McGill University - Kirsten Rempel
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
already present thermal energy in near sun objects accreted to form the earth
collisions - kinetic energy from objects impacting earth transformed to heat
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?
earth got so hot that the metals and silicate minerals melted
molten metals were denser and sank inward to form the core - the silicate minerals floated upwards and became the crust and mantle ==> differentiation
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
divergent - new crust created
transform - crust neither created/destroyed
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
tsunami waves | wind waves |
---|---|
influence entire water depth | influence the upper ~100m |
have wvl of 10s to 100s of km | have wvl of 10s to 100s of m |
wave heigh and wvl unaffected by wind speed | wave height and wvl related to wind speed |
wave velocity max several hundreds of km/hr | wave velocity max 10s of km per hour |
waves arrive as a raised plateau that pours onto the land w minor dissipation | waves break in shallow water and expend all stored energy |
how to stay safe in an earthquake
drop
take cover
hold on to a table until the shaking stops
preparation is the best safety method
earthquake predictions aren’t always perfect; tsunami early warning systems are effective but have to be implemented worldwide
Continental drift theory
Alfred wegener noticed that the continents fit together like a jigsaw puzzle
in 1912, he surmised that the continents were once a big land mass called Pangea - this broke up allowing the continents to slowly drift around the planet
evidence of continental drift
jigsaw puzzle fit of the contents
glacial deposits far from polar regions
paleoclimatic belts
distribution of fossils
matching geologic units
glaciation 180 million yrs ago
wegener’s hypothesis was ridiculed by mainstream geologists but eventually became accepted
luckily for wegener, geologists found supporting evidence from observations of glaciation in tropical countries
once the southern continents are fitted together, the glacial striations points to a single glaciated or polar regions in which South America, Africa, India, and Australia are connected to Antartica
glacial features
as glaciers move across the land, rocks embedded in their basal surface abrade the bedrock and leave scratches or gouges (striations)
glaciers also leave behind characteristic erosional and depositional landforms
equatorial forests and coal
coal deposits result from buried plants in equatorial forests and their transformation into carbon rich rock
when the continents are assembled, the deposits form a belt that could coincide w a hypothetical equator
the fossil record
fossils of animals that couldn’t swim were found on several continents
mountain belts
the roots of former mountain belts can be traced across the continents
the rate of continental drift
continents are moving apart at rates of cm per year
plate velocities may be mapped by measuring volcano ages & their distance along a hot spot track or by using the gps coordinates of plates over time
supercontinent break up and assembly
There is evidence for the existence of six previous supercontinents
Supercontinents breakup because of rifting and seafloor spreading and assemble through subduction
earth’s magnetic field
you can thank earth for being a giant magnet bc otherwise we wouldn’t exist
solar wind distorts the magnetosphere - shaped like a teardrop
deflects most of the solar wind, protecting earth
the strong magnetic field of the van Allen belts intercepts and collects dangerous cosmic radiation
earth’s magnetic field is generated by fluid circulation in the liquid outer layer of the core
an electric current is created in a similar way to electricity generated by a dynamo
the dynamo theory
describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time scales
magnetic field lines
invisible lines of force
radiate from the North Pole to the South Pole and extend into space, weakening w distance
charged particles get trapped by the field lines, forming the earth’s magnetosphere
northern lights
there are weak points in earth’s defences
these occur above the planet’s north and south magnetic poles
solar wind particles leak into the magnetosphere and spiral down towards the earth along magnetic field lines
they heat up atmospheric gasses and cause the shimmering sheets of colour known as the auroras (northern and southern lights)
magnetic declination
earth’s geographic and magnetic poles do not coincide
a compass points to magnetic north not geographic north
the difference btwn geographic and magnetic north = declination
it depends on: positions of the 2 poles, geographic north, magnetic north, longitude
magnetic inclination
Earth is not flat, which means that magnetic field lines are not parallel
Magnetic inclination depends on latitude:
The dip is horizontal at the equator and vertical at the poles
a compass needle moves 360º in a circle but is also inclined when held in a vertical orientation
the angle btwn the magnetic field line and surface of the earth is Called the inclination