Performance Benchmark N.8.A.3
Students know different explanations can be given for the same evidence.
E/S
“Evidence is almost always incomplete, inconclusive, and amenable to multiple
explanations...we always reason in the presence of uncertainty.” —Robert Mislevy, Professor of
Measurement, Statistics, and Evaluation at the University of Maryland
Evidence from the natural world is collected through observations and experimentation but it is
up to the scientist to make sense of the data and draw conclusions. Therefore, two different
scientists may draw two different conclusions from the same evidence. Scientific evidence is
interpreted using reason and logic. However, scientific interpretation is embedded within the
dogma of the time. To counter human nature, science requires that conclusions be validated by
repeated experimentation and are subjected to peer review. Lastly, scientific explanations
(conclusions) are well founded in logic but are tentative as scientists must be willing to modify
their ideas as new evidence is uncovered.
The extinction of the dinosaurs is a good example of how different explanations are derived from
the same evidence. Looking at the same evidence found in the rock strata, four dominant
hypotheses are being further investigated: asteroid impact, increased volcanism, mammal
competition, and continental drift (climate change). Figure one shows how evidence supports
each of these hypotheses.
Hypothesis
Asteroid
Impact
Volcanism
High Iridium
Level in
Rocks
Melted
Rock
Fractured
Crystals
Fossil
Record
Impact
Crater
X
X
X
X
X
X
X
X
Mammal
Competition
Continental
Drift
Lava
Flows
Sea
Level
X
X
X
X
Figure 1. This table shows how the abundant evidence supports multiple
hypotheses on the cause of the extinction of dinosaurs.
(From http://www.pbs.org/wgbh/evolution/extinction/dinosaurs/index.html)
Most scientists agree that an asteroid impact in the late Cretaceous off the Yucatan Peninsula
was a dramatic event that sealed the dinosaur’s fate. But many argue that increased volcanism,
the rise of mammals, and gradual climate change (wet/hot to dry/cool) due to continental drift
may have each contributed to the demise of the dinosaurs or one idea individually may have
actually been the driving force that ended the Age of Dinosaurs. Which idea is the right one?
All are equally valid and additional evidence may further support one hypothesis over another or
completely discount one or more hypotheses.
A current issue that is being debated by scientists is global warming. Most scientists agree that
in the short run (last 100 years) global temperatures have increased significantly, but they
disagree on the cause. Some scientists say that the increase in temperature is solely
anthropogenic caused by the burning of fossil fuels. Other scientists say that human impact is
minimal and that the climatic change is due to normal Earth cycles supported by long range
(400,000 or more years) data. Figure 2 shows the change in global temperature since 1860. It
shows that the last 30 years have exhibited warmer temperatures than the preceding 100 years.
Coupled with Figure 3, the change in atmospheric CO2, a relationship between temperature and
CO2 is strongly suggested.
Figure 2. Global average surface temperatures since 1860.
(From: http://www.grida.no/climate/vital/17.htm )
Figure 3. Atmospheric CO2 since 1958
From ( http://www.exo.net/~pauld/workshops/globalclimate/atmospherecarbondioxide.htm)
Plotting atmospheric data over 400,000 years, as shown in Figure 4, the debate becomes even
more ardent. A relationship between CO2 and temperature is also suggested since both
parameters show the same trends over time. Again, scientists present different explanations for
the same data. Some suggest that we are just living through a natural peak of CO2/temperature
fluctuations, while others contend that humans are the current cause of the shown results.
Figure 4. Global temperature and atmospheric CO2 concentrations over the last 400,000.
(From http://www.grida.no/climate/vital/02.htm)
A scientific consensus as to cause and effect of CO2 and global temperatures does not exist.
Does the CO2 level cause the temperature change? Does the temperature change cause the
change in CO2 level? Is there a third factor affecting both? Are we to blame for the climatic
shift? Is this just a natural long term Earth cycle? Only time will tell.
