Front

What is the age of the Earth?

Back

Approximately 4.6 billion years old.

Front

What is a half-life in radioactive decay?

Back

The time required for half of the radioactive isotopes in a sample to decay.

Front

If the original mass of a radioactive isotope is 24 grams, how much remains after 3 half-lives?

Back

3 grams.

Front

What is an igneous intrusion?

Back

A body of igneous rock that has crystallized from molten magma intruding into pre-existing rock.

Front

What can be inferred if Organism Y is found in an older rock layer than Organism X?

Back

Organism Y lived before Organism X.

Front

What are trilobites?

Back

An extinct group of marine arthropods that are among the oldest known fossils.

Front

What does the presence of brachiopods and ammonites in the same rock layer suggest?

Back

There is some overlap in the presence of these organisms on Earth.

Front

What is the significance of fossils in geological layers?

Back

Fossils help determine the relative ages of rock layers and the organisms that lived during those times.

Front

What does the term 'geological time scale' refer to?

Back

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

Front

What is the principle of superposition?

Back

In undisturbed sedimentary rock layers, the oldest layers are at the bottom and the youngest are at the top.