Exam 1

Question 1

Averaged characteristics of the ocean? (depth, temp, salinity)

Answer 1

depth = 3.8 km
temp = 3.9 C
salinity = 34.5 g/kg

Question 2

Explain the origins of the ocean

Answer 2

Earth formed from accretion, meteorites contained water as ice, Earth was extremely hot so ice in meteorites was outgassed into the atmosphere (as water vapor), earth cooled down and there was a long period of rain that created the oceans

Question 3

Explain why life originated in the oceans

Answer 3

1) water has high specific heat so it had a stable temp
2) water is polar so it can hold lots of chemicals/nutrients
3) water is a good shield of solar radiation

Question 4

Old life hypothesis vs current life hypothesis of life in oceans?

Answer 4

Old: life began in shallow tidal pools (photosynthesis)
Current: life began near hydrothermal vents (chemosynthesis)

Question 5

Explain historical ocean exploration methods

Answer 5

1800s: point sediment samples (using weighted wires)
early 1900s: echo soundings (using sound waves to determine depth, temp, and salinity)
late 1900s: more advanced SONAR (multibeam and side scan)

Question 6

Main challenges to studying the ocean? (there are 5)

Answer 6

1) seeing through seawater (electromagnetic spectrum nearly completely absorbed by water)
2) pressure (1 atm increase for every 10m)
3) inaccessibility (long transport times/ remote areas/ very expensive equipment)
4) Conductivity (seawater very conductive… shorts), Corrosion (seawater very corrosive), bio-fouling (organisms will colonize on equipment)
5) weather

Question 7

Explain the electromagnetic spectrum in water

Answer 7

• all wavelength are eventually absorbed by water
• best transmission (lowest absorption) is the visible portion specifically
• blue has the longest transmission thus its reflected the most which is why everything is blue underwater
• exception: fluorescence (objects absorb one wavelength and emit another)

Question 8

Explain sonar in water

Answer 8

• compressional wave and is weakly absorbed by water but scattered eventually
• sound moves 1500 m/s in water
• this is how bathymetry is measured

Question 9

What is satellite altimetry?

Answer 9

using microwave pulses from satellites to measure sea surface elevation … altimetry can reflect bathymetry because sea surface will be slightly higher at ridges and slightly lower in basins

Question 10

What are the two types of seismic waves and what are their characteristics?

Answer 10

P-waves (compressional waves), arrive first, travel through solid, liquid, and gas, has two small shadow zones, vibrates parallel to wave propagation
S-waves (shear waves), arrive second, travel only through solid, has 1 large shadow zone, vibrates perpendicular to wave propagation

Question 11

How do velocities of waves change through earth’s interior?

Answer 11

Velocity increases with more density and more rigidity

Question 12

Fluid vs Liquid?

Answer 12

Fluid: substance that flows under an applied stress
Liquid: fluid that conforms to shape of its container

Question 13

How does buoyancy and gravity influence the layers of the earth?

Answer 13

Gravity causes fluids of different densities to form layers, negative buoyancy = more dense fluids sink, buoyancy = less dense fluids rise

Question 14

What are Earth’s layers?

Answer 14

• Crust = felsic (Al, Si, O) and mafic (Mg, Fe), least dense (3 g/cm^3)
• Mantle = ultramafic (Mg, Fe)
• Core = Ni and Fe, most dense (13 g/cm^3)
• crust (6 km), center of earth (6400 km)

Question 15

What are earth’s layers by physical properties?

Answer 15

• Lithosphere (crust and upper mantle) = rigid plates (100 km)
• Asthenosphere (rest of upper mantle) = partially molten
• Solid Mantle = (rest of mantle) = solid but can still undergo plastic deformation
• outer core = molten (liquid)
• inner core = solid

Question 16

What is the relation between pressure and phase?

Answer 16

melting/freezing and boiling/condensation points are functions of temp and pressure
- deep earth rocks can be solid despite the high temps
- phase of lithosphere and asthenosphere are more a function of temp than pressure

Question 17

Ocean crust vs Continental crust?

Answer 17

Ocean: denser (2.9 g/cm^3), more uniform, mafic, thinner (6 km), younger
Continental: less dense (2.7 g/cm^3), less uniform, felsic, thicker (30-70 km), older

Question 18

What is Archimedes’ principle?

Answer 18

mass of displaced fluid = total mass of floating solid

Question 19

Explain isostasy in Earth’s crust

Answer 19

crustal topography is balanced by displacement of denser mantle below
- airy isostasy: thicker crust has higher topography
- pratt isostasy: less dense crust rides higher (ocean ridges)

Question 20

What is a continental margin and what are the categories?

Answer 20

Continental Margin = where continental crust meets ocean crust
- continental shelf: submerged continental crust
- continental slope: continental sediments spill over boundary and cover oceanic crust (large slope)
- continental rise: sediments piled up on ocean floor
- abyssal plain: deep ocean, thick blanket of fine sediments, flat and featureless