Show Menu
Cheatography

Earth Science Cheat Sheet (DRAFT) by

Basic earth concepts including rock formation, volcanic events, and tectonic processes.

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Plate tectonics

Lithos­phere
7 major and 8 minor lithos­pheric plates. On average plates are 125km thick, oceanic 50-100km and contin­ental up to 200km. Made up of the crust and upper mantle it is classified as a solid. Contin­ental crust is feldspar and quartz making granite whilst oceanic is basalt.
Moho
Underneath crust. Rich in iron and magnesium - perido­tite. Upper mantle of Earth.
Plate bounda­ries:
Divergent
New lithos­phere is created as plates move away. Oceanic plates create ocean ridges or rises. Contin­ental plates create rift valleys. Decomp­ression melting as plates move away. Produces basal. Magnetic stripes help to show movement.
Convergent Bounda­ries:
Oceani­c/c­ont­inental
Oceanic plate subducts under. Both plates fracture and deform. Shallow earthq­uakes creating Benioff zone. Sediments on top of crust create accret­ionary wedge. Flux melting occurs creating andesite.
Contin­ent­al/­con­tin­ental
Creates large mountain ranges of folded rock. Earthq­uakes are common in these areas.
Oceani­c/o­ceanic
Volcanic islands form on a volcanic arc. Made out of andesite and andesite which was created through flux melting.
Conser­vative boundary
No volcanic activity. Extensive shallow earthq­uakes which can occasi­onally have high intensity.
Hotspot
Caused by mantle plumes which originate at outer core. Create shield volcanoes.

Unifor­mit­ari­anism

The laws of physics have applied wherever and whenever events occurred. Long gradual processes that are interr­upted by catast­rophic events. Laws of strati­graphy can be applied.
Venus
Similar size and structure to Earth, extreme surface pressure and heat, runaway greenhouse effect, extensive volcanism, potential life.
Mars
Most "­Ear­thl­ike­" body in our solar system, realistic host of life until loss of magnet­osp­here, volcanism, evidence for fluvial and lacustrine processes occurring.
Places of interest:
4 Moons of Jupiter and Saturn as they contain evidence for conditions supporting life. In particular water or hydros­phere, building blocks of life and an energy source.
Io
Most volcan­ically active, 100s of volcanoes, tug of war between Europa and Ganymede.
Europa
Most promising for life, icy surface over water, water vapour detected.
Enceladus
Icy crust exhibiting liquid water, some water jets have hydroc­arbons salts and organic materials.
Titan
Bigger than moon and mercury, only moon with a nitrogen atmosp­here, mercury in liquid form

Mineral identi­fic­ation

Identi­fic­ation is done by the physical properties of the mineral.
Lustre and colour
The type of reflection of light. Metallic, submet­allic, non-me­tallic glassy. Colour can be misleading due to variations in minerals. Some minerals only display one colour.
Streak
Colour of the ground mineral. More useful than colour.
Hardness
The ability to scratch other substa­nces. Diamond is a 10 and a steel knife at 5.5 splits hard and soft minerals.
Habit
The pattern in which crystals grow. Anhedral crystals are constr­ained so cannot form properly. Subhedral are partially formed and euhedral are perfectly formed. Some minerals have multiple habits.
Cleavage and fracture
The way in which a mineral breaks. Arises when certain bonding is weaker than other parts. Some minerals have stronger cleavage and others fracture.

Atmosphere

Water vapour is the most abundant greenhouse gas in the atmosphere however carbon dioxide, methane and nitrogen are other notables. Thermal radiation is absorbed as it reflects off the earth and is stored in the gases. Atmosp­heric density and thus pressure decreases with height.
Layers of the atmosphere from surface going up are tropos­phere, tropop­ause, strato­sphere, strato­pause, mesosp­here, mesopause thermo­sphere. Temper­ature decreases up to the tropop­ause. Weather occurs in the tropos­phere and aircraft fly in the tropop­ause. The strato­sphere has a temper­ature that increases with height and contains the ozone layer. The mesopause has a decreasing temper­ature with height. The thermo­sphere has temper­ature fluctu­ations and is where auroras occur. Beyond is the exosphere which is the upper limit to the atmosp­here. Different molecules in different layers absorb different UV rays.
Global circulation:
Differential heating is caused by the curvature of the earth thus causing different amount of the sun's radiation to hit areas. Greatest heating is at the equator. Pole-wards of 40 degrees latitude more radiation exits then enters causing global circul­ation.
Atmosp­heric cells:
Nearest the equator are the Hadley cells which extend up to the tropop­ause. They have rising heat from the equator spreading to the poles where it gradually sinks. The polar cells are the smallest and extends to 60-70 degrees latitude. As air laves poles it warms and rises before returning to poles. Ferrell cells sit in between and flow in opposite direction and are not temper­ature driven. Rising air creates low pressure leading to raingall., sinking air high pressure leading to deserts.
Coriolis effect:
Apparent motion to the right in Northern hemisphere and left in Southern. Earth rotates faster at equator rather than poles. Causes wind to move in a curved direction. As air moves in the Hadley cell it curves and speeds up. By 30-40 degrees latitude it is moving eastward at 12-15 kilometres height called Jetstream. Polar front jet marks difference between cold polar air and warm tropical air. Sits at 11-13 km and result of temper­ature contrast. Tradewinds are another effect of Coriolis but is the air from the Hadley cell moving towards the equator. .

