Chapter 17 Studyguide

 

Multiple Choice

Earth’s atmosphere, oceans, and continents began to form during the first several hundred million years of

a. the Cenozoic Era. b. Precambrian Time. c. the Mesozoic Era. d. the Paleozoic Era.

 

During the Cambrian Explosion that began the Paleozoic Era, the many new forms of life that evolved

a. were single-celled. b. were invertebrates that lived in the sea. c. were vertebrates covered with scales or fur. d. lived on land.

 

The law of superposition states that, in horizontal layers of sedimentary rock, each layer is

a. older than the layer above it and younger than the layer below it. b. always older than any vertical layers. c. younger than the layer above it and older than the layer below it. d. neither older nor younger than the other layers.

 

The Paleozoic, Mesozoic, and Cenozoic are divisions in the geologic time scale called

a. centuries. b. layers. c. periods. d. eras.

 

In which type of fossil might you find the remains of an insect preserved with little or no change?

a. replacement fossil b. trace fossil c. fossil in amber d. mold

 

What do most scientists think caused the mass extinction of dinosaurs and other organisms at the end of the Cretaceous Period?

a. The dinosaurs ate too many other organisms and then starved. b. An ice age covered most of Earth with ice. c. An object from space struck Earth. d. Volcanic eruptions covered large areas with lava.

 

A fossil formed when minerals replace all or part of an organism is called a

a. trace fossil. b. cast. c. petrified fossil. d. mold.

 

The Mesozoic Era is divided into the Triassic, the Jurassic, and the Cretaceous. These divisions of the geologic time scale are called

a. eras. b. unconformities. c. periods. d. decades.

 

The geologic time scale is a record of

a. the life forms and geologic events in Earth’s history. b. the time since the evolution of dinosaurs. c. the thickness of sedimentary rock layers. d. the rate of fossil formation.

 

How do most fossils form?

a. The soft parts of an organism change to stone. b. The hard parts of an organism dry out in the air. c. Freezing preserves the remains of an organism. d. Living things die and their remains are buried by sediments.

 

Precambrian Time, which includes most of Earth’s history, began with

a. Earth forming from a mass of dust and gas. b. the formation of thick deposits of sediment. c. an asteroid impact. d. an ice age.

 

The fossils of organisms that were widely distributed but only lived during a short period of time are called

a. index fossils. b. trace fossils. c. petrified fossils. d. carbon film fossils.

 

The Cenozoic era is often called the Age of

a. Mammals. b. Fishes. c. Amphibians. d. Reptiles.

 

Which type of fossil can provide clues about the activities of ancient organisms?

a. carbon films b. molds and casts c. remains preserved in amber d. trace fossils

 

Why are index fossils useful to geologists?

a. They tell the relative age of the rock in which they occur. b. They tell the ages of many different rock layers. c. They tell the absolute age of the rock in which they occur. d. They tell the age of the rock at one location only.

 

What is a fossil?

a. the preserved remains or traces of an organism b. any dead organism c. an unusual type of rock d. a perfect copy of a rock

 

Originally, the geologic time scale placed Earth’s rocks in order by

a. decades and centuries. b. composition. c. relative age. d. radioactive dates.

 

The fossil record shows that life on Earth has changed over time. For example, paleontologists have found that older rocks contain fossils of

a. only organisms that are alive today. b. organisms that are simpler than those alive today. c. both simple and complex organisms. d. organisms that are more complex than those alive today.

 

True/False

Footprints and trails are examples of trace fossils.

 

Fossils usually occur in metamorphic rock.

 

On the geologic time scale, the Mesozoic Era is divided into the Triassic, Jurassic and Cretaceous periods.

 

Generally, only the soft parts of organisms become fossils.

 

Life on Earth first appeared during the Cambrian Period.

 

Geologists divide Earth’s long history into smaller units that make up the geologic time scale.

 

The era before the Mesozoic Era is the Paleozoic Era.

 

Completion

 Plant leaves may form a fossil called a(n) ____________________, a thin layer of carbon on rock.

 

 Certain ammonites are used as ____________________ fossils because they lived in many different areas but for only a brief time.

 

 Geologic time begins with the long span of time called ____________________ Time.

 

A(n) ____________________ fossil forms when dissolved minerals replace the remains of an organism and then harden to form rock. 

The mass extinction at the end of the Paleozoic Era may have occurred because Earth’s ____________________ moved together into one large landmass, changing Earth’s climate.

 

During the Quaternary Period, a series of ____________________ occurred when Earth’s climate cooled.

 

Paleontologists are scientists who study ____________________.

 

Scientists know how groups of animals changed over time by studying information contained in the ____________________.