Physical
Geology R.
Lopez
1)
Geologists
deal with two types of ages (i.e. time).
What are they and how do they differ?
2)
What
are the five principles used to determine relative ages. State a definition or
give an example of each on.
3)
Who
is credited for the first three relative time principles?
4)
Who
is credited for the last two relative time principles?
5)
Who
was Charles Lyell? What book and when did he publish this work?
6)
What
is the connection between Darwin’s On The
Origin of Species and the work done by Lyell?
7)
What
is the principle of uniformitarianism and who is credited for this principle?
8)
Name
three of the four primary structures (paleo-up indicators) in rocks that can be
used to determine if beds have been overturned (three found in sedimentary
rocks and one in lavas)? Be able to
recognize these structures in slides.
9)
What
is an unconformity?
10)
Distinguish
between disconformity, nonconformity, and angular unconformity? Draw sketches of each below.
11)
Work-out
the relative ages (youngest to oldest) of the rock units, unconformities, and
faults on Pamala Gore’s Historical Geology Lab (I always use one of her
diagrams on our exam): relative
time exercises.
12)
What
experiment did Lord Kelvin do to claim that he destroyed the uniformitarian
foundation?
13)
What
did Henri Becquerel discover to level a heavy blow to Lord Kelvin?
14)
Explain
the Pb-Pb or U/Pb evolution curve for the age of Earth (the one that used
meteroites and well mixed terrestrial sediment).
15)
What
is absolute dating based on? Be able to
define “atomic number” and atomic mass number of an isotope.
16)
What
are good isotopes for dating old rocks?
17)
What
is a half life (T½)?
18)
Radioactive
C-14 decays to stable daughter isotope N-14.
The T½ = 5730 years.
If you measure a P/D ratio of 6.25/93.75, how many
half-lives have elapsed?
19)
What
is the age of the sample measured in the problem above.
20)
Name
examples of parent-daughter pairs used in absolute dating, and know the
approximate half-life of the parent isotope.
21)
Read
“The Asteroid Impact Theory Becomes Testable” at the following url: (http://rainbow.ldeo.columbia.edu/courses/v1001/23.html) You will have to scroll down to get the
outline numberal II. Most geologists
now accept that the dinosaurs were wiped out by a cataclysmic asteroid impact. What are some of the lines of evidence that
support Dr. Alvarez’s theory?
22)
In
the Asteroid article, what is the significance of the element iridium?
23)
What
could have caused the spike in iridium in the clay layer and what two
hypotheses did the Alvarez’s propose?
24)
What
is a supernova?
25)
What
was their argument against the supernova hypothesis for the spike in
iridium?
26)
Where
is the location of the K-T impact crater?
27)
What
is the age of the Earth?
28)
Using
our decay equation, determine the age of the following rocks using the
235U-207Pb isotopic system (l = 9.8485x10-10/yr): Sample 1 – D = 2722, N = 85; Sample 2 –
D = 998, N = 555; Sample 3 – D = 122, N = 111; Sample 4 – D = 1555, N = 1001.
1)
Relative time simply deals with the order
of events; no information on how long the events lasted or the length of time
between events.
2)
Absolute time assigns absolute age to
events, usually in “years before present”. 1 Ma = one million years before present.
3)
Superposition: in any sequence of strata
not overturned, the order of deposition is bottom to top.
4)
Original horizontality: water-laid sediments are deposited in strata that are horizontal.
(Note: cross beds are within beds or
strata.)
5)
Use
of inclusions: a rock or sediment containing fragments or
other rocks must be younger than the rocks it contains.
6)
Unconformity: a break or gap in the stratigraphic record. Also, a hiatus; i.e. a lapse in time.
7)
The
nucleus of an atom contains protons
(+ charge) and neutrons (no charge, or you can think of a neutron as having
both a + and – charge which balance each other).
8)
Atomic number: an element is defined by its atomic number, that is the number of
protons in the nucleus of the atom. All
atoms of an element have the same atomic number.
9)
Atomic weight (mass number) of an atom is
the sum of its protons and neutrons.
For example, the most common atoms of oxygen contain eight protons and
eight neutrons, and thus have an atomic weight of 16.
10)
Isotopes: atoms of an element that
contain different numbers of neutrons, and consequently, have different atomic
weights or mass numbers.
11)
Radioactive Isotopes: isotopes that spontaneously
transform into either a more stable isotope of the same element or an isotope
of a different element. Parent isotopes
decay to daughter isotopes. Energy is produced with radiometric decay.
12)
Half life: time needed for the number
of parent atoms to be reduced by one-half.