Chapter 8- A Trip Through Earth's History

How do most fossils form?

The process by which living things have changed over long periods of time is called

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

Plant leaves may form a thin layer of carbon on rock called a

Type of fossil that can provide clues about the activities of ancient organisms.

The geologic time scale begins with a long span of time called

Oceans- rain began to fall, forming oceans

What Era is referred to as the "Age of Reptiles"?

Scientists who study fossils

Fossils usually occur in what type of rock

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

The geologic time scale is a record of

The relative age of a rock is

Fossils of organisms that were widely distributed but only lived during a short period

The end of the Paleozoic was marked by the

Continents- began to break apart, forming new ones as a result of continental drift

Which Era is divided into the Triassic, Jurassic and Cretaceous periods?

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

A gap in the geologic record where some rock layers have been lost because of erosion

Many scientists hypothesize that dinosaurs went extinct because

Fossil forms when dissolved minerals replace the remains of an organism, then harden into rock

Atmosphere was made of hydrogen and helium

The present day is part of what period

A rocks actual age, the number of years since it was formed

A type of organism that no longer exists on Earth is said to be

Atmosphere -carbon dioxide, water vapor and nitrogen

Oceans- too hot, all water evaporated

Continents- rocks started cooling, forming landmasses

A fossil is