ERTH1000 Mid-semester exam

Where does basalt dikes inject? And where does gabbro form?

Above the magma chamber. At depth

Explain andesitic

Andesitic: Intermediate - Erupts at <1000C° - Higher silica content than basaltic lava - Intermediate Si content. - Higher viscosity than basaltic lava and thus flows at a slower rate - Typically originates from stratovolcanoes and usually comprises a small volume that progress no further than the volcanoes base described as block flow.

How big percentage wise is the land and water on the earth's surface?

Approximately 30% land, 70% water.

What can be used to determine environment of deposition?

Assemblages of sedimentary structure can be used to determine environment of deposition. Deep channel, shallow channel, floodplain.

Explain carbon atom

electron cloud, nucleus, carbon has 6 negatively charged electron in a cloud surrounding a nucleus of 6 positively charged protons and 6 neutrons having no charge.

Explain tensional tectonics

extension of continental crust produces normal faults with high dip angles in the upper crust that flatten with depth, forming curved fault surfaces.

Explain pumice

extured volcanic glass which is created when super-heated, highly pressurized rock is violently ejected from volcano. The unusual foamy configuration of pumice happens because of simultaneous rapid cooling and rapid depressurization.

explain felsic

feldspar - silica, very high in silica content, has high viscosity

Define minerals

feldspar, hornblende and quartz make rock: granite.

What are the four compositional groups of igneous rocks

felsic, intermediate, mafic and ultramafic.

Define natural diamond

formed at high pressures and temperatures in Earth's mantle. Strong bonds connect closely packed carbon atoms in a tetrahedral structure.

Explain metamorphic rock

formed by an alteration of any pre-existing rock by high temperatures and pressures.

How are submarine fans formed?

formed from turbidity currents. These currents begin when a geologic activity pushes sediments over the edge of a continental shelf and down the continental slope, creating an underwater landslide.

Explain overturned folds

have limbs that dip in the same direction but one limb has been titled beyond the vertical.

Explain symmetrical folds

have limbs that dip symmetrically from the axial plane

Explain asymmetrical folds

have one limb that dips more steeply than the other. Stronger pushing forces.

Explain isostacy

how the crust flows on the lithosphere in the mantle

Define and explain graphite

is formed at lower pressure and temperatures than diamond. Strong bonds connect carbon atoms arranged in sheets. Weak bonds connect carbon atoms between alternating sheets.

What happens with magma as it rises?

it begins to degas and reduces density. - It lowers pressure = more degassing = rises faster.

Define cleavage

tendency to break along smooth surfaces.

Wilson cycle: explain ridge push

uplifted asthenosphere at ridge exerts a force on overlying lithosphere like continental rifting. Opposed by viscous drag in asthenosphere.

Define flood plain

vertical accretion: heterolithic bedding, roots, desiccation cracks, caliche nodules

Explain Transportation

via streams, glaciers, and wind moves particles downhills

Explain Shock metamorphism

which results from the heat and shock waves of a meteorite impact, transforms rock at impact site.

What are the five characteristics about earth?

- 1: Dipole magnetic field > deflects solar wind and protects from solar radiation. - 2: Stratified atmosphere, mainly composed of Nitrogen and Oxygen. - 3: Composed of minerals, glasses, melts, fluids (water etc) and volatiles, all materials left behind during the birth of the solar system. - 4: Layers: a thin silicate crust, a thick iron & magnesium silicate mantle and a thick metallic core - 5: Divided into a rigid outer lithosphere and a plastic/ductile asthenosphere.

List the types of faults

- 1: Normal fault: tensional forces - 2: Reverse fault: compressive forces - 3: Strike slip fault: shearing forces

List the three factors that affect whether rock melts and explain them

- 1: The temperature of the rock increases to above the melting point of minerals in the rock. - 2: Excess pressure is removed from rock that is hotter than its melting point. - 3: Addition of fluids such as water decreases the melting point of a rock.

How do we categorise volcanic activity?

- Active: eruption continuous - Dormant: not erupted recently but may in future - Extinct: no eruption for considerable time. No longer with active magma chamber. Extensive erosion.

Explain the graphic sedimentary log of braided river deposits

- Bottom: scourced base of channel - Middle: channel-fill succession of cross-bedded sands, decreasing cross-bed set thickness upwards, fining up - Overbank muds and thin sands with soil and roots.

Describe carbon minerals

- Carbonate ion, (carbon, oxygen) - Calcium carbonate structure (calcium ion, carbonate ion) Arrange in alternating sheets. - This is how corals make their skeleton. - Mineral: calcite

List non clastic for sedimentary rocks

- Carbonates (limestone) - Evaporites - Others: coal, ironstones, phosphates - Biogenic material (shells, skeletal material, plant debris, algae/bacteria, bone) - Others, carbonates: chemical precipitates, different rocks may include: carbonates, chlorides, silica, sulphates

List the physical characteristics of minerals and explain them

- Colour, dark minerals have more mg, fe associated with mantle. - Hematide: to obtain a streak of a mineral. May leave black red or brown streak. - Luster: how shiny it is. Vitrouch luster (glossy), deluster (not shiny), metallic luster - If it reacts to acid to produce carbon dioxide gas - Magnetic abilities - Shape - Density

Explain folds

- Common form of deformation observed in layered rocks - An originally planar structure, such as a sedimentary bed, is bent into a curved structure. - Produced by either horizontally or vertically directed forces in the crust. - A horizontal fold has a horizontal fold axis - Anticlines fold upward. - Synclines fold downward - A plunging fold has an axis at an angle to the horizontal.

Explain P-wave motion

- Compressional waves that travel quickly through rock. - Compressional-wave crest - P waves travel as a series of contractions and expansions pushing and pulling particles in the direction of their path of travel. - P waves has higher speed of propagation and reaches a seismic recording station faster than s-waves.

Describe the structure under a volcano

- Country rock: rock native to an area - Stock: tube for lava to come out of volcano. - Dikes: cut across layers of country rock, vertically - Sills run parallel to dikes, horizontally - Pluton a body of intrusive igneous rock that is crystallized from magma slowly cooling below the surface of the Earth. - Batholiths are the largest forms of plutons, covering at least 100km2

Name the 5 components and systems of the earth

- Cryosphere - Atmosphere - Hydrosphere - Lithosphere (most common is the solar system) - Biosphere

How does river carry sediments?

