-
How-To-Do-It
A Toilet Paper Timeline of Evolution5 E Cycle on the Concept of
Scale
Thomas O’Brien
The theory of evolution of the Earthsystem including both
geological andbiochemical parameters is challengingfor both
teachers to teach and studentsto learn due to a number of
synergisti-cally interactive conceptual, historical,methodological,
philosophical, politi-cal and theological factors (see Miller1998
and National Academy of Sci-ences 1998 & 1999). In fact, the
AAASBenchmarks (1993) argues that:
In the twentieth century, no scientifictheory has been more
difficult for peopleto accept than biological evolution bynatural
selection. It goes against somepeople’s strongly held beliefs about
whenand how the world and the living thingsin it were created. It
hints that humanbeings had lesser creatures as ancestors,and it
flies in the face of what peoplecan plainly see . . . (p. 122).
That this is the case is clearly evidentin the long running
debate over teach-ing evolution in public schools [seethe
eight-part series ‘‘Creationism inthe United States’’ in The
AmericanBiology Teacher, September 1998 to May1999]. This debate
continues to therecent situation in which the state ofKansas has
removed any mention ofthe theory from its curricular stan-dards and
assessments. Yet, there isnear universal consensus among
scien-tists and science educators that evolu-tion is a central
explanatory and pre-dictive theory that demands attentionin both
biology and geology curricula.
While teachers cannot be expectedto single-handedly resolve the
reli-gious and political issues surroundingthe misconstrued and
ill-constructed‘‘evolution 4 atheism vs. creationism
Thomas O’Brien, Ph.D., is an AssociateProfessor of Graduate K-12
ScienceEducation in the School of Education& Human Development
at Bingham-ton University, Binghamton, NY 13902-6000; e-mail:
[email protected].
578 THE AMERICAN BIOLOGY TEACHER, VOLUME 62, NO. 8, OCTOBER
2000
debate,’’ they can and should beexpected to confront students’
motiva-tional barriers and misconceptionsabout evolution and the
nature of sci-entific inquiry. Unfortunately, all toofrequently,
core scientific concepts andtheories such as evolution are
‘‘taught’’without adequate attention to:
1. Personal and social relevanceand usefulness
2. Analogies and models or physicalrepresentations that make
other-wise abstract, counter-intuitiveand difficult-to-conceive
ideasmore ‘‘sensible’’
3. A sense of ‘‘how we know (or atleast tentatively believe)
what weknow,’’ including especially theinterconnections with other
scien-tific concepts and theories
4. The amount of time it takes toeffect conceptual change
andmeaningful, lasting learning.
Without these components, science ispresented as a form of
indoctrination,wherein students are expected toquickly, mindlessly
accept (and subse-quently regurgitate) the ‘‘answers’’from the
unquestioned authority of thetextbook and teacher. Such a
‘‘rhetoricof conclusions’’ type approach doesnot usually raise
concerns among par-ents (perhaps regrettably so), becausemost
scientific concepts and theoriesdo not seem to pose a challenge to
theirmore personal, deeply held religiousand/or philosophical
beliefs, whereasevolution does challenge those whobelieve in a
strict, literal interpretationof the Bible. Clearly, teachers
needhigh-quality hands-on/minds-on activ-ities that make the theory
of evolutionsensible and relevant via an extended‘‘dialogue of
discovery’’ and reasonedargumentation. Books published bythe
National Academy of Sciences(1998), the National Association
ofBiology Teachers (McComas 1994) andThe Woodrow Wilson National
Fel-
lowship Foundation (1995) are won-derful sources of such
activities.