Bowen's Reaction series

Descri­ption of temper­ature at which minerals crysta­llize. 700 degrees is the temper­ature most minerals exist as solids whilst 1250 degrees is the opposite. This is for 1 bar of pressure.
Right hand column shows compos­itional categories with ultramafic at the top. Down arrows shown increase in silica, sodium, aluminium, and potassium as you near felsic and magnesium, iron and calcium as you near mafic. Minerals near the top crysta­llize at higher temper­atures.
This temper­ature difference can explain why certain minerals always crysta­llize together.

Rising sea level

Key issues:
-Where will sea level refugees go?
-What happens to trade when island nations disappear?
-What happens to coastal groundwater?
-What is connection between flooding, infras­tru­cture and storm severity in coastal cities?
-What is the effect of mangrove destruction?
-What feedback loop is there between ocean rise and global temper­atures?
Potential solution:
-Social protection
-Livelihood diversification
-Hazard-proof housing and infrastructure
-Ecosystem measures to reduce flooding
-Mangroves to reduce storm energy
-Reservoirs to buffer low-flows and water scarcity
-Coastal retreat and resettlement
-Risk sensitive land use planning
-Early warning systems and evacuation

Volcanism

Volcanos mainly occur on tectonic plate boundaries but occasi­onally occur in the middle of plates.
Mid ocean
Most common. Slow, gentle oozing eruptions creating basaltic pillow lava. Hydrot­hermal vents called black smokers.
Subduction
2nd most common. Flux melting causes eruptions of mostly silica rich rocks. Andesite, rhyolite, pumice and tuff.
Rift
Basaltic lava, flood basalts, cinder cones.
Hotspots
Mantle plume below volcanos variety of magmas.
Volcanos:
Shield
Largest volcanos. Broad low angle with mafic magma chambers. Typically MOR, hotspot or contin­ental rift. Built up from numerous low viscous eruptions. Fissures can occur with magma erupting.
Strato­volcano
Steep flanks, distinct crater and prominent rise. Altern­ating pyrocl­astic and lava layers. Felsic to interm­ediate chambers. Viscous flows with explosive eruptions.
Domes
Accumu­lation of silica rich magma that cannot move far from eruption. Often form in collapsed strato­vol­canos.
Caldera
Steep walled, basin shaped depres­sions formed by collapsed magma chambers. Commonly used to describe a volcano with high viscosity and volatile eruptions.
Cinder cones
Small volcanos with short eruptions of cinders and volcanic bombs. Violent eruption, cone formation, flow from base.
Flood basalts
Lowest viscosity event, may be the cause of mass extinction events.
Carbon­atites
Rift valleys, carbonate based magma, over 50% carbonate with low viscosity and temper­ature.
Hazards and monito­ring:
Pyrocl­astic flows
Most dangerous hazard. Mixture of hot rock and gas with high speeds. Most composite volcanos have flows.
Landslide and tsunami
Slope failure can occur which can lead to landslides and eruption events. If enough material reaches the ocean a tsunami may be triggered.
Tephra
Ejected rock material. Hot ash can disrupt air travel, and cause building collapse.
Volcanic gas
As pressure decreases gases may escape. Non erupting volcanoes may emit gases. Some gases sink which can cause increased risk
Lahars
Volcanic mudflow resembling wet concrete. These can reach large speeds.
Slow release causes small eruptions sudden release causes explosive.

Ocean circul­ation

Density difference is a driving factor of ocean movement. Temper­ature and salinity are two big effects on desnity.
Temper­ature
Temper­ature of water is highest at the equator where most heat is absorbed. Warmed water moves towards the poles.
Salinity
Salt concen­tration varies ocean to ocean. North Atlantic has some of the highest.
Water generally is denser at poles and lighter at equator. This means water sinks at poles and rises at equator. The layers of water only mix in certain areas.
Ocean currents are masses of water in motion and come in two main types wind-d­riven and thermo­haline.
Surface currents:
Primarily driven by wind and help atmosphere move heat from equator to poles. Warm surface currents move to the poles whilst cold move to the tropics. Coriolis effect causes movement to the west of each basin. Flows clockwise in the north and anticl­ockwise in the south. Driven by tide wind and shape of land.
Thermo­haline currents:
Deep below the surface the currents transport cold saline water. When winds blow across ocean surface upwelling occurs which brings dense water up.
Global conveyor belt brings dense water from North Atlantic across ocean floor to south Atlantic through the Indian ocean before reaching the pacific where it mixes with the surface currents. This can take thousands of years.

