Exam 18: Geologic Time

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

Consider the names of the eras in the geologic time scale. What is meant by "zoic"?

The remains or traces of prehistoric life are called _________.

Which of the following best characterizes an angular unconformity?

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

What term denotes blocks of older rock enclosed in a body of younger igneous rock?

In a given area where you have little knowledge of the local geology (rocks types, fossils, etc.), what type of unconformity would be the most difficult to recognize in an exposed sequence of rocks? Why?

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?

What process involves identifying and matching rocks of similar ages in different areas?

What kind of unconformity is produced when tilted, older strata are eroded and buried by younger strata?

What fundamental concept states that in a horizontal sequence of conformable sedimentary strata, each higher bed is younger than the bed below it?

Examine the illustration below (a cross section through the Earth as you might observe on the wall of a quarry or a road cut). Give two reasons why the granite must be older than the sedimentary layers.

What is the name of a Phanerozoic era that means ancient life?

Isotopes of what element are the stable, end products of both uranium decay series?

Which of the following describes radioactive decay by beta particle emission?

The half- life of carbon- 14 is about 6000 years. Assume that a sample of charcoal formed by burning of living wood 15,000 years ago. How much of the original carbon- 14 would remain today?

The ratio of parent to daughter isotopes in a radioactive decay process is 0.40. How many half- lives have elapsed since the material was 100% parent atoms?

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

Who is credited with formulating the doctrine of uniformitarianism?

You are asked to interpret the geologic history of a county in California where the geology is quite complex. Aside from visiting various sites in the county for observing geologic sites firsthand, you are permitted to request five different pieces of information or data to aid in your interpretation. List the five that you would choose and explain why each is important for your study.