Chapter 4

Who came up with the concept that geologic processes operating at present are the same processes that operated in the past?

James Hutton

In which of the following time periods were dinosaurs the dominant creatures?

Mesozoic

How does an angular unconformity form?

Older rocks are tilted, eroded, and overlain by younger rocks.

Which of the following is the earliest (oldest) chapter of geologic time?

Precambrian

How would we use isotopic ages to infer the ages of the upper and lower unit in this diagram?

The dike is younger than the lower unit but older than the upper unit.

This photograph shows light-colored granite and darker diorite (both igneous rocks). Which of the following statements is true?

The granite is younger because it crosscuts the diorite.

Upon what basis were the upper and lower boundaries of the Mesozoic Era defined?

abrupt changes in the types of fossils, representing mass extinctions

The geologic timescale details and divides geologic time based upon

fossil data.

This figure shows the main subdivisions of the geologic timescale. Which of these is the Cenozoic?

geologic time A

What type of feature is shown in this photograph of Siccar Point, Scotland?

unconformity

Of the following numbered units, which is the youngest?

unit 9 The top

The oldest known rock found on Earth is dated at

over 4 billion years old.

What type of feature is represented by the boundary between geologic units 2 and 3?

unconformity

What would fossil ages from the geologic timescale tell us about the age of this unconformity?

All of these choices are correct.

Which of the four numbered features on this figure is the oldest?

1

Which numbered layer in this photograph represents the oldest layer?

1 the hillside

Which sequence of numbers reflects the order in which the layers were deposited?

1, 2, 3, 4

If a rock started with 1,000 atoms of a parent but now contains 250 atoms, how many half lives have passed?

2 half lives

Which of the four numbered features on this figure is the youngest?

4 surface

What factors are the most critical in determining whether a fossil is preserved?

Whether the creature had hard parts and how fast it was buried.

Which principle can be used to determine the relative age of an igneous intrusion called a dike?

cross-cutting relations

Which principle of relative age dating can be used to determine when the river formed on the landscape?

cross-cutting relations

What is the youngest event represented in this block diagram?

erosion of a canyon by a river

The term half life represents the time it takes

for half of the parent atoms to decay into daughter atoms.

The fossil ferns in this photograph probably indicate that the rock was deposited

on land.

Which principle is used to determine the age of rocks by ordering them from oldest on the bottom to the youngest on the top?

superposition

Using the data in this table, calculate the number of half-lives that have passed for the dike (unit D on this table).

table of isotopic measurements 1

The geologic relationships in this figure indicate

that the lava flow is younger than the landscape surface partially covered by the lava flow.

Early Earth would have been inhospitable to many life forms of today because

the atmosphere lacked oxygen.

Of the following numbered units, which is the oldest?

the granite 4

Missing geologic time caused by erosion is called a(n):

unconformity

How did an oxygen-rich atmosphere develop from a carbon dioxide-rich atmosphere?

through photosynthesis by cyanobacteria