The Rock CycleGlobal Geography 12

http://www.learner.org/interactives/rockcycle/types.html

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 Videohttp://www.youtube.com/watch?v=SRaInMDNyE8

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 obsidian.

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 fossils.• 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 RocksSome examples of changes from one rock type into a metamorphic rock type due to high temperatures and pressures include…

Metamorphic Rocks

• 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

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 through?

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 down.

• 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.

http://www.livephysics.com/ptools/dig-hole-through-earth.php

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.