The structure of the earth Flashcards
what is on the outside layer of our earth?
a rocky crust
what is the outer layer of the earth made from?
tectonic plates
how fast do tectonic plates move?
very slowly
where are tectonic plates found?
on the outer layer of our earth
what does the movement of tectonic plates cause?
earthquakes and volcanoes at the plate boundaries`
how long has it took continents to move apart?
millions of years
what is the outer layer of the earth called?
the lithosphere
what makes up the lithosphere?
the crust and part of the mantle
explain what the lithosphere is?
relatively cold and rigid
finish this sentence… The tectonic plates that make up the earth’s crust is less dense than what
the rest of the mantle below
why has the theory of plate tectonics been accepted?
it explains the evidence. It has been tested and the results discussed by many scientists
can we drill through the crust?
no
how do we judge the thickness of layers in our earth?
by the use of seismic waves produced by earthquakes and by artificial explosions
explain what the lithosphere is?
rigid and brittle
what is the lithosphere divided into?
tectonic plates
what is the semi-rigid layer called?
the asthenosphere
explain the asthenosphere
it is hotter and like plasticine, which can flow even though its a solid
how is energy through the earth’s core transferred towards the surface?
by convection currents in the mantle. These convection currents slowly move the plates
what directions can tectonic plates move?
apart, collide, scrape past eachother
which is more dense continental or oceanic?
oceanic
what are the two types of plates?
continental and oceanic
where can we find continental and oceanic plates?
oceanic accumulate on top where oceanic plates float higher in the mantle
what is subduction?
where the oceanic plate sub ducts under the continental
what causes an earthquake?
when the sinking plate descends, it may get stuck and then suddenly move
what happens further down?
it partially melts to form magma
how are volcanoes formed?
magma working its way up to the surface creating a chain of valcanoes on the edge of the plate
How is igneous rock formed?
when magma cools and solidifies
how are small crystals formed in igneous rock?
when it cools rapidly close to the surface
how are large crystals formed in igneous rock?
when it cools slowly further from the surface
what is lava
molten rock that reaches the surface of the earth from volcanoes
how can you tell a safe volcano form an unsafe volcano?
if the lava is runny it is safe. If it is thick and sticky then an eruption can be explosive
why do some people live near volcanoes?
because the ash makes a rich soil that is good for growing things
why does magma rise through the earth’s crust?
because it is less dense than the crust
what was the theory called that meant all continents wear joined at one point
the continental drift theory
who suggested this theory?
Alfred wegner
why was his theory not accepted?
no one could explain how the continents were able to move through the rocks of the ocean floor
why was his theory accepted later?
because geologists found a huge ridge in the middle of the Atlantic ocean
what does this prove?
that the sea floor is spreading outwards at this point. This is where plates are being formed
what are subduction zones?
where plates are being destroyed
explain iron-rich magma?
tends to be runny so if it spills people can get away (safe)
explain silicia- rich magma?
forms rhyolite if it cools rapidly and is less runny
what causes explosive volcanoes?
when dissolved gases in the magma have no time to escape the stiff liquid. The magma erupts like spray. It shoots out as clouds of searingly hot ash and pumice
