Structure of the Earth
Meilien Lam
Sedimentary rocks are formed when different layers of sediments join together over a
long period of time. These rocks can be found on the surface of the earth or lithosphere.
Rocks on the surface of the earth keep changing and recycling. However, this is a very
slow process and takes a long time for the rocks on the Earth’s surface to move down
towards the centre of the Earth.
1. Visit the following website and then label the following diagram. Give a short
description for each part.
http://mediatheek.thinkquest.nl/~ll125/en/struct.htm
Crust
The
Mantle
Outer Core
Inner Core
Crust – The crust is a thin layer of earth. It is 6378 km away from the core.
The crust is made from granite and basalt and can be 8 km thick or 1.
Mantle – The mantle is between the crust and the outer core. It is made up of
hot, solid rock. It can be around 2900 km thick.
Outer Core – The outer core is made up out of liquid iron and nickel. The
temperature in the outer core can be around 4400 degrees Celsius to 6100
degrees Celsius. It is around 2270 km thick.
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Inner core – the inner core is a solid ball of iron-nickel alloy that is 1220 km
thick. The temperature is nearly as hot as the sun with temperatures around
5450 degrees Celsius.
The following website shows the rock cycle. Click on different parts of the rock cycle
diagram for more information. If you find the information a little hard to understand here
is what you can do: look above the page on your left hand side and click on the beginner
for simpler explanation.
http://www.windows2universe.org/earth/geology/rocks_intro.html
You can also find the same information in the ‘Rock cycle’ program. Use this program
and give at least two examples for each type of rock that you are learning about.
Write a short description for each type of rock.
1. Sedimentary rocks,
Sedimentary rocks are rocks made out of little bits of eroded rock and earth. Three
quarters of all earth’s rocks are sedimentary rocks. These types of rock form anywhere
where sediments can be collected. A lot of sedimentary rocks are clastic sedimentary
rocks. Clastic sedimentary rocks are made from sediments, or bits of sand, pebble, mud
etc., that are cemented together with tons of pressure. Other types of sedimentary rocks
are chemical sedimentary rock, which is made from mineral crystals, and organic
sedimentary rock, which is made from dead remains of animals and plants. Different
types of sedimentary rocks include sandstone and limestone.
2. Igneous rocks,
Igneous rocks are made out of cooled molten rock, or lava. There are two types of
igneous rocks depending on where the rock forms. They are intrusive and extrusive.
Intrusive igneous rocks are formed below the earth’s surface. Intrusive igneous rocks
form from magma that has entered an underground chamber and is cooled very slowly.
These rocks include large crystals. Extrusive rocks are the opposite. Instead of forming
below the surface, extrusive rocks form above earth surface. This means extrusive
igneous rocks are formed when volcanic lava is cooled quickly, above or at the earth’s
surface. Igneous rocks include granite, scoria and andesite.
3. Metamorphic rocks,
Metamorphic rocks only form when the temperature is very hot and there is a lot of
pressure, like when the earth’s tectonic plates are clashing together. Deep underground,
rocks are heated with scorching magma and are squashed together by the colliding plates.
While this is happening, the rocks are changing inside as well. The same chemical
ingredients form new crystals and sometimes, minerals that weren’t in the rock before,
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form as well. All 3 types of rock can be metamorphosed. Different types of metamorphic
rocks are amphibolite, slate and gneiss.
Activity:
1. Open the following program (rock cycle (labeling activity)) and see if you can
label the diagram.
2. Now open the following program’ Pearson Rock cycle’ and explain how rocks
can be changed from one form to another.
All three rocks can change into any of the other types of rocks. Example, sedimentary
rocks can turn into igneous rocks after melting into magma and then harden into
igneous rocks. Sedimentary rocks can also turn into metamorphic rocks when it is
under pressure and heat. It can be turned into sediments after erosion. Igneous rocks
can change into metamorphic rocks when it is also under heat and pressure. Ot can
turn into sedimentary rocks after eroding and turning into sediments and then
cementing. Metamorphic rocks can turn into igneous rocks after melting into magma
and then hardening into igneous rocks.
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