- Current flowing over a bed of gravel, sand, silt and clay carries a suspended load of finer particles and a bed load of material sliding and rolling along the bottom. - As current velocity increases, the suspended load grows and the increased force of the flow generates an increase in the bed load. - Particles moved by saltation, jumping along a bed. At a given current velocity, smaller particles jump higher and travel farther than larger particles

Where do earthquakes occur?

- Divergent boundaries - Convergent boundaries - Transform-fault boundaries - Intraplate earthquakes

List the classifying of igneous rocks

- Extrusive pyroclasts form i violent eruption from lava in the air: volcanic ash, bomb and pumice - Extrusive igneous rocks cool rapidly and are fine grained: basalt (mafic) and rhyolite (felsic) - Intrusive igneous rocks cool slowly allowing large coarse crystals to form. Gabbro (mafic) and granite (felsic).

Why do earthquakes occur?

- Faults may move several meters in a second, this movement within the earth's crust usually generates an earthquake. - Rocks being stressed suddenly break along a new or pre-existing fault

Explain river deltas

- Forms where rivers carry more sediments to the ocean tha marine processes can carry away. - May resemble a rough triangle - Important host rocks for coal and petroleum - They prograde (built out) from the shoreline - Influenced by balance of marine/fluvial processes.

Which factors affect sedimentary environment and sediments deposited.

- Geographic location and plate tectonic setting - Transport agent and medium - Biological processes and organisms that modify sediments - Climate

Which was the third plate boundary to be proposed, by who and what year?

1965 third plate boundary type transforms was proposed by Tuzo Wilson

What are the risks of earthquakes?

- Ground motion: L waves amplified by local rock types such as sand that are water rich are worse than basalts. Liquefaction - Often associated with fire - Often always have aftershocks - Faulting ground rupture - Landslides, if you have soils that are not very stable. - Mass wasting

List the crystal shapes

- Halite: cubic - Diamond: prism - Staorite: - Quartz - Gamet - Stonite - Calcite - Kyanite

Describe Carbonates

- Hardness: can't be scratched with steel - Habit: rhombohedral/massive - Colour: white/transparent - Fracture: good, basal - Cleavage: 3, good - Luster: vitreous - Fizzes upon contact with HCI

Explain Mercalli intensity scale

- He would go around and map, he would go to local communities and ask them what they felt and then he would map is systematically at a certain radius from where the damage had been and give people a description of what they felt. - Very subjective. - Kind of worked - While richter magnitude is unique for the quake Mercalli scale depends on location.

Explain rocks cycle

- Igneous rock Extrusive (stuff that comes out of volcanoes) and Intrusive (intrude into already existing rocks). - Sedimentary rock Clastic (eroded and weathered material) and Carbonate (example great barrier reef, fossils) - Metamorphic rock Created by high pressures

Describe oxides

- Includes many economically valuable minerals. - Can be Hematite: usually red, iron and oxygen. - Can be Spinel:

Explain fault

- Is a fracture that displaces the rock on either side of it. - A fracture in a rock formation along which there is no movement is a joint.

Describe Tectosilicates: feldspar

- K feldspar and plagioclase - Hardness: can't be scratched with steel - Habit: various, tabular - Colour: pink, white, grey and brown - Fracture: good, basal - Cleavage: 3, good - Luster: vitreous

Explain continental transform fault

- Lateral (transform faults and earthquakes. - Some transform-plate boundaries cut continental crust, for example San andreas fault, the pacific plate moves northwest relative to the north american plate

What controls amount of damage from earthquakes

- Location, proximity to focus/epicenter - Waves characteristics: amplitude, duration, frequency - Local geology, underlying material - Building codes

Explain metamorphic textures foliated rocks and intensity of metamorphism scale

- Low grade: slate and phyllite, slaty cleavage, smaller crystals, - Intermediate: Schist, medium crystals, schistosity - Intermediate: Gneiss, medium crystals, banding - High grade: Migmatite, large crystals, banding.

How does volcanoes work?

- Magma, which originates in the asthenosphere as it comes up through these pipes it interacts with country rock forming crustal magma chambers. - Lavas erupt through a central vent and side vents, forming systems of sills and dikes.

What is the difference between magma and lava?

- Magma: under surface - Lava: above surface

Explain Braided river systems

- Morphological features: floodplains on either side and vegetated formed bars. Also have mid-channel bars in the middle of the river. - Mid-channel bars: development depends on the flow of the river. Varies up and down.

List the mineral structure for silicates

- Olivine: 1 plane, isolated tetrahedra. - Pyroxene: 2 planes at 90°, single chains - Amphibole, 2 planes at 60° and 120°, double chains - Mica (muscovite), 1 plane, sheets - Feldspar, 2 planes at 90°, three dimensional frameworks

What are seismic waves?

- P-waves (primary) - S-waves (secondary) - Surface waves (L-waves) - Microseismicity, very very small earthquakes, occurs before and after an earthquake.

Explain how point bars are created

- Point bar deposits of a meandering river laterally migrating left to right: mud forms the final channel fill. - Point bar, lateral accretion: trough cross-bedding, ripple cross-lamination

Explain Mohs hardness scale

- Ranks 1-10 - Lowest on scale talc, gypsum - Highest up: Diamond, corundum, topaz - Quartz: 7.

Name the techniques for measuring grain size

- Sedigraph - Laser size analysis - Point counting

What are the tree types of volcanoes?

- Shield volcano (Mauna Loa), usually largest. - Stratovolcano (Mt fuji) - Cinder cone (SP crater)

What percentage of gas in the atmosphere lies below 100km?

99.9998%

Describe Quartz

- SiO2 - Hardness: can't be scratched with steel - Habit: hexagonal, prismatic - Colour: transparent/translucent but many colours depending upon impurities - Fracture: conchoidal - Cleavage: none - Luster: vitreous

What is the difference between storm waves and tsunamis?

- Storm waves can be high but because they have short wavelengths they contain relatively little water, most waves runs out of water by the upslope edge of the beach. - A tsunami is not very high out in the open ocean but as it approaches the land friction slows the front of the wave so the rear catches up and the wave grows. It is so wide that it can cover a wide area of low-lying land.

Explain Strain and stress and what are the types of stress? And what does strain cause?

