EPSC 201 Midterm Notes

Big Bang

• 13.7 B years ago, the universe exploded into existence

• sudden expansion of matter, energy, space from a single point

• universe is continually expanding

infrared satellites observing heat signature

• 400 000 years after big bang

• how we know about big bang

• no stars at this point

• particles initially very close together

  • so close that light travels only a short distance before bumping into a particle and getting in another direction

• this effect filled the sky with glowing fog - the afterglow from the formation of the universe

raisin bread model of universe expansion

• universe is getting bigger

• spreads raisins apart as it gets baked (things get further w expansion)

red shift

• wavelength of light is related to the colour of the visible light spectrum

• light from stars in galaxy stretch as galaxy expands

• this exhibits a longer WVL

• as stars in the universe move away from us, they shift red

Doppler effect

• red shift is caused by the expansion of the universe but the effect is similar to that seen from sound waves

• short WVL = high frequency

• wavelength = velocity / frequency

baby photo of the universe; cosmic microwave background is light from ~400 000 after Big Bang

• w the info from the cosmic microwave background, physicists used theory of relativity to calculate how fast the universe has been expanding

• back calculated to the pt where it had 0 size

• using this method, universe is ~13.7 B yrs

  • red = highest density, blue = lowest density

  • higher density regions formed the stars, planets, other space objects

nuclear fusion

• created the elements

  • atomic nuclei combine to make larger atomic nuclei and subatomic particles (protons and neutrons)

• difference in mass btwn reactants and products is accounted for by the release of energy

stars as natural fusion reactors

• the larger the star, the heavier the element it can make

• large stars go supernova ejecting material into space (incl their newly-formed heavier atoms)

• heat and pressure inside the stars causes smaller atoms to fuse together and create larger ones

• this causes the release of energy - making the stars shine

• the sun is avg sized and only has enough H to make elements up to Fl

  • once it does this it begins to die by cooling and getting larger

  • took many gens of stars to send out heavy enough elements into space for the formation of terrestrial planets like earth

matter is converted to energy

e = mc²

• energy = e

• mass = m

• speed of light = c

• created by Einstein in 1905

what does nuclear fusion require?

• requires fuel and a confined environment w enough temp, pressure, and confinement time to create plasma in which fusion can occur

steps to building a solar system

• collapse of a nebula

• make a disc and put a star at the centre

• make planets

collapse a nebula

• solar system when small patch in nebula collapses in on itself

• triggered by nearby stars that release energy & matter

• collapse keeps going - first bc of static electricity pulling dust particles and gas molecules together and then by gravity

• nebula condenses into a swirling disc which has a central ball that is surrounded by rings

  • 2nd or 3rd gen nebula forms from H & He left over from Big Bang & heavier elements created by fusion rxns in stars or during explosion of stars

make a disk and put a star at the centre

• star forms from material drawn together from nebula’s collapse

• rest of the dust/gas settle into a protoplanetary disc rotating around star

• planets start to form by sweeping together the dust and gas thus leaving dark rings in the disc

• ball at the centre grows dense and hot enough for fusion to begin - becomes the sun, dust (solid particles) condense in rings

  • dust particles collide and stick together which form planetesimals

Stellar evolution - as the H in the core of a star becomes He, it grows bigger and into a red giant - when all fuel is consumed, it will collapse into a white dwarf, ejecting the outer layers as a planetary nebula.

• if its about 10x bigger than our sun, it’ll explode to make a supernova after collapsing and leave behind a neutron star/black hole

terrestrial planets

earth, mercury, Venus, mars

• metal core surrounded by rock

gas giants

Jupiter, saturn

• made of mainly H and He

ice giants

uranus, neptune

• made of ice - water, methane, ammonia - rocky cores

3 types of planet occur in this order:

1) terrestrial —> 2) gas giant —> 3) ice giants

the nature of the matter condensed depends on the temperature

• distance from earth to sun:

  • iron and olivine condense

• distance of jupiter

  • ice and ammonia condense

• distance of neptune

  • methane condenses

life on europa

Jupiters moon = europa

contains the key ingredients for life: water, chemistry (C, H, N, O, P, S), energy (likely powered by chemical rxns)

• surface blasted by radiation from Jupiter - bad for life on the surface, couldn’t survive but it may create fuel for life in an ocean below the surface

• may have had plenty of water - a salty ocean beneath crust has more water than earth’s ocean