Transport processes

Gravity
Angular, poorly sorted, usually further transp­ort­ation,
Wind
Angularity is distance from the source. Sorting related to water velocity.
Water
Well rounded and frosted, well sorted.
Glacial
Indisc­rim­inate angula­rity, completely unsorted, diamict.
Mud flow
Angularity decreases with distance, very poorly sorted, behaves like concrete,

Metamo­rphic rocks

Metamo­rphic rocks are rocks that have been changed by heat, temper­ature and/or fluid. Occurs when solid rocks changes compos­ition or texture without melting. The rock that undergoes metamo­rphosis is called a protolith.
Temperature:
Increase in temper­ature means increase of energy. As energy increases there becomes a potential for atoms to swap within the solid lattice. Heat metamo­rphism can occur at temper­ature between 200-700 degrees possibly reaching up to 1,100.
Pressure:
There are two groups of pressure confining pressure and directed stress. Stress is a force whilst strain is the result. Confining pressure has equal pressure from all direct­ions. pressures range from 3,000 bars to around 50,000 bars, which occurs around 15-35 kilometres deep. Directed stress has unequal pressures causing deform­ation. Occurs at lower pressures and causes mechanical change.
Fluids:
Chemically reactive fluids enter the rock and can change the compos­ition. It can incorp­orate surrou­nding rocks into the protolith. This is commonly called hydrot­hermal metamo­rphism. MOR
Metamo­rphic textures:
Texture is the descri­ption of the shape and orient­ation of grains.
Foliated
Minerals lined up in planes. Appear like the minerals are stacked like pages of a book. No common direction
Lineated
Lines of minerals that point in a common direction.
Non-fo­liated
No lineation, foliation or alignment of minerals. Usually only contain one type of mineral.
Metamo­rphic grade:
Metamorphic grade refers to how much the rock has changed. Low-grade metamo­rphism starts just above sedime­ntary condit­ions. Slate→­phy­lli­te→­sch­ist­→gneiss shows increasing metamo­rphic grade. Index minerals can be used to identify the protolith and condit­ions.
Metamo­rphic environments:{{nl}Metamorphic facies are a set of minerals that show metamo­rphic condit­ions.
Burial
Occurs when rocks are buried below 2000km. Occurs in sedime­ntary basins and a extension of diagen­esis. Low grade metamo­rphism.
Contact
High temper­atures and low pressures. Hot magma intruding on a protolith. Different pressure produces different facies.
Regional
Increased temper­ature and pressure over large areas. Often in mountains with contin­ental conver­gence. Lowest grade on flanks, highest in core. Foliated rocks.
Subduction
Regional metamo­rphism that occurs as a plate subducts. High pressure low temper­ature.
Fault
Faults create rock flour from constant grinding. Creates fine grained rocks.
Shock
Metamo­rphism resulting from a meteor or bolide impact. Creates a range of products.
Exhumation:
The processes which bring the rocks to the surface.
Orogenesis
Lower portion of the crust gets warm and weaker before collapse. Crustal thinning letting rocks get closer to surface.
Erosion
Surface erodes away which thus exposes deeper rock.
 

Laws of strati­graphy

Superp­osition
In sedime­ntary terms oldest layers are at the bottom
Original horizo­ntality
Sediments are deposited horizo­ntally, meaning tilted layers were one horizo­ntal.
Lateral continuity
Rock layers are laterally continuous and can be broken up by later events.
Cross-­cutting
Cutting features are younger than the surrounds
Inclusion
The included piece of matter is older than the surrou­nding material
Fossil sucession
Fossils have evolved in a fixed timeline and once a species has gone extinct it cannot reappear in younger rocks.

Weather

Wind is created by differ­ences in pressure. Low pressure systems are created by heating causing molecules to rise, and high pressure is caused by cooling causing molecules to sink. Wind is the movement of air from high to low pressure.
Hotter air has higher saturation point which is the largest amount of water the air can hold without precip­ita­ting.
Clouds form when air masses rise and cool enough to reach satura­tion. Air must be warmer than the enviro­nment to rise or be forced upwards.
Orographic lifting:
Mountains force clouds upwards. Precip­itation of windward side, rain shadow on leeward.
Convective lifting:
Localised heating, small convective cell, localised thunde­rst­orms, small amount of precip­ita­tion.
Conver­gence lifting:
Winds converge towards centre of low pressure, clouds and precip­ita­tion, stronger conver­gence means stronger effects.
Frontal lifting:
Meeting of two air masses with different temper­atures, different behaviours based on which mass moves in.
Cold fronts
Steep slopes, strong centred winds, clouds, thunde­rstorms precip­ita­tion.
Warm fronts
Diffuse clouds, spread out showers.
Fronts move through quickly.