The following 5 E Teaching Cycle(see Trowbridge et al. 2000 for
a gen-eral discussion on 5 E Teaching Cycles)was designed for and
tested in a seriesof two-week teacher institutes titled‘‘Evolution
and the Nature of ScientificInquiry’’ which ran at
BinghamtonUniversity in the summers of 1996-99with the support of a
grant from theHoward Hughes Medical Institute. Ithas subsequently
proven to be one ofthe most used teaching cycles fromthe institute
in both grade 7/life sci-ence and grade 10/biology classrooms.It
addresses one of the more basic,discrepant and truly
mind-bogglingconceptual barriers related to the the-ory of
evolution: the idea of geologictime. Most people have trouble
con-ceptualizing numbers larger than athousand, much less the
millions andbillions of years of Earth history. TheNational Science
Education Standardsclearly identify this as an issue: ‘‘instudying
the evolution of the Earthsystem over geologic time . . . [to] . .
.unravel the interconnected story ofEarth’s dynamic crust,
fluctuating cli-mate, and evolving life forms. . . . Thechallenge
of helping students to learnthe content of this standard will be
topresent understandable evidence fromsources that range over
immense timescales. . . . Many students are capableof doing this
kind of thinking, butas many as half will need concreteexamples and
considerable help in fol-lowing the multistep logic necessary
todevelop the understandings’’ (NationalResearch Council 1995, p.
188). Thissentiment was also expressed in theAAAS Benchmarks
(1993): ‘‘Most vari-ables in nature . . . show immense dif-ferences
in magnitude. . . . A millionbecomes meaningful, however, as
athousand thousands, once a thousandbecomes comprehensible.
Particularlyimportant senses of scale to develop forscience
literacy are . . . the enormous
-
age of the earth and the life on it’’(p. 276).
The problem of the immense scaleof evolutionary time is
exacerbated bythe way it is typically treated in text-books.
Specifically, textbooks com-monly show split timelines with wavyor
broken lines for the PrecambrianEra (87% of Earth’s history) and
datespecific periods back from the present(millions of years
ago/mya) ratherthan forward from Earth ‘‘time zero.’’Additionally,
the numerous, hard-to-pronounce labels associated with thevarious
eras, periods and epochs fur-ther alienate novice learners, as
doesthe quick ‘‘one time topic’’ (vs. recur-ring theme) treatment.
Of course, trun-cated time scales are a necessary evilgiven the
dimensions of a textbook,but teachers should not be limited bythe
textbook scale. What is needed isan approach to the scale of time
thatis analogous to what Morrison, Mor-rison & Eames (1994) did
for the ‘‘rela-tive size of things in the universe’’ intheir
groundbreaking book and late1970s film, ‘‘The Powers of Ten.’’
The following 5 E Teaching Cyclegoes beyond artificial
constraints of ‘‘2x 4’’ teaching (i.e. two covers of thetextbook
and four walls of the class-room) and moves the class out into
aschool hallway to enable students tobetter visualize how ‘‘far
out,’’ seem-ingly OUTrAGEous, yet FUNdaMEN-TAL scientific concepts
and theoriescan be. While other published activitiesmake use of
either relatively longscales [a football field (McComas1994)] or
scales that are rather short[five meters of adding tape
(NationalAcademy of Sciences 1998, pp. 90–92)];this one employs an
intermediatelength that requires getting out of theclassroom, but
not outside of theschool building. This particular 5 Eapproach also
provides a rich opportu-nity to teach the time scale of evolutionin
a way that goes beyond the linguis-tic and logical-mathematical
levels toinclude the musical, spatial, bodily-kinesthetic, and
personal intelligences(Armstrong 1994).
‘‘Wiping Clean’’Misconceptions AboutEvolutionary Time
EngageConsider wearing a ‘‘Whoa, 40 (or
50) is getting pretty serious’’ or similar‘‘old’’ age-related
T-shirt into classand/or playing any one of a numberof popular
songs from the last 50 yearsthat feature the word ‘‘time’’ and/
EVOLUTION TIMELINE 579
or ‘‘changes’’ (examples of 1960-90ssongs: ‘‘Turn, Turn,
Turn’’/Byrds;‘‘Long Time Gone’’/Crosby, Stills,Nash & Young;
‘‘Time in a Bottle’’/Jim Croce; ‘‘Time Keeps on Slipping’’/David
Bowie; ‘‘Longer Than’’/DanFogelberg; ‘‘It’s About
Time’’/JohnDenver; ‘‘Time Passes By’’ and ‘‘Lone-some Standard
Time’’/Kathy Mattea,etc.). If an ‘‘older,’’ less familiar songis
used, challenge the students toexplain the phrase ‘‘time is
relative’’with respect to the fields of biologyand geology vs.
popular music.