• may be a rocky seafloor at the bottom of the ocean

• interaction btw rocks and ocean could possibly supply chemical nutrients for living organisms

our solar system

hazards of gravity

• Jupiters gravity interferes w other solar system objects - takes objects from asteriod and even Kuiper belt and flings them toward sun

• some have impacted earth - catastrophic

• comets as objects approach the sun and the dust and gas is blasted from their surface, creating a tail

why are larger planets farther?

bc solar winds blow matter away from the sun

• size and composition of objects in solar system depend on their distance from the sun

what changes at the frost line?

past the frost line, planets can have liquid ice —> before this pt only rock and metal can solidify

what are stars and planets made from?

clouds of dust and gas in solar nebula

formation and differentiation of earth

• planetesimals grew by continuous collisions

• interior heated and softened

• gravity reshapes proto-earth into a sphere

interior differentiated into:

• stony outer shell = mantle

• central iron rich core = molten outside and solid inside

formation of the moon

• earth was formed, mars sized protoplanet (theia) collided w it

  • planet and a part of earth’s mantle were disintegrated

  • collision debris formed a ring around earth

  • debris coalesced and formed the moon

• moon has a similar to earth’s mantle

  • tells us the earth was differentiated into the mantle and core before the collision (bc otherwise the composition of the moon would be similar to the avg of all earth materials)

how was earth formed?

• additions of material from other protoplanets and space objects it collided w - this happened inside a ring of the solar nebula

• as earth grew, the inside began to heat up bc of compression and gravity - once the interior softened it started to differentiate into a metallic core and rocky exterior

  • all of the impacts contributed to high temps = volcanic activity

  • volcanic gases began to make an atmosphere dominated by CO2 and H2O vapour

how was the moon created?

a major impact w a planet the size of mars created the moon - has a comp similar to earth’s mantle

temperature of early earth

it was HOT

• large parts were molten

where did the heat from early earth come from

1. already present thermal energy in near sun objects accreted to form the earth

2. collisions - kinetic energy from objects impacting earth transformed to heat

3. gravitation and compression (pressure)

As Earth accreted, it collected silicate minerals, iron and nickel. At first, these materials were scattered throughout the planet. When Earth started heating up, this changed. what happened next?

1. earth got so hot that the metals and silicate minerals melted

2. molten metals were denser and sank inward to form the core - the silicate minerals floated upwards and became the crust and mantle ==> differentiation

3. gravitation and compression (pressure)

volcanism

• earth’s high temp meant that early tectonic processes were accelerated

• surface was more geologically active

• led to volcanism

• earth was also under heavy bombardment - energy from the collisions vaporized some of the crustal materials and blasted out gases

atmosphere and oceans

• earths atmosphere dev from volcanic gases - took a long time to happen

• when earth became cool enough, moisture condensed and accumulated & oceans came into existence

• at first, earth was surrounded by a thin layer of H and He which eventually bled off into space (light gasses)

• then the gasses released by volcanic eruptions began to build up: H2O vapour, CO2, CO, SO2, H2S, H2, CH4

• water and nitrogen gas (N2) were brought by meteorites and comets

• no oxygen gas at this point - mostly CO2, N2, H2O vapour

Earth at that time didn’t have the atmosphere it does today, but eventually, oceans began to form. Water vapour from volcanoes and comets condensed into surface water.

comets

• carried water to earth

rust as proof

Terrestrial sediments from that time period were not stained red from oxidized iron

O2 was produced when the Sun’s UV rays broke apart water molecules

H2O=H2 +0.5O2

However, this was quickly removed from the atmosphere by chemical reactions

free oxygen in the ocean

was taken up by banded iron formations (BIFs)

when life began, the atmosphere started to oxygenate

Photosynthesis!

• Cyanobacteria in the oceans used CO2 as food and released oxygen into the atmosphere

• Eventually, oxygen began to accumulate, though present levels (21%) didn’t occur until 350 Ma

sun is more luminous today than during the evolution of the planet

• sun was abt 25% less luminous

• decrease in CO2 (greenhouse gas) may have cooled the earth enough for an ice age at 2.5 Ga

oldest life on earth

• bacteria in 3.5 B yr old chert - Australia

• stromatolites - early life on earth dominated by microbial mats of cynobacteria

the great oxidation event

• beginnings of life as we know it and the first extinction event - the sudden injection of toxic oxygen in an anaerobic biosphere caused the extinction of many existing anaerobic species on earth

the atmosphere

Our atmosphere is mostly nitrogen and oxygen. It thins and dries away from the surface.

