Unit C: The Changing Earth

Lesson 1.3: Strange Rocks

Spiral-shaped rocks and other rocks with the shape of living things have always been important as curiosities. Before people knew how fossils formed, such rocks would have seemed particularly strange. In this lesson you will find that the strange rocks and the sedimentary rock in which they are found have become even more important; they are now known to reveal the geological history of Earth.


Determining which organism a fossil represents involves interpretation. Try interpreting fossil evidence in the next activity.

  • Read the investigation on page 306 of the textbook. Follow the directions, and answer the question.

    Check your answers with those in the “Suggested Answers” in the online course.

  • Read pages 307 and 308 of the textbook. Answer the questions as you encounter them.

    Check your answers with those in the “Practice Answers” in the online course.

Imagine walking along a mountain trail and finding rocks that resemble shark teeth. How could you explain the mysterious location of such rocks high above sea level? The next activity will aid you in solving this mystery.
 
Although designed for group work, this activity can be done on your own. Then, you would omit step 5 of the procedure and question 2 of “Evaluation”. Instead of showing your presentation to other student groups for feedback, you can show it to family members or friends.

  • Read the activity on page 309 of the textbook. Follow the directions, and answer the questions.

    • Check your answers with those in the “Suggested Answers” in the online course.

\You have learned that with careful observation and interpretation, Nicolas Steno identified tonguestone as the fossil of shark teeth. Understanding how fossils form will help you to recognize fossil evidence. In the next activity you will begin the formation of a simulated fossil. You will use this fossil in Chapter 2 to interpret fossil evidence.
 
  • Read the activity on page 309 of the textbook, and follow the directions.

To prepare for Chapter 2, make a note of where you place the plaster mould and the object.
 
  • Read page 310 of the textbook and “A Big Puzzle” on page 311. Answer the questions as you encounter them.

    • Check your answers with those in the “Practice Answers” in the online course.

In the next investigation you are presented with a puzzle to solve. You will build a large stratigraphic sequence from a number of smaller sequences.
 
Note: You will need to print the “Eight Fossil Cards” handout. Group work is not required for this activity.

  • Read the investigation on page 311 of the textbook. Follow the directions, and answer the questions.

    • Check your answers with those in the “Suggested Answers” in the online course.
 
  • Read page 312 of the textbook. Be sure to carefully study Figure C1.25 and Figure C1.26.

You may have noticed that in Figure C1.25, the scale of the oldest era is compressed in comparison to the most recent era. Although the Precambrian Era has a span of almost 4000 million years, its length on the scale is not much more than the length of the Cenozoic Era. Yet the Cenozoic Era spans just 65 million years. The next activity shows what the Geological Time Scale would look like if the eras were shown proportionately.
 
  • Read the activity on page 313 of the textbook. Make a labelled sketch of the sand-filled graduated cylinder.

    • Check your answers with those in the “Suggested Answers” in the online course.

  • Read “1.3 Summary” on page 313 of the textbook. Then, complete “1.3 Questions”.

    Check your answers with those in the “Practice Answers” in the online course.

Go to Assignment 1.3: Strange Rocks.