Table of Contents

Fossils

The Relative Age of Rocks

Radioactive Dating

The Geologic Time Scale

Early Earth

Eras of Earth’s History

A Trip Through Geologic Time

Wyoming, 50 Million Years AgoToday, Wyoming has areas of dry plateaus, but 50 million years ago it was very different.

Fossils

The diagram below shows rock layers found at a site. Identify the area on the diagram that shows an intrusion. What is the oldest layer of rock in the diagram?

The Relative Age of Rocks

Index FossilsScientists use index fossils to match rock layers. Match the rock layers in locations 2, 3, and 4 with first area shown. Which fossils can be used as index fossils?

The Relative Age of Rocks

The Relative Age of Rocks

Unconformities and FoldingWhat are the oldest and youngest layers in the last two diagrams? Identify the unconformity. Which is the part of the fold that is overturned?

Radioactive Dating

Half-LifeThe half-life of a radioactive element is the amount of time it takes for half of the radioactive atoms to decay. What pattern do you see in the graph? Use the pattern to complete the last bar.

Elements Used in Radioactive Dating

Radioactive Dating

Earth's History in a DayIf all of Earth's 4.6-billion-year history could be squeezed into one 24-hour day, it would have been a timetable something like this.

The Geologic Time Scale

The Geologic Time ScaleThe divisions of the geologic time scale are used to date events in Earth’s history. What is the duration of each period?

The Geologic Time Scale

Early Earth

Early EarthThis artist’s illustration shows Earth shortly after the moon formed. Earth was hot and volcanic, and contained no liquid water. The moon was much closer to Earth than it is today. Over time, Earth’s surface began to cool, forming solid land.

Development of the AtmosphereThe illustration shows the difference between Earth’s first and second atmospheres. What is the missing information for each atmosphere?

Early Earth

Eras of Earth’s History

Cambrian LifeThe illustration shows one artist’s idea of what Anomalocaris (the large organism) and other organisms looked like.

Eras of Earth’s History

Changing LandscapesHow do the organisms of each period differ and what are their characteristics?

Eras of Earth’s History

The illustrations show a flying reptile called Dimorphodon and one of the earliest birds, Archaeopteryx. What do the two animals have in common and how are they different?

The End of the DinosaursMany scientists hypothesize that an asteroid hit Earth near the present-day Yucatán Peninsula, in southeastern Mexico.

Eras of Earth’s History