Geological Timeline 2

Which term describes a gap in the geologic record that occurs when sedimentary rocks cover an eroded surface?

• extrusion

• fault

• intrusion

• unconformity

Which term describes the time it takes for half of a radioactive element's atoms to decay?

• absolute age

• half-life

• radioactive decay

• relative age

Which statement best describes one rule for determining the relative age of a rock layer?

• A fault is always younger than the rock it cuts through.

• An extrusion is always older than the rocks below it.

• An index fossil is always younger than the rock layer is occurs in.

• An intrusion is always older than the rock layers around it.

Which of the following conclusions can geologists draw about a limestone rock layer based on the law of superposition?

• The limestone layer is 2 million years old.

• The limestone layer contains 2 million fossils.

• The limestone layer is younger than the sandstone layer below it.

• The limestone layer is the same age as another layer 100 kilometers away.

Radioactive dating is a method used by geologists to determine the _____ age of rocks.

• absolute

• relative

• general

The process in which the nuclei of radioactive elements break down, releasing fast-moving particles and energy.

• relative age

• radioactive dating

• radioactive decay

• absolute age

Which of these choices is an example of the way a geologist would use relative dating?

• determining the minerals that make up rocks
• placing rock layers in order of oldest to youngest
• classifying rocks as igneous, sedimentary, or metamorphic 
• using radioactive isotopes to determine the exact age of rock samples 

A geologist is studying three layers of sedimentary rock in an area. The geologist records the relative ages of the rocks. The bottom layer is listed as the oldest. The top layer is listed as the youngest. What did the geologist use to determine the relative ages of the rocks?

• mineral content 
• radioactive decay 
• the law of superposition 
• the principle of unconformity 

What is the oldest layer?

• a
• b
• c
• d

Which conclusion correctly describes the youngest rock layer in the diagram?

• Layer W is the youngest because it is the top layer of sedimentary rock and the only layer that contains fossils.
• Layer X is the youngest because it is the middle layer of sedimentary rock.
• Layer Y is the youngest because it is the bottom layer of sedimentary rock.
• Layer Z is the youngest because it was once molten rock that moved through all three layers of sedimentary rock.