Hydros­phere

The water cycle is the continuous cycle of water in the atmosp­here. Evapot­ran­spi­ration is the mix of evapor­ation from water bodies and transp­iration from plants. Conden­sation is the vapour forming droplets and precip­itation is the droplets leaving the sky. This water can move into bodies of water or infiltrate the ground an become ground­water.
Water basins are areas which catch precip­itation and channel it into a certain area. Drainage divides are topogr­aphical high points which separate these areas. Each stream or tributary has a basin. Smaller streams combine and the end is called the mouth. Some streams end in closed basins where only outflow is evapor­ation. Perennial streams flow year round in high humidity and rainfall areas. Ephemeral only flow during wet periods. Water budgets compare incoming and outgoing water for certain areas.
Surface water:
Streams are rivers of water confined to a channel, they erode and transport sediment. Gradient and velocity are big factors of erosion. Increase gradient and velocity increases erosion.
Discharge
The volume of water flowing past a point in the stream over a defined time interval. Discharge increases down stream and with stream size.
Velocity
Velocity varies with shape, width and depth. Narrower streams and heavy rain events increase velocity. In curves highest velocity is on the outside of the bend, whilst straight it is in the centre at the top.
Drainage patterns
Dendritic patterns are random tribut­aries and occur in flat areas. Trellis drainage occur where rocks have been tilted and have various strength. Rectan­gular patterns occur in areas with bedding planes, joins and faults. Radial patterns occur when water flows away from a high point. Deranged occurs in areas of high limestone with subter­ranean drainage.
Fluvial processes:
Dictate how a stream behaves. These impact velocity, sediment, and gradient. Longit­udinal profiles of the stream show base level over a distance.
Sediment production
Located at headwaters where rills and gullies erode sediment. Steepest part of the stream and small channels.
Sediment transport
Moves sediment from headwaters to ocean. Transport is related to velocity and gradient, higher gradients and velocities mean larger sediments. As velocity slows larger sediments settle. Large particles are the bedload and move along the bed, smaller sediments are the suspended load, while the smallest are dissolved load commonly from chemical weathe­ring.
Floodp­lains
Flat land adjacent to a stream which floods regularly. Velocity is greatest when river is full, if it overflows velocity decreases and sediment is deposited.
Sediment deposition
Occurs when velocity decreases to a point where the load cannot be transp­orted. Deltas and oceans.
Fluvial landforms:
Channel types
Straight - near headwater, low velocity & discharge, steep, narrow.
Braided- multiple channels, low gradient, high sediment areas.
Meandering- Single channel snaking across a flood plain. Outside edge is cut bank with high erosion, inside point bar with deposi­tion.
Meander channels are confined by natural levees. These can isolate and direct flow. Isolated streams are called yazoo streams.
Meander landforms
Crevasse splays- breaking of levee causing deposition in flood plain.
Oxbow lake- Forms when part of the channel is cut-off, eventually becoming a meander scar.
Alluvial fans
Occurs when stream leaves a valley causing sudden spread and velocity drops. Sediment depositon.
Delta
Occurs in quiet waters where deposition is greater than erosion.
Stream terraces
Old flood plains located above current flood plain and stream.
Ground­water:
Porosity and permea­bility
Porosity is the water holding space between grains. Permea­bility is the connec­tivity of these openings. Porosity reduces during cement­ation and compac­tion. Hydraulic conduc­tivity measures above plus the fluid involved.
Aquifers
A good aquifer has high porosity and permea­bility. They can vary is scale and depth.
Ground­water flow:
As water infilt­rates it enters the vadose zone which has a mix of water and air in the pores. It sits above the saturation zone. Below the vadose is the capillary and saturation zone which have water filled pores. Wells are conduits that extend into the ground and can be used to extract, measure and add water to aquifers. The water table is the area with its pores fully saturated with water.
Percol­ation varies with vegeta­tion, rock type, rock fractures, soil type and moisture. Completely dry soil is hydrop­hobic.
Confining layers
Layers above or below aquifers that constrict flow of water. Aquicludes completely stop water whilst aquitards slow.
The potent­iom­etric surface is the level which water would rise to in a penetr­ating well. Water table generally mirrors surface level however if it intersects there will be water on the surface. Gaining streams lie above the water table and gain water, while losing streams lie below and lose water. Pumping water from a unconfined aquifers lowers the water level producing a cone of depres­sion. Pumping water from confined aquifers lowers the potent­iom­etric surface.
Recharge and discharge:
Recharge is when surface water enters the table through infilt­ration. Generally topogr­aph­ically high locations with vegeta­tion. Discharge areas are where the water table or potent­iom­etric surface intersects the surface.
Ground­water mining:
Freshwater is finite and the only natural source is precip­ita­tion. When water is extracted faster than it is replen­ished. Called ground­water mining and leaves the possib­ility that water runs dry. Reduce is pore pressure can cause collapse called subsid­ence.
Water contamination:
Water can be contam­inated by natural and human processes. Point source contam­ination occurs at a single source while nonpoint occurs at many. Point sources include sewage facilities and dumps whilst non point are nutrients from farms and fertil­isers from neighb­our­hoods. Remedi­ation is the act of cleaning contam­inants.
Karst:
Landforms created by water dissolving limestone. Carbonic acid dissolves the calcite creating karsts.

