Earth Science Summaries

*when reading through this, when it comes to diagrams, draw them on paper!
TECTONIC IMPACTS

Lithospheric (crust and upper mantle) plates characteristic are very different:

Oceanic / Continental
Density / 3.1g/cm3 / 2.7g/cm3
Composition / Mafic- basalt, gabbro, dolerite / Silica rich (felsic) mixed e.g. granite and sedimentary
Thickness / 7km / 60-100km
Age / <200my / 3.8by
Primary wave speed / 7km/s / 6km/s

There is a relationship between rock composition and plate boundary:

Divergent- Mafic, low quartz (oceanic)
Convergent- Felsic, varied, (continental)

Convection currents and subduction drive plate motion

Heat from core
hot rise-cold sink. Less dense float.
Convection is very slow in solid mantle. Hot, less dense basalt made at MOR. Colder, denser subducts MOR.

SLAB PULL- denser subducting plate sinks down into mantle- pulls plate with it.
RIDGE PUSH- MOR- plate is higher up and hotter/less dense. Gravity pulls plate down into mantle at subduction zone.
TRENCH SUCTION- 2 converging plates- subducts. One subducts and convection current occurs. Sucks plates together.
WHAT RESISTS MOTION?
COLLISION RESISTANCE- two plates resist each other at subduction.
SLAB RESISTANCE- friction between subducting plates resists motion
Tectonic super cycle takes 400my:
20my- super continent (PANGAEA). Thick, cold climate, low co2 + sea-level.
70my- heat builds up underneath plate. Extension and sagging of crust.
70my- super continent splits. Co2 rise + sea level + temp. MOR form.
75my- rapid seafloor spread. High co2, temp, sea level, lots of MOR, high plate movement.
165my- continents come together. Low sea level, co2, temp. COLD. Super continent getting made.

Plate motion and types of boundaries: ROTE LEARN.
Aus. –Indian- north
south American- west
pacific- east
north American- NW
Nazca-east

Eurasian- east
DIVERGENT- MOR, Graben, mafic igneous, shallow quakes, transform faults.
CONVERGENT- Ocean-ocean: subduction, island arc e.g. Indonesia. Ocean continent: subduction, volcanic mountain e.g., ANDES. Continent- fold mountains Himalayas.

1906 San Fran Quake is likely to occur again:
Gas lines- fires. 3000 dead. WHAT PLATES? N.A and North Pacific. San andreas fault rupture. WHAT HAPPENED? Strike slip movement of the plates. NP- northwest. NA- southwest. Released pressure in a quake. 7.9 magnitude- rupture in fault spread north and south 476 km. displaced ground 6m. Main shock most destructive-42 seconds. Reclaimed San Fran bay soil liquefaction. Untrainedfiremen used dynamite to make firebreaks- more fires.
DISTANCE FROM DISASTER AREA- epicentre offshore san Fran. plate movement 300km north San fran.
PROBABILITY- 80% chance quake 6.2 or higher. Continualplate movement- pressure has to be released somehow.
HOW TO PREDICT- Geiger counter- radon gas released from crystals cracking from high plate movement. Seismometer- monitors p and s waves. Bigger time difference between waves means bigger distance device is from epicentre. Triangulate results to locate epicentre. Use past data to predict where a quake will occur and when.
HOW TO MINIMISE EFFECTS OF QUAKES- Good warning systems- TV, radio, newspapers, loudspeakers in major cities, good training and coordination of emergency services, ensure all households have emergency kits ready e.g. clothes, food, water, masks to stop dust inhalation etc. Build in reduced risk areas- map geotechnical hazards and computer simulation of quakes. Better local building codes. Quake proof buildings- BASE ISOLATION- Teflon pads or springs separate building from ground. Reduced shearing forces. DIAGONAL BRACING- braces across building keeps it intact made from wood or steel. STRONGER FRAMEWORKS- reinforced steel > masonry.
Faults and folds cause different mountain structuresDIAGRAM:
Anticline, syncline, monocline, recumbent, overturned.Results in shortening and thickening of crust.
Faults
Normal = divergent. Reverse/thrust (two come together and push up a bit). Conservative= strike slip. Horst- bit pushed up (convergent). Graben- (divergent) layered stairs kind of thing. Faults occur because brittle rocks crack instead of fold.

