Chapter 12 Activity

Part 1: How many half-lives have passed if a rock contains 25% parent isotopes and 75% daughter isotopes? Part 2: If the parent isotope has a half-life that equals 1.75 million years, how old is the rock?

2 3.50 Ma

Select statements true of unconformities.

B. There are three major types of unconformities. C. Unconformities represent periods of nondeposition in the rock record. D. Unconformities represent periods of erosion in the rock record.

Although depositional environments (and the resulting rock types) can change over broad areas, fossils within the rocks allow geologists to correlate units despite any lithological differences. Below is an image of fossils found in an outcrop. A limestone in another outcrop 150 miles away contains fossils C and E. Which bed (labeled 1 through 10 on the image) does this limestone correlate to?

Bed 6

In this relative age dating interactivity, order the geologic events chronologically from oldest to youngest, with the oldest being labeled "1st" and the youngest being labeled "4th."

From left to right: D A C B

The diagram depicts the distribution of rock units and structures in a given location. Indicate the type of unconformity shown and the type of underlying geologic structure by labeling the image.

From top to bottom: A, B, C

A number of geologic principles allow geologists to observe the relative ages of rocks. Which of these images illustrates the principle of inclusions?

Image B Image C

Geologists use epochs to further divide geologic eras and periods. Put the following epochs from the Cenozoic Era in chronological order, from the earliest to the most recent.

Pilocene, miocene, oligocene, eocene, paleocene

Why are geologists not able to date sedimentary rocks directly?

Sedimentary rocks are younger than their composite minerals.

The oldest known mineral grain is a 4.4-billion-year-old zircon crystal found in an ancient sandstone. Which of the following statements applies to this zircon grain?

The sandstone is younger than 4.4 billion years old.

Consult the stratigraphic column for the Grand Canyon in your text or ebook. The A represents the Supai Group. The B represents the Redwall Limestone. The C represents the Mauv Limestone. The D represents the Tapeats Sandstone. The E represents the Unkar Group. Identify the places where there is an unconformable contact.

between A and B between B amd C between D and E

Use the above drawings of stratigraphic columns in Bryce Canyon/Cedar Breaks, Zion Canyon/Painted Desert, and the Grand Canyon area, and the principles of cross correlation, to place the geologic formation in time order.

dakota, curtis, wingate, supai, zoroaster, vishnu

This outcrop of Precambrian and Paleozoic rocks in northern Cape Breton, Nova Scotia, provides a great example of the kinds of relative age relationships that geologists observe in the field. Put the features in order from oldest (bottom) to youngest (top). The rocks have not been overturned.

fault, conglomerate, mafic intrusion, felsic crystalline

Given the relationships shown in the block, what is the relative age of the features labeled, from oldest to youngest?

sedimentary pluton fault dike

Which of the following is/are useful in identifying mountain belts that have eroded away and therefore do not have obvious topographic features?

uncomformities