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Earth’s Crust

Pages 311 - 453Discovering Science 7

Investigating Minerals

PA mineral is a pure, naturally occurring,inorganic, solid substance.

P Inorganic refers to something that does notcontain any carbon-based compounds.

PMost minerals are very rare.

PThere are about 4000 different minerals onearth, but only about 150 are common.

PMany of these are found in Newfoundland &Labrador


Properties of Minerals

PMinerals can be classified based on manyproperties< color< streak< hardness< lustre< cleavage< fracture


Lustre

PThe shininess or lustre of a mineral dependson how light is reflected from its surface.

PThere are three classifications of lustre< Metallic - if it has the appearance of metal< Glassy - surface has a reflective nature like glass< Dull - if it does not reflect light.

Chalk has Dull lustre Calcite has a Glassy lustre Pyrite has a Metallic lustre

Investigating MineralsColour

PColour may seem like a good way to tellminerals apart, however, many differentminerals share the same colour.

PFor example, Gold and Pyrite both appear tobe a metallic golden colour. Gold is veryvaluable and Pyrite is practically worthless.

PQuartz, calcite and corundum can all bewhite.

PSome minerals like corundum can be manycolors depending on what’s mixed in it.


Streak

PWhen you rub a mineral across the surface of anunglazed porcelain tile, it leaves a powderedmark. This mark is called the streak.

PGold leaves a yellow streak while Pyrite leaves agreenish-black or brown-black streak.

Hematite on the left, Pyrite on the right


Hardness

PA german scientist, Friedrich Mohs,developed a hardness scale, called MohsHardness Scale, to aid in the classification ofminerals

PHe took 10 representative minerals andclassified them from 1(softest) to 10 (hardest).

Investigating MineralsCleavage

PWhen a mineral has cleavage, it has theproperty of splitting along smooth flatsurfaces called planes.

PAn example of a mineral with cleavage isMica.


Fracture

PWhen a mineral has fracture it means it splitswith a rough or jagged edge.

PAn example of a mineral with fracture isQuartz.


Other Properties

PThere are several other properties that couldbe used in describing and identifying minerals< Crystal formation - some minerals form very large

crystals while others have crystals so small theycan’t be seen.

< Heft - how heavy a mineral feels< Odour - how it smells< Surface texture - does it feel powdery, greasy,

soapy, etc.

Investigating Rocks

Rock Families

PRocks can be classified into one of threefamilies, depending on how they wereformed.

PEach type of rock can usually be identifiedby its appearance and by the arrangementof mineral grains within it.

PThe three familes are< Igneous< Sedimentary< Metamorphic

Investigating Rocks

Igneous Rock

P Igneous Rock results from the cooling ofmolten (melted) rock material which comes tothe surface from under the earth’s crust.

Investigating Rocks

Igneous Rock

PAs this material cools, crystals are formed.

PThe crystals are different sizes depending onwhether the rock cools quickly or slowly.

PThe longer the molten material takes to cool,the larger and more organized the crystals willbe. The shorter the cooling time, the smallerthe crystals will be.

Granite is a common form of igneous rock

Note the crystals

Investigating Rocks

Igneous Rock

PMagma is the molten rock material foundunder the Earth’s crust. It is formed by theimmense pressure and extremely hightemperatures. Magma that goes to the surfaceof the Earth is called Lava.

P It is the high pressure that can force magma tothe surface of the Earth or just below thesurface.

Magma that hashardened below thesurface - Intrusive Rock

Magma that has come tothe surface beforehardening - ExtrusiveRock

Investigating RocksIgneous Rock

PScientists classify Igneous Rock based onwhere it hardens

P Intrusive Rock - is igneous rock that getsforced close to the surface (but doesn’t breakthe surface) and then hardens.< Example - granite

PExtrusive Rock is igneous rock that comes tothe surface of the Earth before hardening.< Example - Obsidian, basalt

Obsidian Basalt

Investigating Rocks

Sedimentary

PSediment is loose particles, such as bits of rocksand minerals and decaying plants and animals.

PSediment can be moved from place to place bywater, wind, ice, and gravity until it finally settles.

PSediment slowly settles on top of other sediment,forming visible layers

PThe weight of the layers on top causes the layersbelow to become compressed.

PThis process of compressing layers of sediment iscalled compaction.

Investigating RocksSedimentary

PSometimes water dissolves minerals asit soaks through the rock. Thesedissolved minerals act as cement,sticking the larger pieces of sedimenttogether.

PThe process in which pieces ofsediment are held together by anothermaterial is called cementation.

PSedimentary rocks form from thecompaction and cementation ofsediments into visible layers calledbeds.

Investigating Rocks

Sedimentary

Investigating Rock

Sedimentary

Investigating Rock

Metamorphic

PMetamorphic means “changed form”.

PA metamorphic rock is made when heat,pressure, or hot fluids change one type of rockinto another type of rock.

PMetamorphic rock can be made from igneous,sedimentary or other metamorphic rock.

PThe formation of such rock is a very slowprocess.