Mountains and structures depend on boundary type DIAGRAM:

Divergent oceanic: MOR, most extensive mountain ranges, 1000km wide, 3000m high. Layers of rocks- basalt, sheeted dyke, gabbro on bottom.
/ Divergent continental: rift valleys, African rift valley, less than 100km wide, less than 300km high, normal faults, graben. Mafic igneious-0 basalt.
Convergent continental C & C: folds, reverse faults, graben, ophiolites, metamorphic e.g. gneiss, schist. Mt Everest / O & C convergent: subduction zones. Andesite, rhyolite, igneous, volcanic mountains, mountains made from compression and uplift of rock and sediment, highly faulted and folded sedimentary rocks.
O & O convergent: volcanic island arc, subduction. Explosive volcanoes and fold mountains INDONESIA.

Aus.through time DIAGRAM:


Achaean- Pilbara Yilgarn. 3.8. By
Proterozoic- north Aus. Cratonised. Gawler craton west of Adelaide. Central Aus. Mobile belt active- not cratonised until end of era.
Palaeozoic- Tasman fold belt
Cambrian- Volcanic island arc Vic.
Ordovician- Narooma subduction.
Silurian/Devonian- Subduction zone went east
Carboniferous/Triassic-Aus. Was extended by coastal extension. Subduction zone attached to land and accreted a lot of sediment and magma onto old cratons e.g. Pilbara and Lachlan Fold Belt. Sediment which become the land. Sydney basin made.
Cretaceous to present- rifting on SEedge of Aus. PNG mobile belt.

CRATON= old stable piece of continent crust. MOBILE BELTS= active part of crust with subduction zones and collision boundaries, they are highly deformed with metamorphic rocks.
EVIDENCE- WA rocks 3.9. by lot older than rocks on East Aus.
Rock types at mountains:

Mountains made by / Formation / Rock type / Structure in mountains
Uplift and rifting / Divergence MOR, basaltic lava magma pours out makes mountains. / Basalt, gabbro, dolerite / MOR, graben ,normal faults
O&O convergence / Island arc/subduction zone INDONESIA / VARIED- rhyolite, pumice, tuff / Thrust faults and subduction zone
O&C convergence / Volcanic continental arcs e.g. Andes / VARIED- rhyolite, pumice, tuff / Volcanic mountain chains, subduction zones, reveres/thrust faults
C&C convergence / Subduction zone, foldmountains / COMPLEX- metamorphic e.g. schist and gneiss, sedimentary e.g. sandstone / Reveres/thrust faults, ophiolites, fold mountains.

Volcanoes can influence global climate:

  • Mount Pinatubo 1991
  • 5km3 of magma and ash and dust could 40km high
  • Huge clouds in stratosphere
  • Injected 17 megatons SO2---- made aerosols reflect solar radiation---moved around globe—global cooling of 0.5 degrees.
  • Eruption and effects stronger than effects of global warming and El Nino at the time.

Earthquakes and volcs. occur at plate boundaries:

Convergent= deeper quakes due to benioff zone and thick lithosphere
Divergent= shallow quakes due to transform faults along MOR
Subduction= explosive composite cones.
EPICENTRE= surface. FOCUS= underground (where it happened).

