THE MYSTERY OF THE
FAR-FLUNG FOSSILS

Evidence for Evolution

Investigating Rock Correlations, Fossils
and Plate Tectonics

Introduction

In the early 1900’s, a famous English explorer, Captain Robert Scott, made a surprising discovery when exploring the cold and forbidding continent of Antarctica.  Captain Scott describes the discovery of his diary in this entry for February 8, 1912:


“We found ourselves under perpendicular cliffs of Beacon sandstone, weathering rapidly and carrying veritable coal seams.  From the last, Wilson, with his sharp eyes, has picked several plant impressions, the best a pieces of coal with beautifully traced leaves in layers, also some excellently preserved impressions of thick stems, showing cellular structure...”

This was written upon Scott’s return from the South Pole. The coal seams and plant fossils had been found at the base of Mount Bowers, at the head of the Beardmore Glacier.

Geologists generally supposed the coal is formed in temperate or tropical regions.  Scott wondered how could it have entirely covered by glacial ice.

Like Robert Scott, you have been chosen to go on a fossil-collecting expedition to the continent of Antarctica. You will also explore South America, Africa, Australia, and the sub-continent of India.  Your fossils of Antarctica occur mostly beneath glacial ice in the mountains on the western shores. In South America you will collect fossils in Brazil.    Some of your African rocks are in a gorge near Capetown.  In Australia you’ll look at rocks on the southern coast.  You will explore the coal fields of Gondwana in southern India. You will look for fossils in sedimentary rocks of three geologic period of time.

Objectives:

After you have completed these activities, you should be able to:

  • Tell how rocks indicated the environment in which they were formed.
  • Use superposition to find the relative ages of rock units.
  • Use fossils to correlate rock units.
  • Describe evidence which supports the theory that certain continents were once joined.

Procedure:

PART A: What can we learn from rocks about past environments?

A geologist is a scientist who studies rocks to learn about the history of the earth.  Your teacher will provide you with six rocks that have been identified and described by geologists.

  1. Identify each of your rocks.  Your group will have one of each of the following:
Basaltic lava: was formed from molten rock that erupted from volcanoes or from long cracks in the earth’s crust.  It is dark and so fine-grained that you will not be able to see individual grains.  It may have round holes formed by gases released from the molten rock and then trapped in the lava as it hardened.
Marine Sandstone: was formed from sediments deposited in a sea or ocean.  Usually it will contain only quartz grains.  Individual grains will all be of about the same size.  Any fossils it may contain usually will be of plants or animals that lived in salt water.
Fluvial sandstone: was formed from sediments deposited in the bed of a stream.  It may have minerals other than quartz, and the mineral grains will be of various sizes.  If there are any fossils , they will be of plants or animals from on land or in fresh water.
Shale: is a very fine-grained rock formed from clay or mud.  It will show some layering.
Tillite: is a rock formed from sediment deposited by a glacier.  These rocks may have a wide variety of grain seized and minerals.  Many of the grains will be somewhat angular.
Coal: is formed from the remains of trees and other plants that grew in swamps.  Coal will be black, brittle, and not very hard.  It may have fossilized leaves and plant stems.
  1. After you have identified all six rocks, place each one on Worksheet 3, PDF on the correct symbol representing that rock.  Have your teacher check your rock identification before you continue with the activity. Notice that each of the symbols on Worksheet 3, PDF is used in the rock column chart on Worksheet 1, PDF. Remember what each symbol means and also the kind of conditions under which each type of sediment or rock material was deposited. Label your rock column with the name for each rock represented next to the symbol.
  2. Apply the "Principle of Superposition" to the South Africa rock column on Worksheet 1, PDF.  Which rock layer is the oldest?  Which rock layer is the youngest?
  3. What was the environment of Antarctica like when the marine sandstone sediment was being deposited?  What was the environment like when the coal material was being deposited?
  4. Does the present environment in Antarctica differ from either of those you describe in question 4 above?  If so, how does it differ?  Could coal be forming in Antarctica today?
     
