Download The Rock Cycle and the three rock types File

11 Sci: “The Rock Cycle” Notes
Achieved Explanation of the Rock Cycle
The Rock Cycle is a group of changes. Igneous rock can change into sedimentary rock or
into metamorphic rock. Sedimentary rock can change into metamorphic rock or into
igneous rock. Metamorphic rock can change into igneous or sedimentary rock.
Achieved Diagram
Merit Explanation of the Rock Cycle
Igneous rock forms when magma cools and makes crystals. Magma is a hot liquid made
of melted minerals. The minerals can form crystals when they cool. Igneous rock can
form underground, where the magma cools slowly. Or, igneous rock can form above
ground, where the magma cools quickly.
When it pours out on Earth's surface, magma is called lava. Yes, the same liquid rock
matter that you see coming out of volcanoes.
On Earth's surface, wind and water can break rock into pieces. They can also carry rock
pieces to another place. Usually, the rock pieces, called sediments, drop from the wind or
water to make a layer. The layer can be buried under other layers of sediments. After a
long time the sediments can be cemented together to make sedimentary rock. In this way,
igneous rock can become sedimentary rock.
All rock can be heated. But where does the heat come from? Inside Earth there is heat
from pressure (push your hands together very hard and feel the heat). There is heat from
friction (rub your hands together and feel the heat). There is also heat from radioactive
decay (the process that gives us nuclear power plants that make electricity).
So, what does the heat do to the rock? It bakes the rock.
Baked rock does not melt, but it does change. It forms crystals. If it has crystals already,
it forms larger crystals. Because this rock changes, it is called metamorphic. Remember
that a caterpillar changes to become a butterfly. That change is called metamorphosis.
Metamorphosis can occur in rock when they are heated to 300 to 700 degrees Celsius.
When Earth's tectonic plates move around, they produce heat. When they collide, they
build mountains and metamorphose (met-ah-MORE-foes) the rock.
The rock cycle continues. Mountains made of metamorphic rocks can be broken up and
washed away by streams. New sediments from these mountains can make new
sedimentary rock.
The rock cycle never stops.
Excellence Diagram
Metamorphic Rocks caused by
Buckling Pressure
Excellence explanation of the Rock Cycle
If we examine the rock cycle in terms of plate tectonics, as depicted in the figure above,
we see that igneous rocks form on the sea floor as spreading ridges. As the rocks cool,
and more magma is introduced from below, the plate is forced away from the spreading
ridge, and acquires a sediment cover. As shown in the figure, in this case, the oceanic
plate eventually "dives" under the adjacent continental plate. As the oceanic plate travels
deeper, high temperature conditions cause partial melting of the crustal slab. When that
occurs, the surrounding "country rock" (existing adjacent rock) is metamorphosed at high
temperature conditions by the contact. The molten material is either driven to the surface
as volcanic eruptions, or crystallizes to form plutonic igneous rocks.
Achieved Explanation for the Three Rock Types
(see also individual handouts)
Igneous Rocks are cooled Magma from deep underground
Metamorphic Rocks have been partly melted from pressure or heat
Sedimentary Rocks are sand and silt from rivers that have washed into the sea. Also
limestone made from sea animals.
Merit Explanation for the Three Rock Types
(see also individual handouts)
There are two types of Igneous Rocks. Plutonic Rocks form when magma cools slowly
forming large mineral crystals. Volcanic Rocks form when magma is erupted, and cools
slowly small crystals are “frozen” in a fine grained “dough” called a ground mass.
Metamorphic Rocks are rocks which have either been heated so some minerals have
melted and then cooled with larger crystals (Contact Metamorphism), or rocks have been
squeezed by Buckling Pressure and liquidized; minerals often form in layers such as
quartz veins.
Sedimentary Rocks form from sediment washed into the ocean from the land. The
weight of the sediment squeezes out liquid with dissolved mineral material (mainly silica
SiO2) which glues the sediment together. Limestone forms further away from the
continents and is glued together mainly by liquid with dissolved calcium carbonate.
