Content Benchmark E.8.C.1
Students know sedimentary rocks and fossils provide evidence for changing environments and
the constancy of geologic processes. E/S
We as human have always been interested and curious about Earth’s history. Our curiosity is
only heightened with the examination of fossils. We can examine life forms from millions of
years ago by looking at the remnants of their imprints in the rocks. Since sedimentary rocks
accumulate over time we have a record of the past environments and ancient life of Earth. This
raises many questions such as: Why are fossils found in sedimentary rocks? What causes a
fossil? Is the rock record complete? How do we determine the age of rocks and the fossils they
contain?
The Rock Cycle and Sedimentary Rocks
The rock cycle is a model of the transition of rock material throughout the Earth. The cyclical
pattern denotes that the material from one phase to another is constantly being recycled through
geological processes. Sedimentary rocks are primarily formed via two processes: chemically,
and compaction and cementation. Depending on the environment, chemically suspended
material within a medium, like salt in water, can yield rocks when the dissolved minerals
precipitate out of the liquid, or the liquid medium evaporates and leaves behind a crystal.
Compaction and cementation occur when fragments of rocks, clasts, are buried and compacted.
The process of compaction occurs when overlying sediments cause pressure, and thus squeeze
the fragments together; if water is present in the process, then cementation can also occur. The
water carries dissolved minerals that may be left behind creating a cement to hold the clasts
together.
For more information on the rock cycle go to
http://www.learner.org/interactives/rockcycle/index.html
Figure 1. The rock cycle.
(From http://www.fas.org/irp/imint/docs/rst/Sect2/Sect2_1a.html)
Sedimentary Rocks and Fossils
Sedimentary rocks are so very important to fossils because they provide the medium of
preservation. In clastic sedimentary rocks, formed from burial, compaction and cementation,
fragments of rock can be as fine as clay and thus settle into the very fine details within a bone or
other hard parts of dead organisms. Typically only the hard parts of an organism are preserved,
but fossils can come from a variety of sources. Three main processes can produce a fossil; traces
of organisms, petrified remains, and preservation of organic material.
Figure 2. Liaoning Fossil Bird, Cathayornis yandica.
(From http://www.fossilmuseum.net/EdResources/FossilImages.htm)
Traces of organisms are most commonly referred to as molds and casts, but trace fossils, and
coprolites, the fecal remains of organisms, are also produced through this method. In traces of
organisms, no part of the original organic material remains. When an organism dies and is
quickly buried the imprint it leaves behind after its decay is called a mold. This empty cavity
can then be filled in by sediment that will eventually harden to produce a cast. The cast can be
extremely detailed depending upon the grain size of the clasts that fills the mold. A casts can
provide great detail for the surface of the buried organism but the internal structure is not
preserved. A trace fossil is a fossil of the movement of ancient life. Footprints and other traces
of ancient life can be produce very similarly to a mold and cast. The footprint can leave a cavity
that sediment can fill and preserve. Coprolites are produced from the preservation of dung and
waste. Petrified remains occur when minerals, carried by water, gradually replace organic
material. The slow process of mineralization often produces a near perfect mineral replica of the
original organism. This process most often occurs with downed trees and other plant parts.
Unlike in the two types of fossilizations described above, it is possible for the remains of the
organic material to be preserved. Preservation of an organism’s organic material can occur if the
organism is mummified or incased in amber, tar, or ice. Mummification may occur in an arid
environment that prevents bacteria from breaking down the remains due to the lack of water.
Amber, hardened tree sap, can incase and preserve small organisms. Tar seeps and freezing can
also preserve organisms by preventing decay. When the original remains of the organism is
preserved the structure and internal organs remain and often DNA can be extracted from the
remains.
For more information about fossil visit
http://www.fossils-facts-and-finds.com/how_are_fossils_formed.html
The Fossil Record
Fossils provide all of the evidence of past life, and due to the nature of their formation, they
contain a record of past environments. Sedimentary rocks cover a large portion of Earth surface
and are therefore more susceptible to weathering and erosion. Because of this the rock record is
like a book with pages, or chapters in some cases, missing. Often paleontologists correlate rock
layers (strata) between different locations in order to fill in the gaps of missing rock. By
examining the rock layers geologists are able to place them in relative date order to better
understand Earth’s history.
