A Trip Through Geologic Time

What are fossils?

• molds and casts of organisms that live today

• drawings of ancient animals and other organisms

• footprints or burrows of small animals that live today

• the preserved remains or traces of organisms that lived in the past

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What has the study of fossils allowed scientists to do?

• describe past environments and the history of life

• study present ocean temperatures at different depths

• analyze the chemical composition of sedimentary rocks and minerals

• predict which organisms will become extinct in the future

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The relative age of a rock is

• its age compared with the ages of other rocks.

• less than the age of the fossils the rock contains.

• the number of years since the rock formed.

• its age based on how much carbon-14 the rock contains.

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The time it takes for half of the radioactive atoms in a sample of a radioactive element to decay is the element’s

• relative age.

• potassium-argon date.

• absolute age.

• half-life.

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Geologists use radioactive dating to

• determine the relative ages of rock layers.

• tell the difference between molds and casts.

• tell where one soil horizon ends and the next one begins.

• determine the absolute ages of rocks.

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

• lived on land.

• were invertebrates that lived in the sea.

• were vertebrates covered with scales or fur.

• were single-celled.

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Earth’s earliest atmosphere lacked which gas that is necessary for life as we know it to exist today?

• nitrogen

• carbon dioxide

• argon

• oxygen

Late in the Paleozoic Era, the supercontinent Pangaea formed. The climate in the center of Pangaea was probably a(an)

• extremely cold, polar climate.

• hot, dry desert climate.

• wet tropical climate.

• warm, mild climate.

Which answer best describes the climates of Europe and North America during the 1.8 million years of the Quaternary Period?

• hot and dry climates

• cool and rainy periods followed by droughts

• warm and mild climates

• a series of ice ages followed by periods when the glaciers melted

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

• mold.

• petrified fossil.

• cast.

• trace fossil.