Earth History exam 4

Front

What can be inferred about the environmental conditions in the Las Vegas valley millions of years ago based on fossils of shellfish and snails?

Back

The Las Vegas valley once contained a shallow sea.

Front

What does the law of superposition state about sedimentary rock layers?

Back

In an undisturbed sequence of sedimentary rocks, each layer is older than the one above it.

Front

What major changes or events divide the geologic time scale?

Back

Mass extinctions.

Front

What is an index fossil?

Back

A fossil that helps determine the relative age of a rock layer.

Front

What principle states that in undisturbed rock layers, younger layers are on top of older ones?

Back

Principle of superposition.

Front

What is a trace fossil?

Back

A fossil that provides evidence of the activity of ancient organisms.

Front

What is the significance of mass extinctions in Earth's history?

Back

They mark major changes in the geologic time scale.

Front

What does the term 'lithification' refer to?

Back

The process of turning sediment into rock.

Front

What is the principle of original horizontality?

Back

Layers of sediment are originally deposited horizontally.

Front

What is uniformitarianism?

Back

The principle that the same geological processes that operate today also operated in the past.