Dating Rocks

The oldest rock layers in an undisturbed outcrop of sedimentary rock is located at

• the middle of the outcrop due to the law of superposition
• the top of the outcrop due to the law of crosscutting
• the bottom of the outcrop due to the law of superposition.
• the top of the outcrop due to the law of superposition.

The relative age of a rock layer tells scientists

• the exact age of the rock in the layer.
• the average age of the rock in the layer.
• the order that the rock layers were formed.
• the exact age of the fossils in the rock layer.

An index fossil is useful for finding the age of a rock layer because it is a fossil that is

• widely distributed but only  existed for a short time.
• existed in many different locations and time periods.
• immune to the melting effects of lava.
• found in many time periods but only occurs in  one location.

The idea that Earth is shaped by process that happen every day such as erosion and weathering is called

• catastrophism
• doomsdayism
• uniformitarianism
• geologic catastrophe

What fraction of the beginning amount of a radioactive element will you have left after 3 half-lives?

• 1/18
• 1/6
• 1/8
• 1/4

If the half-life for a radioactive element is 1,000 years and you have 1/4 of the starting amount of the element left, how many years have gone by?

• 10,000 years
• 2,000 years
• 5,000 years
• 3, 000 years

Radioactive dating does not work very well for sedimentary rock layers because

• it will find the age of the particles in the rock layer and not the layer itself.
• rock layers are too old measure with this method of dating.
• radiometric dating only works on organic materials.
• the metamorphic rock in the layers will make the rock layers appear older than they are.

A gap in the geologic column as a result of sedimentary rocks covering an eroded surface is called

• an uncomformity
• a geological catastrophe
  
• a glacier till
• an intrusion

A geologist finds identical fossils index fossils in the Grand Canyon  in Arizona and in a rock layer in northern Utah, more than 675 km away. What inference can she make about the ages of the two rock layers?

• the rock layer in the Grand Canyon is older.
• the rock layer in Utah is older.
• the rock layers are about the same age.
• not enough information is given to make an inference.

If a fault is cutting through a layer of sedimentary rock we can infer

• the fault was there before the sedimentary rock layer.
• the sedimentary rock layer was there before the fault.
• that if the fault starts beneath the sedimentary rock layer the fault occurred first.
• that the rocks above the fault are older than the fault.