- Strain: change in volume or shape of a rock body - Stress: forces that acts on a rock unit to change its shape and/or its volume Types of direct stress: compression, tension, shear - Causes strain of deformation

Describe Sulphides and sulphates

- Sulphise: iron pyrites. Lone sulphur atom. - Gypsum: sulfate formed when seawater evaporates. Help separate clays. Used to make plasterboard. Sulphur bonded to oxygen.

Explain surface wave motion

- Surface waves ripple across earth's surface, where air above the surface allows free movement. There are two types of surface waves. - In one type the ground surface moves in a rolling elliptical motion that decreases with depth beneath the surface. - In the second type the ground shakes sideways with no vertical motion.

List factors that affect deformation

- Temperature - Pressure - Strain rate - Rock type - The variation of these factors determines if a rock will fault or fold. - Elastic and brittle near the earth's surface - More plastic and ductile deeper in the crust

Explain S wave motion

- Travel at about half the speed of p waves - Shear-wave crest - S waves are shear waves that push material at right angles to their path of travel

explain sieving

- Unconsolidated sediment - Mechanically sieved - Sieves relate to phi scale - Mass of size fractions

How can we identify minerals?

- Using X-rays and electron beams to characterise the internal structure of minerals. - Water waves diffract when the pass through a gap. The waves produced by adjacent gaps interfere. Where crest overlap the signal is stronger. - Diffraction of an x-ray beam passing through a crystal produces a pattern of dots on a screen. - We can also look in a microscopy, which requires a little more skills

Describe Phyllosilicates: clay

- Variety of types - Hardness: very soft - Colour: white/grey - Examples: kaolinite, illite, vermiculite

Describe Phyllosilicates: micas

- Variety of types: muscovite, biotite - Hardness: very soft - Habit: platy - Colour: white, transparent, brown - Fracture: micaceous - Cleavage: perfect basal - Luster: vitreous

List clastic for sedimentary rocks

- Volcanisticastic (tuffs, ignimbrites) - Terrigenous clastic (mudrocks, sandstones, conglomerates), - Carbonates (limestone), - Volcaniclastic, terrigenous clastics: Mineral grains different rocks may include: quartz, mica, feldspar, calcite - Volcaniclastic, terrigenous clastics, carbonates: Lithic fragments: broken up pieces of rocks (limestone, mudrock, volcanic rock, chert, metamorphic rock), - Terrigenous clastics, carbonates: Biogenic material (shells, skeletal material, plant debris, algae/bacteria, bone)

Explain Alfred Wegener's theory of continental drift

1915 proposed that all continents once formed a single supercontinent called Pangea. Theory was based on empirical evidence, meaning something you can see. Empirical evidence is one of the keystones of science. What Wegener observed was the fit of continents for example between Africa and South America. If you were to remove the ocean today those continents would fit together like a jigsaw puzzle.

How old is the earth?

4.56ga

Explain submarine fans

A body of sediment on the seafloor deposited by mass-flow processes that may be fan-shaped, but more elongate, lobate geometries are also common.

Explain silicate ion

A central silicate ion surrounded by four oxygen atoms forms a tetrahedron. Has silicate ion, oxygen ions and silicon ion. Quartz is made of silicate tetrahedra arranged in the same way as the tetrahedra in diamond.

Define minerals

A naturally occuring, solid crystalline substance, usually inorganic, with specific chemical composition. .

Explain fractional crystallization

A process by which a chemical compound is separated into components by crystallization. In fractional crystallization the compound is mixed with a solvent, heated, and then gradually cooled so that, as each of its constituent components crystallizes, it can be removed in its pure form from the solution.

Explain the richter scale by Charles Richter

A seismologist measure the amplitude of the largest seismic wave and the time interval between the p and s wave arrivals to determine the distance from the epicenter to the seismograph. By plotting the two measurements on these graphs and connecting the points, the seismologist determines the richter magnitude of the earthquake. - Richter scale is logarithmic, e.g. an earthquake at 6 on the scale is 10x bigger than a 5. - Scale 1-10 - Biggest one chile 1960 9.5

Explain Regional metamorphism

At convergent plate boundaries occurs at moderate to deep levels under moderate to ultra high pressure and high temperatures.

What happens when you transport sediments in fluid of high velocity?

At highest velocities, current erode both large and small particles from the streambed.

What happens when you transport sediments in fluid of intermediate velocity?

At intermediate velocities particles may erode or settle depending on their grain size and cohesiveness

What happens when you transport sediments in fluid of low velocity?

At lower velocities particles of all sizes settle on the streambed.

Explain basaltic

Basaltic: Mafic. - High in Fe, Mg and Ca - Erupts at 1000-1200C°. - Comprises the least amount of silica - Relatively low viscosity and the fastest flowing lava. - Often expelled from shield volcanoes. - Roped lava - Blocky lava - Pillow lavas - Columnar basalt: slow cooling may allow gas to escape - can lead to columnar jointing at surface owing to contraction. May be vesicular where lava cools and traps gas bubbles.

Explain earth's magnetic field

Basically the magnetic field appears to emanate from the outer core. Outer core is liquid or behaves like a liquid, composition is very metallic, as it rotates around it behaves like a geodynamo. Magnetic field is never fixed but constantly fluctuating.

Why does atmospheric change with elevation?

Because molecules pack together more tightly at the base of the atmosphere

How come rocks are important hosts for freshwater

Because they are porous and permeable

When is the mantle hot enough to flow

Below 100-150 km, it convects hot mantle rises cold mantle sinks.

Explain the sedimentary structure of submarine fans

Bottom, massive granules to sans, then parallel laminated sand, then cross laminated sand at least mud.

What are the key elements?

CHON, carbon, hydrogen, oxygen and nitrogen

Explain compressive forces

Compressive forces, which squeeze and shorten rock formations, dominate at convergent boundaries, where plate move toward each other.

Explain divergent boundary, with continental separation

Continent plate separation, rift valleys, volcanoes and earthquakes. - East African rift valley: african plate, somali subplate. Example of active rift that is underlain by a mantle plume. - Rift zones on land (continental rifts) have been responsible for the break up of land masses. Africa and Arabian Peninsula. - The red sea started as a rift 30 mya but evolved into a narrow basin 5 mya and the rift axis became a mid ocean ridge.

What did Arthur Holmes suggest 1930?

Continental drift could be related to mantle convection. Wegener theory could be related to this. Proposed that ocean floor spread apart at the top of mantle convection cells. Hypothesis was theoretical based on convection.

