Student Paleontologists - Delving into Microfossils

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Indiana Expeditions Show

Earth Science

Overview

Given a small clay sample, students will use a simple cleaning procedure to search for microfossils.  They will choose a specific physical characteristic to sort the samples, classify the samples by phylum, and then display the samples for others to examine.

Background Information

Microfossils are the fossilized remains of complete organisms.  These small fossils usually vary in size from roughly 0.05mm to 3mm, although some microfossils may reach much larger sizes.  Microfossils range from single-celled organisms to multicellular organisms.  The most common types of microfossils are foraminifera; marine protozoans, with shells that have small openings; and ostracods, small crustaceans that live inside a bivalve shell. However, there are many other types of microfossils.   

Microfossils are very important to paleontologists (a specialist who studies life forms from previous geologic eras).  Paleontologists can use microfossils to date the age of rocks, particularly rocks from boreholes since microfossils are small and thus, may be abundant in a borehole sample.  Microfossils can also provide a paleontologist with information about the type of environment that existed where the microfossils were found.  For example, foraminifera live in marine or slightly salty environments where seawater and fresh water meet.

Microfossils are usually found in sedimentary beds of shale, limestone, and clay.  If the sedimentary rock is firmly cemented together it can be challenging to remove the microfossils, so clay sediment is often the best place to explore for microfossils.

Connections to the Indiana Academic Standards for Science

3.1.2, 3.1.3, 3.1.4, 3.1.5, 3.2.4, 3.2.6, 3.4.5, 4.1.3, 4.2.5, 5.1.3, 5.1.4, 5.4.8, 5.5.6,

6.1.4, 6.1.5, 6.2.7, 6.2.8, 7.1.4 

Science Process Skills

• Communicating
• Classifying
• Hypothesizing
• Inferring
• Measuring
• Observing

Estimated Time Requirement

Three or four 45-minute sessions

Materials

• One liter of fossil-bearing clay per class of 30 students (found at road cuts, creeks, and rock quarries in and around Brookville, Bloomington and other limestone areas)
• One aluminum pan per group of three students
• One plastic cup per group of three students (prepare cups with fossil-bearing clay as described below)
• Two pairs of nylon stockings (cut to form small bags as described below)
• String (cut into pieces for tying bags as described below)
• Paper towels
• Liquid hand soap
• Water source
• One hand lens per student
• Large bucket for waste water
• One roll of clear tape per group of three students (Note: be sure to use clear cellophane tape, not “invisible” tape that is translucent)
• One pair of scissors per student
• One package of 3” x 5” index cards
• Five microscopes
• Fossil reference materials (The internet can be a rich source for fossil reference materials.)
• Several layers of cheesecloth

Objectives

Students will be able to

• Design a system for sorting microfossils based on physical characteristics.
• Compare and contrast various microfossils.
• Classify microfossils into their correct phyla.

Procedure

Preparation prior to the lesson: 

• Obtain approximately 1 liter of fossil-bearing clay for each class of about 30 students.
• Prepare nylon bags for cleaning the microfossils by cutting each nylon stocking leg into four pieces.  Tie one end of each piece of stocking to make a small bag.
• Divide the fossil-bearing clay into enough cups to have at least one cup of clay per group of three students. 

Anticipatory set:

• View the Earth Science Indiana Expeditions segment.
• Show the students an actual fossil or a picture of a fossil and ask them to describe what they see.  Ask the students about their experience with fossils and if they have ever found a fossil.  Explore the students’ thinking about where fossils are found and how large fossils are.

Lesson sequence

• Ask the students if they know what a paleontologist does.  Explain to them that they will be working as paleontologists for the day and will be exploring some fossil-bearing clay to find microfossils.

Cleaning the Microfossils

• Divide students into groups of three and give each group this equipment: one aluminum pan, one plastic cup containing fossil-bearing clay, one nylon bag, one piece of string, and paper towels
• Instruct students to pour the dry clay into the aluminum pan.  Students should use their fingers to crush the clay until all of the large pieces of clay are broken up. 
• Have students remove any large macrofossils for later cleaning and examination. 
• Instruct students to carefully place all of the material that remains in their pan inside the nylon bag.  Bags should be tied shut using the string. Make sure the knot is one that can be easily untied.
• Have students place the nylon bag containing the crushed clay into their aluminum pan. Fill the pan halfway with water and a little hand soap. 
• Instruct students to gently swish the bag in the water to rinse the material.  The bag should be gently squeezed and swished several times until all of the clay is dissolved.  Note: This process will separate the microfossils from the clay.  Clay consists of very small particles that will dissolve in the water forming a gray silt solution. The larger microfossil particles will stay in the nylon bag.  Some very small fossils may go through the bag.  Students should collect any of these they notice.
• Have students carefully pour the silt from their aluminum pan into the large bucket provided for waste water.  It will be necessary to rinse and drain the bags several times until the water in the aluminum pan looks clear. When the water looks clear, all of the clay particles will have been dissolved. CAUTION: DO NOT pour this waste water down a sink drain.  The clay particles WILL clog the drain.  If desired, this waste water can be filtered through several layers of cheesecloth.  After filtering the waste water through cheesecloth, dispose of the waste water outside in an area covered with soil.  Spread the cheesecloth in your classroom to dry.  After it has dried, students can examine the cheesecloth for additional microfossils.
• When all of the clay is dissolved, students should remove the nylon bag from the aluminum pan.  Instruct students to dry out the aluminum pan and line it with a paper towel. Carefully turn the nylon bag inside out and place the contents on the paper towel lining the aluminum tray.  Leave the microfossils to dry.

