ESCI Quiz 1

background to johnstown flood

-may 31st 1889

-pennsylvania and killed 2000 people

-Collapse of south fork dam 14 miles upstream following several days of heavy rain

-Dam was originally built prior to 1853 to provide water for canal transportation system

-South fork fishing and hunting club bought it 1881

explain how the dam's construction and design contributed to the its eventual collapse

-Original dam was an earth dam (mud construction)

-summary of issues:

-Lowered dam to make top wide enough for a road

-Built fish screen across spillway with no maintenance

-Built dam with mud, brush, hay, and manure

-Allowed center to sag

-Did not replace safety release pipes sold previously

-And torrential rain on top of that

Why did the area's terrain increase the flood's risk

-johnstown was in a ravine type area

-no escape if there were to be a sudden flood

role of two bridges

-first bridge: debris from flood caught in the bridge and created a temporary dam that eventually gave way which gave the water more momentum just before it hit the town

-second bridge: was on the outskirts of town and the debris again formed a temporary dam which sent a second wave of floodwater back into town from downstream direction, debris caught fire in bridge and 80 people burned

explain the cultural legacies that the Johnstown Flood had on modern American society

-anger over court ruling changed our legal system (fault based to strict liability-if your actions or choices lead to harm you can be held responsible for damage

-carnegie felt guilty about the flood so he did more philanthropies like public libraries and eventually they became normal

-American red cross: clara barton already founded it at the time of the flood but after the flood the ARC shifted towards natural disasters (changed our approach to disaster releif)

how do geologists understand the earth at most basic level

-through reading, thinking, and hammering

-also observation is key

how does time, perspective, familiarity, and travel influence how we understand earth

time:

-time is sometimes the only difference between two scenes

-carman quarry vs death valley polygonal shapes

-small earthquakes can add up over time and eventually create mountains

traveling:

-helps to see connections

-water sorts grains by size so why is grain all mixed up

-study glaciers to find out (ice transports sediment not by size)

perspective:

-dark rock layers were cut off by sandstone but why, it was the edge of a channel but in cross section

eratosthenes background

-made first attempt to map world

-father of geography

-Used positions and relative angles of the earth, moon, and sun to estimate distance between sun and earth

-Realized earth was tilted and even measured the tilt 23.5 degrees

-came up with leap year

how eratosthenes found circumference of earth

-Measured shadows

-1/50th of a circle 7.2 degrees (meaning alexandria was this far away from syene)

-7.2 / 360 = x / earths circumference

-All he needed now was distance between the two cities

-He may have estimated it by using the time camel caravans took to travel between two cities

-Then divided by the speed at which they moved

-Or he may have record distances by professional distance walkers (dematists)

-Estimated 800 km

-He then estimated the earth's circumference to be 40,000 km (actual is 40,075)

What were Eratosthenes' original evidence and assumptions- What new data did he need and why was his estimate of the Earth's size slightly off

-assumed cities were directly north and south of one another

-but they weren't

-also there were minor errors in measuring angle (1/50th of a circle is not very accurate)

-same with camel speed

Why can meteorite impacts end up having so much effect on Earth systems and why would the angle of its approach affect the extent to which the K-Pg impact altered global Earth systems

straight on angle:

-Only goes through small amount of atmosphere so it doesn't slow down very much so it hits earth at greater speed

Force may be greater but still may have less of an effect on earth's systems than glancing blow

glancing blow (very angled):

-Goes through thicker section of atmosphere so it generates more heat

But if angle is too low its likely to explode before it hits

intermediate angle:

-Big danger - heat and reach the surface

K-Pg

-60 degree angle

-Heat generated due to compression of atmosphere not friction

-Set continents on fire (south and north america)

-So much smoke blocked sunlight and decreases global photosynthesis

-Led to destruction of ecosystems and mass extinction

What hypothesis and evidence has been put forth for the Moon's origin

hypothesis:

-biggest meteor impact known

-shortly after earth formed

-theia and earth shared same orbit and collided at oblique angle

-theia was vaporized along with big part of earth

-part of earth fell off and formed moon

evidence:

-moons relatively large size

-moons relatively small core

(If moon and earth formed normally they should have similar composition but they don't, Moon's core is 1/50th of its mass but earth's core is ⅓, This means earth's mantle was blasted away)

-mantle composition is different too

What were the implications moons creation on Earth's subsequent history, life and ecosystems?

tides would be insignificant:

-Tides allowed organisms and their descendants to colonize on land

responsible for earth's tilt:

-Knocked earth off center

-Reason we have seasons

-Also the reason earth rotates quickly

earth is rotating slower than it used to

-daily cycle was just 10 hours long

-caused by moon creation (gravitational pull)

What roles does solar energy play in Earth systems and why would our planet's size make a difference in its suitability for life?