Explain continent-continent convergence

Crustal thickening, folded mountains and earthquakes. - Example Himalayan mountains (Indian plate, eurasian plate) - Himalayan Orogeny (mountain) can be divided into two phases. The first phase was a collision between indian and a microcontinent to the north of india at 50 mya. The second phase was the more substantial india-asia collision with thicker indian continental lithosphere which started about 25 mya which has continued on until present day. As continental crust was pushing against continental crust the himalayan mountain belt was pushed up. Mt Everest is the highest altitude mountain on our planet. - Continental crust is too buoyant to subduct: when two continents converge, rock undergoes compression and shearing and a mountain range develops.

What causes sedimentary rocks to form cleavage planes

Direct pressure causes sedimentary rocks, such as shale to form cleavage planes that may differ from their bedding planes. Slaty cleavage planes; vertically, bedding planes; horizontally.

Which are the tree types of boundaries?

Divergent: boundaries moving apart and new oceanic lithosphere is created at mid-ocean ridges Convergent: move towards one another. If one plate slides under the other it creates a Subduction zone alternatively mountains belts are formed as both plates push upwards. Transform: they slide past each other along strike-slip faults.

Why does the moon have many craters?

Due to no atmosphere, no water, no plate tectonics.

What affects the rate of weathering

Duration of weathering: - Less time: less weathering - More time: more weathering Mineral composition of parent rock - Lower mineral stability: more weathering, feldspar - Higer mineral stability: less, quartz Temperature - Lower temperature: more chemical weathering, more physical weathering (eg thermal expansion and contraction. - Higher temperature: Less physical weathering, more chemical weathering (dissolution of minerals) Amount of rainfall - Low rainfall: Less physical and chemical weathering (eg fragmentation, erosion and dissolution of minerals) - High rainfall: more physical and chemical weathering (eg more fragmentation, erosion and dissolution of minerals) Rainfall acidity - Less acidic rainfall: less physical and chemical weathering (eg less dissolution of minerals) - More acidic rainfall: more chemical weathering (eg more dissolution of minerals) Topography - Low slope steepness: less erosion, more chemical weathering - High slope steepness: more erosion, less chemical weathering Physical weathering - climate dependent - On mountains we get ice, when it freezes it causes rocks to shatter - Frost shattering in polar regions. - Exfoliation in hot/dry climates: when heat gets absorbed by the rocks they swell and when they cool down at night so the outside cracks open as the inside is still hot. Chemical weathering Cracks forms along crystal boundaries, felspar start to decay. The decay processes and cracks open, the rock weakens and disgenerate

What happens during major floods in meandering rivers?

During a major flood when velocity and water volume increase, the river takes a new shorter course, cutting across the loop - The abandoned loop remains as an oxbow lake

Explain why we have a moon

During middle to late stages of earth's accretion about 4.5 billion years ago a mars sized body impacted the earth and the giant impact quickly propelled a shower of debris from both the impactor and Earth into space. The impact sped up earth's rotation and tilted earth's orbital plane 23 degrees. Earth reformed as a largely molten body and the moon aggregated from the debris. Moon rocks 4.47 billion years old brought back by the Apollo astronauts support this impact hypothesis.

Explain how the structure of the earth was 4.56ga

Early on Earth was fairly homogenous inside and when the temperature got hot enough iron began to melt, the iron accumulated at the center of the planet to form a metallic core. Process called differentiation. Heavier elements sink, lighter elements stay on top. The core has the highest density, then the mantle, oceanic crust, continental crust, hydrosphere and atmosphere.

What and when did Marie Tharp and Bruce Heezen publish?

First physiographic map of the north atlantic in 1957.

What proof did Arthur Holmes have?

First proof came from paleomagnetisme (first proof of continental drift), looking the earth's magnetic field and figuring out where rocks were deposited and then reconstructing them back to their original position. We can do this due to the Earth's magnetic field having a north and a south pole, so the earth is a dipole. Magnets that are contained in little rocks will aline with the earth's magnetic field. Iron minerals in rocks achieve the magnetic field at time of formation: in hot magma, magnetic dipoles are randomly oriented and no magnetization is possible.

What does ocean-continent convergence through subduction create

Fluid induced melting in subduction zones.

How does igneous rocks differ from one another

For example looking at granite and basalt: their differ in texture and also chemical composition. Colour is also different. Colour usually represent chemical composition, but also grain size. The smaller the grain size the darker the rock usually is. Granite is intrusive which means that it is a coarse-grained rock, meanwhile basalt is extrusive meaning it is a fine-grained rock. The faster you cool the less time the rock has to develop crystal structure.

What is the difference between quartz and clay in transportation in fluid

For small but cohesive particles such as clay, a stronger current is required to erode them. For small non cohesive particles such as quartz the gentlest current can erode them.

What happens inside of a volcano

Gas charged magma from deep in the mantle forces its way upward, fracturing the lithosphere. Rapidly ascending magma breaks off and carries crust and mantle fragments as it explodes at supersonic speed. After eruption the feeder channel forms a diatreme made up of solidified magma and these rock fragments or breccia. The softer sediments of the cone and surface of the crust erode leaving the diatreme core and radiating dikes we see today.

Explain the geodynamo

Geodynamo: Flow in the liquid iron outer core creates a magnetic field. Diplo - two poles (N and S pole), protects us from the solar wind.

Explain maturity

Grain size = larger: closer to the source, smaller further away. Angularity = rounder the further it gets from the original ''parent'' Sorting: If transport sifts grains, carrying smaller ones farther and leaving coarses ones behind, grains in a sediment tend to be the same size.

What were the results of the detailed mapping of the ocean floor?

Harry Hess 1962 made a breakthrough when he proposed the theory of seafloor spreading which states that: - Magma from the mantle flows up in linear spreading centres beneath the mid-oceanic ridges and that consequently. - The existing ocean floor is pushed laterally away from the spreading ridges to make space for the accommodation of the new basalts. - The new material that then erupts at the spreading center enlarges the margins of the two areas (plates) on both sides of each ridge. - On a planet that is not expanding or shrinking, seafloor production must correspond to the amount of crustal material that is finally returned to the mantle to what we call subduction. - Cross section of a mid-ocean ridge: A magma chamber beneath the ridge axis. In the spreading axis we will have basalts erupting to the surface through these magma chambers and on their way up from the asthenosphere this hot magma will cool and make crystals and also gambros and as it moves upwards it will have little feeters called dikes.