For more information on Global Warming:
General information from the EPA, http://www.epa.gov/climatechange/
General information geared to students, http://epa.gov/climatechange/kids/index.html
“The Other Side of Global Warming Debate:”
http://personals.galaxyinternet.net/tunga/OSGWD.htm
Performance Benchmark N.8.A.3
Students know different explanations can be given for the same evidence.
E/S
Common misconceptions associated with this benchmark
1. Students incorrectly believe that “evidence accumulated carefully will result in sure
knowledge”
McComas, William, Ten myths of science: Reexamining what we think we know...., Vol. 96,
School Science & Mathematics, 01-01-1996, pp 10
More information pertaining this misconception can be found at
http://www.geocities.com/otisbrown17268/scihist.html
Scientists are required to evaluate each new piece of data and modify their model to include the
new data. Any designed model must be flexible to allow the addition of newly discovered items
or relationships. Science can only produce possible explanations for natural phenomena. With
new data collected with new technologies, tools, and techniques old models are replaced with
new findings. For example, the reclassification of Pluto has changed the model of our solar
system. Models change as more information is discovered.
2. Students incorrectly believe that there is only one accepted model for a given scientific
concept/belief.
Many models may be designed to explain a phenomenon using the same data set to meet the
needs of the user. One scientist may be interested in macro level relationships while another
may design a model that shows micro level relationships. Therefore, a model may be extremely
simple or very complicated when more specificity is needed.
The following link can be used to show students the evidence and dominant theories associated
with the extinction of the dinosaurs.
http://www.pbs.org/wgbh/evolution/extinction/dinosaurs/index.html
Performance Benchmark N.8.A.3
Students know different explanations can be given for the same evidence.
E/S
Sample Test Questions
Questions and Answers to follow on a separate document
Performance Benchmark N.8.A.3
Students know different explanations can be given for the same evidence.
E/S
Answers to Sample Test Questions
Questions and Answers to follow on a separate document
Performance Benchmark N.8.A.3
Students know different explanations can be given for the same evidence.
E/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. The Earth is Flat!!
This is a great activity that makes students evaluate data and draw logical conclusions.
According to the website, “Students are exposed to a compelling idea: the Earth really IS flat!
They are challenged to provide the evidence for a spherical earth, then present the evidence
(experiences) for a flat earth, discuss the relative strengths of the evidence, and reach
conclusions. The Social Context of science is also explored, with the roles of collaboration and
past experience biases being emphasized. “
To access this activity visit http://www.indiana.edu/~ensiweb/lessons/flaterth.html
2. Drawing Conclusions
This website provides a free downloadable activity appropriate for grades 6-12. The activity
walks students through how to draw a conclusion. An extension to this activity is to have
students draw their own conclusions from the available data and discuss and defend their
conclusion. This should drive home the point that multiple logical conclusions are possible from
the same data.
This activity can be downloaded from,
http://www.teachervision.fen.com/tv/printables/SISA00151_3.pdf
3. What killed the dinosaurs?
This website provides an interactive survey of the evidence that supports five different theories
for the extinction of dinosaurs as discussed in the content section of this webpage. Students can
click on each piece of evidence and see how it supports one or more proposed hypothesis. The
information is supported with animations, hyperlinked glossary for vocabulary,
pictures/diagrams, and grade level appropriate text.
This activity can be accessed at
http://www.pbs.org/wgbh/evolution/extinction/dinosaurs/index.html
4. Rickshaw or Rowboat? Is Climate Change Coming?
This webquest is a problem-based learning activity. “The target class of this activity is eighth
grade Integrated Science in Bangladesh but it could be adapted to higher levels and other
locations very easily. Students should have previous knowledge of the water and carbon-oxygen
biogeochemical cycles, as well as local weather events, collecting data on them, and basic
understanding of the role of the ocean in regulating regional climates.” Students are assigned
roles (environmentalist, climatologist, economist, and social scientist) and research climate
change and draw their own conclusions on how rural Bangladeshis’ lives might be affected. A
construct a feasible proposal to the UN to assist where needed.
To access this webquest, go to
http://teacherweb.com/BD/AIS_D/Rickshaw_or_Rowboat/index.html