Focus Questions1. How ‘‘old’’ is the Earth? What waysdo
scientists have of estimating thisnumber? SW2C: So What, Who (or
whyshould I) Care(s)?
Have students make guesses aboutthe age of the Earth and compare
theirideas to the scientific estimate of 4.5billion years. Briefly
discuss how fun-damental concepts and theories in sci-ences as
diverse as astronomy, biology,chemistry, climatology, geology,
pale-ontology and physics have all contrib-uted to and are somewhat
dependenton the idea of a ‘‘very old’’ Earth asindicated by
radiometric dating. Con-sider having students ‘‘analyze’’ sci-ence
cartoons by Sidney Harris, GaryLarsen and others in terms of
howthey ‘‘play with’’ the concept of theEarth’s (vs. human)
history. Challengestudents to explain the scientific con-cepts (or
misconceptions) that makethe cartoons funny.
2. How much is and how can we con-ceptualize one million? One
billion?
The children’s book How Much is aMillion by David M. Schwartz
andSteve Kellogg (1985) contains a num-ber of fun, visual
representations andanalogies for a million (e.g. a fish bowlbig
enough to hold a million goldfishwould be large enough to hold a
60-foot whale), a billion (goldfish wouldneed a bowl as big as a
sports stadium)and a trillion (goldfish would need abowl as big as
a city harbor). Challengestudents to come up with their
ownrepresentations for these large num-bers. A simple model that
can be dis-played on the classroom walls is dots(as many as 4000 to
5000) on standard11 x 8 1/2’’ stationery (for a total of 200to 250
pages to represent 1 million).
3. Has the Earth always contained abiosphere with living
organisms?What evidence do scientists use toanswer this question?
In what waysdid early life forms transform theirenvironment?
Elicit and record student ideas thatwill undoubtedly contain a
variety of
misconceptions about the idea of thefossil record and the long
time frameduring which microbes were the onlylife forms present. Do
not be concernedwith teaching/telling the ‘ ‘r ightanswers’’ at
this time, but have stu-dents begin to explore the questionsby
consulting their textbook, referencematerials [such as Hoagland
& Dodson(1995) and Whitfield (1993)], and Websites (see listing
under Explain).
Briefly discuss the notion of decou-pling Earth and human
history bylabeling 4.5 billion years ago as ‘‘timezero’’ for our
planet vs. the standardmethod of dating the Earth’s eventsin
millions (or billions) of years ago(mya) from our current time.
Segmentsfrom the videos listed below underthe Explain section may
also be usefulhere for motivational purposes.
ExploreRelevant data on the Earth’s evolv-
ing natural history needs to be sup-plied by teacher, textbook,
or multime-dia or Internet source to teams work-ing with
calculators. Detailed timelinesof key points in evolutionary
historyare available in McComas (1994, pp.34–39), National Academy
of Sciences(1998, p. 91), Tarbuck (1994, CD-ROM)and most
extensively, in the CorrelatedHistory of Earth Poster, a highly
de-tailed, full-color poster from Pan Terra,Inc. (available from
the WorldwideMuseum of Natural History at 800-216-8130 or
www.wmnh.com). Whilethis information is provided to stu-dents as
‘‘received knowledge,’’ it isimportant to emphasize again the
con-currence of views arrived at throughmultiple scientific
disciplines and tochallenge students to consider if thesequence of
interrelated events ‘‘makessense’’ from a developmental
per-spective (as such evolution must be atheme that is repeatedly
returned tothroughout the entire school year).