Why is the Earth's crust so enriches in O and Si?

Has more o and si than in the average earth, this is due to plate tectonics. Mantle is mobile and can move and it convects. Heat mantle rises moves laterally cools becomes denser then sinks back down. Moves plates around the planet, creates new lithosphere but destroys older lithosphere. Minerals with high O and Si have lower melting temperatures and minerals more stable. Therefore end up at the surface.

What empirical evidence did Alfred Wegener use for his theory?

He observed the similarity of rock assemblages and ages across present day oceans. Similar links to an ancient continent. Piece of Canada stuck in Georgetown, assembled rocks from Canada, who has not been seen anywhere else in Australia. Based his empirical evidence on old freshwater fossils (reptiles), that was found on either side of the Atlantic ocean suggested in south america and Africa and because they are freshwater fossils they would not have travelled very far, certainly they would not cross an entire ocean basin. This suggest that Africa/South America was together and drifted apart. Distribution of certain climatically sensitive rocks. Wegener believed that these glacial deposits must have once been together. Tillites are in general laid down in higher latitudes and Wegener suggested that they were deposited near the south pole in ancient time.

Explain High pressure metamorphism

High pressure metamorphism: along linear belts of volcanic arc, produced by continent-continent collision, occurs at high pressure

What can help determine the direction of plate movement?

Hotspots

What are the surface manifestation of lumes rising from deep mantle?

Hotspots lavas (as iceland or hawaii) and ancient large igneous provinces (LIPs) or super volcanoes. LIPs punctuate plate tectonics by creating new plate boundaries as well as driving rapid climate change and extinctions.

What element is the universe mostly made out of?

Hydrogen

What are the most important elements for life?

Hydrogen and oxygen

How thick is the mantle? How big percentage wise it of earth's volume? What is it made of? and what is its density?

Is above the core. 82% of the earth's volume. Made of ultramafic rock called peridotite. Density = 3-3.4g/cm3.

What is silici: clastic sediments important for?

Important for: Hydrocarbon reservoirs Aquifers Hosts for hydrothermal mineral deposits Coal Palaeoenvironmental information Archaeological finds

What is carbonate rocks important for?

Important for: Hydrocarbon reservoirs Aquifers Cement Building materials Paleoclimate

What is chemically mediated important for?

Important for: Hydrocarbon traps Fertilizers Explosives Batteries

How is the reversal in earth's magnetic field recorded?

In iron rich rocks such as basalts. During reverse magnetic polarity the magnetic dipole points in the opposite direction. During these conditions a compass needle would point to South magnetic pole

Explain the pale blue dot for the solar system.

In the 70s we sent out probes around the solar system, voyeur to the jovian system, voyeur 1 its trajectory after it encountered jupiter and some of its moons it flung of way above the disc of the solar system. Managed to get them to turn around and take a picture of the solar system.

What does ocean-ocean convergence, subduction create?

Island arc volcanoes. Fluid induced melting in subduction zones. As it subducts it will carry sediments with is, that contains water as that enters the subduction zone that material is dehydrating and starts melting, escaping through volcanic systems. Water lowers melting point.

Explain meandering river systems

It is one main channel, which shift from side to side in a snaking motion. he current is faster at outside banks which are eroded and sediments get deposited at inside banks where the current is slower, forming point bars. As we move away from the hinterland, the gradient and speed of water diminishes. The average size of particles will diminish. At the erosion and deposition process continues, the bends grow closer and the point bars bigger

What is the outer core made of, what is its radius and its density?

Liquid iron nickel sulfur radius of 2255km thick density 10-12g/cm3

Explain Wilkinson Microwave Anisotropy probe

Looking into the deep universe and what it's looking at is anisotropic, isotropic is when everything looks the same in every direction and anisotropic is the opposite looking in slight variations in the microwave background leftover from the big bang and it's been able to look way back into the past, been able to see these periods of initial inflation, the idea of the dark ages, etc.

What are some features of the jovian planets?

Made out of lighter elements. They also have massive atmosphere and rocky moons around them.

How can magnetic inclination be and declination be determined and what does the data show?

Magnetic inclination and declination can be determined in a laboratory for an oriented rock sample. These data can help determine the latitude and rotation at formation. Lava cannot have permanent magnetization due to dipoles changing orientation rapidly, as rocks cools dipoles align with Earth's magnetic field. With more cooling the dipoles lock into this orientation. The magnetic signature depends on the latitude where the lava cooled. The position (paleo-latitude) of australia has changed through time. We can calculate the original latitude and the angular orientation for a continent from the directions of remanent magnetization through time.

Explain the pacific ring of fire

Major area in the basin of the pacific ocean where large numbers of earthquakes and volcanic eruptions occur. In a 40000 km horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs and volcanic belt and/or plate movements.

By who was the seafloor first mapped?

Mapping the oceans, mostly through US NAVY activities during the second world war. The floors of the oceans were mapped and their contours charted comprehensively for the first time, and thus the amazing extent and size of the mid-ocean ridges, which consist largely of basaltic volcanic rock, became known.

Define volatiles

Materials that turn into gas at surface temperature.

Define mineral silicates

Most abundant class of rock-forming minerals 90% in the earth's crust.

What is the inner core made of, what is its radius and its density? And how do we know about this?

Solid iron-nickel alloy. Radius of 1220km Density 13g/cm3. Know about this due to drilling attempts: Project Mohole, Kola superdeep borehole. Drilling down into the earth. Use seismic waves instead these are waves of energy caused by sudden breaking of rock within the earth. - Primary waves = compressional (up and down) - Secondary waves = shear (sideways) Waves that are pass through the planet. Remote sensing the deep earth is important. As the waves pass through material that makes up the earth, the velocity change depending on the composition of the material.

What can cause structures to form in sedimentary rocks?

Moving water or burrowing animals can cause structures to form in sedimentary rocks, these are very useful for determining environment of deposition. Sands are also useful: two sediments of similar composition that are textually different: well sorted (the same size), poorly sorted (different sizes)

Explain nebula

Nebula - cloud of gas & dust from which solar systems form. Rotating clouds of gas and dust (H, He). What happens is that there is some slight preferential movement in the cloud of gas and dust and eventually one rotation will take over as the dominant one, as gravity and rotation are acting on a mass, as they draw the mass in so that the angular momentum is conserved, the mass is conserved and as the radius decrease the velocity must increase, as radius contracts the velocity increases. Eventually it will form a disc so that the rotation occurs in such a way that things are moving that rotation allows everything to not collapse completely into the middle but everything else under gravity collapses down to a flat form. Within that disk we start getting small secretion of of larger and larger particles that eventually will form planetesimals, they coalesce into discret bodies and we end up with these orbiting discrete masses around the sun, they all end up going in the same direction.