11Sci: Mantle, Crust and Core Notes
Achieved Information
The Earth is made up of three main parts. The Core is at the centre of the Earth and is
3400km across. This is Iron rich and is dense. The core is covered by 3000 km thick layer
of hot melted rock which is solid at depth closer to the core. This is called the Mantle.
The mantle is more fluid from a depth up of 1000 km. On top of the Mantle “floats” the
Crust. The Crust is made up of lighter rocks. The Crust is broken up into Plates which
move on top of the “boiling” Mantle. The Plates therefore can crash and grind up against
each other forming mountains and other land features.
Merit Information
You will need the Achieved Level information, plus some of the following. The core is
composed of heavy iron. The mantle is composed of iron and magnesium rich minerals,
so the molten rock material has a lot of heavy metal molecules. The crust contains a lot of
aluminum and potassium rich minerals, so contain a lot of lighter metal molecules.
When the crustal plates crash into each other often one plate goes under the other plate
(see Excellence rock cycle diagram). The crust that goes under is called subduction and
is melted when it enters the molten mantle. The lighter aluminum and potassium rich
rocks “float” up and force there way to the surface as volcanoes such as Ruapeheu,
Tongariro, and Ngaruhoe. These hot melts can sit under the surface for a time, where they
heat up the surrounding rock and water. This hot water is what causes the geothermal
activity near Rotorua and Taupo. This volcanic activity is usually a typical distance from
the subduction zone. Look at The Andes, Indonesia, Japan, Alaska, and New Zealand.
Excellence Information
The solid part of the Earth is made up of a core coved by semi molten and solid rock
called the lithosphere (litho = rock, sphere = ball, so rock ball).
The lithosphere comprises two shells—the crust and upper mantle—that are divided into
a dozen or so rigid tectonic plates. These are constantly in movement, driven by the flow
of “boiling” magma in the interior. The plates (continents) move like conveyor belts,
being drawn downward under each other into the crust when they crash and being
replaced with rising molten rock in other areas. Continents are carried on the plates, at
rates of movement measured in centimetres per year.
The crust itself has two parts. The upper, crust, of which the continents consist, is made
up of igneous, metamorphic, and sedimentary rocks whose average chemical composition
is similar to that of granite and whose density is about 2.7. The lower, crust, which forms
the floors of the ocean basins, is made of darker, heavier igneous rocks such as gabbro
and basalt, with an average density of about 3.0.
Under the crust is the upper mantle which is the lower part of the lithoshere. Rocks at
these depths have a density of about 3.3. The upper mantle is separated from the crust
above by a seismic discontinuity, called the Moho, and from the lower mantle by a zone
of weakness known as the asthenosphere. Sliding across the gooey, partially molten rocks
of the asthenosphere, 100 km (60 mi) thick, under the lithosphere enables the continents
to drift across the Earth’s surface and oceans to open and close.
Upper Mantle, part of the interior of the Earth. It is about 650 km (400 mi) thick and
features two distinct layers. Directly beneath the crust is a solid layer that, combined with
the crust, forms the lithosphere, which makes up the Earth’s plates. Beneath this layer is
the asthenosphere, where semi-molten rock flows slowly like hot tar. It is believed that
convection currents, which move within this area like boiling water, drive the overlying
plates.
Lower Mantle, part of the interior of the Earth, about 2,300 km (1,430 mi) thick. Even
though temperatures are higher here, this part of the mantle is solid. Tremendous
pressures keep the rock material from melting.
The dense, heavy interior of the Earth is divided into a thick shell, the mantle,
surrounding an innermost spherical core. The mantle extends to a depth of about 2,900
km (1,800 mi). It is mostly solid, and its density, increasing with depth, ranges from 3.3
to 6. The mantle is composed of iron and magnesium (i.e. heavy metal) minerals which
are therefore heavier than the aluminum potassium rich minerals of the crust
The core has an outer part 2,225 km (1,380 mi) thick with an average density of 10 which
behaves like a thick fluid, while, the inner core, which has a radius of about 1,275 km
(795 mi), and is solid. Both core layers are thought to consist largely of iron, with a small
percentage of nickel and other elements. Temperatures in the inner core have been
estimated at 5,500° C (9,932° F), while the average density is estimated to be 13 or 7
times as heavy as the rocks we know from the crust.