Weathering & Erosion

Water has polarity due to the oxygen on one side and hydrogen on the other. This creates adhesion and cohesion. Universal solvent dissolving more substances than natural liquid.
Weathering is the process of turning bedrock into sediment. Mechanical weathering is pressure, frost, roots, salt. Chemical is carbonic acid, hydrol­ysis, dissol­ution and oxidation. Resistance is important in features.
Mechanical weathe­ring:
Pressure
Uplifting of rock causes sudden pressure change but no temper­ature change. Causes rock to expand and crack. Exfoli­ation is when they come of in sheets.
Frost
Water works its way into cracks. As water freezes it expands causing rock to push apart. Repetitive cycles cause change.
Root
Roots work their way into cracks. Rhizolith if it becomes fossil­ized. Tunnelling organisms can have similar effects.
Salt
Evapor­ation of saltwater causes salt to precip­itate. Crystals expand into rock.
Chemical Weathering:
Dominant weathering in warm humid enviro­nments. Occurs when reactants break rocks down into water soluble ions. Only works on surface. SA:Vol, more weathe­ring, faster weathering occurs.
Carbonic acid Hydrolysis
Carbonic acid naturally created in clouds. Hydrolysis is carbonic acid ionizing water and replacing mineral cations in lattice. Carbonic acid can also directly react with minerals high in silica and aluminium. Hydrolysis is the main processes for silicate rocks and creates clay minerals. .
Dissol­ution
Dissol­ution is hydrolysis but the ions stay in the solution. Water dissolves any rock, more acidic = quicker. Dissol­ution series states that minerals higher on Bowen's series more prone to weathe­ring. Areas with high carbonate may produce karsts.
Oxidation
Reaction causing iron to rust. Any rock with iron may oxidize. May cause oxide to permeate the rock causing weakne­sses.
Erosion
Mechanical processes driven by water and gravity. Removes sediment from place of weathe­ring. Different erosion resistant created Grand Canyon.
Soil
Combin­ation of air, water, minerals, and organic matter that forms at the transition between biosphere and geosphere. Organisms turn sediment and the minerals within into organic substa­nces. Organic material in soil is humus.

Magma generation

Magma contains three components melts, solids and volatiles and the abundance can effect the behaviour of the magma.
The geothermal gradient is how much the temper­ature increases as you enter the earth. In the upper 100km it is roughly 25 degree­s/km. The solidus is where rocks begin to melt. Naturally 125km is the closest the geotherm and solidus come.
There are 3 main ways to make rocks melt. Decomp­ression melting, flux melting and heat-i­nduced melting. As minerals melt at different temper­atures most of the time it is partial melting.
Decomp­ression
Mainly occurs at mid ocean ridges and hotspots. Crust is a bad conductor of heat so temper­ature of magma stays the same. Convection currents push magma up as plates move apart. Hotter magma at lower depths.
Flux
Mainly occurs in island arcs and subduction zones. Volatiles are added to mantle which decreases its melting point.
Heat-i­nduced
Mainly occurs at mantle plumes or hotspots. Some decomp­ression melting is involved as magma moves towards surface. Extreme heat is applied from plume.
Partial melting is important when dealing with the mantle. Silica rich portions of mantle melt first which means the magma gets increa­singly rich in silica.
Magmatic differ­ent­iation changes the chemistry of resultant rocks towards felsic compos­itions.
Assimi­lation
Incorp­oration of surrou­nding rocks into the magma.
Fracti­onation
As temper­ature drops mafic minerals crysta­llize and settle to the bottom of magma chamber creating a more felsic compos­ition.