What elements does the Stratified atmosphere consists of?

Nitrogen (78.08%), Oxygen (20.95%), other gases (0.97%)

What type of faulting does Mid ocean ridge, divergent have?

Normal faulting

In which direction is the pacific plate moving?

Northwest

What does earth's crust mainly consist of?

O and Si (60.4% oxygen and 20.5% silica).

What happens when the earth shakes?

Observe seismic waves during earthquakes. They will spread out from earthquakes point of origin - focus. Travel away from point of origin. - Point on surface directly above point of origin is called the epicenter. - Earthquakes are recorded by seismographs

Explain ductile deformation

Occurs at lower strain rates. When rocks bend or flow, like clay.

What are rocks important hosts for?

Oil, gas and freshwater

How is the relation between two plates described?

On a sphere the relationship between two plates is described by a rotation pole. Spreading ridges define great circles while ocean fracture zones define small circles. Movement of plates, explains distribution of volcanoes, mountains etc Mantle plume/hotspot not tied to plate motion. Hawaii sits on top of a hotspot. Hotspots track can help determine the direction of plate movements

What is the earth's crust mainly made out of

Oxygen

Explain stellar nucleosynthesis

Periodic table showing the different elements for Big bang, Supernovae, large stars, small stars and cosmic rays. Different events for different elements. Heavier elements created by fusions.

What does molten rock that flows onto the sea floor produce?

Pillow basalt

What are the highest causes of fatalities from volcanoes?

Pyroclastic flows, indirect factors (famine), tsunamis, lahars

Define metals

Solids made of metallic elements.

Explain rhyolitic

Rhyolitic: Felsic - Erupts at 600-800C° - Granitic lavas - Greatest content of silica 68% - Highest viscosity of any type of lava - It flows much slower than andesitic and basaltic lavas - Rhyolitic lava tends to ooze from erupting stratovolcanoes.

Explain foliation

Rocks develop foliation when they contain platy minerals that align along a preferred orientation. Depending on their preferred orientation, compressive forces cause the mineral crystals in the rock to grow or to align perpendicular to the compressive forces.

Define melts

Rocks that have been heated to a liquid. Magma, Lava

Which three groups are rocks classified into?

Sedimentary, igneous and metamorphic

What will tell us about the transport history?

Shape of the grain will give information about the transport history: rounded = long history.

Explain shearing forces

Shearing forces, which shear two parts of a rock formation in opposite directions, dominate at transform-fault boundaries, where plates slide past each other.

What elements is the earth mostly made out of?

Si, Mg and Fe

Wilson cycle: explain slab pull

Sinking of slab into mantle at subduction zone pulls plate - motion is opposed by viscous resistance i the mantle.

What effect does Jupiter have on the orbit?

So big that the barycenter, point that everything rotates around. Slightly weird orbits due to jupiter being so big, causing the orbit to be elliptical instead of round.

Explain solar wind

Solar wind: Electronic Magnetic particles that are deflected by earth's field. Distort the shape of earth's magnetic field in space. Protects us from incoming radiation.

Explain differentiated stone meteorites

Stone meteorites, two kinds: differentiated and undifferentiated. Have undifferentiated chondritic meteorites. Named for the chondrules that they contain. Spherical shaped silicate minerals (olivine, pyroxene), texture suggests rapid cooling of molten droplet floating in space.

What small scale deformation?

Structural geology

Why does micas (biotite and muscovite) have a perfect basal cleavage. And which other two minerals have good cleavage?

Structure: Sandwich: silicate sheet, aluminum hydroxide sheet. Then potassium ions And another sandwich below. This is why they have a good cleavage as it occurs between aluminum hydroxide. Pyroxene and amphibole.

Explain Udden-Wentworth scale

Tells us the scale of different rock types. -Clay is the smallest, siltstone next, then sand, then conglomerates (granule, pebble, cobble, boulder) - Medium silt, visible to the naked eye.

Explain tensional forces

Tensional forces, which stretch and pull rock formations apart, dominante at divergent boundaries, where plates move away from each other.

What are the planets closer into the sun called and which are they?

Terrestrial planets: mercury, venus, earth, mars.

What do we call the earliest period on earth?

The Hadean period due to Hadeous due to it being to hot

Explain lithosphere

The brittle portion, non flowing and rigid, moves as tectonic plates, comprised of two components: crust and upper mantle.

Explain triangulation

The distance between the beginning of the first P wave and the first S wave tells you how many seconds the waves are apart. This number will be used to tell you how far your seismograph is from the epicenter of the earthquake

What are the planets farther away from the sun called and which are they?

The jovian planets, jupiter, saturn, uranus, neptune

What was Fred Vine and Drummond Matthews theory?

The linear magnetic anomalies parallel to active ridges by correlating earlier theory on seafloor spreading with research then being done on the time scale for geomagnetic reversal. 1962 two types of plate boundaries had been proposed - 1 Divergent (seafloor spreading) - 2 Convergent (subduction)

Why did physicists say that Wegener was wrong?

The lithosphere is rigid and is comprised of the crust and upper mantle. It is thicker under the continents; thinner under the oceans. The asthenosphere below is soft and able to flow. Less dense continental crust floats on denser mantle. Continental crust is less dense than oceanic crust and therefore rides high. Physicists said that it is impossible for less dense continents to move through more dense oceanic crust and therefore must Wegener be wrong

Explain the forms of modern deltas

The nile delta: relatively small, - River dominated delta: sticks right out from the edge of the shore, the channels have built their own runway to the shoreline. - Wave-dominated delta: not an enormous amount of sediments, does not stick very far out from the shoreline. - Tide-dominated delta: lines of sand and mud, wide open channels that go far up into the delta.

Explain metamorphic textures foliation and cleavage

The original bedding in a sample of shale is marked by the thin sandstone layers. Regionally metamorphosed rocks show foliation caused by compressive forces.

