands such as iceland
define transform neutral conservative plate boundary
when two plates slide past each other either in opposite directions or in the same direction but at different speeds
also results in some displacement of crust
little to no volcanic activity therefore crust is neither destroyed or created
– san andreas fault in california where pacific plate is moving north in relation to the north american plate
explain how earthquakes are formed as a result of transform plate boundary
plates slide past each other in sudden and rough movements where it jolts and is not smooth resulting in the buildup of energy which is released as seismic waves and felt as earthquakes on the ground
haiti 2010 between caribbean plate and north american plate