Mineral formation

Different minerals form in different condit­ions. Temper­ature, pressure, compos­ition and enviro­nment all effect which mineral will form. This inform­ation can also be used in reverse to find out what conditions certain areas must have.
Minerals can help to tell us temper­ature, pressure of areas. In certain scenarios water temper­ature, degree of diagen­esis, burial depth and magma qualities.
Examples of partic­ulars are age of Earth, volcanic events, thermal history, deform­ation events, extinction events, lunar samples, ore/oil deposits.
Most important for rocks are carbonates and silicates while ore is oxides and sulphides.
Noble gases and actinides are the least useful elements in minerals.

Minerals

Minerals are naturally occurring crysta­lline solids that are formed by geological processes. They are homogenous elements or compounds which can be defined by a chemical formula.
Minerals have different varieties that are based of colour, occurrence or crystal shape. This variance can be caused by small amounts of transition metal ions.
Gems can be artifi­cially created and be very similar to naturally occurring minerals.
Crysta­lline
having an orderly and repetitive structure
Naturally occurring non crysta­lline substances can be called amorphous solids and can be catego­rised as minera­loids. An example is obsidian.
Biomin­erals
Minerals produced by a living organism
Anthro­pogenic
Type of mineral that only exists due to human activity
Polymorphs
Crystals with the same chemical formula but different structure
Rocks are made up of minerals. Minerals are made up of elements. Some minerals have variations that occur in nature.
Crysta­lline rocks occur when minerals crysta­llize together. Usually this is magma, metamo­rphism or precip­ita­tion. Clastic rocks form when minerals are cemented together.
Dana system of mineralogy catego­rises minerals based off chemical compos­ition. From these classes there are many smaller divisons.
Some minerals can have substi­tutes that are chemically similar which can be switched out.
The main formation of minerals is precip­itation from aqueous solutions, crysta­lli­zation from magma, and biological precip­ita­tion.
Aqueous
Occurs when saturation is reached due to temper­ature drop, or changing chemical condit­ions.
Magma
The ions in the magma cool and crysta­llize forming minerals.
Organic
Organisms precip­itate minerals and when they die they build up.
 

Sedime­ntary Rocks

Two main categories are clastic and chemical. Clastic rocks are made from broken pieces of bedrock and sediment derived from mechanical weathe­ring. These are classified by grain shape, size and sorting. Chemical are precip­itated from water saturated with dissolved minerals.
Lithif­ication and Diagenisis
Lithif­ication turns sediment into clastic rocks through three steps. Deposition occurs when friction and gravity force sediment to settle. Compaction occurs as the sediment build up creating pressure. There is also weak attractive forces aiding this. Finally minerals from ground water cement the rocks together. Diagenesis is the accomp­anying process which is low temper­ature metamo­rph­osis.
Clastic rocks:
Mostly mechan­ically weathered sediment, some chemical.
Grain size
Grain size is a classi­fying factor which looks at the average diameter. Large fragments are larger than 2mm and include boulders, cobbles, granules, and gravel. Silt is the lower end.
Sorting and rounding
Sorting describes the size range withing the rock. Well sorted is a small range whilst poorly sorted is the opposite. This can help to identify deposition energy. Rounding occurs when angular corners are removed by abrasion. Roundness indicates transport length and mineral hardness.
Compos­ition and provenance
Compos­ition is the mineral components found in the rock. Commonly found are quartz, feldspar and lithic fragments. Provenance analyses compos­ition and texture to try and identify the source of the sediment.
Clastic rocks are classified according to grain size. Conglo­merates are rocks containing coarse rounded clasts, while breccias are angular clasts. Both are usually poorly sorted. Medium grains containing mostly sand are sandstone and arenite is well sorted. Fine grains are mudstone if they separate into sheets then shale.
Chemical, bioche­mical and organic rocks:
Chemical rocks are rocks that do not involve mechanical weathering or erosion.
Inorganic chemical
Rocks formed when minerals precip­itate out of a solution. Form salts called evapor­ites. Tufa is a calcium evaporite. Chert is silica precip­itated from ground­water.
Bioche­mical
Form from ions dissolved in a solution however relies on organisms to extract from solution. Main formation of limestone.
Organic
Organic pieces of material preserved in geologic record. Follow similar processes to sedime­ntary rocks.
Classified based on mineral compos­ition. Limestone is an exception. Rocks containing halite are rock salts. Calcite fizzes in acid.
Sedime­ntary structures are visible arrang­ement or textures in a rock. Use unifor­mit­ari­anism to compare past to present.
Bedding planes
Layers denoting change in deposition condit­ions. Displayed as lines. Varves are repetitive cycles of deposition
Graded bedding
Refers to a change in grain size. Develops with a change is deposition energy.
Flow regime and bedforms
Sand is the most easily moved grain size by fluids. Bedforms are the structures created by the process. Flow regimes are divided in upper and lower. Upper signifies faster movement. Plane beds created in lower regime similar to bedding planes. Ripples are small rises and falls created by deposition of sediment. Dunes are large ripples, large cross bedding structure. Anti-dunes occur in high flow regime and is sediment settling in small indents.
Biotur­bation
Organisms burrowing through soft sediment. Occurs mostly in shallows.
Mud-cracks
Clay rich sediment that has dried out. Crystals shrink causing cracks which fill with sediment. Tidal flats.
Sole marks.
Small features denoting flow direction or up. Flute casts are carved out by flow, groove casts are carved out by debris. Load casts are heavier sediments on softer sediment.
Imbric­ation
Large clasts aligned in flow direction. Common in alluvial fans.
Geopetal
Used to identify which way was up when rock formed.
Deposi­tional enviro­nments:
Marine
Abyssal plains have flat floors and most sediment is fine grained. Exception are submarine fan and turbidite. Lowe shoreface not effected by daily waves but effected by abnormal. Upper shoreface has well sorted fine sand.
Coastline
Beaches consist of homogenous well sorted sand grains that are highly weathered. Tidal flats have areas of fine sediment but may contain coarse sediment. Reef have fine mostly carbonate sediments. Lagoons are areas of water separated by some features usually fine grained sediment. Deltas are places rivers meet sea and deposit sediment.
Terres­trial
Fluvia­l(r­iver) have meandering and braided varieties. Meandering has a single channel and mostly fine grained material. Braided usually have coarser sediments. Alluvial fans have interm­ittent water flow that can change sorting. Lacustrine (lake) have well sorted fine sediments. If evapor­ation outpaces precip­itation a playa may form. Paludal have high organic matter. Aeolian is a deposit of windblown sediment. Fine grained and well sorted. Glacial is the worst sorted and so large it may create many enviro­nments.

