Geology 001B                                                                                      West Valley College

Historical Geology                                                                                   R. Lopez


Study Questions: Geological Time


1)      What sets geology as a science apart from other sciences?



2)      What is Deep Time?



3)      How old is the Earth?



4)      What is this age based on, in other words, what did we use to date the origin of the Solar System and planet Earth?



5)      Know who made the early estimates of the Earth’s age: Archbishop Ussher, John Jolly.



6)      What is Uniformitarianism?  What is Actualism?  What is the modern view of Uniformitarianism?



7)      Who was James Hutton and what was his contribution to geology?



8)      Who was Charles Lyell and what was his contribution to geology?



9)      Who was Nicolas Steno and what principles did he conceive?



10)  Describe Neptuism and Catastrophism.  What were the problems with these hypotheses?



11)  Geologists deal with two types of ages (i.e. time).  What are they and how do they differ?




12)  Discuss and apply the principles used to determine relative ages as discussed in lecture (superposition, original horizontality, lateral continuity, cross-cutting relations, inclusions or xenoliths).




13)  Name four primary structures in rocks that can be used to determine if beds have been overturned (three found in sedimentary rocks and one in lavas)?




14)  What is an unconformity?  Definitely be able define and distinguish between disconformity, nonconformity, and angular unconformity?




15)  Be able to work out the relative ages (youngest to oldest) of the rock units, unconformities, and faults on diagrams like we did in class.




16)  Who was Lord Kelvin, how old did he calculate earth to be, and what was his reasoning?




17)  What was the final blow to Lord Kelvin’s calculation of a young earth?




18)  Know, be able to use, and arrange in order the following terms from the geological time scale (see Appendix page 584):  Precambrian, Hadian, Archean, Proterozoic, Phanerozoic,  Paleozoic,  Mesozoic,  and Cenozoic.  Also know the periods of the Paleozoic, Mesozoic and two periods of the Cenozoic (Tertiary and Quaternary) as well as the epochs of the Tertiary and the Quaternary.





19)  What is the geologic column and what is stratigraphy?




20)  Define fossils, fossil correlation, and fossil succession (Who was William Smith?)




21)  What are the two major subdivisions of geologic time?





22)  What was Lord Kelvin’s argument for a young Earth?





23)  What is absolute dating based on?  Be able to define “atomic number of element” and mass number of an isotope.  What is an isotope?  Give some examples of isotopes.





24)  Be able to explain the concept of half-life using the example of some given number of parent atoms with a specific half-life (e.g. one hour).  Be able to calculate the ratio of parent to daughter atoms after some given amount of time has passed.





25)  Name examples of parent-daughter pairs used in absolute dating, and know the approximate half-life of the parent isotope (see your text Table 6-2 page 165).





26)  The radioactive parent Carbon-14 isotope decays to the stable daughter isotope of Nitrogen-14.  The half-life of this isotopic system is 5730 years.  If you measured and Parent/Daughter ratio of 25/75 is a piece of charcoal, how many half lives have elapsed?




27)  What is the age of this piece of charcoal?




28)  How many half lives have elapsed if you measure a P/D ratio of 75/25?  Use the U-238/Pb-206 isotopic pair with a half-life of 4.46 Ga.  What is the age of the sample?





29)  What is stratigraphic correlation?





30)  What are radioactive isotopes, radiogenic isotopes, protons, and neutrons?




31)  What is Half-Life?



32)  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.





Definitions Related to Study Questions 6: Geological Time


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.

12)  Half life: time needed for the number of parent atoms to be reduced by one-half.