Unit 2 Test Review

What are fossils?

• molds and casts of organisms alive today
• drawings of ancient animals and other organisms
• footprints or burrows of small animals alive today
• the preserved remains or traces of organisms that lived in the past

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

The relative age of 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

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

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

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

• mold
• petrified fossil
• cast
• trace fossil

What is the age of an intrusion of igneous rock in relation to the sedimentary rock layers through which it passes?

• sometimes younger, sometimes older
• always older
• the same age as the other rock layers
• always younger

Radioactive decay occurs when atoms of some elements

• become part of a fossil
• join with atoms of another element
• break down to form atoms of another elements
• are exposed to chemical weathering

Radioactive dating works best with what type of rocks?

• igneous rocks
• sedimentary rocks
• metamorphic rocks
• fossilized rocks

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

• radioactive dates
• relative age
• composition
• decades and centuries