-Main drive of hydrologic cycle (including biota) and climate/weather

-Also results in recycling of lighter elements

-And reworking of material formed deeper within earth

-Rock weathering and subsequent release of nutrient

-size plays role

-larger means thicker atmosphere

-Greenhouse gases are able to accumulate and warm the planet

sources of earths internal heat

-Relict heat from earth's initial accretion

-gravitational compaction as earth squeezed together

-radioactive decay

-Tidal friction (from moon)

why is heat important and what role does size play in how a planet retains heat

-if the planet is too small then it can't retain heat like the moon

How does energy (heat) move most effectively through the Earth's different internal layers or from its surface

-at the earth's surface, heat is lost by radiation to space

-internal heat flow (conduction and convection)

-metals are great conductors of heat because it has a field of loosely held electrons so metallic core can transfer heat by conduction

-Conduction is in solid core

-Convection is in liquid outer core (also conduction)

-Rocky mantle is poor conductor of heat (convection occurs) slow

convection vs conduction

-conduction: heat transfer with no movement of materials

-convection: heat transfer by movement of hot material

how can a planet have internal layers with very different compositions such as the Earth's core and mantle

heat lead to earth's partial melting

-formation of layered earth

-core-mantle-crust

-denser materials went to the middle and lighter materials went to surface which resulted in earth's layers

how does gravity measures, meteors, and earthquakes contribute to our understanding of earth's interior

earth's effect on other planet's orbit:

-Astronomical measurements of earth's gravitational effect on other planets = earth's mass, which together with eratosthenes volume we get earth's density (greater than surface rock)

-doesn't tell us internal material though

meteors:

-emnants of original solar nebula

-Provide some idea of materials present in early solar system

-Two groups

-Metallic: iron and nickel (probably core material)

-Stony: (probably mantle material)

earthquakes (provide us with most of our knowledge):

-Energy from earthquakes travel through earth's interior

-Recorded on global network of seismic stations and interpreted to tell us info about layers and internal heat flow

why are drilling and volcanoes less useful in telling us about interior

they aren't deep enough

-with drilling we only reach crust

-volcanoes only tell us about crust and uppermost mantle

earths layers (physical state)

-Lithosphere (rigid solid-outside layer)

-Asthenosphere (heat softened ductile solid, low velocity)

-Lower mantle (ductile sold, more rigid than asthenosphere)

-Outer core (liquid)

-Inner core (solid)

earths layers (composition)

-Core (dense metals)

-Mantle (dense rock)

-Crust (less dense rock)

how do layer differences play a role in earth's climate, plate tectonism, or magnetic field

composition

-impacts mass, which affects gravitational pull, atmosphere, and climate (GHG)

physical state

-Impacts plate tectonics

-Lithosphere = plates

-Convection in weaker asthenosphere and ductile lower mantle allow plates to move

Both

-play role in generating magnetic field

-Electric current moving through a wire generates a magnetic field

-Convection of liquid metal in outer core generates magnetic field

probable origin of earth's magnetic field - how does it compare to other inner planets

what you need:

-metal core (free electron field)

-liquid outer core (convection)

-solid inner core (spiral pattern)

-rapid rotation (movement)

other planets:

-Moon is too small core has cooled to be solid

-Mars is too small core has cooled to be solid

-Venus still has hot liquid core but does not rotate fast enough to generate field same with moon

effects of earths active magnetic field

-Northern lights

-Protects earth from harmful solar radiation

-Helps retain atmosphere's lighter elements

-Navigation (magnetic compass)

Birds use it too and sharks and marine life and cows

What were some of the lines of evidence that were used to support the concept of continental drift

-coastline fit

-geological evidence: diamond deposits found in eroded roots in mountains of continents that lined up, africa and south americas geological patterns lined up, same for appalachian mountains

-fossil biota ranges: Mesosaurus=water animal found in two continents but couldn't have crossed ocean, Lystrosaurus= land animal found in two continents but had to have crossed over somehow, Cynognathus=found in three continents too, Plant fossils means southern continents were once joined

-living/fossil biota ranges: african and south american ancestral vs immigrant animals

-rock records: Glacier deposits found in other continents suggest that continents were once together, If continents were together the glaciers make sense

-coal deposits: same latitude

why was continental drift idea discarded - weaknesses

-problem with wegener's theory

-how did they drift apart?

