4500 million years old as it is
older than oldest rocks
studying rocks tells us more
about earth
erosion - the earth's
surface is made of rock
layers, the layers are
compacted sediment
produced by weathering
and erosion
craters - the moon's surface is
covered with impact craters from
meteors, earth also has been been
eroded
mountain formation - if
new mountains weren't
being formed, earth's
surface would have
eroded down to sea level
folding - some rocks look as if they've
been folded in half, requires huge force
over time
Structure Of Earth
thin rocky crust
- thickness varies between
10km and 100 km
- oceanic crust lies
beneath the oceans
- continental crust forms continents
the mantle
- extends almost halfway to the centre of the earth
has a rougher density than rock in crust
very hot but under pressure
the core
- accounts for over half of the earth's radius
-made of nickel and iron
- decay of radioactive
elements inside the earth,
keeping hot
Sea Floor Spreading
1. convection currents in the mantle cause magma to
rise
2. the current moves the solid part of mantle and the tectonic
plates
3. when the plates are moving apart, magma reaches the suface and hardens,
forming new areas of oceanic crust
plate tectonics
earth has a magnetic field,
changes polarity every m years
combined with sea floor
spreading produces rock stripes
of alternating polarity
4. this pushes the existing floor outwards, and the the new crust is
continuously forming at the crest of an oceanic rifge - leads to sea
floors seperating a few cm each year
can be used to see how quickly crust formed by
width of stripes
when oceanic and continental plates
collide the denser oceanic plate if
forced under (subduction)
the oceanic plate melts and molten rock can rise
to form volcanoes
mountain ranges form
along plate boundaries
as sed rock is forced
up by pressure in
collision
earthquakes
waves from earthquakes
primary waves
travels faster than s-waves
can travels through both liquids and solids
can travel through liquid region of outer core of
earth
longitudinal
vibrates backwards and forwards
moves backwards and forwards in the
same plane as the direction of wave
movement
sound waves travel as longitudinal
secondary waves
can only travel through solid
cannot travel through liquid region of outer core
tranverse
each particle vibrates up and down in normal position
moves up and down at right
angles to the direction of wave
movement
light and water ripples and
electromagnetic waves travel in
transverse
example: /\/\/\/\/\/\/\/\/\/\
wave features
amplitude - the maximum disturbance
caused by a wave, measured by the distance
from a crest of the wave to the undistrubed
wave length - the distance between corresponding
points on two adjacent disturbances
frequency - number of
waves produced per
second (hertz, hz)
1. Plates slide past eachother
2. pressure builds up as
plates push on each
other
3. eventually stored energy is
released and waves from energy
spread from epicenter
crucial in rock cycle
- old rock is destroyed through subduction
- plate collision can produce high
temps causing rock to fold
- igneous rock is formed when magma
reaches surface