to go out on a narrow point with a jackhammer, the tourist said no, because the rocks might fall off and slide
down into the Canyon. When the professor pointed out the many places that rocks had fallen off and slid down,
the quickwitted tourist figured out that the Canyon has been widened by such rockfalls as the river has cut
downward.
6.
The age of the Earth can be estimated in many ways. Which statement below is most accurate (remember that
uniformitarian calculations involve looking at the thickness and type of sedimentary rocks, and similar things, but
do NOT include radiometric dating or counting of annual layers)?
A) Annuallayer counting shows that the Earth is more than about 100 million years old.
B) Annuallayer counting shows that the Earth is more than about 100 thousand years old, uniformitarian
calculations show that the Earth is more than about 100 million years old, but we don’t know how to estimate how
Points Earned:
1.0/1.0
Correct Answer(s):
C
Points Earned:
1.0/1.0
Correct Answer(s):
E
Points Earned:
1.0/1.0
Correct Answer(s):
D

11/3/2016
RockOn #10
3/8
much more than 100 million years the Earth is.
C) Annuallayer counting shows that the Earth is more than about 100 thousand years old, uniformitarian
calculations show that the Earth is more than about 100 million years old, and radiometric techniques tell us how
old the Earth is.
D) Annuallayer counting shows that the Earth is 4.6 billion years old.
E) Uniformitarian calculations show that the Earth is 4.6 billion years old.
7.
One practical radioactive system used to date lava flows involves:
A) The gas argon40, which decays to the gas potassium40.
B) The gas argon40, which decays to solid potassium40.
C) The solid potassium40, which decays to solid argon40.
D) The solid potassium40, which decays to the gas argon40.
E) The solid potassium40, which decays to the solid moosemossium41.
Feedback:
Potassium40 is common in solid minerals, and decays to produce the gas argon40. And despite his
great contributions to humanity, no one has named an isotope after moose moss (the favorite food of Thidwick,
for you Dr. Suess fans).
8.
You start with 400 parent atoms of a particular radioactive type, which decays to give stable offspring. You wait
just long enough for three half lives to pass. You should expect to have how many parent atoms remaining (on
average):
A) 400.
B) 200.
C) 100.
D) 50.
E) 25.
Feedback:
After one halflife, you’ve gone from 400 parents to 200; after a second halflife you go from 200
parents to 100, and after a third halflife you go from 100 parents to 50. (Typical studies of radioactive decay use
many more atoms, to avoid statistical fluctuations, but the question says “on average”, so we asked you about 400
rather than 400,000,000,000,000 to make the math easier.)
9.

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- Fall '08
- ALLEY,RICHARDBANANDAKRISHNAN,SR
- Rockon 10, Quiz 10, Correct Answer