layers of earth

crust - solid silicates

• continental crust

• oceanic crust

mantle - solid silicates

• upper mantle

• lower mantle

outer core - liquid Fe and Ni

inner core - solid Fe and Ni

what is the earth made of

91% is composed of: Fe, O, Si, Mg

other 9% is the other 114 elements - they form the minerals, liquids and gasses of earth

• main solids to condense from solar nebula at the distance of earth’s orbit were metallic iron and olivine (Fe Mg)2SiO4

the crust

variable in composition, density and thickness

• thickest under mountain ranges

• thinner under oceans

• the Moho discontinuity divides the crust from the mantle

continental crust

• underlies continents

• avg thickness 35-40 km

• lower density and more silica rich

• felsic (feldspar and silica)

oceanic crust

• underlies the oceans

• avg thickness 7-10 km

• higher density, more Fe and Mg minerals

• mafic (Magnesium and ferric iron)

crustal composition

98.5% of the crust is composed of just eight elements

Oxygen and silicon are the most abundant elements in the crus This reflects the importance of silicate (SiO4) minerals

the mantle

• solid rock soft enough to flow over time

• 82% of earth’s volume

• 3 sub layers: upper mantle, transitional zone, lower mantle

  • convection below ~100km mixes the mantle - hot rises, cold sinks, driving force for plate tectonics

mantle composition

• mostly olivine and pyroxene

• 45% O, 23% Mg, 22% Si and 6% Fe, with a little Ca, Al, Na

  • Samples of peridotite are sometimes brought up by volcanic eruptions, or by uplift of the ocean floor onto the continents during subduction.

lithosphere

the outermost 100–150 km of Earth

• Behaves rigidly, as a non-flowing material
• Composed of two components: crust and upper mantle • This is the layer that makes up tectonic plates

asthenosphere

upper mantle below the lithosphere
• Shallow under oceanic lithosphere; deeper under continental • Flows as a soft plastic solid

the core

• Iron rich sphere w a radius of ~3 500 km

• seismic waves segregate 2 radically different parts, the outer core is liquid and the inner core is solid

outer core

• liquid iron alloy

• 2 255 km thick

• liquid circulates easily

• flow of liquid generates earth’s magnetic field

inner (innermost) core

• ~650 km thick

• speed of seismic waves change when passing through

• suggests 2 sep cooling events in earth’s history

density in earth’s interior

denser material must be concentrated in the center

• thin brittle crust

• thicker and denser mantle

• inner very dense, metallic core, liquid layer & solid inner part

The properties of Earth’s layers change with depth

Pressure (P)

• The weight of overlying rock increases with depth

Temperature (T)

• Heat is generated in Earth’s interior

• Temperature increases with depth

Geothermal gradient = change in temperature with increasing depth inside the Earth

The gradient is different for each of Earth’s layers:

• ~ 20-30°C per km in crust

• < 1oC per km at greater depths
  Earth’s core may reach more than 4,700oC!

seismic waves

The energy released by an earthquake is propagated in the form of seismic waves

• They give us information about the density and composition (solid or liquid, rock type) of the material they pass through

• Seismic waves are also used to find the origin (epicenter) of earthquakes

Seismic refraction

The path of a seismic wave depends on its velocity, which is proportional to the density of the material

Seismic waves crossing into lower-density materials slow down and are refracted into those materials

Conversely, waves moving into higher-density materials are refracted away from those materials, toward the surface

type of seismic waves

(1) Bodywaves

Travel through Earth’s interior

Provide information about underground materials

(2) Surface waves

Travel just under Earth’s surface

Disrupt the surface during large earthquakes

p waves

primary / push waves

• Propagate by compressing & expanding material like a slinky

•  Material moves back and forth parallel to wave direction

• Fastest waves

  • arrive 1st at seismic stations

•  Travel through solids, liquids & gases

S waves

secondary / shear waves

• Propagate by moving material back and forth

• Material moves perpendicular to wave direction – like shaking a rope up and down

• Slower than P waves

•  Travel through solids, NOT liquids or gases

surface waves

Rayleigh waves

• ground roll

• analogous to p waves intersecting w ground surface

• cause ground to ripple up and down like water waves

love waves

• analogous to S waves that intersect w grounds surface

• make ground move back and forth like a snake

• most destructive seismic waves during earthquakes
  

S waves cannot move through liquids

P-waves are compressional in the direction of movement, so they propagate through liquids, whereas S (shear) waves shear the liquid side to side and do not propagate in the direction of movement

earthquake

Earthquakes are vibrations caused by the rupture and displacement of rock along a fault plane

rupture surfaces

• rupture doesn’t occur over an entire fault plane but rather over a small surface = the rupture surface