Explain the crust

The outermost skin of earth with variable thickness. Thickest under mountain ranges and thinnest under mid-ocean ridges. Moho is the lower boundary, separates the crust from the upper mantle. Discovered in 1909 by Andrija Mohorovicic which made change in the velocity of seismic p waves

What is the building block of many earth materials ?

The silicate ion

Explain plate tectonics

The theory that earth's outer shell is divided into several plates that glide over the underlying mantle. Plate tectonics is as fundamentally unifying to the Earth Sciences as Darwin's theory of Evolution to life sciences. Without plate tectonics nothing in the Earth's sciences can be linked to each other. Over a decade australian plate moves approximately 1 meter one of the fastest moving (northeast) GPS can't keep up with continents in constant motion.

How many meteorites fall per year? Explain meteorites

There are around 550 falls per year. Leftover primordial rocky material from the beginnings of the solar system. Fall out of the sky

Explain LIPs

They are exceptional intraplate igneous events throughout Earth's history (about 30 in the past 300 Myrs). Their significance and potential global impact are related to the total volume of magma intruded and released during brief geological events (peak eruptions often within 1-5 Myr in duration). LIPS are dominated by basalt. LIPs are areas of dominantly basaltic igneous rock mainly in flows and sills, and very large in volume. They erupted in a very short time over an extensive area

What are some features of the terrestrial planets?

They are small and rocky, dominated by lithosphere (means rock)

How do we think that early planets formed?

They were formed by collisions of these planetesimals which released huge amounts of energy and reshaped the planets again and again. We got gravitational collapse (high pressure, collision, fricture), radioactive decay and asteroid impacts = kinetic energy.

What size were the atmosphere though to be? What was the name? And what size was it actually?

Thought that the atmosphere were about 200,000km and this is known and Geocorona = Hydrogen. Solar and Heliospheric Observatory measured atmosphere to be 630,000km.

What does the seismic waves tell us?

Through these wave patterns radiating away from point of origin this is actually how we know about the inner structure of earth. As waves travel differently we know for example that primary waves will be able to travel through liquid meanwhile secondary waves will not, this is how we know that the earth's outer core is liquid. - All waves move at different speeds.

Explain mid ocean ridge transform fault

Transform faults on the ocean connect and offset ridge segments. Active faulting as indicated by earthquakes only occurs in the part of the transform between ridge axis.

Which layer of the atmosphere do we live in?

Troposphere

How do tsunamis occur?

Tsunamis occur at subduction zones, when one plate goes under the other, interlocks and some at point in time it will fail. When the plate is going down it wants to drag the upper plate down as well, at some point it gives in, this drags water masses up as well. Water will move away out into the sea. Waves will go from high amplitude to low amplitude.

Describe Jupiter's atmosphere and what it is made out of and it's gravity.

Turbulent atmosphere made out of 89.9% hydrogen and 10.2% helium. Gravity is 2.4 of earths.

Explain divergent boundary, with two oceanic plates

Two oceanic plates separate from each other, rifting, volcanoes. Sea floor spreading. - Axis of a mid-oceanic ridge has a central valley and lava flows out onto sea floor through long fissures. - The ridge is offset along its length by transform fault ''fracture zones'' - Newly created oceanic crust is carried away from the hot central ridge and cooled as it travels. - Erupted rock termed as mid-oceanic ridge basalt. - Iceland has a divergent plate boundary running through its middle. - As the North American and Eurasian played were pulled apart, volcanic activity occurred along the cracks and fissures.With many eruptions over time the island grew out of the sea. Long fire curtains = fissures. Rift band through Iceland is youngest and as you move out from the middle is gets older.

Explain undifferentiated stone meteorites

Undifferentiated meteorites are not melted - primordial. Derived from original condensation of gas, ice and dust of the solar nebula, approx composed of material that accreted to form planets. We can also date them, can look at the age of them and can then see the age of the solar system and then the earth. Complex life evolved approx 0.6Ga ago.

List the key morphological features of streams

Uplands, floodplains, tributary streams, valley, channel, former channels of sand and gravel, floodplain deposits of silt and clay.

Explain viscosity

Viscosity: resistance to flow - High viscosity: stiff

What are the sedimentary environments?

We can have lake, river, desert lake, glacier, delta, beach and tidal flat systems. Deep sea, continental shelf, organic reef

Explain why the terrestrial planets are not as light?

We think it's like this as the closer into the sun the solar wind which is energetic particles which are constantly streaming out of the sun as strong enough that they are able to strip away a lot of the lighter elements, stripped away helium and hydrogen by the time we get to jupiter the solar wind is not strong enough to do so.

Explain the formation of the solar system simply

We think that the stars have formed and turned into supernova and exploded and produced big clouds of gas & dust forming nebula.

Explain brittle deformation

When a rock breaks

Explain decompression melting

When you have increase in depth and pressure. If you move the rock through the earth's mantle closer to the surface you will change the melting curve. From dry mantle rock you will pass through this field cross the solidies line and go into liquid. Rock is moved toward the surface. - Hot mantle rises, decompresses and melts in the spreading center. Pillow lavas at surface. - The ascending mantle rock moves into lower pressure zones which lower rock melting points and generates voluminous magma.

Which are the are the tree meteorite groups, and which is the majority?

With the majority being stone, then stone iron and and last iron

As parent rock is metamorphosed is progress from low grade to high grade metamorphic rock. Is this correct?

Yes

Does the does crystal size and coarseness of foliation increase as intensity of metamorphism increases

Yes

Is mantle plume stationary for hotspots?

Yes

Metamorphic facies correspond to particular combinations of pressure and temperature and can be used to indicate specific tectonic environments. Is this correct?

Yes

Have geologist found a pattern regarding the ocean floor?

Yes, have found a pattern especially basalts och black to normal and light to reverse and they were able to tie it to age by dating these rocks and they have found that we have a pattern of dark light dark light dark which allows us to go and examine the ocean floor with this kind of pattern. This was called barcode for the oceans 1963

Explain ocean-ocean convergence

You get oceanic trench, volcanic island arc and deep earthquakes. -Marianas trench (philippine plate and pacific plate creating trench in subduction zone)

Explain pyroclastic flow

a dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing at great speed.

Explain Contact metamorphism

affects a thin zone of country rock around an igneous intrusion

Define structural geology

aims to characterise deformation of structures(geometry),to characterise flow paths followed by particles during deformation (kinematics), and to infer the direction and magnitude of the forces involved in driving deformation(dynamics).

