Geological Time Flashcards
What principles of geologic time did
Nicolas Steno discover? Hutton?
Steno created relative age dating practices like original horizontality and superposition.
Hutton-erosional unfonformity
What does “superposition” mean? Give
an example.
oldest beds on bottom, youngest on the top
What other principles of relative geologic
age-dating do geologists use to analyze
the ages of rock?
cross cutting relationships, dating strata, dating intrusions, dating inclusions, dating unconformites.
How does the geological age of a pebble
of granite compare to the age of the
conglomerate of which the pebble is a
component?
The pebble of granite that is within the conglomerate is older than the conglomerate itself.
How does the geological age of a granitic
intrusion compare to the “country” rock
which contains it?
The intrusion is younger than all the country rock beds which it passes through.
How does the geological age of the
famous San Andreas Fault in California
compare to the “country” rock through
which it cuts? Explain.
The San Andreas Fault is younger than all of the country rock that it intrudes through.
What was James Hutton’s famous
discovery?
deep time and eroisional unconformity
What is an “unconformity”? How is an
unconformity recognized in some strata?
the boundary between underlying strata and the newly deposited strata.
Who was William Smith? What principles
did William Smith discover?
He discoverd fossil succession.
What does “Silurian” refer to? Does
Alabama contain any “Silurian” age
rocks?
An age of rock history. No.
What are some methods by which
scientists of the 18th and 19th centuries
tried to determine the “age of the Earth”?
Paleontological Stratigraphy, Numerical Stratigraphy
Loss of heat energy, radioactivity, earth cooling time
What is radioactivity? What is radioactive
decay?
Radioactivity- particles emitted from nuclei as result of nuclear instability.
Radioactive decay- nuclear transformation of one isotope to another
What atomic particles can be found in the
nucleus of an atom?
protons and neutrons
What does “atomic number” refer to?
What does “atomic mass” refer to?
atomic # - number of protons
atomic mass - number of protons and neutrons
How does a parent isotope differ from a
daughter isotope? Give an example for
potassium-40.
a daughter isotope is the result of radioactive decay. K-40 has a daughter isotope of Ar-40
What are the “rules” of radioactive decay?
Explain each one.
Electron capture
Explain what happens during electron
capture. Give an example.
protons transform into neutrons
What is a “half-life”? Explain. Give an
example.
you know what a half life is
Name some isotopes with different halflives?
C14->N14, K40->Ar40, U->Th
What is a “parent decay curve”? What is a
“daughter growth curve”? Explain.
parent isotopes decrease with decay, and daughter isotopes increase with decay
What is the rule by which the amount of a
parent isotope changes with each
additional half-life?
50%
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!)
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!)
What are “bracketed” numerical ages?
Give an example.
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.
