PHSC 210 Week 3 Mastering Geology Assignments 6

PHSC 210 WEEK 3 Mastering Geology Assignments 6

Mastering Geology Assignments 6

Item 1

Geologists study the natural history of an area by investigating outcrops, which are rock formations exposed aboveground. Determining the age of outcrop layers is an important step in interpreting the area’s geologic history. Methods to date the layers fall into two categories:

• Absolute dating methods,such as radiometric dating, provide the age of layers with values such as number of years. However, suitable material to date is not always present.
• Relative dating determines the sequence of events relative to each other. For example, the age of a fault can be determined to be younger or older than certain layers, although the age in years of the fault or layers will not be determined.

Part A - Relative dating

The following diagram depicts a map area and the underlying geology.

• Rock layers are approximately parallel to the ground surface. The rock types of the layers are labeled.
• Dikes (lineations) and faults (tubular features) cut through the rock layers vertically.

Use the relative dating principles described in the introduction to reconstruct the geologic history of the area depicted in the diagram. Drag and drop the correct descriptions for the order of events conveyed in the accompanying diagram.

Part B - Interpreting inclusions

Fragments of rock can be separated from its parent layer, and be relocated into another layer. Inclusions are rock fragments that are relocated into another layer.

Interpreting inclusions are another relative dating technique. The principle of inclusions is described below.

• Rock fragments included within another rock must be older than the rock in which they are included.
• For example, if eroded fragments of one rock layer become part of another sedimentary rock layer, the rock with the included fragments must be younger than the fragments themselves. However, in contrast, if magma intrudes into surrounding host rock, the latter is older, as are any inclusions of the host rock found in the intrusion.

The following illustration depicts an area and its underlying geology. Three points in time are depicted.

• Time A: An igneous rock exists underground.
• Time B: The ground surface is eroded, which exposes the igneous rock.
• Time C: Layers of sedimentary rock are formed atop of the igneous rock.

Using the principle of inclusions, rank the labeled areas from oldest to youngest.

Part C - Principles of relative dating

The sentences below describe different techniques involved in relative dating. Complete the sentences using the following phrases.

First, you can refresh your memory by revisiting the principles of relative dating:

• Law of superposition:When comparing two sedimentary rock layers, the bottom layer must be older than the layer above it. The logic is a lower layer must already exist for another layer to be deposited on it.
• Principle of original horizontality: Sedimentary rocks were originally deposited as flat-lying, horizontal layers. If a layer is tilted, it must have moved.
• Principle of cross-cutting relationships:Any rock or feature, cutting through another rock or feature, must be younger than the material through which it cuts.

Match the words in the left column to the appropriate blanks in the sentences on the right.

Item 2

Part A

Which of the following statements about relative and absolute age dating is correct?

Part C

What is the Principle of Superposition? 

Part E

Which event is generally used to indicate the beginning of the Phanerozoic eon?

 Item 4

How long has man lived on Earth? How many years have the mountains and rivers existed? How long has Earth existed? You can find the answers to these questions using radiometric dating. Geologists and archeologists have found the age of rocks, minerals, fossils, and ancient remains using radioactive isotopes. These radioactive isotopes decay at a defined rate. By determining the extent of decay in a sample, we can determine the age of a sample. The first step in this process is to assess the type of radioactive decay that is occurring.

Although some isotopes are stable, others are unstable because the forces binding protons and neutrons together are not so strong. Unstable isotopes decay to a more stable configuration. The three main types of decay used for radiometric dating are:

Part A - The types of radioactive decay

  Part B - The half-life of an isotope

Use the same principle to answer the question below.

An isotope sample initially weighing 500 grams decays to produce a daughter element. What is the amount of parent element remaining after two half-lives?