For more information about weathering and erosion see MS TIPS Benchmark E.8.C.2
For more information about the fossil record go to http://www.fossilmuseum.net/fossilrecord.htm
For a database of fossils go to
http://www.paleoportal.org/index.php?globalnav=fossil_gallery&sectionnav=main
Relative Age Dating
James Hutton’s principle of uniformitarianism is the basic principle that guides the relative age
dating process. The principle of uniformitarianism states that the geologic processes that
occur today occurred in the past. From this principle and observation geologists can examine
rock strata and view them as pages in the book of Earth’s history. The first law derived from the
principle of uniformitarianism is the law of superposition. The principle of original
horizontality uses uniformitarianism to state that sedimentary rocks are originally deposited in
horizontal layers. The law of superposition states that, because all sedimentary rocks are
originally deposited in horizontally beds, the oldest rock stratum is at the bottom with successive
younger strata as you get to the surface. The law of crosscutting relationships, another relative
dating practice, states that any fault or intrusion within strata must be younger than the strata in
which it cuts across. The law of inclusion states that if a rock fragment is found within another
layer the rock must be older than the layer in which it is found.
For more information about relative age dating go to
http://pubs.usgs.gov/gip/geotime/relative.html and
http://www.talkorigins.org/faqs/dating.html#princ
Within time the strata can become distorted by uplifting crust, weathering and erosion can
remove entire layers, and magma can rise and solidify. These distortions over time can cause a
break or gap in the rock record which is called an unconformity. There are three types of
unconformities; angular unconformity, disconformity, and nonconformity. In an angular
unconformity, strata is uplifted and tilted, then weathered and eroded. New strata are then
deposited on top of the tilted layers.
Figure 3. Angular unconformity diagram.
(From http://earthsci.org/education/teacher/basicgeol/geotim/geotim.html)
A disconformity occurs when strata is uplifted, weathered, and eroded. New sedimentary rock
forms over the weathered surface, as the strata subside, causing an unconformity (missing layers
of sedimentary rock) in the rock record.
Figure 4. Disconformity diagram.
(From http://earthsci.org/education/teacher/basicgeol/geotim/geotim.html)
Nonconformities occur when strata (sedimentary rock layers) rest in contact with igneous or
metamorphic rock. Because igneous and metamorphic rock do not stratify (form layers),
determining if layers of sedimentary rock have been removed becomes difficult. It would be
impossible to tell if uplift, erosion and new stratification of sediment had occurred without
correlation from other locations.
Figure 5. Nonconformity diagram.
(From http://earthsci.org/education/teacher/basicgeol/geotim/geotim.html)
For an on-line tutorial, with diagrams, of relative age dating and unconformity formation go to
http://www.classzone.com/books/earth_science/terc/content/investigations/es2903/es2903page01
.cfm
Try It Out: Sample strata that can be used to practice dating the events.
Which layers came first?
1. Q (deposition)
2. O (deposition)
3. N (deposition)
4. L (deposition)
5. M (principle of inclusion,
and contact metamorphism
to produce a
nonconformity)
6. P (principle of cross-cutting
relationships, with contact
metamorphism)
7. Tilt and Uplift
8. Weathering and erosion
9. H (deposition, produces an
angular unconformity)
10. I (deposition)
11. J (deposition, possible
disconformity)
12. Weathering and erosion
13. K (deposition)
Figure 6. Sample geologic strata that can be used to test your understanding of Relative Age Dating.
(From http://highered.mcgraw-hill.com/sites/0078664233/student_view0/unit6/chapter21/section2/selfcheck_quiz.html)
Absolute Age Dating
The process of absolute age dating, radiometric age dating, is the use of radioactive isotopes to
give an exact date or age of that material (rock or organic remains). With the discovery that
radioactive isotopes decay at constant rates, the age of rocks and other material can be found by
comparing the amount of radioactive parent material to the stable daughter product. The time it
takes for half of the radioactive isotope to decay is referred to as the half-life. For example,
carbon 14 has a half-life of 5,730 years. If a sample of organic material is found to have 50%
daughter product (nitrogen 14 in this case) and 50% carbon 14, then the sample is 5,730 years
old. If two half-lives have gone by from the previous example then the sample (75% stable and
25% radioactive) then the sample is 11,460 years old. Radioactive isotopes are not affected by
weathering or erosion, heating and cooling processes (given that the sample does not melt).
Radiometric dating has produced strong evidence that the Earth is 4.5 to 4.6 billion years old.
The oldest discovered rocks on Earth (zircon crystals) were found to be 4.0-4.2 billion years old,
the oldest known fossils were found to be 3.5 billion years old, and the most recent ice age was
found to have ended 10,000 years ago.
Figure 7. Graph comparing the number of parent atoms to daughter atoms in half lives.
