Activity 4 The Fossil Record - Woodstown-Pilesgrove Regional … · 2011-11-03 · Activity 4 The Fossil Record GOALS In this activity you will: • Model ways in which fossils are

Coordinated Science for the 21st Century637

Activity 4 The Fossil Record

What Do You Think?

To hold a fossil in the palm of your hand is to have millionsof years of history at your grasp. Fossils tell you about history,and like all good history, they help you to understand both thepresent and the past.

• What is a fossil?

Write your answer to this question in your Active Biology log.Be prepared to discuss your ideas with your small group andother members of your class.

For You To Do

In this activity you will have an opportunity to modeldifferent ways in which some fossils are formed. You will visitseveral stations.


GOALSIn this activity you will:

• Model ways in which fossilsare formed.

• Explain the differencebetween a body fossil and atrace fossil.

• Describe the importance offossils.

• Predict which animals aremore likely to be found inthe fossil record.

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Active Biology

A Highway Through the Past

Station 1: Preservation in Rock

You will mold a clamshell in plaster tomodel how it might be preserved in rock.

1. Obtain a large paper cup. Identify thecup with the name of your group.With a paper towel, smear petroleumjelly over the inside of the cup.

2. Mix plaster in another containerfollowing the directions on thepackage. Work quickly to completethe next four steps.

3. Fill the cup half full of plaster.

4. With the paper towel smear somepetroleum jelly on both surfaces of aclamshell. Gently press the clamshellinto the plaster.

5. Sprinkle a few pieces of confetti overthe surface, enough to cover about50% of the surface.

6. Fill the rest of the container withplaster.

7. Let the plaster harden overnight.

8. In the next class, remove thehardened plaster from the container.Set the plaster on its side and cover itwith a towel. With a hammer gentlyhit the plaster to break it at the layerof confetti.

9. Observe your plaster molds andanswer the following questions inyour Active Biology log:

a) What does the plaster represent?

b) If you had never seen theclamshell, how would you figureout what the shell looked like bystudying the fossil?

c) Clamshells have two parts to theirshell. How many possible imprintscould a clamshell form?

d) Why are fossils most often foundin sedimentary rock formations?

Station 2: Preservation in Resin

You will encase a seed in glue to modelhow it might be preserved in a materiallike resin.

1. Obtain a small paper plate. Writeyour group’s name on it. Use a papertowel to smear a small amount ofpetroleum jelly on a spot on theplate.

2. Using a hot-glue gun, put a bead ofglue on the greased area of the plate.

3. Using tweezers, place the seed on thebead of glue. Add a few more dropsof glue on top of the seed.

4. Let the glue harden overnight.

confetti

plaster

clamshell

Wear goggles and be very careful when handling thehot-glue gun. Keep the hot part of the glue gun away fromskin and flammable materials. Keep the glue away from skin,cloth, or other materials that may be damaged by it. Work ona surface that will not be damaged by the heat or the glue.Tell the teacher immediately of any accidents, including burns.

Weargoggleswhen usingthe hammer.Be sureothersnearby arealso wearinggoggles. To containany bits ofplaster, coverthe fossilmodel withcloth orpaper beforehitting it.

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5. In the next class, remove the bead ofglue and observe. Answer thefollowing questions in your ActiveBiology log:

a) Compare your preserved seed witha sample of amber provided byyour teacher. How are theydifferent? How are they similar?

b) Explain how a seed might endup being preserved in the resin.

c) Would you ever expect to see alarge animal preserved in resin?Explain your answer.

d) Which type of fossil would beeasier to identify: one preserved in rock, or one preserved inresin? Explain your answer.

Station 3: Preservation in Ice

You will freeze a small object in a cupof water to model how organisms canbe preserved in ice.

1. Your teacher will provide you with a paper cup half full of water that isbeginning to freeze. Put your group’sname on the cup.


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2. Gently push the object under thesurface of the ice.

3. Add more water on top of the object.

4. Let the water freeze overnight.

5. In the next class, remove the ice fromthe paper cup. Answer the followingquestions in your Active Biology log:

a) How do you think an organismcould end up being preserved inice?

b) What type of organisms could bepreserved in ice?