Many technologies exist that can predict quakes and volcs:

Quakes / Volcs.
Groundwater level and temp- rise before a quake. Need thermometer in groundwater monitoring constantly. ALREADY COVERED IN SAN FRAN / Steam from vents- increase before eruption.
Change in gas levels- more hydrogen, CO2, water, H2S before eruption
Vegetation dieback- happens a while before eruption. Toxic gases kill them.
Gravity and tilt meters- magma rises before eruption. Volcanoes change shape as magma rises
Lasers- detect change in shape of cone.
GPS- of cones position is altered on GPS map, eruption soon.

People live in dangerous zones for many reasons:

  • High altitudes= good rainfall. Clouds condense on mountains.
  • Rich soils= high trace elements + high rainfall=good for agriculture. Grow rice.
  • People forget about eruptions because they’re infrequent- stories aren’t passed down through cultures.
  • Cultural value to volcanoes- religious beings.
  • Pop. Pressure- no land means forced to live in risky areas.

Shockwaves from quakes are disastrous:
P, S, L waves. L most destructive. Impact depends on proximity to epicentre, type of wave, intensity of quake and type of substrate (ground).

Natural / Built
Landslides / Soil liquefaction: reclaimed swamps. Makes quicksand.
Tsunamis: coastal regions get hammered. Change river direction. Also destroy built e.g. Japan 2011. / Destruction of buildings: rigid masonry is bad.
Forests get destroyed: only in huge quakes. / Fires: broken gas mains and power lines. Water lines get broken. Can’t extinguish.
Flooding: Dam walls break.
Roads destroyed: Can’t get emergency services to areas easily.

Volcanoes are dangerous lots of hazards:
Poisonous gases: asphyxiate e.g. Lake Nyos (sleeping African town all dead at night from gas from lake). Sulfuric acid formed- destroy lungs.
Ash flows: pyroclastic flows. Gas and dust. 200km/hr, 400 degrees. Travel up to 20km. destroy everything. Composite cones.
Lahars: Hot mud. “Dams” of debris on cones break with rain from eruption. Shaking from cone and lots of rain – race down hill. Max destruction. Move down water courses- dangerous areas for people.
Lava flows: Common with shield volcanoes.
Types of volcanoes:
Plinian eruption: Stratosphere. Ash is aircraft hazard- clog engine. Global cooling.
Shield volc: Hot basaltic lava, high silica, low viscous lave (runny), 1200 degrees. Not explosive.
Composite cone: Explosive, cooler felsic lava 850 degrees, viscous lava. High dissolved gas. Magma rises in cone, pressure reduces, gas out of solution makes high pressure in cone- explosive from side = lateral blast, gas escapes. Pyroclastic flow.

Research into prediction of quakes and volcs is justified:

For: / Against:
Reliable early prediction = less death / Too difficult to predict quakes. Money better spent on hazard reduction e.g. safety measures and better houses.
High cost of technology to predict is low cost compared to loss of life. Is there a price on a life? / Warnings cause panic and stampedes- death
Computers and remote sensing has greater prediction potential / Better to spend money on education of people about how to live with the hazards e.g. what to do in a quake.
Unreliable prediction of events will mean people won’t move to safety because they think event won’t happen / Volcs easier to predict.

Cristal movement at collision boundaries can be predicted:

Technology / How does it work?
Laser geodimeter / Measures change in distance between stationary recording stations on opposite sides of a boundary. Detects movement.
10m long wire strain gauge / Measures strain and change in surface of ground at fault line.
Tilt meter / Ground tilting.
GPS measurements / Measures distance plates have moved from a satellite. Bases measurement from stationary recording stations either side of converging plate.

1989 Newcastle quake occurred intra-plate:

  • 5.6 Richter and shaking felt 200,000km2 in NSW.
  • Old fault line under Newcastle reactivated with coal mining. Water pumped out to keep mine dry. Stress on rocks increased. Coal extraction deformed crust.
  • Deformation over time got too much---- pressure released in quake.
  • FOCUS- 15km SW Newcastle shallow 10km depth.
  • Disastrous because city buildings not built for quakes. $4 billion damage.

