Geo-Earth History

The major source of oxygen in Earth’s Early Proterozoic atmosphere is inferred to have been produced by

• oceanic cyanobacteria
• outgassing from volcanic eruptions
• radioactive decay in Earth’s inner core
• evaporation of ocean water

Volcanic ash deposits found in the geologic record are most useful in correlating the age of rock layers if the volcanic ash was distributed over a

• Large area during a short period of time
• Large area during a long period of time
• Small area during a short period of time
• Small area during a long period of time

Which event is generally accepted as the cause of the mass extinction that occurred 65.5 million years ago?Question*

• Volcanic eruption
• Continental collision
• Asteroid impact
• Sea-level change

The geologic cross section below includes an unconformity and an igneous intrusion.  Which two events produced the geologic unconformity in the rock record?

• Intrusion of magma, followed by contact metamorphism
• Intrusion of magma, followed by erosion of rock layers
• Erosion of rock layers, followed by deposition of more sediments
• Erosion of rock layers, followed by intrusion of magma

The timeline below represents time on Earth from the beginning of the Paleozoic Era (A) to the present (B). Which numbered position best represents the time when humans first appeared in the fossil record?

• 1
• 2
• 3
• 4

The cross sections below represent three outcrops, labeled I, II, and III, containing some New York State index fossils. The rock layers have not been overturned. When the rock layers in the three outcrops are correlated, the oldest layer is the

• Shale layer in outcrop I
• Siltstone layer in outcrop II
• Limestone layer in outcrop III
• Conglomerate layer in outcrop III

The geologic cross section below shows rock layers that have not been overturned. The fault is older than the

• Slate
• Marble
• Unconformity
• Shale

Four rock outcrops, labeled 1, 2, 3, and 4, found within the same plateau, are represented below. Index fossils found in some of the rock layers are shown. The rock layers have not been overturned. Which rock layer is the youngest?

• sandstone in outcrop 1
• breccia in outcrop 2
• conglomerate in outcrop 3
• sandstone in outcrop 4

Base your answers to questions 91 through 93 on the rock columns below and on your knowledge of Earth science. The rock columns represent four widely separated locations, W, X, Y, and Z. Numbers 1, 2, 3, and 4 represent fossils. The rock layers have not been overturned. Which numbered fossil best represents an index fossil?

• 1
• 2
• 3
• 4

Which rock layer is the oldest?

• tan sandstone
• gray limestone
• green shale
• black shale