GEOLOGY 103 - Exam 1

latitude

• "parallels” = east-west grid lines that are parallel to the equator

• 0 degrees at the equator, 90 degrees N at the North Pole, 90 degrees S at the South Pole

• 0-90 degrees N = Northern Hemisphere

• 0 - 90 degrees S = Southern Hemisphere

• distances between latitudes same everywhere on earth’s surface

longitude

• “meridians” = north-south grid lines that intersect at the poles

• 0 degrees = Prime Meridan (passes through Greenwich, England)

• 180 degrees = halfway around earth (roughly approx. international dateline

• 0 - 180 deg west of Greenwich = Western Hemisphere

• 0 - 180 deg east of Greenwich = Eastern Hemisphere

• longitudinal distances vary with distance from the equator

  • at 90 deg latitude, 1 deg longitude = 0km

how are latitude and longitude used to describe our location on the surface of the Earth?

in degrees-minutes-seconds, or decimal fractions of degrees

What direction does earth rotate on its axis? What is the rate of this rotation per hour?

The earth rotates about its axis in an eastward direction at a rate of 360 degrees/24 hours = 15deg/hour

what latitudes is UMass at? what climate is this?

UMass is in the mid-latitudes (temperate climate belt) of the Western Hemisphere

LORAN-C

• long range navigation

• land based, hyperbolic radio navigation system using low frequency radio transmitters in multiple deployment to determine the location and speed of the receiver

GPS

• global positioning system

• U.S operated global navigation satellite system

• provides reliable positioning, navigation, and timing services to worldwide users on a consistent basis any weather, anytime, anywhere on Earth using satellites, tracking systems, and receivers

  • positions and elevation determined using trigonometry (triangulation) and satellites

What has LORAN-C been replace by and for what purposes?

LORAN-C (land-based radio signal) has been replaced by GPS (satellite-based global positioning system) for navigation at sea (and land)

What is the time difference (earlier/later) depending on your position?

• time is later to the east of your position

• earlier to the west

How many degrees longitude is one hour time difference?

15 degrees

chronometer

seaworthy clock invented by John Harrison; used to measure time accurately at sea

How do you calculate time location with a chronometer?

• earth rotates toward the East (eastward) at a rate of 360deg/24hrs = 15deg/hr

• record time of chronometer at noon (sun directly overhead

• compare ship time (at noon) with Greenwich time (clock)

• how many hours ahead of behind Greenwich time?

sextant

handheld device used to measure the angle between the horizon and a celestial object; helpful for latitude

equation to calculate time difference using longitude?

longitude/15deg per hour = time difference (hours)

equation to convert degrees-minutes-seconds into decimal degrees?

decimal degrees = degrees + (min/60) + (sec/3600)

how do you calculate latitude in the northern hemisphere with a sextant?

your position is the angle measured between the North Star (polaris) and the horizon

in the north pole, where is the north star above you? what is the angle measured on a sextant?

directly above you; 90 degrees N latitude

at the equator, where is the north star? what angle is measured on the sextant?

north star is on the horizon; 0 degrees latitude

Eratosthenes

• lived in capital city of Alexandria on Nile Delta (latitude 31.2N)

• noticed at high noon 6/21 (summer solstice) sun directly overhead in city of Syene in southern Egypt in well w/out touching sides

• but the sun cast a shadow of a tall monument that made an angle of 72deg w top of actual monument where he lived

• knew dist. between two cities → used this info to accurately estimate Earth’s circumference w/ trig (about 40,000 km or 24,000 mi)

Pytheas

• 325 BC Greek astronomer-geographer Pytheas worked out simple method for determining latitude:

  • determine the angle between the horizon and the North Star (Polaris)

how was the ocean floor originally mapped?

using weighted lines lowered from ships — soundings — to reveal water depth and ocean basin features

bathymetric maps

depict the topography, or relief of the seafloor; isobaths connect points of equal depth

echo sounder

• sound source & receiver (hydrophone) on ship

• high frequency sound waves travel from the ship, through the water, reflect off the seafloor, and return to the ship where they are recorded by the hydrophone

• provide continuous 2D depth profiles of the seafloor along a ship’s track

velocity formula

v = dist./time → depth/time

depth formula

d = v*t

depth formula for echo sounding

d = (v)(t/2)

what do multibeam sonar (and sidescan sonar) show that echo sounders can’t?

allow 3D swaths of the seafloor to be mapped; overlapping swaths = complete coverage; side scan sonar produces high res images but takes very long

what kinds of waves are used in 2D and 3D seismic reflection surveys? what do they reveal?

• lower frequency sound waves

• reveal the sub-seafloor structure of the sediments and crust below the seafloor

  • used extensively for science and in the exploration of natural resources (hydrocarbon exploration)

satellites

• equipped w/ precise altimeters, can map the ocean floor

• the ocean surface is distorted by gravitational features of the seafloor

Matthew Maury

“Pathfinder of the Seas”; constructed the first ocean-wide bathymetric map

How is the Earth layered?

it’s layered by density:

• inner — solid

• outer — liquid

• FeNi nore

• dense silicate mantle

• less dense crust

• ocean, atmosphere

seismic waves. what are the 3 kinds?

generated by earthquakes (seismic energy, seismicity) allow us to study the internal structure of the Earth.

