Exam 8: Geologic Time

James Hutton's proclamation that "we find no vestige of a beginning-no prospect of an end" is a concise summary of the philosophy of catastrophism.

A datable mineral crystal contains 40% parent isotope. How many half-lives have passed since the crystal formed?

"This rock is fifteen million years old," is an example of ________.

Among the following radioactive parent isotopes, which has the shortest half-life?

Is there any way to say for sure whether rock unit A or rock unit D is older? Why or why not?

An unconformity is a buried ________.

All else being equal, in a horizontal sequence of sedimentary rock layers, each higher bed is younger than the bed below it. This idea is the principle of ________.

Examine the figure that shows the age ranges of some fossil groups. If trilobites ranged from the Cambrian to the Permian, and ferns ranged from the Devonian until the present day, then rock unit B must have been deposited ________.

Match the items in the first column with the correct descriptions in the second column. A)fossil poop B)a fossil organism that is restricted to a certain brief stretch of geologic time, but was widespread and abundant during its time on Earth C)the notion that we can understand the geologic past by focusing on present day processes and physical laws; geologic change may be slow or gradual D)a group of fossils that co-existed at the same time. Their overlapping ranges can help constrain the age of a rock unit that contains them E)fossil tree sap F)the defunct notion that the Earth is only a few thousand years old, and that all geologic change is accomplished rapidly through violent events G)indirect evidence of ancient life, such as footprints, bite marks, and gastroliths H)the remains or traces of ancient life -1)catastrophism 2)fossil 3)amber 4)fossil assemblage 5)coprolite 6)uniformitarianism 7)index fossil 8)trace fossil

Identify and label the three types of unconformities shown in this cross-section of the Grand Canyon.

The idea of ________ suggests that the physical, chemical, and biological laws that operate today have also operated in the geologic past.

What is the sense of offset on fault G?

The longest subdivision of the geologic time scale is the ________.

Sedimentary layers can be important indicators of past environmental conditions that existed when the sediments were deposited.

Permineralization and carbonization are methods of correlating rock units.

A sandstone is found to overlie a shale. The shale contains a volcanic ash layer that has been radiometrically dated to 84 million years ago. Both the shale and the sandstone are cut by a pluton of gabbro that has been dated to 60 million years old. How old is the sandstone layer? ________

A granite dike cuts across a shale. The dike gives a radiometric date of 84 million years old. The shale was therefore deposited more than 84 million years ago.

Examine the geological cross-section and describe the order of all the geological events that can be depicted from this image. Don't limit yourself to merely the lettered rock units; include episodes of folding and erosion, too. Use descriptive geologic verbs like "deposition" and "intrusion" rather than simply saying the "rock unit J was formed."

Examine the figure that shows the sequence of strata in three Colorado Plateau national parks. Which unit(s)are shared by Grand Canyon National Park and Zion National Park?

Using the known rates of radioactive decay to date the crystallization of certain minerals is known as ________ dating.