With some flair and sense of fun,introduce the ‘‘Toilet Paper
Timelineof Science’’ as an inexpensive, longroll of paper that can
be used as asimulation for geological time. Priorto unrolling the
toilet paper down along hallway and marking key pointsof interest,
have groups check eachother’s calculations. The scale can begiven
to or derived by the studentsdepending on their experience and
theamount of time allotted. Many com-mon brands of toilet paper
have 280sheets per roll and will easily fit intypical school
hallways. (Alternatively,some cheaper, single-ply brands of toi-let
paper come with 1000 sheets.).
-
SCALE: 4.5 x 109 yrs /280 sheets 4450 x 107/280 4 16 x 106
yrs/sheet
16 x 106 yrs/11.1-cm sheet 4 1.44 mil-lion yrs/1 cm 4 1 million
yrs/0.69 cm
Focus Questions1. How does the history of livingorganisms
(including eventuallyhumans) compare in length (duration)to Earth’s
history? How many sheetsof toilet paper would this be fromEarth
time zero?
Microbial Life (prokaryotes) beganapproximately 3.8 x 109 yrs
ago or 0.7x 109 yrs from Earth ‘‘time zero’’:
0.7 x 109 yrs/4.5 x 109 yrs 4 0.1555[During the first 15.5% of
Earth’shistory, there was no life presentor, conversely, life has
been pres-ent for 84.5% of Earth’s history.]
0.1555(280 sheets) 4 43.54 sheetsfrom Earth ‘‘time zero.’’
Until recently, it was believed thatprokaryotes were the only
forms oflife for roughly the next two billionyears. Research by
Brocks et al. (1999)now seems to indicate that eurokary-otes
evolved as early as 2.7 billionyears ago. To help students better
visu-alize the idea of ‘‘billions of years,’’have them work with a
Time TravelAnalogy: Assuming a year of time wasrepresented by one
mile and that youcould travel back in time in a conven-tional car
traveling at the speed limitof 65 mph (or use 100 mph for
easiercalculations if desired).
2. How long would your auto trip backto see the beginning of
life on Earthtake? How many typical human life-times is this? How
many generations?
3.8 x 109 miles x 1 hr/65 miles x1yr/8760 hours 4 6674
years[Note: The earliest human citieswere built approximately
6000years ago.]
6674 yrs/80 yr lifespan 4 over 83lifetimes of auto speed travel
time
6674 yrs/20 yrs reproduction cycle4 approximately 334
generations
3. Given that bacteria can still argua-bly be considered the
most prevalentlife form on Earth and assuming bacte-ria can
reproduce every 20 minutes,what’s the maximum number of
gener-ations of bacteria that could have theo-retically existed
over the last 3.8 bil-lion years?
3.8 x 109 yrs x 8760 hrs/1 yr x 60min/1hr x 1 generation/20
min
4 1013 generations 4 a lot of evolu-tionary time
4. Where would the following signifi-cant events occur on the
Toilet Paper
580 THE AMERICAN BIOLOGY TEACHER, VOLUME 62, NO. 8, OCTOBER
2000
Timeline? Any of the previously citedevolutionary timelines can
be used toidentify the developmental timelinefor all the major
plant and animalgroup [fish—amphibians—reptiles(including
dinosaurs)—mammals—birds] ‘‘firsts’’ that occur betweenpoints (a)
and (b). The Correlated His-tory of Earth poster is
especiallydetailed and includes pictures of thecoinciding positions
of the Earth’s con-tinents. Look for connections such aslinks
between plant reproduction andanimal pollinators and be sure
thatstudents note that the poster’s timelineis NOT/cannot be drawn
to a uni-form scale.
(a) Cambrian ‘‘Explosion’’: 570 mil-lion yrs ago 4 0.57 x 109
yrs: seg-mented worms, coral anemones, jelly-fish, sponges, lamp
shells, clams, snail,squid, trilobites, crabs, etc.
