Exploring Fossils and Rock Layers in Earth's History

What is the geologic time scale?

• A timeline of the solar system

• A timeline of Earth's history based on geological events

• A timeline of the universe

• A timeline of human history

What do geologists use to map out Earth's history?

• Astronomical data

• Tree rings

• Ancient texts

• Fossils and rock layers

What is the law of superposition?

• Older layers are on top of younger layers

• Younger layers are on top of older layers

• Layers are always horizontal

• Layers are randomly arranged

How do geologists determine the relative age of rock layers?

• By counting the number of layers

• By using the law of superposition

• By examining the color of the rocks

• By measuring the temperature of the rocks

What is an igneous intrusion?

• A break in the rock layers

• A layer of sedimentary rock

• Molten rock that has cooled and solidified

• A fossilized organism

What does the law of cross-cutting relationships state?

• Younger features cut through older features

• Features do not intersect

• Features are always parallel

• Older features cut through younger features

What are index fossils?

• Fossils that are not useful for dating

• Fossils found in all rock layers

• Fossils that indicate a specific time period

• Fossils of modern organisms

How can geologists use volcanic ash layers in relative dating?

• By identifying the same ash layer in different rock layers

• By determining the chemical composition of the ash

• By measuring the temperature of the ash

• By counting the number of ash layers

What did relative dating help geologists determine about stegosauruses and T-rexes?

• They never existed

• Stegosauruses were extinct long before T-rexes existed

• They lived at the same time

• T-rexes were extinct long before stegosauruses existed

When did modern humans first appear according to the geologic time scale?

• About 2 million years ago

• About 200,000 years ago

• About 600 million years ago

• About 3.8 billion years ago