Explain pyroclasts

are any volcanic fragment that was hurled through the air by volcanic activity

Explain volcanic ash

are fragments of mm-scaled pulverized rock, minerals and volcanic glass

Explain Erosion

away particles produced by weathering

Explain igneous environments for hotspots

basaltic intrusives and basaltic extrusives.

What does spreading center and mid ocean ridges create?

basaltic magma comes up to the surface and make spreading centers. Decompression melting. involves the upward movement of the earth's mantle to an area of lower pressure. The reduction in overlying pressure enables the rock to melt, leading to magma formation.

Explain Weathering

breaks down rocks physically or chemically

Explain fluid induced melting

by adding water you shift the melting curve. - Sediments carry water into subduction zone, as this enters it will heat up the pressure will increase and the trapped water is released causing the sedimentary rocks to melt at lower temperatures. - Convergent margins: the crust descends into the mantle, the slab is heated and dehydrates. Releases fluid from the slab reduces melting point of rock causing melting.

What are the two types of volcanism?

decompression melting and hydration melting.

Explain elastic deformation

change in shape of a material at low stress that is recoverable after the stress is removed

Explain compressive tectonics

compression of continental crust occurs on low angled thrust faults.

Which earthquakes occur at deep focus at convergent boundaries?

large shallow earthquakes occur mainly on thrust faults at the plate boundary. Intermediate-focus earthquakes occur in the descending slab. Deep focus earthquakes also occur in the descending slab.

What types of lava are there and what is lava?

lava is molten rock that flows out of volcanoes. Depending on its composition lava can be either basaltic, andesitic, rhyolitic.

Explain Diagenesis

lithifies the sediments to make sedimentary rocks

Define sedimentary rocks

made of sediments formed from the weathering and erosion of any pre-existing rock. Deposition, burial and lithification (compaction and cementation) transform loose sediments into sedimentary rocks.

Explain igneous environments for ocean-continental convergence

mafic to intermediate intrusives and mafic to intermediate. Continental margin volcano, Mt Rainier Washington - With higher melting temperatures rock composition is more mafic and pressure increases however in lower melting temperatures water content increases and rock composition is more felsic.

Explain igneous environments for ocean-ocean convergence

mafic to intermediate intrusives plutonism & mafic to intermediate volcanism. Island arcs, Java Indonesia - Spreading center: basaltic intrusives and basaltic extrusives. Spreading center, Mid-Atlantic Ridge Iceland

Explain Explosive eruptions:

magma is violently fragmented and rapidly expelled from a volcano. More like honey.

Explain mafic

magnesium - ferric, high in iron, magnesium and calcium content, lower in viscosity and therefore higher density

Explain bombs

mass of molten rock larger than 64 mm in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground.

Explain tectonic

means ''to build''. It is the serie of how the earth's lithospheric plates are moving relative to each other. Plates acts like a rigid shell and the strong outer layer is called the lithosphere (crust & uppermost mantle)

Define fracture

minerals break along curved surfaces break irregularly.

What are the chemical elements of the earth's mantle and upper crust?

mostly silica and oxygen and also magnesium.

Define glasses

non crystalline minerals like matter: Cool too quickly to form structure.

Explain faults and complimentary stress

normal, reverse/thrust, strike slip, transform tensional, compressional, shear

Explain Burial

occurs as layers of sediment accumulate and compact previous layers

Explain Seafloor metamorphism

occurs at mid-ocean ridges where intruding magma drives seawater circulation through extruded basalts.

Explain Deposition

occurs when particles settle out or dissolved minerals precipitate

Explain ocean-continental convergence

oceanic plate moves towards continental plate and at a convergent boundary where continental crust pushes against oceanic crust, the oceanic crust which is thinner and more denser than the continental crust sinks below the continental crust. - You get volcanic mountain chain, folded mountains and deep earthquakes. - Oceanic lithosphere subducts underneath the continental lithosphere. - Water and sediment material enters the trench, magma chambers. - Oceanic lithosphere heats and dehydrates and releases water as it subsides. - The addition of water into the mantle wedge changes changes the melting point of the molten material there, forming nw melt which rises up into the overlying continental crust forming volcanoes. - Subduction is a way of recycling the oceanic crust. Eventually the subduction slab sinks down into the mantle to be recycled. It is for this reason that the oceanic crust is much younger than the continental crust which is not recycled.

What does hot spots create

oceanic plates moves above a fixed hotspot which makes basaltic volcanoes. Decompression melting in a mantle plume.

Define general features of deltas

salt marshes in between channels, at the end of the delta we have sand bars. Places where the delta enters the ocean, slows the water down, sediments gets dropped here, first thing to go is sand, finer particles of silt and clay will go down the slope into the deep ocean. Foreset beds: slope into deep ocean. Bottomset beds: deep ocean beds.

Which fault occurs at transform boundaries

shallow earthquakes coincide with normal faulting at divergent boundaries and with strike-slip faulting at transform fault boundaries.

Explain asthenosphere-the ductile portion

shallower under oceanic lithosphere but deeper under continental lithosphere. Flows as soft, ductile solid.

Explain shearing tectonics

shearing of continental crust occurs on a nearly vertical strike-slip fault.

Explain igneous rock

solidify from molten liquid (magma). Forms from liquid rock (magma) in several different ways. Crystal size with igneous rocks is largely determined by the cooling rate. - Igneous processes within earth produce intrusive igneous rocks - Igneous processes on or near Earth's surface produce extrusive igneous rocks.

Define composition

the kinds and proportions of minerals that make up the rock.

Define texture

the size, shapes and spatial arrangement of crystals or grains.

Define stellar nucleosynthesis

the theory explaining the creation (nucleosynthesis) of chemical elements by nuclear fusion reactions between atoms within stars.

How do you get volcanoes?

through subduction, rifting and hotspots.

Explain Burial metamorphism

transforms sedimentary rocks at progressively increasing temperature and pressure

Explain van allen belt

two belts in the inner magnetic field where high energy cosmic rays are trapped. A zone of energetic charged particles, most of which originate from the solar wind, that are captured by and held around a planet by that planet's magnetic field.

Explain Effusive eruptions

type of volcanic eruption in which lava steadily flows out of a volcano onto the ground. More runny.

Explain continental crust

underlies continents, felsic most common rock granite. Average thickness 35-40km.

Explain oceanic crust

underlies ocean basins, mafic especially basalts. Average thickness 7-10km.