4.5 x 109 yrs—0.57 x 109 yrs 4 3.93x 109 yrs from Earth ‘‘time
zero’’
3.93/4.5 4 0.8733 [87% of Earth’shistory occurred before
inverte-brates]
0.8733(280 sheets) 4 244.53 sheetsfrom Earth ‘‘time zero’’
(b) First ‘‘Homo’’: 2 million yrs ago:Homo habilis → Homo
erectus
4500 x 106 yrs—2 x106 yrs 4 4498 x106 yrs from Earth ‘‘time
zero’’
4498/4500 4 0.999550.99955(280 sheets) 4 279.88 sheets
from Earth ‘‘time zero’’0.88 sheets(11.1 cm/sheet) 4 9.8 cm
from start of last sheet #280 on roll
(c) Homo sapiens neanderthalis:200,000 yrs ago 4 0.2 x 106
yrs
4500 x 106 yrs—0.2 x 106 yrs 4 4499.8x 106 yrs from Earth ‘‘time
zero’’
4499.8/4500 4 0.9999550.999955(280 sheets) 4 279.9875
sheets from Earth ‘‘time zero’’0.9875 sheets (11.1 cm/sheet)
4
1 0 . 9 6 c m f r o m s t a r t o f l a s tsheet/ #280
Homo sapiens sapiens: The sole‘‘survivors’’ of the Homo line
date toapproximately 100,000 yrs ago, appar-ently overlapping in
time and locationwith the Neanderthals whom they sub-sequently
re/displaced, and show upin the last 0.1 cm (or 1 mm) of thetoilet
paper timeline.
ExplainUse discussions, simulations, videos,
virtual trips on the World Wide Web,etc. to explain the idea
that currentspecies have evolved via descent withmodification over
long expanses oftime and to provide a clearer sense of
the data and reasoning that supportsthis idea.
InternetAmerican Museum of Natural History
in NYC: http://www.amnh.org/Human Origins & Evolution in
Africa:
http://www.indiana.edu/;origins/National Museum of Natural
History
(Smithsonian Institution), Departmentof Paleobiology:
http://www.nmnh.si.edu/departments/paleo.html
Online Literature Library (Voyage ofBeagle, Origin of Species
& Descentof Man):
http://www.literature.org/authors/darwin-charles/
Paleontological Research
Institution:http://www.englib.cornell.edu/pri/
Royal Tyrrell Museum: http://www.tyrrellmuseum.com/home
UC-Berkeley Virtual Museum of Pale-ontology:
http://ucmp.berkeley.edu
U.S. Geological Survey:Dinosaurs: Fact & Fiction:
http://
pubs.usgs.gov/gip/dinosaurs/Fossils, Rocks and Time: http://
pubs.usgs.gov/gip/fossils/Geological Time (online edition):
http://pubs.usgs.gov/gip/geotime
MultimediaLife on Earth: A Natural History.
(David Attenborough). Two 233-min.videos with Chapter Search and
on-screen numerical codes for quickaccess to each of the program’s
13chapters (keyed to the accompanyingbook published by Little,
Brown &Co., 1979). Carolina Biological: 1-800-334-5551 for
$39.95 (K3-49-1150-V).
Planet of Life (Discovery Channel): 6hrs 50 min. on 4
videotapes: #1: Part1/Birth of Earth & Part 2/AncientOceans;
#2: Part 1/When DinosaursRuled & Part 2/Creatures of the
Skies;#3: Part 1/Insect World & Part 2/Apesto Man; and #4:
Evolution’s Next Step.Discovery Channel Video, PO Box4055, Santa
Monica, CA 90411-4055; 1-800-207-5775. [$49.95].
A Science Odyssey: The Journey of aCentury (Host: Charles
Osgood). Fivetwo-hour videos including ‘‘How WeKnow What We Know’’
about Origins(1st hr: Wegener & continental drift/plate
tectonics, geological forces, ageof the Earth, Darwinian evolution,
pale-ontology ` 2nd hr: genetics, DNA,Miller & Urey and the
first life forms).PBS Home Video, 1-800-645-4727.$79.98/A3078 `
$30/B3078/accompa-nying book by Charles Flowers (Wil-liam Morrow
& Co., Inc. 1998, pp.126–177).