  5. Locate India on the world map.  What type of climate do you think India has today?
  1. Now examine the rock column from India.  Could rocks similar to those represented by the rock columns be forming in India today?  Which ones?  Could tillite be forming today in India?
  2. You have observed that both India and Antarctica have rocks that were formed in environments that were much different from the environments in those two places today.  List as many explanations as you can, to account for this situation.
  3. Examine the rock columns from all five areas.  List each similar order of rock layers that you can find.
  4. One similarity that you will have noticed is the presence of basalt at the top of each of the rock columns.  How is basalt formed?
  5. Can you tell whether the basalt in each of the areas was formed at the same time?  Explain.  How about the coal?  Explain.

Procedure:

PART B: How old are the rocks?

You found in step 11, Part A, that you really could not tell from the information provided, weather layers of similar rock type from different areas were formed at the same time.  If you could find out the ages of these rocks, then you could determine whether the same environment existed in all five areas at the same time.  You could also learn whether the environment changed in the same way in each of the five areas.  This would certainly tell us something interesting about the history of the areas.

To determine the age of a sedimentary rock, we must find fossils.  Certain fossil species are always the same age wherever they occur.  All rocks containing these fossils are the same age even if found in different places and even if they are different kinds of rocks.  Matching the ages of rocks is known as correlation.

Imagine that the five continents are each represented by a stack of sedimentary rocks.   The continents are in their natural geographical shape and their sizes are proportional.  The colored layers represent rocks found during a specific geologic period. The blue, top layer represents modern times; and the pictures of the modern animals you see are native to the continent.  The three lower layers depict sedimentary rocks of three past ages:

Blue Rocks Modern Age Present
Green Rocks  Late in the Age of Dinosaurs  100 mybp*
Yellow Rocks  Early in the Age of Reptiles  200 mybp*
Red Rocks The Coal Age 300 mybp*

*mya = million years before present

The plant fossils found by Scott’s expedition have been identified by geologists as Glossopteris.  These plants have been found in coal seams in many places around the world.  Glossopteris is of Permian age. You will identify other fossils from each continent. These represent the rock columns from Worksheet 1. PDF.

In 1967, a geologist with the Ohio State University institute of Polar Studies found a jaw fragment belonging to an ancient amphibian, not far from where Scott’s party found the coal seems and the Glossopteris fossils.  A team from the institute of Polar Studies, encouraged by this find, returned to the same are in 1969 with the specialist in identifying fossil amphibians and reptiles.  On the first day of the expedition, the team’s leader, David Elliot, climbed a bluff near the base camp.  He found an ancient stream channel containing bones and teeth.  Edwin H. Colbert, the specialist in amphibian and reptile fossils, identified a jaw-bone he found there later as being that of Lystrosaurus, a reptile previously found in India and South Africa in rocks of Early Triassic age.  It was a land reptile, not adapted for swimming long distances. 

Use the following information to identify fossils you find. Fossils can be seen in sedimentary rocks of each past age.  These are some of the important organisms that lived on the continents at those times.  To identify and learn more about each fossil, refer to the FOSSIL CATALOG.

Record on your data sheet the names of the fossils you find in the rocks of each continent for the past ages.  Also record the names of the animals now living in the present day continents.

DATA SHEET

Fossils and living animals found on the five continents of Gondwanaland

CONTINENT

Time

South America

Africa

Antarctica

India

Australia

Present day (blue)

          

100 million years ago (green)

          

200 million years ago (yellow)

          

300 million years ago (red)

          
  1. On the basis of what you found in the red rocks,
    a)     which continents had similar fossils?
    b)     from this fossil evidence, which continents seem to have been connected 300 million years ago?
  2. On the basis of what you found in the yellow rocks,
    a)     which continents had similar fossils?
    b)      from this fossil evidence, what can you tell about the connections of the five continents about 200 million years ago?
  3. On the basis of what you found in the green rocks,
    a)     which continents had similar fossils?
    b)     from this fossil evidence, which continents seem to have been connected 100 million years ago?
  4. a) Arrange cutouts of the continents from according to where you think they were situated during each of the three past ages.  Arrange them also as they appear in the present.