Natural disasters are focused round plate margins ASSESS:

DISASTER / ABOUT
Krakatoa / 1883, tsunami, quake and volcano, 2000 death.
Sumatra / Quake and tsunami, 200,000 dead, 9.1 Richter, 2004 BOXING DAY
Japan (Fukashima disaster) / Tsunami and quake, 18,000 dead, 9 Richter scale, 2011

Assess: natural disasters are focussed, more frequent and violent around destructive plate margins. Forces acting on plates cause huge pressure and energy released- sudden movement occurs as plates slip past each other. Hypothesis arguing for this are correct.
Plate margin and intra-plate quakes are different:
Most severe at plate boundaries, intraplate less severe. INTRAPLATE AUS- Aus. Plate move north, stress and compaction, existing fault lines are where quakes occur, heat flow from asthenosphere changing is also a cause.

Plinian eruptions cool then warm planet- affect local and global climates:

  • Lots of gas in eruption.
  • Green house gases absorb suns infrared. WARM.
  • Sulphuric acid causes fine milky aerosol. COOLING GLOBALLY.
  • Scale of eruption alters degree of cooling.
  • Stratosphere >15km- no weather so aerosol stay for long time.
  • Wind in troposphere spread aerosol.
  • CO2 in atmosphere from eruption later causes warming

LOCAL / GLOBAL
Severely affected- ash smothers crops. 1883 Krakatoa. Heavy rain and lahars washes away crops and infrastructure. / Global cooling. Slow crop growth. 1815 Tambora reduced temp by 3 degrees.
No light due to clouds- can’t grow crops / Ash and aerosol block sunlight- no photosynthesis.
Acid rain destroys crops and stock- no food for stock.
Ash smothers crops and stock- dead. Poisonousgas kill stock and crops -1783 Laki eruption. Pyroclastic flow kill everything- Pinatubo 1991.
Area affected >100km.

Plate tectonics affect the climate:

  • Single eruptions only reduce temp by few degrees.
  • ICE AGES CAN BE CAUSED BY MANY THINGS- 11 year solar cycle, changes in Milankovich cycle- earth orbit and tilt change, Bolide impact- cooling from dust, warming if bolide hits limestone deposit- CO2 in atmospheres, Plate tectonic supercyle- warming and cooling as super continent breaks and forms. SNOWBALL EARTH WHEN A SUPER CONTINENT EXISTS.

ENVIRONMENTS THROUGH TIME

Changes in lifeforms means a change in eon:

Cryptozoic- “hidden life”. No fossils- hadean, Achaean, protoerozoic.
Hadean- Oldest rocks 3.8by.Young earth. Oceans made at end.
Archaean- First life 3.8by Isua Greenland. Pillow lava shows oceans present. Stromatolites 3.45 bya North Pole Pilbara.
Proterozoic- max stromatolites.Shallow seas good for stromatolites. BIF made. RODINIA supercontinent made 700mya. SNOWBALL EARTH- 3% Oxygen levels. Increase O when broke up. Ediacaran metazoans- visible life.
Phanerozoic- “visible life”.More O. Cambrian- hard parts.

Fossil evidence for cyanobacteria exist in Aus in NorthPole Marble Bar Pilbara:

  • UV resistant. Make oxygen. Tolerate low oxygen and light.
  • EVIDENCE OF FOSSILS: 3.45 bya in rocks PILBARA.

BIF require certain processes and conditions:

PROCESSES / CONDITIONS
Cyanobacteria photosynthesis in top of ocean. / Shallow water
Iron oxide precipitates. / High iron
Iron washed from rocks by acid rain into ocean. / Acid rain
Bands of silica and iron occur when O builds up to kill cyanobacteria. / Anoxic atmosphere and oceans + high UV

DRAW DIAGRAM HERE:

Isotopes of carbon are evidence for life in 3.8.by rocks:

  • 3 carbon isotopes.
  • C14 unstable 5670 year half life.
  • Plants like to take up C12 over C13. Observing ratio of C12:C13 in rocks can indicate whether organic or not.
  • ISUA GREENLAND ROCKS FIRST EVIDENCE OF LIFE
  • C12:C13 organic material is 102:1
  • C12:C13 inorganic material is 100:1.

