Online quiz #8 Flashcards
(36 cards)
Which of the following is the best statement of the principle of original horizontality?
-Metamorphic isograds are horizontal before deformation.
-Igneous intrusions form horizontal layers.
-Most igneous, metamorphic, and sedimentary rocks in Earth’s crust form horizontal layers.
-Sediments are deposited as horizontal layers.
Sediments are deposited as horizontal layers.
An undeformed sedimentary layer is ______ than the layer above and ______ than the layer below.
older; younger
The principle of superposition states that
undisturbed sedimentary layers get progressively younger from bottom to top
Fossils are most common in which rock types?
sedimentary
What is an unconformity?
a gap in the geologic record
A disconformity is _
an erosional surface between horizontal layers of sedimentary rocks.
What is an erosion surface that separates two sets of sedimentary layers with nonparallel bedding planes?
angular unconformity
When did the Mesozoic era begin?
251 Million years ago
Almost nine-tenths of Earth’s history occurs during the
Precambrian
Which of the following statements regarding radiometric dating is true?
Sedimentary rocks can be dated more easily than igneous rocks.
After two half-lives, no radioactive atoms remain.
The radioactive decay product is called the parent atom.
Carbon-14 cannot be used to date material more than 100,000 years old.
Carbon-14 cannot be used to date material more than 100,000 years old.
Which of the following can change the rate of radioactive decay?
changes in temperature
chemical reactions
changes in pressure
none of the above
None of the above
A rock formed with 1000 atoms of a radioactive parent element, but contains only 250 radioactive parent atoms today. If the half-life for the radioactive element is one million years, how old is the rock?
2 million years
Radiometric dating is least useful for dating __________ rocks.
sedimentary
Human beings (homo sapiens) evolved during which geologic era?
The Cenozoic
The absolute age of a geologic event in the rock record is
the number of years that has elapsed between the event and the present day.
Abrupt changes in the faunal succession in the rock record represent
mass extinction events
The largest mass extinction event in Earth’s history took place at the end of
Permian period
The half-life of a radioactive isotope is
the time it takes for half of the radioactive atoms to decay
A radioactive element inside has been decaying for 2 million years? Given that the half-life is 500,000 years, what percent of the parent is currently left?
6%
A radioactive isotope has decayed to the point that one-eighth of the original content is left. How many half-lives have passed?
To determine how many half-lives have passed, you need to see how many times the original amount has been halved to reach one-eighth of its initial value.
- After 1 half-life, the isotope has 1/2 of the original amount.
- After 2 half-lives, it has 1/4 of the original amount.
- After 3 half-lives, it has 1/8 of the original amount.
So, 3 half-lives have passed!
Who came up with the principle of faunal succession?
William Smith
Who invented the geologic map?
William Smith
The first geologic map covering an entire country was for
England
Before the division of the geologic time scale into eons, the Hadean, Archean, and Proterozoic eons were collectively called
Precambrian time
