The Rock Cycle

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Transcript The Rock Cycle

The Rock Cycle
Global Geography 12
The Rock Cycle
• The rock cycle refers to the process of rock
types changing into other types of rocks.
• There are three different types of rocks:
– Igneous rocks
– Sedimentary rocks
– Metamorphic rocks
Rock Cycle Video
Igneous Rocks
• Igneous rocks are formed when magma (molten rock)
cools and hardens.
• Sometimes the magma cools inside the earth; other
times it erupts onto the surface from volcanoes.
• When lava cools very quickly, no crystals form and the
rock looks shiny and glasslike.
• Sometimes gas bubbles are trapped in the rock during
longer cooling processes, leaving tiny holes and
spaces in the rock.
• Examples of this rock type include granite, basalt, and
Igneous Rocks
Sedimentary Rocks
• 70% of all rocks on Earth are sedimentary rocks
• Sedimentary rocks are formed from particles of sand,
shells, pebbles, and other fragments of material.
• Gradually, this sediment accumulates in layers and
over a long period of time hardens into rock.
• Generally, sedimentary rocks are fairly soft and may
break apart or crumble easily.
• You can often see sand, pebbles, or stones in the rock
• It is the rock type that most commonly contains
• Examples include conglomerate and limestone.
Sedimentary Rocks
Metamorphic Rocks
• The oldest known rock lies in Canada (NWT). The
Acasta gneiss, a metamorphic rock, is 3.96 billion years old.
• Metamorphic rocks are formed under the surface of
the earth from the change that occurs due to intense
heat and pressure.
• The rocks that result from these processes often
have ribbon-like layers.
• They may have shiny crystals on their surface,
formed by minerals growing slowly over time.
• Examples of this rock type include gneiss and marble.
Metamorphic Rocks
Some examples of changes from one rock type
into a metamorphic rock type due to high
temperatures and pressures include…
Metamorphic Rocks
Digging Through Earth
• Scientifically speaking it would be impossible to dig
a tunnel through to the other side of the world.
• If you attempted to dig a hole to the other side of
the Earth, you would be digging through:
» More than 12 000 kilometres of solid rock
and molten magma
» Rock reaching temperatures up to 6000 ºC
» Extreme pressures up to 300 million times
greater than the pressures we experience
on the surface of the Earth!
Digging Through Earth
• If you did manage to dig a hole through to the
other side of the Earth, how long do you think
it would take you if you were digging at a rate
of 0.3 meters per minute (1 foot per minute)?
Digging Through Earth
• Scientists have calculated the time it would
take for you to dig a tunnel through to the
other side of the Earth (at a rate of 1 foot per
minute) at 87 years.
• If you did somehow manage to dig a hole to
the other side of the Earth, would you fall
Digging Through Earth
• Theoretically the answer is NO!
• This is because gravity changes as you fall to
the Earth’s centre and friction would slow you
• However, if you ignored gravity and friction
altogether, how long do you think it would take
you to fall through the tunnel if you jumped in
on one end of the Earth?
Digging Through Earth
• Scientists think it would take about 42 minutes
to fall through the Earth’s tunnel to reach the
other side.
• If you started digging in Nova Scotia, where do
you think you would end up coming out on the
other side?
If you started digging a tunnel in Nova Scotia through the centre
of the Earth, you would come out to the south of Australia.
The Earth is not a
perfect sphere. It is
slightly flattened at the
poles, and bulges a
little at the equator
due to the Earth’s spin.