-he thought continents had to move across or plow through older seafloor

-he had no viable mechanism to account for continental drift

-maybe it was the earth's spin

-this is wrong because spin wasn't strong enough

scott's south pole expedition evidence of continental movement

-found glossopteris fossils proving Antarctica was connected to southern continents

-collected rock samples which proved connection not climate

rock magnetism - How can its different components be used to determine the rock's original position, relative to the magnetic pole that existed at the time the rock formed?

-Movement of liquid iron in outer core generates magnetic field

-As iron bearing minerals form from a magma (or as very fine iron bearing sedimentary grains settle) they can be aligned with respect to the earth's magnetic field

-It is permanent unless it's heated high enough to reset it - new one will reflect earth's magnetic field

-Even as earth's active field continues to change

paleomagnetic signature

-A rocks magnetic field is its paleomagnetic signature

-Reflects the magnetic field at the time the rock was formed rather than earth's present magnetic field

-Signature has two things

1- a compass direction that varies with its original magnetic longitude

2- and an inclination that varies with its original magnetic latitude

-So direction and distance to original magnetic pole can be calculated

How did apparent polar wandering data provide irrefutable proof that the continents had indeed moved

-Continental rocks from different ages have different paleomagnetic signatures which suggested that the magnetic poles may have "wandered"

-Construct a path that shows the movement

-two things that could have happened

1) continents moved through time

2) or north magnetic pole moved through time

-we know continents moved because on different continents, rocks of similar ages point to different apparent poles

-at any one time, there can only have been one pole so continents must have moved

polar wandering vs magnetic reversals

-polar wandering: changing paleomagnetic signatures over time

-magnetic reversals: led to recognition of motion mechanisms

Why would the Earth's magnetic field have reversed its polarity in the past

-Don't know exactly

-But maybe because metals in the outer core begin to crystalize along the bottom of the core mantle boundary as the earth slowly loses heat

-Any crystals formed would be denser than the liquid below and if one broke off and sunk it might mess up outer cores flow

-Once flow became reorganized its just as likely that the polarity is the other way

What caused the paleomagnetic pattern recorded in seafloor rock- How did this pattern lead to a recognition of how the seafloor formed and continents moved?

-zebra stripe pattern of high and low magnetic field intensity

-symmetrical pattern can only be explained by magma rising along ocean ridges and cooling to form seafloor

-polarity reversals over time are recorded in seafloor rock

-so seafloor is not all the same age and is relatively young

-this was the missing mechanism of wegeners

-continents didn't scrape seafloor

what happens if our polarity reverses again

-although our magnetic field is fading that doesn't mean a reversal is coming

-if it is coming it could take 1500 years

-true: Earth's magnetic field weakens during reversal event, The magnetic field helps protect against solar radiation

-false: could cause mass extinction

-what would happen: increased cosmic radiation, knock out power grids, disrupt satellite communication, and cause ozone depletion

difference between plate tectonics and continental drift

-continental drift: only continents move

-plate tectonics: underlying asthenosphere is broken into plates

concepts of plate tectonic theory

1) lithosphere is broken into discrete plates

2) oceanic and/or continental crust is simply the uppermost part of these lithospheric plates

3) plates move in response to earth's internal heat flow

4) many geological processes, like mountain building, volcanoes, and earthquakes, are tied to plate interactions

How can the difference between continental and oceanic crust help explain why some plate segments subduct, as well as the relative elevations and ages of land and seafloor areas?

