Geological Time

Question 1

What principles of geologic time did
Nicolas Steno discover? Hutton?

Answer 1

Steno created relative age dating practices like original horizontality and superposition.

Hutton-erosional unfonformity

Question 2

What does “superposition” mean? Give
an example.

Answer 2

oldest beds on bottom, youngest on the top

Question 3

What other principles of relative geologic
age-dating do geologists use to analyze
the ages of rock?

Answer 3

cross cutting relationships, dating strata, dating intrusions, dating inclusions, dating unconformites.

Question 4

How does the geological age of a pebble
of granite compare to the age of the
conglomerate of which the pebble is a
component?

Answer 4

The pebble of granite that is within the conglomerate is older than the conglomerate itself.

Question 5

How does the geological age of a granitic
intrusion compare to the “country” rock
which contains it?

Answer 5

The intrusion is younger than all the country rock beds which it passes through.

Question 6

How does the geological age of the
famous San Andreas Fault in California
compare to the “country” rock through
which it cuts? Explain.

Answer 6

The San Andreas Fault is younger than all of the country rock that it intrudes through.

Question 7

What was James Hutton’s famous
discovery?

Answer 7

deep time and eroisional unconformity

Question 8

What is an “unconformity”? How is an
unconformity recognized in some strata?

Answer 8

the boundary between underlying strata and the newly deposited strata.

Question 9

Who was William Smith? What principles
did William Smith discover?

Answer 9

He discoverd fossil succession.

Question 10

What does “Silurian” refer to? Does
Alabama contain any “Silurian” age
rocks?

Answer 10

An age of rock history. No.

Question 11

What are some methods by which
scientists of the 18th and 19th centuries
tried to determine the “age of the Earth”?

Answer 11

Paleontological Stratigraphy, Numerical Stratigraphy

Loss of heat energy, radioactivity, earth cooling time

Question 12

What is radioactivity? What is radioactive
decay?

Answer 12

Radioactivity- particles emitted from nuclei as result of nuclear instability.

Radioactive decay- nuclear transformation of one isotope to another

Question 13

What atomic particles can be found in the
nucleus of an atom?

Answer 13

protons and neutrons

Question 14

What does “atomic number” refer to?
What does “atomic mass” refer to?

Answer 14

atomic # - number of protons

atomic mass - number of protons and neutrons

Question 15

How does a parent isotope differ from a
daughter isotope? Give an example for
potassium-40.

Answer 15

a daughter isotope is the result of radioactive decay. K-40 has a daughter isotope of Ar-40

Question 16

What are the “rules” of radioactive decay?
Explain each one.

Answer 16

Electron capture

Question 17

Explain what happens during electron
capture. Give an example.

Answer 17

protons transform into neutrons

Question 18

What is a “half-life”? Explain. Give an
example.

Answer 18

you know what a half life is

Question 19

Name some isotopes with different halflives?

Answer 19

C14->N14, K40->Ar40, U->Th

Question 20

What is a “parent decay curve”? What is a
“daughter growth curve”? Explain.

Answer 20

parent isotopes decrease with decay, and daughter isotopes increase with decay

Question 21

What is the rule by which the amount of a
parent isotope changes with each
additional half-life?

Answer 21

50%

Question 22

A. If a radioactive parent isotope has a
half-life of 1,000 years, what fraction of
parent will be left after 4,000 years?

B. If
the original number of parent atoms is
10,000, how many parent atoms remain
after 4,000 years?

C. How many daughter
atoms remain after 4,000 years?
(Answers on last page – don’t look ahead
and cheat yourself to a learning
experience!)

Question 23

A. If a geologic sample has ½ the original
amount of a radioactive parent isotope,
how many half-lives have passed since the isotope was trapped in the sample?

B. What fraction of the sample is now the daughter isotope?

C. If the original
number of parent atoms was 3,500, how
many parent atoms are left?

D. How many daughter atoms are present in the
sample?

E. If the parent half life is
400,000 years, how old is the sample?
(Answer on next page – don’t look ahead
and cheat yourself to a learning
experience!)

Question 24

What are “bracketed” numerical ages?
Give an example.

Answer 24

The age between two geological ages such as an igneous intrusion of 66 million and a certain type of stone of 120 million. So >60million but <120million would be a bracketed numerical age.

Question 25

How old are the oldest rocks in Alabama?

Answer 25

1 billion years as discovered to date.

Question 26

How old is the oldest known rock on
Earth?

Answer 26

4.28 billion years as discovered to date. Discovered in W. Greenland

Question 27

How old is the oldest known mineral on
Earth?

Answer 27

4.36 billion years as discovered to date.

Discovered in Australia

Question 28

How old is the Moon?

Answer 28

4.53 billion years

Question 29

How old is the Earth? How do we know?
Explain.

Answer 29

4.55 billion years. Based upon max age of meteorite in our milky way