Pre-Lab: Using Index Fossils
Problem How can fossils be used to determine the relative ages of rock layers?
Materials scissors
Lab Manual Chapter 19 Lab
Skills Focus Interpret Visuals, Sequence, Draw Conclusions
Connect to the When detectives work on a case, they may look for items with a time stamp, such as parking tickets and credit card slips. Such items can help detectives piece together a sequence of events. Events related to a crime usually occur within a relatively short period of time. In contrast, the events that paleontologists study will have occurred over millions of years. Placing these events in their proper order can be challenging. The clues that a paleontologist uses to sequence events in the history of life are fossils buried in rock layers. In this lab, you will use fossils to place rock layers in order from oldest to youngest.
Review What is a fossil? What are the characteristics of a good index fossil?
Explain What characteristic of radioactive decay allows scientists to assign specific ages to rock layers?
Classify How do fossils help geologists decide where one division of geologic time should end and another division begin?
Preview the procedure in the lab manual.
Organize Data After you cut out the drawings of the rock layers, how will you begin the process of sorting the layers by age?
Infer Desmatosuchus was a crocodile relative that lived only during the Triassic Period. Horsetails are plants that first appeared in the Triassic Period and still exist. Which of these organisms would be more useful as an index fossil for the Triassic Period? Why?
Use Analogies Luke found a box of photos labeled 1970–1995. Each photo shows his entire extended family. No dates appear on the photos. Luke knows that his grandmother died in 1985 and his uncle was born in 1975. Luke's sister was born in 1990. How can Luke use this information to sort the photos into four batches? How are Luke's relatives similar to index fossils?
Visit Chapter 19 online to test yourself on chapter content and to find activities to help you learn.
Untamed Science Video Go back in time with the Untamed Science crew to find out what fossils reveal.
Art in Motion View a short animation that shows how fossils form.
Art Review Review your understanding of the composition of Earth's early atmosphere as compared with the composition of Earth's current atmosphere.
Visual Analogy Compare geologic time to a 24-hour clock.
Data Analysis Correlate data on extinction events with other types of data to identify likely causes of extinction.