Relative vs. Absolute Age

A geologist in the field examines a series of rock units. She observes that the rocks at the base of the sequence are much older than the layer directly above it. Which of the following principles best explains this discovery?

• The principle of lateral continuity

• The principle of original horizontality

• The principle of superposition

• The principle of cross-cutting relationships

A layer of sandstone (C) deposited on top of an older layer of rock (D) is an example of which principle?

• principle of inclusions

• principle of superposition

• principle of cross-cutting relationships

• principle of original horizontality

Small pieces of older igneous rock (E) found within a layer of younger sedimentary rock is an example of which principle?

• principle of inclusions

• principle of superposition

• principle of cross-cutting relationships

• principle of original horizontality

A dike (B) cutting through several layers of older rock, and lying underneath several layers of younger rock is an example of which principle?

• principle of inclusions

• principle of superposition

• principle of cross-cutting relationships

• principle of original horizontality

When an unstable isotope breaks down, or decays, it is said to be _____.

• radioactive

• explosive

• stable

• none of the above

If a fossil starts out with 100 grams of a radioactive isotope, how much will remain after 3 half lives?

• 50 grams

• 25 grams

• 12.5 grams

• 6.25 grams

Using radiometric dating, scientists have established the age of Earth to be about 4.6 billion years old. This is an example of an absolute age because the age in years has been calculated.

• True

• False

Which type of unconformity happens when metamorphic or igneous rock is eroded and later sedimentary rock forms on top of the eroded surface?

• nonconformity

• angular unconformity

• inclusion

• disconformity

The half-life of a radioactive substance is the amount of time it takes for _____ of the parent atom to decay.

• 1/4

• 1/2

• 3/4

• all

Which of the following is a limitation to radiometric dating?

• Not enough parent and/or daughter material to measure

• Being an igneous rock

• Being a metamorphic rock

• Too much parent and/or daughter material to measure