Investigating RockMetamorphic

PMetamorphic rocks form below the surface ofEarth where heat and pressure are very high. Hotfluids can flow into igneous, sedimentary, orother metamorphic rock and change the rockboth physically and chemically.

PThe type of rock you start with beforemetamorphic rock is formed is called the parentrock.

PFor example shale (a sedimentary rock) can bechanged to slate (a metamorphic rock) whenextreme pressure is applied.

Investigating Rocks

Metamorphic

PMetamorphism may change the properties ofthe rock (colour, lustre, hardness, and the wayin which a mineral breaks).

PThe rock can change so much that it doesn’tresemble the parent rock at all.

Limestone Marble

The Rock Cycle

P In the rock cycle, different conditions producedifferent types of rocks. Rocks are constantlychanging as they are heated up, cooled down,worn away, and placed under pressure.

The Rock Cycle

PRocks continue to change in ongoing processescalled the rock cycle.

PWeathering & erosion of igneous, sedimentaryand metamorphic rock creates sediments whichare deposited and over time the layers create newsedimentary rock

PThis sedimentary rock can be changed into newmetamorphic rock. Sometimes this metamorphicrock can go so deep that it is changed back intomagma.

PMagma is forced upward to produce new igneousrock and so the cycle continues.

Rocks & Minerals as Resources

PA rock or mineral resource is a rock ormineral that can be mined and used for aspecific purpose. For example, petroleum,metals, and gems are all resources.< Petroleum (crude oil) - is used to make fuels,

plastics, and many other useful products.< Metals - Commonly used metals include gold,

silver, copper, iron, zinc, aluminum, and nickel.We use metals to make cars, applicances,computers, and tools.

< Gems - are highly prized minerals because they arerare and beautiful. Because diamonds are thehardest of all minerals, they are used on drill bitsand other instruments to cut through hardsubstances, such as steel and rock.

The Moving & Changing Crust

Structure of the Earth

PEarth’s crust is made up of a series of crustalplates that are always moving.

PWe cannot observe the inner structure of theEarth directly, but by using shock wavesmade by earthquakes and satellite images, wecan predict what the layers of the Earth mightbe like. This is called indirect evidence.


Structure of the EarthP Inner Core< deepest and hottest layer< Thought to be made of iron and nickel

POuter Core< So hot it is probably made of liquid iron and nickel< Sulphur & oxygen may also be present

PMantle< Largest and most complex layer< upper part is solid rock, made from minerals rich

in iron, magnesium, silicon, and oxygen< lower part the temperature is so high that the rock

is partly melted. Consistency of taffy.


Structure of the Earth

PCrust< Top layer where life exists< thin layer of solid rock< valuable rock and mineral resources are found< Thickness varies from less than 5 km up to 70 km< Thickest under the continents, thinnest under the

oceans< Crust is broken into several large areas called

plates which are constantly “floating” and movingover the mantle.

Tectonic Plates


Earth’s Moving Crust

PMany years ago, a German meteorologist (AlfredWegener) noticed that the shape of Earth’scontinents fit together like puzzle pieces.

PBased on this, the theory of Continental Drift wasdeveloped. This basically says that the continentsof the Earth are actually moving at a very slow rate.

PWegener suggested that there was once a supercontinent called Pangea.

PHe felt that Pangea began to break apart about 200million years ago.

Pangea

The Moving & Changing CrustEarth’s Moving Crust

PBiological Evidence - there was muchbiological evidence to suggest that all thecontinents were once joined.< Fossils of the same species of animal were found

on separate continents thousands of kilometersapart. Many of these animals either lived infreshwater or could not swim at all, so the idea thatthey swam across the ocean does not make sense.

< Fossils of plants that can only grow near theequator have been found in Antarctica andLabrador. Suggesting that these land masses wereonce near the equator.


PGeological Evidence< geologists had found similarities in rocks on both

sides of the Atlantic Ocean. For example, theAppalachian mountain range in eastern NorthAmerica is made of the same kind of rock as themountain range that runs through Britain andNorway.

< The ages of rock in eastern North America and inBritain and Norway are the same as well.

< Both of these factors suggest that the land wasonce joined.


PMeteorological Evidence (Climate Change)-coal can only form in areas where the plantlife is rich and abundant and temperatures arewarm as in the tropical regions around theequator.

PHowever, coal beds have been found in areassuch as Antarctica, Canada and Europe wherethe climates are cold.

PThis would suggest that these areas were oncelocated in tropical regions and throughcontinental drift were moved to their presentlocation.


Rejection of Wegener’s Theory

PEven though Wegener’s ideas were good, hecould not explain how the continents werebeing moved.

PHe thought the continents were beinginfluenced by the gravity of the moon, just asthe tides are affected by the moon’s gravity.

PThe rest of the scientific community could notaccept that idea, so therefore, they rejected histheory of continental drift.

PHe died in 1930 without getting the evidenceneeded to support his ideas.

The Moving & Changing CrustEvidence from the Sea Floor

PWegener collected all of his evidence fromthe continents themselves.

PNew technologies came along in the 1940's toget a better picture of what was happening atthe bottom of the oceans and the interior ofthe Earth.


