THE UNIVERSITY OF WESTERN ONTARIO

Fall Term 2003………………Mid-Term Test

Earth Sciences 240A (Section 001)

PLEASE HAND IN THIS SHEET WITH YOUR EXAM BOOKLET

 

NAME: ____________________________________ Student #: __________________

Part A: Each Question has a value of 1; total value of Part A: 13

  1. The Juan de Fuca Plate is a fragment of the old __Farallon_______ Plate.
  2. The Late Heavy Bombardment period ended roughly ___3.8__ billion years ago.
  3. The relatively hot layer of Earth immediately beneath the lithosphere is called the _asthenosphere__.
  4. The ‘expanding globe theory’ of plate tectonics was promoted by __Sam______ __Carey__ (name).
  5. The largest impact crater we see preserved on Earth is located at ______________ _Sudbury__.
  6. If a 10 m diameter meteoroid impacted Earth, we might expect to see a crater measuring about __150-200km___ diameter.
  7. Although not strictly correct, we commonly use a factor of ___4____ (number) – times background as an indicator of mass extinction.
  8. ‘Sand blows’ are little sand pyramids produced by a process called __liquefaction____.
  9. Name one of the two types of surface seismic waves. _Love/Raleigh__.
  10. An explanation of the observed paleomagnetic patterns near spreading ridges was first proposed in 1963 by __Vine and Matthews________.
  11. The current seismic activity in such US states as Nevada and Utah is initiated by what type of stress action? _extension_________.
  12. Is it true that during ‘elastic stress’ the deformation produced in any object ALWAYS disappears when the stress is removed? __YES____.
  13. In the equation of kinetic energy (as we use it in this course), which provides a greater contribution: mass or velocity? ___velocity____

 

Part B: Each question has a value of 3; total value of Part B: 18

Define each of the terms.

  1. Astronomical unit: Distance from Earth to Sun
  2. Meteor: ‘Fireball’ of light made as a space object interacts with Earth’s atmosphere.
  3. Iron catastrophe: Very rapid gravitational collapse of heavy metals (particularly iron) to Earth’s core in early period of differentiation.
  4. Isotope: one of 2 or more atoms of an element with same atomic number but different number of neutrons.
  5. Stishovite: Very high pressure form of SiO2; formed only by impact event.
  6. Paleoseismology: study of seismic features from older rocks.

 

 

Part C: Each question has a value of 5; total value of Part C: 35.

  1. Explain why the monetary cost of catastrophes continues to increase dramatically.

Human population increase means that people are living in increasingly unstable environments; examples are flood plains, sea shores, hurricane-prone regions, earthquake-prone areas, etc.

  1. Who was Nicholas Steno and what contribution(s) did he make to geology?

Italian philosopher. Devised aids for relative age dating: Principles of Superposition, Original Horizontality, Original Lateral Continuity.

  1. Explain briefly how carbon dating works.

N14 of atmosphere converted by cosmic radiation to C14; incorporation of all C isotopes into living organisms (in whatever ratio existed in the atmosphere at the time). Upon death of organism, reversal takes place (C14 to N14). Use of analysis of C12/C14 ratio and knowledge of C14 decay half-life allows calculation of time since death.

  1. List 5 features you should see in and around a large impact crater.

A number were possible, but easiest to recall are:

      - breccia

      -disrupted strata

      -overturned rim rocks

      -ejecta blanket

      - central peak (if over 4 km)

      - high pressure forms of silica: coesite/stishovite

      -deformed mineral fragments

      -tektites

You would be VERY much less likely to find bits of the meteorite, Ir in the soil, tsunami deposits.

 

  1. Explain the theory of elastic rebound.

This can be stated in a number of ways, but essentially it’s the statement that movements along a fault are the result of abrupt releases of stored energy, after which the rocks on either side of the fault are stress-free.

  1. Name the 3 types of plate boundaries; note what type of stress is responsible for each; and indicate one geographic location where such a boundary exists.

Divergent – tensional stress – Mid-Atlantic Ridge

Convergent – compressional stress – west coast of South America

Transform – shear stress – San Andreas Fault

  1. Detail how you should go about locating the site where an earthquake began.

Triangulation using at least 3 seismographs. Measure of time interval between P and S waves at each site; use of standard graph correlating the P-S time to distance making the assumption that seismic wave travel correlates to ‘average’ velocity; construction of circles on map about each site corresponding to determined distance; epicenter is location of unique circle intersection.

 

Note: the total value of the above questions is 66%;

your mark will be pro-rated to 100%.