Station 4: Preserving Animal Traces

1. Flatten or roll out a piece ofmodeling clay to create a flat surface.

2. On the surface of the modeling clay,produce the pathway that anorganism might leave in a muddysurface. Use your imagination toproduce the pathway. You couldrepresent anything from a wormcrawling to a dinosaur trudging.

3. With a paper towel spread a smallamount of petroleum jelly over theimprints you left in the modelingclay.

4. Mix plaster in a small plasticbag following the directions onthe package. Cut the corner offthe plastic bag. Squeeze enoughplaster over the impression tofill the area.

5. Let the plaster dry overnight.

6. In the next class, remove themodeling clay from the plaster.Answer the following questionsin your Active Biology log:

a) In what kind of ancientenvironment(s) might youexpect to have footprintsformed?

b) Once a set of fresh footprintshave been made in the mud,what would have to happento preserve them as rock?

Do notattempt toremove theobject fromthe ice.




THE NATURE OF THE FOSSIL RECORD

Making Models

Scientists often make models to help them understand how livingthings work. Models can be small-scale structures that simulate whatis found in nature. For example, a scientist might reconstruct theclimatic conditions of 65 million years ago to uncover what might havehappened to the dinosaurs.Another type of model could be nonlivingstructures that work in a similar fashion.The human heart is oftenunderstood from the model of a pump. Recently, scientists have begunusing computers to make mathematical models. Unlike the structuralmodels, these models only exist as numbers. In this activity youmodeled the formation of fossils.

The Importance of Fossils

What does the fossil record tell you? Among a number of things, it tellsyou that species are not unchangeable.The species you see around youtoday are not the ones that have always existed. Fossils provide directevidence that organisms are continually evolving. However, it isimportant to note that evidence of evolution is very different from thetheories of evolution, which you read about in the previous activity.Fossils tell you that life forms on Earth have changed.The theoriesattempt to explain how and why these changes took place.

Fossil Formation

Fossils are preserved evidence of ancient life. Some fossils are calledbody fossils.These are the preserved parts of plants and animals.Fossils may also be trace fossils.These fossils are traces of theactivities of plants and animals, for example, tracks, trails, or scratchmarks.

As you investigated in this activity, fossils form as a result of manyprocesses. For example, most animals become fossilized by beingburied in sediment.The sediments then accumulate and consolidate toform rock. Molds are fossils formed from the impressions in softsediment of shells or leaves, for example, or from footprints or tracks.Casts are replicas formed when a hollow mold is subsequently filledwith sediment—mud, sand, or minerals. Sometimes an insect might

Bio Wordsfossil: any evidence of past life preserved insediments or rocks

body fossil: a fossilthat consists of thepreserved body ofan animal or plantor an imprint of the body

trace fossil: anyevidence of the lifeactivities of a plantor animal that livedin the geologic past(but not includingthe fossil organismitself)


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become trapped in a sticky substance called resin, produced by sometypes of trees.The resin hardens to form amber.The insect fossil ispreserved in amber, often perfectly.At other times natural mummiesform when organisms are buried in areas like tar pits and peat bogs ordry environments like deserts or certain caves. Organisms buried in

Body fossil. Trace fossil.

Cast.




glacial ice also can remain preserved forthousands of years. Finally, the cells andpore spaces of wood and bone can bepreserved if filled with mineral deposits,a process called petrifaction.

Not all organisms become fossils.Tobegin with, very few escape the foodchain.They are either eaten by otherorganisms or are broken down bydecomposers. Soft body parts decayvery quickly.You know from experiencethat it takes little time for meat andvegetables to spoil if left out of therefrigerator. More resistant parts,such as the exoskeletons of insects,vertebrate bones, wood, pollen, and

spores take much longerto decay.Thus, thelikelihood of finding thesein the fossil record is muchgreater.