SonarPSonar< sound wave technology that sends out sound

waves and then records the time that the soundwaves take to bounce back.

< It is used to map the features of the sea floor aswell as the depth.

PUntil the use of Sonar, it was thought that thesea floor was flat.

PThrough the use of Sonar, it was discoveredthat the features of the sea floor were muchthe same as those on land. For example,mountain ranges were discovered.


Sonar


Magnetometer

PMagnetometer - is an instrument that can detectthe direction and strength of a magnetic field.

PWhen a magnetometer is towed across theAtlantic Ocean, sometimes it points north andsometimes it points south.

P It is known that over long periods of time(thousands of years), the Earth’s magnetic fieldflips. The north pole becomes the south poleand the south pole becomes the north pole.

The Moving & Changing CrustMagnetometer

PAs the ocean floor spreads, magma from themantle fills in the spaces. The magma has acertain iron content that reacts to the magneticfield and lines up in the direction of the magneticfield before it cools down.

P If the magnetic field is pointing north then theiron particles align northward. If the field hasflipped, the iron particles align southward.

PThe changes in the way the iron particles line up,indicates that new ocean floor was added at pointswhen the magnetic field flipped. Which, ofcourse, means the plates are moving.


Deep Sea Drilling of Core Samples

PA third piece of technology that supports theidea of plate tectonics is Deep Sea Drilling.

PWhile drilling for oil in the ocean, it wasnoticed that the rock samples near the Mid-ocean ridge were not as old as the rock samplescloser to the continents.

PThis indicates that the ocean floor is spreadingand new rock is being added.

Sea Floor Spreading


Plate Tectonics

PThe theory of Plate Tectonics states that the crustof the Earth is broken up into several separateplates that float on top of the semi-liquid, plastic-like mantle.

The term ContinentalDrift is no longer used,since the ocean floorsmove as well.

The Moving & Changing CrustPlate Tectonics

PThere are three waysthe plates move< Divergent boundaries -

the plates move awayfrom each other

< Convergent boundaries- the plates movetowards each other

< Transform boundaries -plates slide past eachother

When two plates collide, often one plate goes under theother. This is called the Subduction zone.


Plate Tectonics

PConvection Currents - hot fluids tend to riseand cool fluids tend to sink. The same processis thought to be occurring in Earth’s mantle.

PHot magma rises and as it cools drops backtowards the outer core.

PThis motion causes the plates to move in thedirection of the convection current.

Convection Currents

Earthquakes & Volcanoes

Earthquakes

PAn earthquake is the shaking of the ground.When the crustal plates move, tension canbuild up in the rock, causing it to suddenlymove or break, resulting in an earthquake.

P Most earthquakes occur along active plateboundaries especially transform or convergentboundaries.


Earthquakes

PThe majority of earthquakes are so minor thatthey cannot be felt by people on land.

PTo measure all earthquakes we use a devicecalled a seismograph.

Seismographs must be attachedto bedrock, which is the solidrock that lies beneath the soil, inorder to detect the vibrations thatresult from an earthquake.


Earthquakes

PSeismologists (scientists that studyearthquakes) use a method of measurementcalled the Richter scale to describe thestrength of an earthquake.

PAn earthquake that registered 7 would beabout 30 times stronger than one thatregistered 6, and about 900 times strongerthan one that registered 5. Most earthquakesthat cause damage and loss of life registerbetween 6 and 8 on the Richter scale.

Earthquakes & VolcanoesTypes of Faults

PFaults are breaks in the rock layers, usuallywhere tectonic plates meet.

PThere are three types of faults, based on theway the rock layers move< Normal Fault - the rock above the fault moves

down< Reverse Fault - the rock above the fault moves up

above the other rock layer< Transform fault - both rock layers move side to

side in opposite directions.


PSeismic Waves - energy waves that traveloutward from the source of the earthquake.

PFocus - The place deep in the crust where anearthquake begins

PEpicentre - The surface location directly abovethe focus


Volcanoes

PA volcano is an opening in the earth’s crust,which allows hot, molten rock, ash, and gases toescape from below the surface.

PVolcanic activity involving the extrusion of rocktends to form features like mountains over aperiod of time.


Volcanoes - Benefits

PEven though a volcano can be destructive, itprovides many benefits that life on earth couldnot do without.< Increase Soil Fertility - Forests and farm crops grow

better because the ash adds nutrients to the soil.< Magma Heats Groundwater - heated water can be

used to heat homes or as an energy source ex. Iceland

< Valuable Atmospheric Gases - carbon dioxide andwater vapor are released from the Earth’s interior.


Volcanoes - Risks

PThe obvious risk is that volcanoes willdestroy anything that is near it, either bycovering it in ash or burning it with moltenlava.

PThe ash can also drift for many miles andcause health risks for those that may alreadyhave breathing problems like asthma.

P In extreme cases, there may be enough ash putinto the atmosphere to change the climate ofthe entire planet by blocking out the sun.


Ring of Fire

POne of the most volcanic regions of the earth iscalled the Ring of Fire. It is located all around thePacific Ocean.

PThere is a great deal of tectonic activity here,especially subduction zones.

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