Fossilisation is rare due to breakdown and scavengers and lack of good conditions and needs certain conditions

Body fossils= once living things. Trace fossils= footprints, croptolites (poo).
PROCESS- Dead organisms with hard parts buried in sediment e.g. storms over shallow seas disturb sediment, turbidites fossilise benthic organisms, floodplain sediment deposition, ash from volcanoes.
Types of fossils:
Petrification: skeletal material/shells in original form. CaCO3 preserved as calcite or aragonite.
Carbonisation: soft parts converted to carbon rich residue e.g. plant fossils.
Replacement: hard parts dissolved away and replaced with other thing e.g. CaCO3 with pyrite (FeS).
Permineralisation: Minerals precipitate in internal organs/tissues. Blood vessels, vascular systems.Petrified wood.

Ozone and oxygen

3O2 ------2O3 can go the other away as well. UV breaks oxygen and one oxygen free radical joins to a spare oxygen molecule. Made 50km up in stratosphere.Ozone 2.5ppm stratosphere, 0.02ppm troposphere.

Cyanobacteria made oxygenated atmosphere:

Atmosphere is 20.9 % oxygen. The more oxygen made, the more ozone that gets made from the UV. First oxygen bonded in BIF. 1.8 by all Fe gone from ocean. Oxygen levels rose and diffused form ocean into atmosphere. In Phanerozoic oxygen reached stratosphere and ozone layer---- helped life onto land.

Ozone enabled life to move onto land as it filtered out the harmful UV.

Ozone filters 99% of UV. UV =mutagen. UV too high for life on land before ozone.400-300 mya ozone high enough for land life in the PHANEROZOIC. Life previously restricted to ocean.

Stromatolites can’t live in most modern oceans because they have predators in them which eat them. Ancient oceans were more suited for them and their predators didn’t exist yet.

They are layeredd accretionary structures of sediments and cyanobacteria. Like harsh environs e.g. high saline, high temp, low oxygen. HAMELIN POOL SHARK BAY WA: water twice as saline as normal ocean. Shallow pool with high evaporation, low oxygen and high temp. Grazing snails can’t survive there!

There were huge changes in life in the PHANEROZOIC:

Palaeozoic: animal phyla appeared, arthropods, amphibians, reptiles, life onto land, trilobites and brachiopods common, ferns rule land, reptiles ruled at end.
Mesozoic: DINOSAURS, mammals and angiosperms ruled at end, conifers (gymnopserms) ruled,marine reptiles e.g. icthyosaurus, ammonites and belemites- marine cephalopods “squids with shells”.
Caenozoic: Angiosperms and mammals ruled. Insects and angiosperms evolved together-mutualism – pollination by bees for example.
ANALYSE: Mass extinctions drive changes in life forms and creation of new eras. New groups radiate out into vacant niches. Life onto land in Palaeozoic because of high oxygen and ozone. Eras end in mass extinctions.
You can find the relative age of a fossil from looking at a stratigraphic sequence:

Fossils won’t be found further up once disappeared from a rock layer. One disappears another appeared- faunal succession. Comparing when a fossil disappears in one layer to another is called CORRELATION. 3 IMPORTANT FEATURES OF STRATIGRAPHY: 1. Sedimentary rocks are layered horizontally. 2. Law of superposition- oldest on bottom- assuming no folding or faulting. 3. Layers of sedimentary rocks continue sideways until they get thin and disappear. IGNEOUS ROCKS ARE YOUNGER THAN ANY ROCK THEY CUT THROUGH. EXACT DATE ABSOLUTE DATING. NO FOSSILS IN IGNEOUS ROCKS.