Sorting the Microfossils   

• When the microfossils are dry, students should use a hand lens to examine and sort the fossils using one of the physical characteristics below.
  • Size (example: small, medium, large or smaller than… and bigger than…)
  • Shape (example: long, branched, symmetrical, flat, round, cylindrical, etc.)
  • Texture (example: smooth, bumpy, patterned like a…)

Reporting on Progress

• Instruct students to write sentences about what they have done so far, including separating the clay from the microfossils. Students should mention which criterion they used for sorting their microfossils and what they learned from this process.  Encourage students to include drawings and captions to explain what they did.

Making Microfossil Microscope Slides

• Distribute these materials to each group of three students: one roll of clear tape, one index card per student, one ruler per student, one hand lens per student, and microfossils from Cleaning the Microfossils activity.
• Instruct students to prepare the microfossil slides by doing the following:
  • Cut the index card into four strips.  Each strip should measure 1 ¼” X 3”.
  • Fold each strip in half and cut a small “V” shape out of the folded seam as illustrated below.
    
  • Open the strips. A diamond shape will be cut in the strip.
  • Students should write their name on their strips.
• Instruct students to place one piece of clear tape on the bottom of each strip so it covers the diamond-shaped window.  Turn the slide over so the sticky part of the tape is now filling the diamond window and is facing up.  The students have now created “slides” on which to save some microfossils.
• Instruct students to examine their microfossils with a hand lens and choose one microfossil to place on each slide.  To place the fossils on the slides, students should separate the fossil of their choice from the group of fossils, pick up one paper slide, and press the sticky side of the diamond window over the top of the fossil.  After trapping the fossil on the sticky slide, students should place another piece of clear tape over the fossil specimen. This will secure it in place.  Each student should each make at least four microfossil slides.

           Classifying, Comparing, and Contrasting Microfossils

• Students will need access to fossil reference materials.  The internet is a good source for pictures that can be used to classify the microfossils.
• Instruct students to examine their microfossils with a hand lens or microscope and to make detailed drawings of what they see.
• Ask students to compare their fossils to the fossils identified in the reference materials provided.   Tell students to label any fossils that can accurately be identified from the reference materials.  The following are the main types of fossils that can be found:
• Phylum Bryozoa – Bryozoans
• Phylum Brachiopoda – Brachiopods
• Phylum Mollusca – Pelecypods, Gastropods, and Cephalopods
• Phylum Arthropoda – Trilobites
• Phylum Echinodermata - Crinoids
• Students should write a paragraph about each of their fossils using their observations and any information they have learned form the reference materials provided in class.  Challenge students to find ways to measure the size (length, width) of their microfossils using a millimeter scale.
• Tell students to choose two of their microfossil samples and develop a Venn diagram to show how they are similar (compare) and how they are different (contrast).
• Select several microfossil slides and written descriptions.  Place five of the written descriptions on the chalkboard.  Label them a, b, c, d, and e.  Set up five microscopes and place each of the five corresponding microfossil slides on a microscope.  Instruct the students to view each microfossil and match it to the written descriptions posted on the chalkboard.  Switch the sets several times so several students can share their microfossils

Closure:                    

• Tell students to use the following prompt to write about what they have learned:

At first I thought ________ about microfossils but now I know_____.

Suggested Student Assessment

Objective #1:

Have students trade microfossil slides with a partner and then sort the four slides they have based on a physical characteristic.  Then, have the student to whom the slides belong try to determine the characteristic was used for sorting the slides. Students self-assess based on answers provided by classmates.

Objective #2:

Provide students with two different microfossils and have them design a Venn diagram to compare and contrast the microfossils based on observations.

Objective #3:

Provide students with a microfossil sample and fossil reference materials.  Ask them to identify the phylum to which the microfossil belongs.

Extending the Lesson

• Teach the students how to use and design a dichotomous key.  Challenge students to design and test a dichotomous key for their microfossils.
• Challenge students to make some additional paper slides to collect other materials.  Encourage the students to use their own imagination and resourcefulness to produce a variety of slides around a theme.  For example, small rocks can be crushed to provide materials for hundreds of slides.  Spices from the kitchen can also yield several interesting slides.  Students can then observe, sort, classify, draw and write about the items on these slides.

Source of Lesson

Rick Crosslin

Educator - M.S.D. Wayne Township

School Liaison for Science Learning - The Children's Museum of Indianapolis 

This lesson is part of a kit designed by Rick Crosslin in the SK Science Kit and Boreal Laboratories Teacher Developed – Classroom Tested products at www.sciencekit.com 

Deb Sachs
Director, Office of Professional Development

School of Education
University of Indianapolia