Relative Dating

Which phrase describes the absolute age of a rock?

• does not provide an exact age

• is the number of years since it formed

• is the age compared to other rocks around it

• indicates whether it is younger or older than the rocks above it

A geologist finds four layers of sedimentary rock. She determines that no geologic events have shifted the layers. She labels the layers A, B, C, and D from the top to the bottom.

Which statement about these layers is accurate?

• A is older than B.

• B is older than C.

• C is younger than A.

• B is younger than D.

According to the law of superposition, which statement is supported by the diagram?

The diagram shows horizontal rock layers.

• Layer C is the oldest layer.

• Layer B is younger than layer D.

• Layer C is older than layer A.

• Layer D is the youngest layer.

The diagram shows horizontal rock layers.

Which statement is accurate?

• Layer C is younger than layer A.

• Layer D has an older relative age than layer C.

• If a geologic event tilted these layers, layer B would no longer be the oldest.

• It is possible to determine the absolute age of layer C with the information given.

A geologist finds some tilted sedimentary rock layers.

Which conclusion can the geologist draw by looking at the rock layers?

• Their absolute age is 600 million years.

• They were tilted before they were deposited.

• They were originally deposited horizontally.

• The youngest layer was originally deposited as the bottom layer.

In which situation is the principle of cross-cutting relationships useful in determining relative age?

• A fault breaks through sedimentary layers.

• Fossils of two different species are found in different rock layers.

• Sedimentary layers form over millions of years in a lake bottom

• Lava flows form on top of one another from several eruptions over time.

Which characteristic is shared by extrusions, intrusions, and faults?

• All are cracks.

• All are igneous rocks.

• All cause gaps in the geologic record.

• All are younger than surrounding rocks.

Which feature forms at Earth’s surface from the cooling of lava?

• extrusion

• fault

• intrusion

• unconformity

This diagram shows rock formations forming.

Which statement describes one or both formations?

• Formation 2 is an extrusion.

• Formation 1 is an intrusion.

• Formations 1 and 2 are faults.

• Formations 1 and 2 are igneous rock.

Which statement explains one reason why unconformities occur?

• Rocks along a fault break and move.

• Igneous rock forms at Earth’s surface.

• No sediment is deposited over a long time.

• Igneous rock forms between sedimentary layers.