The Fossil Record

Fossils typically formwhere sediments such asmud or sand accumulateand entomb organisms ortheir traces.The layers ofhardened mud, sand, andother sedimentarymaterials are like a naturalbook of the Earth’s history.Interpreting each layer islike reading the pages of abook. Unfortunately, thereare many surfaces on theEarth where layers are not

Major Divisions of Geologic Time(boundaries in millions of years before present)

Pal

eozo

icP

rote

rozo

icA

rche

anC

enoz

oic

Mes

ozoi

c

modern humans

abundant mammals

flowering plants; dinosaur andammonoid extinctions

first birds and mammals;abundant dinosaurs

abundant coniferous treesextinction of trilobites and other marine animals

fern forests; abundant insects;first reptiles

sharks; large primitive trees

amphibians and ammonoids

early plants and animals on landfirst fish

abundant marine invertebrates;trilobites dominant

primitive aquatic plants

oldest fossils; bacteria and algae

Quaternary

Period EventEra

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Pennsylvanian

Mississippian

Devonian

SilurianOrdovician

Cambrian

1.8

65

145

213

248

286

325360

410440

505

544

2500

Time Not to Scale


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accumulating or where erosion is removing other layers.Thus,interpreting the layers is like reading a novel that is missing most of itspages.You can read the pages that are preserved and even group theminto chapters, but much important information is missing from eachchapter. Paleontologists (scientists who study fossils) use indexfossils.These are fossils of organisms that were widespread but livedfor only a short interval of geological time.They use index fossils todivide the fossil record into chapters. For example, dinosaurs areindex fossils for the Mesozoic era, the unit of time that runs fromroughly 245 million years ago (abbreviated Ma) to 65 Ma. In other

Rel

ativ

e A

bund

ance

Geologic Time (millions of years ago, Ma)

200 100 0

high

low

Tria

ssic

245

to 2

08 M

a

Tria

ssic

245

to 2

08 M

a

Mesozoic Cenozoic

Jura

ssic

208

to 1

44 M

a

Jura

ssic

208

to 1

44 M

a

Cre

tace

ous

144

to 6

5 M

a

Cre

tace

ous

144

to 6

5 M

a

Tert

iary

65 to

1.6

Ma

Tert

iary

65 to

1.6

Ma

Qua

tern

ary

1.6

to 0

Ma

Qua

tern

ary

1.6

to 0

Ma

reef corals

dinosaurs

mammals

oceanphytoplankton

Bio Wordsindex fossil: a fossil of anorganism that waswidespread but lived foronly a short interval ofgeological time




words, all dinosaur species evolved and became extinct during theMesozoic era.Whales, horses, and many other mammal groups, on theother hand, are index fossils of the Cenozoic era, the unit of time thatruns roughly from 65 Ma to the present. Using this and additionalfossil evidence, paleontologists infer that the Mesozoic and Cenozoiceras represent two of the major chapters in the history of life.

The graph on the previous page summarizes the distribution of fourgroups of animals during the Mesozoic and Cenozoic eras. (Please notethat this graph is not drawn to scale along the vertical axis; forexample, the peak in dinosaur diversity is comparatively a small fractionof present day mammal diversity.) Although the graph is a roughsummary of just a small part of the fossil record, paleontologists canget a much more accurate picture of life’s history by examining specificpages in the record.You will do this in the next activity.

1. What is the difference between a body fossil and a trace fossil?

2. What are the chances of an organism becoming a fossil? Explain your answer.

3. a) What is an index fossil?

b) How do paleontologists use index fossils?

4. Use evidence from this activity to explain how the biosphere and the geosphereare connected.

Reflecting on the Activity and the Challenge

In this activity you modeled some of theways in which fossils can form. Youalso read about different types of fossilsand the incomplete nature of the fossilrecord. You may have now developed asense of the importance of fossils.

You can begin to appreciate what mightbe lost if fossil records were destroyedor disrupted. You will need to explainthis at the town-hall meeting if you arerepresenting one of the paleontologists.


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Inquiring Further

1. Carbon-14 dating

How is it possible to determine the ageof organic matter using carbon-14?Research to find the physical and

chemical principles on which thistechnique is based. What are thelimitations of carbon-14 dating?


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Activity 4 The Fossil Record - Woodstown-Pilesgrove Regional … · 2011-11-03 · Activity 4 The Fossil Record GOALS In this activity you will: • Model ways in which fossils are