ElaborateFormative assessment is ongoing
throughout the various activities. If the
-
students have not already done so inthe Explore phase, use the
aforemen-tioned timelines to ‘‘fill in the details’’of major
‘‘firsts’’ in the evolution oflife. If the toilet paper timeline is
tapedto the walls in the hall, students canadd relevant artwork and
informationabove and below the timeline for semi-permanent display
to catalyze out-of-class conversations about expandingthe idea of
‘‘prehistory’’ to includethe huge expanses of time before
thearrival of humans.
EvaluateStudents can be challenged to
develop other models such as a 365‘‘day’’ 4 Earth’s 4.5 billion
year calen-dar for display and/or check the accu-racy of geographic
analogy scales (1mile 4 million years) such as thatpublished by
Packard (1994). Othersummative projects might includegraphic
displays, computer simula-tions, cartoons, science songs,
fictionalnews releases challenging Darwin’scritics (such as Lord
Kelvin’s faultyestimate for the age of the Earth), skits,etc. for
individual students and/or stu-dent teams. Another possible
extensionis to challenge students to criticallyanalyze the flaws in
the arguments of
EVOLUTION TIMELINE 581
young Earth creationists by reviewingInternet sites such as:
Creationism &
Pseudoscience:http://users.deltanet.com/;fsteiger/
creation.htmDialogue Between Science & Reli-
gion/AAAS:http://www.aaas.org/spp/dspp/
dbsr/default.htmEvolution Controversy/Talk Origins
Archive: Exploring Creationht tp ://www.ta lkor ig ins .org/
origins/other-links.htmlNational Center for Science
Education:
http://www.NatCenSciEd.org/Science & Creationism:
http://www4.
nas.edu/opus/evolve.nsf
The key factors to remember through-out this 5 E Teaching Cycle
are:
1. Students need multiple, rationallysequenced experiences that
drawon a full array of intelligences tocounter their everyday
concep-tions of ‘‘history’’ and its undulyrestrictive association
with humansand human lifespans.
2. Engaging students in a ‘‘dialogueof discovery’’ and
‘‘questioningthe answers’’ takes more timethan simply providing
themauthoritative, ‘‘just the facts’’
answers. Conceptual change is anevolving, dialectical process
aswas the development of the targetscientific theory.
3. Some students will find it difficultto ‘‘believe’’ the
scientific view,even if they understand it concep-tually, due to
deeply held, con-flicting personal religious beliefswhich must be
respected. Mini-mally, assure such students thatscience in general
(and evolutiontheory in particular) does notrequire one to be an
atheist, butrather is simply agnostic in itsmethodological
approaches todeveloping provisionally accepted,proximate causes
(‘‘how’’) to nat-ural phenomena. Science does notdirectly address
the domain ofultimate, perhaps supernaturalcauses (‘‘why’’) that
are the terri-tory of religion.
Evolution, properly addressed as atheme that pervades an entire
courseof study, provides a perfect opportu-nity to engage students
in criticallyanalyzing the nature of scientific in-quiry, including
the scientific meaningof the term ‘‘theory’’ (Rudolph &
Stew-art 1998) and other commonly held‘‘myths’’ about science
(McComas
-
1996). The mistaken separateness ofthe numerous topics and
chapterswithin textbooks belies the underlyingunity that powerful,
interlinked theo-ries provide to science and scienceeducation
(Duschl 1990). Science asan evolving product and process
isinherently constructivist and economi-cal in its efforts to
explain the broadestrange of phenomena in terms of thefewest number
of unifying basicassumptions, concepts, and empiri-cally supported
laws and theories. The‘‘ever-evolving’’ theory of evolutionmakes a
perfect case study for thispoint.
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Need to Know about the Way All LifeGrows, Develops, Reproduces,
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