An unconformity is a buried ________.
surface of erosion separating younger strata above from older strata below
The radioactive isotopes uranium-238, uranium-235, and thorium-232 eventually decay to different, stable, daughter isotopes of ________.
Which of the following best characterizes an angular unconformity?
Tilted strata lie below the unconformity; bedding in younger strata above is parallel to the unconformity.
Consider the names of the eras in the geologic time scale. What is meant by "zoic"?
life; living things
What fundamental concept states that in a horizontal sequence of conformable sedimentary strata, each higher bed is younger than the bed below it?
law of superposition
What of the following refers to the investigative process by which geologists identify and match sedimentary strata and other rocks of the same ages in different areas?
The ________ is the idea or concept that ancient life forms succeeded each other in a definite, evolutionary pattern and that the contained assemblage of fossils can determine geologic ages of strata?
principle of faunal succession
Which of the following is an essential characteristic of an index fossil?
The organism only lived for a short period of geologic time.
The half-life of carbon-14 is about 6000 years. Assume that a sample of charcoal is formed by burning of living wood 15,000 years ago. How much of the original carbon-14 would remain today?
between one-fourth and one-eighth
Visualize five, horizontal, sedimentary strata exposed in a cliff or canyon wall identified by consecutive numbers, 1 being the lowest bed and 5 being the highest. Which of the following statements concerning the strata are true?
beds l and 3 are older than bed 4
Which of the following denotes the divisions of the geologic time scale in correct order of decreasing lengths of time beginning with the longest time interval and ending with the shortest?
eon, era, period, epoch
Assume that man's recorded history can be stretched back to 4600 years before the present. This is approximately what fraction of geologic time?
________ is an erosional contact between tilted, older strata below and horizontal, younger strata above.
An angular unconformity
Sandstone strata and a mass of granite are observed to be in contact. Which of the following statements is correct geologically?
The granite is older if the sandstone contains pebbles of the granite.
Abundant fossil evidence did not appear in the geologic record until about ________.
550 million years ago
___________ era could also be called the "Age of Flowering Plants." Flowering plants (angiosperms) strongly influenced the evolution of both birds and herbivorous mammals.