    5. Southern Hemisphere

    300 million years ago

    200 million years ago

    100 million years ago

     Present                                                      

4.     b) Explain your reasons for putting the continents together as you did for each time period:

        300 million years ago

        200 million years ago

        100 million years ago

The rock columns are from five different areas.  South America, Africa, Antarctica, India, and Australia.  Write the names of these areas in their proper places on the outline map of the world (Worksheet 2), PDF.
  1. Color in each time period in the time Scale, on the left edge of the rock columns chart (Worksheet 1), with a different color.  (These distinctive colors will then be used later to mark the same ages on the five rock columns).  Color in the beds containing the Glossopteris fossils with the color you used for Permian on the Time Scale.  Place a “G” on your world map (Worksheet 2), PDF where Glossopteris has been found.
  2. How can you explain the presence of Glossopteris in five such widely separated areas?
  3. Fossilized pollen found in the tillites indicates that they are Late Carboniferous.  Color the tillites with the color you used for that age in the Time Scale.
  4. In the rock columns, color those sediments containing Lystrosaurus with the color you used in the Time Scale indicating their age.
  5. Place an “L” on Worksheet 2 beside the names of those areas where Lystrosaurus has been found.  How can you explain the presence of a reptile, like Lystrosaurus, in such widely separated areas?
  6. Certain shells found in the marine sandstone’s of Brazil, South Africa, Australia, and Antarctica have been determined to be of Devonian age.  Color in these portions of the rock columns with the appropriate color.  Dicroidium is a plant fossil restricted to the Late Triassic.  Color in the portions of the rock columns containing Dicroidium.

The age of igneous rock, such as the basalt at the top of each of the rock columns, can be determined through a process called radiometric dating. In this procedure, the amounts of certain radioactive elements in the rock are measured.

  1. The basalts in Brazil and India are Cretaceous age.  In South Africa, Antarctica and Australia, they are from the Jurassic Period.  Color the basalt in the rock columns with the colors you used for these ages in the Time Scale.
  2. Now correlate the rock units for each area.  Draw lines between the columns indicating the rock boundaries between each of the ages.  The line dividing the “Basement” rock (pre-Devonian) from the Devonian has already been drawn in for you.  The Early Triassic layers of Brazil and South Africa have also been correlated.  Have your teacher check your correlation’s before you continue.
  3. When were four of the areas covered by the sea?
  4. During what age did all five areas have extensive swamps?
  5. How can you explain that in the past the environments of these five areas, as indicated by their rocks, were very similar when today their environments are so different?

Look at the black arrows on the red rocks of the continents.  The arrows represent grooves in the rock.  The grooves were carved by advancing continental glaciers. The arrows point in the direction the glaciers were moving.

  1. During what age were glaciers present in all five areas? 

  1. Suppose you were the first person to have found the glacial grooves in the south-eastern South America.  From where would it seem the glacier came?  Could the glacier have come from the ocean?  Explain your answer)      Why would the geologist who first found the glacial grooves in India be puzzled by the discovery? 
  2. How might the idea of continental drift explain 300 million year old glacial grooves on four separate southern continents?
  3. Where was the probable spreading center of the glaciers?  Make an “X” to mark the location on Worksheet 2.  Where on the surface of the earth was the probable location of the “X” 300 million years ago?  (Remember that a continental glacier tends to move out and away from its center, the North or South Pole - like a spreading mass of bread dough)
  4. Where would you look for glacial grooves in the 300 million year old rock of Antarctica?  Draw arrows where you would expect to find glacial grooves in Antarctica on the map above.
Two species of living earthworms in the soils of southern South America and Africa were found to be very closely related (members of the same genus).  Also, two species  of living earthworms in soils of southern India an southern Australia were found to be very closely related (members of the same genus).
  1. How was the theory of continental drift strengthened by discoveries of closely related earthworms on widely separated continents?

Examine the mammals pictured on the continents of South America, Africa, India, and Australia.  These living animals are native on their continents.  Each eats insects, and is a major ant/termite eater among all the mammals there.  Each species belongs to a different order of mammals.  These four mammals are very distantly related, even though each is highly specialized for eating ants and/or termites.

  1. Explain in terms of plate tectonics and evolution how four very different kinds of ant/termite eaters could occur in India, Africa, South America, and Australia (Remember, the Age of Mammals began on earth AFTER Dinosaurs become instinct about 65 million years ago).

Conclusion: Now that the expedition is over, what sense can you make of your data?

How do geologists determine the type of environment that existed in an area during the past? A geologist found several layers of sediment exposed in a river bank.  Which was the oldest layer?  The youngest? What is meant by correlation of rock layers? Describe the evidence for the former existence of the continent Gondwanaland. Does this evidence support the Theory of Evolution? How?