A Trip Through Earth's Past

Many scientists hypothesize that the dinosaurs became extinct because

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

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

Radioactive decay occurs when atoms of an unstable element

What type of fossil leaves a thin layer of carbon on rock?

The present day is part of the

How do most fossils form?

What Era is known as the age of invertebrates?

Certain ammonites are used as what types of fossils?

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

The end of the Paleozoic was marked by the

Radioactive dating enables geologists to

The relative age of a rock is

The evolution of photosynthetic organisms about 2.5 billion years ago led to

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

What is a gap in the geologic record where some rock layers have been lost because of erosion?

The first vertebrates were

What Era is known as the age of reptiles?

What type of fossil is this?

Geologic time begins with the long span of time called

What type of scientists study fossils?

What type of fossil is this

What type of fossil is this?

The geologic time scale is a record of

What type of fossil is shown

When all of the living things have changed over long periods of time it is called

The earliest life forms were

A rock layer's age compared to the ages of other rock layers is called...

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

Fossils usually occur in what type of rock?

What type of fossil can provide evidence of ancient organisms activities?

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

A fossil is...

What type of fossil occurs when dissolved minerals replace the remains of an organism?

What type of fossil is this?

What era is broken down into the Triassic, Jurassic and Cretaceous?

What type of fossil is shown?