Geology - 1.1

1.1.1
1. Asteroids
  1. Collisions happen which creates meteorites
  2. Large rocky objects left over from the formation of planets
2. Planets
  1. Terrestrial
    1. All have similar characteristics, All 'Earth Like' in structure
    2. formed in a similar way to Earth
    3. Mercury, Venus, Earth, Mars
  2. Gas Giants
    1. Jupiter, Saturn, Uranus, Neptune
    2. All made of Gas
3. Origins
  1. Big Bang = 14billion yrs ago
  2. Formed when a giant molecular cloud of gas and dust collapsed. Eventually formed was a rotating disc material was drawn towards the centre, it triggered nuclear reactions=Sun's formation, dust particles began to stick together (accretion), forming larger objects, finally resulting in planets
  3. Solar System = 4500million yrs ago
1.1.2
1. Types
  1. Iron
    1. Composed of alloy of iron and nickel, 6% of known meteorites
    2. core of a small plant-like object
  2. Stony
    1. Composed of silicate minerals
    2. mantle of a small plant-like object,
  3. Carbonaceous chondrites
    1. contains water and organic compounds
    2. Similar to composition of the sun but with fewer volatiles
2. Impact Craters
  1. Formation
    1. • Material to be ejected and quartz grains to be violently shocked and even melted • Rock strata to be tilted • Material at depth to be broken up• The ejected material falls back to the surface inverted
  2. Evidence
    1. • Vaporisation and partial melting of host rock • Seismic activity • Giant tsunamis • Wildfires • Dust in atmosphere = global cooling and ecosystem collapse
3. Found more commonly in the deserts and antarctic
4. Mostly from the asteroid belt
5. Volcanic Activity
  1. Seen on Mars and Venus in a similar way to Earth's volcanos, as similar structure
  2. Gas Giants Moons, tidal heating = volcanism
6. Dating Planets
  1. Can't be measured directly as surface was originally molten
  2. Erosion and other processes have dystroyed the old rocks
1.1.3
1. The inner core from the centre- 6371km -5100m: The inner core is made of a solid material due to extreme pressures,Both P and S waves travel through, Mix of iron and nickel, based on meteorites evidence and the idea of correct densities.
2. Lehmann Discontinuity at 5100km: Phase boundary. Zone of about 100km where material changes state
3. OUTER CORE from 5100km to 2900km: Liquid iron and nickel , S waves can’t travel through. P waves slow down due to reduction in rigidity. Pressure in the outer core
4. Lower mantle from 2900km to 700km: Solid as S waves can travel through it, P waves increase steadily in velocity because of its pressure,Same type of silicate found in stony meteorites
5. Upper mantle from 700km to an average of 35km: Contains solid silicates but less dense than lower mantle, Main rock is Peridotite, Consists of the asthenosphere and lithosphere
6. Gutenberg discontinuity at 2900km: Boundary marking a change in material from metallic iron nickel to stony silicate. Also changes state. P waves velocity decreases, S waves stop
7. The Asthenosphere: A layer of soft but solid rock mobile rock, with high 'plasticity', comprising the lower part of the upper mantle from about 100 to 200 (up to 350 kilometers) beneath the Earth's surface.
8. The Lithosphere: A layer of solid, brittle rock making up the outer 100 kilometers of the Earth, encompassing both the crust and the outermost part of the upper mantle.
1.1.4
1. Volcano’s bringing magma from depth
  1. Carries up rock from these layers from depth
  2. Basalt layers which erupt at mid-ocean ridges - partial melting of the upper mantle
  3. Kimberlite pipes are results of explosive volcanism from deep mantle sources.
  4. Xenoliths (foreign rocks in magma)
2. Mines and Boreholes
  1. Boreholes go further but people cannot go in them
  2. Direct access to the higher levels of the crust by mining/digging
  3. Mines become too hot to be in, with little ventilation to go any further
3. Geothermal Gradient
  1. Rate of increase in temperature per unit of depth.
  2. Temp gradient is lower in the mantle because of the radioactive heat production is concentrated in the crust, thermal transport changes from conduction to convection on the asthenosphere and upper mantle and this transports the heat differently
4. The Crust
  1. Geological maps show what things look like but with some debate over detail. show varied continetal crust materials
5. Ophilite Suites
  1. During the collisions, continental plate that has broken off may be thrust onto the oceanic plate instead of going into the mantle, 7km thick
1.1.5
1. Shadow Zones
  1. P and S Waves: 142 degrees from the epicentre and 103 degrees from the epicentre
  2. S Waves: 103 degrees from the epicentre and 103 degrees from the epicentre
2. Seismic Activity
  1. Body Waves- travel faster if rock is more rigid and incompressible and slower if more dense ● S Waves - only liquid zones ● P waves - solid and liquid zones
  2. Seismic Reflection: ● Return of some energy to the surface from a boundary of two layers of differing density
  3. Seismic Refraction: ● Occurs if velocity differs in each layer caused by density differences ● Bending of waves
3. Densities
  1. Earth density = 5.5 g/cm cubed
  2. Oceanic crust= 2.9 g/cm cubed
  3. Continental crust = 2.7 g/cm cubed
4. Meteorites
  1. similar compositions to our mantle and core
  2. Iron me. are more dense 7-8g/cm3
  3. Stony me. are more dense 3-3.7g/cm3
1.1.6
1. Apparent Polar Wander Curves
  1. The continents move so it looks as if there are 2 pole although not.
2. Variation in the field
  1. field fades over several thousands of years it then increases again but with inverted poles
    1. Evidence = Remnant magnetism: is magnetism shown by rocks due to the alignment of their magnetic minerals according to the Earths magnetic field at the time of their formation
3. Magnetic Inclination
  1. latitude of a volcano at the time it erupted its lavas by using the magnetic inclination
  2. is the angle of dip of the lines of a magnetic field. It is the angle with the horizontal made by a compass needle
4. Origins of the earth’s magnetic field
  1. liquid core causes the magnetic field. The convecting mass of molten Fe will make electricity, which induces magnetism (which repeats).
  2. generation and destruction allows the earth to show a weak continuous magnetic field
  3. Curie point - where a rock loses magnetism so not permanent and constantly changing in earth
5. Magnetic reversals and palaeomagnetism
  1. Iron rich minerals in lavas align themselves with the earths magnetic field
  2. Cool through the curie point and retain there magnetism permanently
  3. Act like frozen compasses showing the direction of the poles at the time of there formation

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