• compressional (P-waves) travel fast through Earth

• shear waves (S-waves) travel slower through earth, but cannot travel through liquids

• rayleigh waves travel along the surface of the earth

why is mapping the ocean important?

• help us find both renewable and nonrenewable natural resources

• U.N. law of the sea provided each coastal country w 200 nautical mile zone of jurisdiction of natural resources: Exclusive Economic Zone (EEZ)

• natural hazards

• national defense

refraction of seismic waves; what can this tell us about the structure of the Earth?

P-waves and S-waves bend (refract) when they pass from a material of one density into a material with a different density

measuring arrival times of P and S waves around the globe from many earthquakes → clear that our Earth is layered in concentric spheres of different composition and velocity

how do we know the age of the Earth and our Solar system?

• radiometric dating of meteorites found on earth + rocks brough back from the moon (meteorites abt 4.56 billion yrs (Ga))

• oldest rock on earth → 4.0 billion years

• early earth very hot w/ high heat flow and rapid degassing (volcanism), and intense meteorite bombardment

how do we know the composition of earth’s early atmosphere?

we know based on composition of gases being emitted by volcanoes today (derived from the mantle)

where did all the water come from to fill the ocean? where is most of it from?

• most of our surface water is derived from the Earth’s mantle via volcanism

  • volcanic gases rich in H2O → earth cooled and water vapor condensed → accumulated as liquid water

• some of earth’s surface water may be extra-terrestrial origin (comets made of ice)

what are the two types of crust on Earth? what does this say about the composition of the earth

oceanic crust & continental crust → why we have continents and ocean basins

characteristics of oceanic crust

• thin, more dense

  • dark colored mafic rocks like basalt

• forms ocean basins

• subducted at trenches during collision

characteristics of continental crust

• thick, less dense

  • light-colored felsic rocks like granite

• “buoyant” continents stand high

• preferentially preserved during collision

continental shelf

the submerged portion of the continent; the edge of the continent is NOT the shoreline; the edge of the continent is beneath the continental slope

lithosphere. what does it include?

• rigid outer shell of the earth

• includes the two types of crust + uppermost mantle

asthenosphere

• low strength, ductile part of upper mantle

• solid rock flows and deforms like silly putty

isostasy. how does this relate to the aesthenosphere and lithosphere?

a condition of equilibrium maintained between crustal blocks of different thickness and density

• the ductile aesthenosphere supports the rigid lithosphere

  • aesthenosphere and lithosphere can accommodate changes in the redistribution load (ice sheets, volcanoes, mtns)

  • the lithosphere is in isostatic equilibrium w/ underlying aesthenosphere

what causes the aesthenosphere to be in motion?

earth’s core loses heat through conduction to the mantle

what are tectonic plates? how do we know they exist?

• a number of rigid pieces the lithosphere is broke into

• the distribution of earthquakes and volcanoes; “Ring of Fire”

three kinds of plate boundaries?

• convergent

• divergent

• strike-slip

convergent boundaries

• converge at trenches (mark plate boundaries)

• subduction of one plate beneath another (downwelling)

• old oceanic crust is recycled back into the mantle w/ volcanism on the overriding plate

• deep focus earthquakes along slope of subducting slab

divergent boundaries

• plates move apart; plate boundaries marked by mid ocean ridges underwater and rift valleys

• new oceanic crust produced at spreading centers by material produces from the mantle (upwelling)

• marked by volcanism in/near central rift valley

strike slip boundaries

• 2 plates slide past one another along transform faults

passive continental margins; why are they passive?

• form during continental break up (rift to drift) and the formation of new ocean basins

• spreading center = plate boundary, not continental margin

• one continent becomes 2, with an ocean basin in between

passive bc there’s no subduction, volcanism, or seismicity

what causes the plates to move?

• convection in the aesthenosphere (like boiling water)

• ridge push

• slab pull

passive continental margins

• continental shelf

  • offshore submerged portion of the continent

• continental slope

  • underlain by thinned continental crust; dissected by numerous submarine canyons

• continental rise

  • thick accumulation of terrigenous sediments at base of the slope (deep-sea fans)

active continental margins

• trenches (deep, long, narrow, steep-sided troughs) mark subduction zones

  • convergent plate boundary; seismically active due to subduction of one plate beneath another

  • associated w/ volcanism landward of the trench on overriding plate

• accretionary prism

  • zone at trench where sediments are squeezed due to convergence of 2 plates

• tend to be narrower than passive margins

ocean basins

• abyssal plains — deep, extensive, virtually flat plains

• volcanoes — island, atolls, guyots, seamounts, abyssal hills

• oceanic ridges & rises (spreading centers)

  • active volcanic mountain ranges rising 2-3km above abyssal plains

  • divergent plate boundary where new oceanic crust is produces

  • seismically active, extensive hydrothermal activity

  • fault scars cut across and off-set these features (transform faults and fracture zones) — transform faults are also plate boundaries