• displacement begins at a focus point in the interior and propagates outward along smaller failures on the surface

• the greater the displacement = stronger earthquake

• earthquake magnitude also depends on the type & strength of rock + the amt of stress on the fault plane

aftershocks

• after displacement, stress is reduced on the rupture surface but it is passed onto adjacent parts of the fault plane

• new high stress areas can rupture = aftershocks

• aftershocks can be any size - usually smaller than triggering event, not always

• can occur w/I minutes or be delayed for years (range)

  • eg Haida Gwaii earthquake - oct 28 2012, aftershocks btw oct 28 and nov 10

earthquake damage from body waves

• waves arrive in a distinct sequence & cause a diff type of motion

  • first P waves, then S waves

• vertical p waves = ground goes up and down

• vertical S waves = ground goes back and forth

• side to side motion from S waves = stronger than motion from p waves = causes more damage

earthquake damage from surface waves

• delayed due to travelling along the surface = arrive after p and s waves at seismic monitoring stations

• love waves undulate the ground laterally

• Rayleigh waves make the ground surface roll like a wave

• surface waves = more damage than body waves = love waves are the most damaging

3 type of plate tectonic boundaries

1. divergent - new crust created

2. transform - crust neither created/destroyed

3. convergent - crust destroyed

plate tectonic boundaries

most earthquakes occur here

earthquakes and subduction zones

As the higher-density oceanic crust subducts underneath the continent at a convergent plate boundary, movement of the subducting slab causes quakes

Earthquakes occur at the top of the subducting plate because of friction that prevents slippage and causes distortion of the overlying plate

collisional zones

Where two continental plates collide, the crust undergoes compression and uplift – mountain building (orogenesis)

• Earthquakes in these settings can be very large

• Orogenic uplift creates landslide/avalanche hazards

mid ocean ridges

At mid-ocean ridges, tectonic plates are moving apart, creating open rifts

These spreading centers are connected to perpendicular transform boundaries

Shallow earthquakes – <10 km depth

transform faults

Some transform plate boundaries occur on continents, most notably the San Andreas fault

Transform earthquakes occur at shallow crustal levels

Large transform earthquakes on continents are usually major disasters

The San Andreas is a very active fault generating 100s of earthquakes per year

seismographs

Seismographs are instruments used to record ground motion –

1) Amplitudes of the vertical and horizontal components

2) Arrival times of waves

seismograms

Amplitudes and arrival times of the different wave types measured by a seismograph are recorded on a seismogram (visual record)

finding the epicentre

p and S wave arrivals are sep in time

• sep grows w distance form the epicentre

• graphic time delay is used to find this distance

• next circles are drawn around 3+ seismographs w radii corresponding to their distance, epicentre is at the intersection of the circles

earthquake magnitude

• Richter scale used for small earthquakes

• inaccurate for larger ones

• the moment magnitude scale (no upper limit) is now in common use

• energy released by an earthquake can be calculated

• an increase in magnitude of one step corresponds to a 32x increase in energy

magnitude vs intensity

An earthquake has a single magnitude, but a variable intensity

The intensity of shaking varies from place to place based on distance, local geology, building construction method (earthquake preparedness)

Intensity is measured on the Modified Mercalli Intensity Scale in Roman numerals, I to XII

landslides and avalanches

Shaking causes steep slopes to fail (collapse)

• Landslides frequently accompany earthquakes, blocking roads for emergency

  vehicles and causing collateral damage

liquefaction

earthquake waves can cause water saturated sediments to lose strength and liquify

• earthquakes shaking can cause the water pressure in pore spaces to increase to the point that oil particles move away from each other

fire

frequently caused by earthquakes

• shaking topples stoves, candles, powerlines

• broken gas mains and fuel tanks ignite

• critical infrastructure is destroyed

• firefighters can’t help bc no road access/water/too many hot spots

tsunami

• tsunamis are caused by displacement of seafloor (earthquake, submarine landslide, volcanic eruption)

• faulting displaces entire volume of overlying water - first recedes from the cost and then forms a giant mound on the sea surface (up to 25 000 km²)

• when mound collapses, huge, rapidly moving waves race towards shore

tsunami vs wind driven waves