Flooding

Occurs when naturally dry areas are covered by water. Riverine flooding is main flooding in Australia and occurs when ground is saturated and there is increased rainfall. Flash flooding is the most dangerous.

Plastic pollution

Plastic can break down into microp­lastics due to weathe­ring.
Garbage patches are created in gyres as currents circle and draw the plastic in.
Issues from plastic:
-8 Millions metric tonnes a year
-Breaks down
-Sea life(s­tar­vation, entang­lement, drowning)
-# of particles increases when breaking down
-Microplastic enter food chain(­tox­icity, accumu­lation)
Potential solutions:
-Curb single use plastic use
-Improve garbage collection
-Improve point collection at river mouths
-Deploy large scale ocean cleaning projects

Droughts, bushfires and floods

Drought & heat:
Global weather cannot be contro­lled. Australia has little topography and its location means there are natural rainfall fluctu­ations. There is not enough glaciers to create meaningful snowpack or glaciers. Meteor­olo­gical droughts are below average rainfall which causes well drop and vegetation drying. Agricu­ltural means there is not enough water to maintain agricu­ltural activity. Native plants will dry or die. Socio-­eco­nomic droughts have impacts on water supply and community decline.
Bushfires:
Changes in weather can create bushfires that are hard to control. Wind can increase fire unpred­ict­abi­lity. Increase in bushfires due to increase in dangerous fire days. Burns large trees and grasses.
Floods:
High rainfall that cannot be absorbed if large bushfires have come through. Vegetation destru­ction making it imperm­eable. Loss of topsoil. Overde­vel­opment increase imperm­eable surfaces.
Potential solutions:
-Limit greenhouse emissions to reduce extreme weather
-Curb land clearing especially on steep slopes
-Rapid replanting after clearing or bushfires
-Harvest storm water, recycle water, water conser­vation, seawater desali­nation, porous pavement.

