Chapter 10: A Trip Through Geologic Time

What is a fossil?

• any dead organism

• the preserved remains or traces of an organism

• a perfect copy of a rock

How do most fossils form?

• Living things die and their remains are buried by sediments

• The hard parts of an organism dry out in the air

• The soft parts of an organism change to stone

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

• organisms that are more complex than those alive today

• both simple and complex organisms

• organisms that are simpler than those alive today

The process by which all the different kinds of living things have changed over long periods of time is called

• sedimentation

• replacement

• evolution

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

• mold

• petrified fossil

• cast

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

• trace fossils

• remains preserved in amber

• carbon films

The relative age of a rock is

• its age compared to the ages of other rocks

• less than the age of the fossils the rock contains

• the number of years since the rock formed

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

• younger than the layer above it and older than the layer below it

• neither older nor younger than the otehr layers

• older than the layer above it and younger than the layer below it

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

• trace fossils

• petrified fossils

• index fossils

Why are index fossils useful to geologist?

• They tell the absolute age of the rock in which they occur

• They tell the ages of many different rock layers

• They tell the relative age of the rock in which they occur