Checkpoint 5: Geologic Time Review

A scientist is analyzing a rock sample that contains 25% of its original radioactive isotope. If the half-life of the isotope is 1.3 billion years, how old is the rock?

• 1.3 billion years

• 2.6 billion years

• 3.9 billion years

• 5.2 billion years

Which of the following best describes why radioactive dating is more accurate than relative dating?

• It determines the exact age of a rock using decay rates.

• It identifies the sequence of events in rock formation.

• It categorizes fossils based on appearance.

• It relies on the presence of fossil evidence alone.

What can index fossils tell scientists about rock layers?

• The exact absolute age of the rock layer

• Whether the rock layer is sedimentary or igneous

• The relative age of the rock layer based on other fossils found in it

• The number of isotopes present in the rock layer

The Blue Ridge Mountains contain rocks from the Precambrian time period. What does this suggest about their geologic history?

• They are composed mainly of recently deposited sediment.

• They contain some of the oldest rocks in Virginia.

• They were formed by the deposition of younger marine fossils.

• They are younger than the Appalachian Plateau.

What type of fossil evidence supports the idea that parts of Virginia were once covered by an ocean?

• Fossils of ancient land plants

• Fossils of marine organisms, such as brachiopods and corals

• Fossils of dinosaurs

• Fossils of early mammals

A geologist finds a sequence of rock layers where a fault has cut through the middle. According to the Law of Cross-Cutting Relationships, which of the following is true?

• The fault is older than the rock layers it cuts through.

• The fault is younger than the rock layers it cuts through.

• The rock layers and the fault are the same age.

• The fault formed at the same time as the oldest rock layer.

Which event is thought to have led to the mass extinction at the end of the Mesozoic Era?

• A rapid cooling of Earth's atmosphere

• A massive asteroid impact near the Yucatán Peninsula

• The explosion of a nearby supernova

• The formation of the Appalachian Mountains

Fossil records show that trilobites were abundant in the Paleozoic Era but disappeared afterward. What does this suggest?

• Trilobites evolved into modern mammals.

• Trilobites went extinct at the end of the Paleozoic Era.

• Trilobites were only found in deep-sea environments.

• Trilobites never existed.

Fossils of which geologic periods are mostly found in Virginia?

• Paleozoic, Mesozoic, and Cenozoic

• Paleozoic, Mesozoic, and Precambrian

• Precambrian, Cenozoic, and Mesozoic

• Precambrian, Cenozoic, and Paleozoic

What is the significance of finding marine fossils in the Appalachian Mountains?

• It shows that the mountains were formed by volcanic activity.

• It proves that the mountains are the oldest in the world.

• It suggests that the region was once submerged under an ocean.

• It indicates that the area was once covered by a desert.