Geologic time

What is the source of natural carbon-14?

Cosmic ray collisions and neutron-capture involving atmospheric nitrogen.

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 is the final stable breakdown product of the radioactive isotopes uranium-238, uranium-235, and thorium-232?

Lead

Which two Paleozoic periods used in North America are combined into the Carboniferous period in Europe and elsewhere?

Mississippian and Pennsylvanian

Who made the first clear statement of the law of superposition? When?

Nicolas Steno; 17th century

Assume that man's recorded history can be stretched back to 4600 years before the present. This is approximately what fraction of geologic time?

One millionth.

In which process of fossilization are the internal cavities and pores of the original organism filled with mineral matter?

Petrification or petrifaction

What happened to create an unconformity?

The older strata below were eroded before the younger layers were laid down.

Which of the following is an essential characteristic of an index fossil?

The organism only live for a short period of geologic time over a broad area.

Which of the following best characterizes an angular unconformity?

Tilted strata that lie below the unconformity; bedding in younger strata above is parallel to the unconformity.

What concept states that "ancient life forms succeeded each other in a definite, evolutionary pattern and the contained assemblage of fossils can determine the geologic age of the strata"?

principle of faunal succession

What is the age of Earth accepted by most scientists today?

4.5 billion years

Complex, invertebrate life forms are common as fossils beginning with marine strata of Cambrian age. How long ago did the Cambrian period begin?

542 million years

What is the maximum limit on carbon-14 dating?

70,000 and 75,000 years

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 1 and 3 are older than bed 4.

The percent of remaining parent isotope in a radioactive decay process is 40 percent. How many half-lives have elapsed since the material was 100 percent parent atoms?

Between 1 and 2

Which of the following is not a very long-lived, radioactive isotope?

C-14

Which of the following investigative processes do geologists use to identify and match sedimentary strata and other rocks of the same ages in different areas?

Correlation

What type of unconformity is an erosional contact between tilted, older strata below and horizontal, younger strata above?

An angular unconformity

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, and epoch

Which of the following geologic observations would not bear directly on interpreting the sequence of geologic events in an area?

The feldspar and quartz content of a granite.

Sandstone strata and a mass of granite are observed to be in contact. Which of the following statements is correct?

The granite is older if the sandstone contains pebble of the granite.

In the names of geologic eras, what does the suffix "zoic" mean?

The suffix "zoic" means life (i.e., living things).