-Parts capped by continental crust rise higher than parts capped by oceanic crust

-Because continental crust is lighter parts of plate capped by continental crust tend to stay at earth's surface

-while parts capped by oceanic crust can sink

-hence the oldest rock occurs in continents not in seafloor

different ways mantle convection occurs

-plumes (columns)

-fronts (linear

-latter occur along plate boundaries

how fast do plates move

-slow plates move about same speed as fingernails grow (1-2 inches per year but inches add up)

-fast plates move about same speed as hair grows (over 6 inches a year)

types of plate tectonic boundaries

1) divergent

2) convergent

3) transform

divergent

-two plates move away

-new lithosphere formed from rising magma

-continental rifts or oceanic spreading zones

-oceanic spreading zone: cover much of seafloor

convergent

-two plates move toward one another

-includes subduction and continent collision zones

-subduction is when old lithosphere is recycled into the earth

transform

slide past one another

-no magma forms and no new lithosphere is created

how does speed of plate motions impact sea level

-changes in the spreading rate of oceanic spreading zones = long term sea level changes

-why: new seafloor is created and destroyed which changes temp of ocean ridges and hence their volume

-Faster spreading rates = hotter, higher ocean ridges = higher sea level

-Slower spreading rates = cooler, lower ocean ridges = lower sea level

why does subduction occur

-As new seafloor moves away and cools, lithosphere thickens as underlying asthenosphere cools to become rigid (becomes part of lithosphere)

-Eventually cooling and thickening lithosphere becomes denser than underlying asthenosphere and can sink (subduct)

What happens when two continental masses collide or island arcs hit continental margins

-continental collision zones: If all intervening sea floor subducts away, lithosphere segments capped by continental crust can come together to form this

-exotic terranes: Are island arcs and micro continents that have been welded onto continents by past subduction

difference between absolute and relative plate motion

Relative plate motion

-Movement of two or more plates relative to one another

-Easy to determine if you place instruments on each, do the plates appear to be moving towards each other, away from each other, or sliding past each other

absolute plate motion

-Absolute rates and motions require a fixed frame of reference

-We can get absolute rates and motion from

-Present motion - satellite/laser data

-Past motion - hot spots

how hotspots can be used to determine a plate's absolute motion

-hot spots; Areas of volcanic activity, due to rising plumes (columns) of hot mantle rock

-Volcanoes form at hot spots, but as the plate moves over the hot spot these volcanoes are cut off from their source of magma, cool and contract

-Forms a line of progressively older, extinct volcanoes that records the plate's movement and direction relative to the more immobile hotspot

-It's not the hotspot that moves it is the plate

What are the possible forces that may help to drive plate tectonic motion

-Ultimate driving force is heat in the earth's interior that drives convection currents in the lower mantle and asthenosphere

-

What roles do the plates themselves play in altering or driving mantle convection

-But movement of lithospheric plates themselves may help drive and define convection in the underlying mantle

-Plate sliding and slab pulling

-Although mantle convection helps to drive plate motion, plate motion helps drive mantle convection

-So past plate motions may have caused some mantle plumes to evolve into larger convection cells

Be familiar with the common misconception that Pangea formed close to the start of Earth's history

-Pangea is actually the most recent supercontinent

-There were others before and there will be more in the future

Why does the Earth tend to have a supercontinent cycle

-supercontinent cycle: General tendency for continental masses to assemble into a supercontinent and rift apart, About every 500 million years

ways that plate tectonic processes can affect the history of Earth's life - and limitations of these slow motions

-impacts through evolution, extinction, and climate

-changing environments = iterative changes in biosphere

-misconceptions:

-continental rifting influences evolution

-motion is too slow to separate animals from their food source to cause evolution

how could plate motions influence global terrestrial diversity or the migration pathways of terrestrial communities

terrestrial diversity

-If there's only one large continent, fauna tends to be similar

-Example = dinosaur fossils are everywhere not just one continent today

-Pangea rifted to form separate continents, evolution proceeds separately on each continent - greatly increasing diversity

migration/contact

-As continents reconnect, new areas are open for colonization

-Contact between different species can lead to a number of new relationships, predation, competition, even disease

ways that plate tectonic processes could affect global climate by altering sea level, ocean and atmosphere circulation patterns, or atmospheric composition

local climate (latitude)

-As a continent moves from equatorial to arctic latitudes obviously the continent's local climate changes

sea level change

-changes in sea level due to spreading rates impacts animal distribution, migration and isolation

global climate

-Water absorbs solar energy more efficiently than land

-Higher sea levels results in warmer climate (more absorption of solar energy)

ocean circulation

-Plate tectonics can affect global climate by affecting ocean circulation (geometry of ocean basins)

-Ocean currents and overlying air masses are important means of heat transfer through climate systems

-Panama connection impacted currents

atmospheric composition

-Increased rates of plate tectonic movement result in increased volcanism

-Leads to higher atmospheric CO2 concentration

-Increased CO2 leads to greenhouse warming

-Increased CO2 also leads to higher O2-