Igneous rocks

Igneous rocks form through the cooling of magma which causes crysta­lli­zation of minerals.
Extrustive
Quickly cooled lava with small crystals. Often called vesicular rocks as gas bubbles can be trapped. Volcanism forms the volcanic rocks different lava form different rocks.
Intrusive
Large crystals that form below the surface. Plutonic igneous rocks. Euhedral interl­ocking crystals.
Igneous rocks can be classified in different ways. These include texture, compos­ition, and rock body.
Texture:
Crystal size:
Phaneritic is the term given to coarse grain rocks that cool slowly. Aphanitic fast cooling rocks with small crystals. Substances that cool so quickly crystals do not form are not considered minerals but volcanic glass. Rocks with mixture of crystal sizes are porphy­ritic. Large crystals are phenoc­rysts whilst small are groundmass or matrix. Indicates multistage cooling. Pegmatites are created during very slow crysta­lli­zation.
Other:
Magma contains gases dissolved in solution. These are called volatiles and as pressure decreases they bubble out of magma. These bubbles become trapped creating vesicles. Common vesicular rock is scoria. In explosive eruptions large particles will be thrown in the air which form pyrocl­astic textures.
Compos­ition:
Refers to rocks chemical and mineral make-up. Igneous rocks are divided into felsic, interm­ediate, mafic, and ultram­afic. These divisions sit on a continuous spectrum. Silica increases viscosity.
Felsic
High in feldspar and silica. Minor mafic minerals. 65-75% weight in silica and poor in iron and magnesium.
Interm­ediate
Roughly equal light and dark minerals. 55-60% range of silica.
Mafic
High in magnesium and iron and plagio­clase feldspar. 45-50% silica.
Ultramafic
Poor in silica >40%. Rare on surface but make up upper mantle.
Rock Bodies:
Igneous rocks are common in the rock record. Intrusive rocks are more common as they aren't exposed to erosion as much.
Dikes
Intrusion of magma into a crack or fissure.
Sill
Exploits a weakness between sedime­ntary layers. Parallel to layers.
Pluton
A cooled diapir. Many merged together are a batholith.
Laccoliths
Upward bulge of magma between sedime­ntary layers. Downward is lopolith.

Weather vs Climate

Weather is single season temper­ature or rainfall variat­ions. Climate is long-term variations or trends.
Australian climate influences:
Sea surface temper­atures include the Pacific, Indian, and Southern oceans whilst other effects include Australian monsoon and Madden­-Julian oscill­ation.
ENSO - El Nino-S­outhern oscillation:
Australian effects include reduced rainfall, warmer temper­atures, shift in temp extremes, increased frost, reduced cyclones, later monsoon, increased fire in south, decreased alpine snow depth.

Climate change

Carbon dioxide and oxygen would have been important gases for early life on the planet. Snowball Earth would have reduced photos­ynt­hesis, volcanic explosion producing CO2 to heat Earth.
Carbon dioxide
76% emitted by human activity, residence time decades to centuries
Methane
More potent effect (25x CO2), residence is a decade, 16% human
Nitrous oxide
300x CO2, century residence time, 6% human caused emission
Fluori­nated gas
thousands of times CO2, 10s of 1000s years, 2% human emission.
Water vapour
Most abundant not linked to human activity.
Australia fuels many other countries fossil fuel emissions.
CO2 ppm is increasing on timescales that have never been seen before. Seasonally CO2 emissions vary due to increase of photos­ynt­hesis in northern summers.
Other controls on climate:
Albedo is the reflec­tivity on Earth largely effected by ice and clouds, water and land. Ocean chemistry and temper­ature. Orogenies- increased weathering means decreased CO2. Milank­ovitch cycles are natural orbital variations
Tipping points are points between two stables once it is crossed it is hard to go back to previous state.
Climate modelling is changing constantly due to improv­ements in techno­logies and changing variables.

Mineral groups

Silicate minerals are built around silico­n-o­xygen tetrah­edra. These ions are a pyramidal shape with the silicon atom at the centre surrounded by 4 oxygen. The corners can bond with other silica tetrahedra or positively charged ions. Silicates are the largest mineral group.
Olivine (Fe,Mg)2SiO4)
Primary mineral in mantle such as peridotite and basalt. Green when not weathered. Mafic mineral also ferrom­agn­esian.
End members refer to minerals that can have substi­tutes and the pure varieties of each.
Pyroxene XZ(Al,Si)2O6
Found in igneous and metamo­rphic rocks. Usually black or dark green colour. Built from polyme­rized chains of silica tetrah­edra. X represents the ions Na, Ca, Mg, or Fe, and Z represents Mg, Fe, or Al. Substi­tutions are possible due to similar ionic size.
Amphibole
Double chain polyme­rized silica tetrah­edra. Common long bladed crystal structure. Compli­cated chemical structure that causes a range of colours.
Sheet silicates
Sheets of tetrahedra with top corner open for bonding. Mica and clay common variants.
Framework Silicates
Silica tetrahedra framework with other ions filling holes. Quartz and feldspar most abundant minerals in crust. Different varieties of feldspar occur due to the incapa­bility of both potassium and calciu­m/s­odium to be in the lattice.
Non-si­licate minerals do not contain the tetrah­edra. They are commonly econom­ically important.
Carbonates
Calcite and dolomite are most commonly occurring. Usually form due to lithif­ica­tion.
Oxide, halide, sulfide
Oxides are metal ions bonded with oxygen. Halide are the halogen bonded with cations. Sulfides are metals bonded to sulfur, important for mining.
Sulfates
Metal ion bonded to a sulfate ion.
Phosphates
Tetrah­edral phosphate unit combined with anions and cations.
Native element minerals
Metals occurring in a pure or nearly pure state. Usually non-re­active elements.