Unit 4: Geologic Time & Dating

Front

What is the term for the length of time required for half of the radioactive atoms in a sample to decay?

Back

Half-life

Front

Which of the following would NOT mark the boundary of a division of geologic time: time change, rock layer, or fossil evidence?

Back

Time change

Front

According to the law of superposition, how can you determine which layer is the youngest?

Back

The youngest layer is the one on top.

Front

What is the definition of half-life in the context of radioactive decay?

Back

The time it takes for 50% of the nuclei in a radioactive sample to decay to its stable isotope.

Front

If a rock sample has 12.5% of the original radioactive atoms remaining, how many half-lives have passed?

Back

3 half-lives.

Front

What principle states that in undisturbed sedimentary rock layers, the oldest layers are at the bottom?

Back

The law of superposition.

Front

What is the significance of the half-life in radiometric dating?

Back

It allows scientists to determine the age of a sample based on the remaining radioactive isotopes.

Front

What is a geologic time scale?

Back

A system of chronological dating that relates geological strata to time.

Front

What are the main divisions of the geologic time scale?

Back

Eons, eras, periods, epochs.

Front

How does radioactive decay relate to geologic time?

Back

Radioactive decay provides a method for dating rocks and fossils, helping to establish the timeline of Earth's history.