Download Unit Test Review – Earth`s Crust

Unit Test Review – Earth’s Crust
 Label the layers of Earth
 3 process which caused earth to heat up
o The impact of particles and rocks as they collided in space caused heat that mostly
radiated out into space, but some was trapped inside of Earth
o Gravity caused the interior to become compressed and further heated
o Some naturally occurring radioactive elements were contained within the rock that was
forming the Earth
 As these elements decayed, they released more energy into the rock in the form
of heat
 2 ways in which the crust can be classified
o Continental crust is thicker and less dense than the oceanic crust
 Volcanoes are the obvious clue as to what may lie beneath the crust
MINERALS
 Minerals are the pure, naturally occurring building blocks of rocks
o Differences in rocks are due to different minerals
 All minerals are non-living, but a few contain minerals that were living things – example chalk is
composed of the shells of tiny organisms that lived in the sea and became fossilized
 Minerals are used in our everyday life
 Most minerals are made in several substances
Minerals are Crystals
 All minerals are pure crystals
 Crystals have regular geometric shapes because they are made up of tiny particles connected in
a repeating pattern
o Cooled slowly = large crystals
o Cooled rapidly = small crystals
Other Ways of Identifying Minerals
 Lustre – shininess
 Cleavage – the way in which minerals split into smaller pieces with flat surfaces due to their
crystal structure
 Hardness- every mineral can scratch another mineral that is softer than itself, but cannot scratch
a mineral harder than itself
 Color – clue to mineral’s identity example – gold is always yellow
o Not a reliable clue though because some minerals appear in different colors
 Streak – the color the minerals leaves behind when ‘streaked’ across unglazed porcelain tile
o Many have to be crushed to powder to determine their streak color
 Magnetism – 2 minerals, magnetite (strongly) and pyrrhotite (weakly), have magnetic properties
 Density
How Minerals Are Mined and Processed
 Small amounts of different minerals are found in most rocks
 Minerals can be found in large amounts (high concentrations) or deposits. When minerals are
found in deposits it allows minerals to be mined and can be profitable
 Rock that contains a valuable mineral is called ore
o High-grade ore contains rich concentrations of a mineral making it the most profitable
to mine
Searching for Deposits
 Some geologists spend their whole life searching for valuable minerals in which to mine
 Geologists study the Earth’s crust to be able to find new minerals
 Once a deposit has been found the process becomes complicated as it is often deep
underground, being trapped in hard rock
 The miner must decide whether strip mining or underground mining would be best to extract
the mineral
o Strip mining – often used when a mineral deposit is discovered near the surface. The
top layer of soil and rock, called overburden is removed until the ore is exposed. The ore
is then dug out using large machinery. The overburden may not be returned after the
ore has been removed.
o Underground Mining – Used when the mineral is located deep underground, and
mining directly from the surface is too expensive. A shaft is dug down into the Earth.
Large drills break up the ore; railcars haul the ore to the shaft. The ore is then crushed
and raised to the surface in cages. This process is called milling. The overburden may be
shaped and covered with topsoil, leaving space for plants to be planted.
Processing the Ore
 All types of ore must be processed to separate unwanted rock from the mineral
 These process includes using large amounts of water and chemicals
 Liquid wastes are placed in tailings pond – these ponds are very toxic and measures must be
taken to ensure they do not leak
When to Close a Mine
 If the value of the mineral is greater than the expense of extracting the mineral then the mine
will close
 When high-grade ore runs out they will close the mine as low-grade ore is not profitable to mine
 Expensive to close- mine needs to be returned as closely as possible to its natural state
Erosion and Weathering
 aWeathering breaks up the rock while erosion is the process in which carries away the rock
 Physical and Chemical Weathering
o Chemical weathering occurs when water, air, and other materials react with rocks,
changing the substances that make up rocks (new substance)
o Mechanical weathering is a form of erosion caused by wind and water
o Recognize examples of physical and chemical weathering
 Erosion by ice – moraines (Once a glacier starts to melt, it leaves the broken rocks it eroded in
enormous piles)
 Weathering by plants
Weathering: Fast or Slow
 Can occur quickly or slowly depending on a couple of factors
o Size of rock
o The mineral in the rock
o Climate is important – cold winters mechanical weathering takes place
 Horizons – layers of soil
 Soil Diagram – label and recognize description of layer
o Litter
o Topsoil
o Subsoil
o Bedrock
 Humus – decaying plant and animal matter
 How bedrock eventually becomes topsoil
Is Soil the Same Thickness Everywhere?
 When bedrock weathers, small rocks break off, deepening the subsoil
 Subsoil is weathered by plant roots and burrowing animals which bring humus down into the
subsoil therefore the subsoil slowly becomes topsoil (thousands of years)
 Thickness depends on
o How long the soil has had to form
o How much was left behind by glaciers
o Amount of erosion that has occurred
 Till – to break up compacted soil with a plough in order to allow water and air into the soil;
prepares the soil for plant growth
 Tilling allows water and air to enter the upper layers of the soil
 The soil is loosened which allows young plants to grow more quickly, but it also allows soil more
exposed to erosion and loss of nutrients
 Zero tillage – stubble from the previous crop, including the roots, is left in the ground, and new
seed is planted into the old stubble; no plough is used
Crop Rotation

