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
- The
Juan de Fuca Plate is a fragment of the old __Farallon_______
Plate.
- The
Late Heavy Bombardment period ended roughly ___3.8__ billion years ago.
- The
relatively hot layer of Earth immediately beneath the lithosphere is
called the _asthenosphere__.
- The
‘expanding globe theory’ of plate tectonics was promoted by __Sam______ __Carey__ (name).
- The
largest impact crater we see preserved on Earth is located at
______________ _Sudbury__.
- If a
10 m diameter meteoroid impacted Earth, we might expect to see a crater
measuring about __150-200km___
diameter.
- Although
not strictly correct, we commonly use a factor of ___4____ (number) – times background as an
indicator of mass extinction.
- ‘Sand
blows’ are little sand pyramids produced by a process called __liquefaction____.
- Name
one of the two types of surface seismic waves. _Love/Raleigh__.
- An
explanation of the observed paleomagnetic patterns near spreading ridges
was first proposed in 1963 by __Vine and Matthews________.
- The
current seismic activity in such US
states as Nevada and Utah
is initiated by what type of stress action? _extension_________.
- Is it
true that during ‘elastic stress’ the deformation produced in any object ALWAYS
disappears when the stress is removed? __YES____.
- 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.
- Astronomical
unit: Distance from Earth to Sun
- Meteor:
‘Fireball’ of light made as a space object interacts with Earth’s
atmosphere.
- Iron
catastrophe: Very rapid gravitational collapse of heavy
metals (particularly iron) to Earth’s core in early period of
differentiation.
- Isotope:
one of 2 or more atoms of an element with same
atomic number but different number of neutrons.
- Stishovite:
Very high pressure form of SiO2; formed
only by impact event.
- Paleoseismology:
study of seismic features from older rocks.
Part C: Each
question has a value of 5; total
value of Part C: 35.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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
- 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%.