Study Guide - GEY 101 - Exam III
Geologic Time

An unconformity if a buried what?

The radioactive isotopes uranium-238, uranium-235, and thorium-232 eventually decay to different, stable, daughter isotopes of what?

Describe and angular unconformity.

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

What are the three processes in which radioactive decay occurs?

Which two Paleozoic, geologic, time-scale periods used in North America are combined into the Carboniferous period in Europe and elsewhere?

What are the names of the eon in the geologic time scale?

What is necessary to describe the sequence of geologic events in an area?

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

What describes the means that are used to recognize, identify, and identify similar-aged strata in nearby areas or widely separated, different areas?

What 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?

What is characteristic of an index fossil?

Which geological eon denotes the first 800 million years of Earth history?

What gas is a radioactive daughter of the U-238 decay series that can accumulate to unhealthful levels in poorly ventilate uranium mines and home basements?

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

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

Visualize five, horizontal, sedimentary strata exposed in cliff or canyon wall identified by consecutive numbers, 1 being the lowest bed and 5 being the highest.† Which bed is the oldest and youngest?

What denotes the paleontological remains of particular organisms that were widely distributed but lived for only a relatively brief interval of geologic time?

What describes the investigative process by which geologists identify and match sedimentary strata and other rocks of the same ages in the different areas?

What are the geologic time divisions in order of decreasing lengths of time?

What geologic law/principle states that fossil organisms changed and evolved in a definite, progressive way such that strata of specific ages can be recognized by the fossils they contain?

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

Of an original amount of radioactive parent isotope, 25 percent remains and 75 percent has decayed.† How many half-lives have elapsed?

The ratio of radioactive parent to stable daughter atoms in a mineral is measured as 1:3 (one third).† How many half-lives have elapsed since the mineral grain formed, assuming that only parent atoms were present when it crystallized?

What the source of natural carbon-14?

Both long-lived, naturally occurring, uranium isotopes decay through intermediate, radioactive, daughter isotopes to stable isotopes of what element?

An erosional contact between tilted, older strata below and horizontal, younger strata above is called what?

Describe a disconformity.

The name of which era means ďancient lifeĒ?

Sandstone strata and a mass of granite are observed to be in contact. What can you say about the relative history?

Be able to determine relative ages of a block diagram.

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