Planting one crop in the same area every year is easier for the
farmer, it creates the problem that the same nutrients are being used from the soil every year

If those nutrients are not replaced, the soil will become less and
less productive

Farmers replace missing nutrients with fertilizer

Insect pests, bacteria, and moulds can stay in a field over the
winter, so if the crop is not rotated they can easily attack the same crop year after year

Crop rotation – a process used by farmers to prevent loss of
nutrients from soil, in each growing season, a different kind of plant is grown in a field
Ice Ages
 External cause
o Fluctuation in earth’s temperature
o Increase in earth’s tilt
 Earth-based cause
o Changes in oceanic circulation patterns
o Periods of frequent and aggressive volcanic eruptions
 Greenhouse theory – increased cloud cover
 Rivers- able to recognize picture or draw picture of young, old, or mature river. As well be able
to say why the river is the way it is.
 What are sediments
 How is sedimentary rocks formed?
 Lithification – the process by which sediments are compacted
 Clastic and chemical rock
Fossils
 Fossils are rocklike casts, impressions, or actual remains of organisms that were buried after
they died.
 Animals or plants can be preserved or fossilized in a number of ways
 The organism can be preserved entirely. For example the Wooly Mammoths found in
frozen Siberian mud
 This type of fossilization is fairly recent since the Ice Age
 Some, or hard, parts of the original organisms are left. Los Angeles tar pits have
preserved some bones of trapped organisms
 Plant life can also be fossilized
 Leaves falling into fine mud are well-preserved due to lack of oxygen, and quick
burial by more mud
 A very detailed impression of the leaf remains including carbon from the original
leaf
 Petrifaction is another form of fossilization by which once living substance, like bone, is
buried in sedimentary rock
o Water seeps through the rock, dissolving minerals from surrounding rock one
molecule at a time
o
o
o
The mineral water changes the molecular structure of the bone into a new mineral
substance such as silica
This type of fossilization that gives geologists the best window into pre-Ice Age
Earth
Can also be covered by volcanic ash, mud or quick sand in which it will eventually
become sedimentary rock
Age of Fossils
 To determine the age of rocks, geologists use fossils
o Both absolute age (the time in years) and relative age (the order of events)
o Absolute age is rarely obvious therefore geologists must use evidence, such as that
taken from fossils, to determine relative age
o Because every period on Earth had its own characteristic set of life forms, the fossils
found in layers of sedimentary strata provide vital information about the age of the host
rock
Continental Drift

Pangea – Wegener’s theory

Plate Tectonics

Moving Plates
o
Earthquakes signal the movement of plates
o
Fault
o
Subduction
o
Ridges
Mountains from Rocks

Fold Mountains

Block Mountains

Dome Mountains
Igneous and Metamorphic Rocks

Igneous rocks- be able to explain the difference between extrusive and intrusive igneous rocks

Be able to explain and label the rock cycle
Volcanoes: Mountains from Magma

Shield Volcanoes

Stratovolcanoes