(From http://www.gpc.edu/~pgore/geology/geo102/radio.htm)

Parent
Daughter t1/2
206Pb
4.5
b.y
207Pb
710
m.y
232Th 208Pb
14
b.y
238U
235U
40K
40Ar &
1.3
Useful
Range
Type of
Material
>10
million Igneous
years Rocks and
Minerals
>10,000
40Ca
b.y
years
87Rb
87Sr
47
b.y
>10
million
years
14C
14N
100 5,730
70,000
y
years
Organic
Material
Figure 8.Radioactive half-life data
(From http://earthsci.org/education/teacher/basicgeol/geotim/geotim.html)
For more information about absolute age dating go to
http://regentsprep.org/Regents/earthsci/radioactivedecay.htm
To learn more about the age of Earth go to
http://geomaps.wr.usgs.gov/parks/gtime/ageofearth.html
Content Benchmark E.8.C.1
Students know sedimentary rocks and fossils provide evidence for changing environments and
the constancy of geologic processes. E/S
Common misconceptions associated with this benchmark
1. Students have difficulties with the scale of time.
Some geological phenomena are so different from everyday reality that their understanding
can be problematic. The scale of geological time, the rate of mountain building or erosion,
the architecture of an oil field or aquifer and the pressures at depth in the earth’s crust are a
few such phenomena. Students must be allowed the time to model geophysical process and
make analogies between their model and the actual process. Without doing so, their
preconceptions and intuition may prevent them from fully grasping the 4.5 billion years of
Earth’s existence.
For an explanation about how to overcome geological misconceptions with hands-on
activities that model Earth’s processes go to http://www.gees.ac.uk/planet/p17/jc.pdf
2. Students have great difficulty in conceptualizing times that stretch into millions or
billions of years.
This problem stems from the lack of understanding of the magnitude. Using analogies is a
great way to get students to start thinking of magnitudes of time accurately, and producing
accurate scales for comparison yields great results. For example, if a human blinks
10,000,000 times a year. Only the last 4,000 blinks (just over 4 hour’s worth) would
represent the time humans have been on the Earth.
For further explanation and a lesson plan for scaling geologic time, go to
http://www.actionbioscience.org/education/lewis_lampe_lloyd.html
3. Students incorrectly believe that fossils are pieces of dead animals or plants.
Students must be made aware that fossils are typically made of rock. Minerals fill in the
spaces left behind by animals or plants, and that no part of the organism remains. Only under
very specific circumstances; freezing, insects trapped in tree sap, tar seeps and
mummification, are there actual organic remains.
For more information and activities go to http://education.usgs.gov/schoolyard/fossils.html.
4. Students incorrectly believe fossils of tropical plants can not be found in deserts.
Students often incorrectly believe that the Earth is sedentary and that the environments of
today’s Earth are constant. With this misconception students can not understand why fossils
of marine organisms could be found at the top of mountains, like Mt. Charleston for example.
The continents have shifted greatly over time and oceans have come and gone. Uplift and
subsidence have produced great changes in the topography of the landscape, but the rock
record remains intact. The fossil record provides clues about past environments of local
areas. In fact, tropical plant fossils have even been found on Antarctica.
To learn more about the dynamic Earth go to
http://www.ucmp.berkeley.edu/education/dynamic/
To learn more about fossils from Antarctica go to
http://www.sciencemag.org/cgi/content/full/282/5397/2199
Content Benchmark E.8.C.1
Students know sedimentary rocks and fossils provide evidence for changing environments and
the constancy of geologic processes. E/S
Sample Test Questions
Questions and Answers to follow on a separate document
Content Benchmark E.8.C.1
Students know sedimentary rocks and fossils provide evidence for changing environments and
the constancy of geologic processes. E/S
Answers to Sample Test Questions
Questions and Answers to follow on a separate document
Content Benchmark E.8.C.1
Students know sedimentary rocks and fossils provide evidence for changing environments and
the constancy of geologic processes. 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. Interactive Rock Cycle
Annenberg Media produced a site with interactive rock cycle and classification information.
The site ends with a printable assessment about the rock cycle that would be a great follow
up assignment after the rock cycle lesson.
To learn more, go to http://www.learner.org/interactives/rockcycle/index.html.
2. Relative Age Dating Lab
Pamela J. W. Gore from the Department of Geology, Georgia Perimeter College has a site
with relative age dating information and instructions about ordering rock strata. The site also
connects to a lab activity for relative age dating. The lab and information is written at a
beginning college level, however the resource could easily be altered for student work or for
a group discussion about relative age dating techniques.
For relative age dating information go to
http://gpc.edu/~pgore/geology/historical_lab/relativedating.htm
For the lab activity go to
http://gpc.edu/~pgore/geology/historical_lab/reldat_exercises.html
3. Relative Age Dating activities and worksheets
Relative age dating is often difficult for students to fully understand because of the time it
takes for sedimentary rocks to form and produce strata. This site uses an analogy to explain
relative age dating. Using the analog of events in a student’s life, the students are then able
to better connect the concept of relatively dating geologic time by relative dating events in
their life. The site offers teacher information and student worksheets.
To access this information go to
http://www.ucmp.berkeley.edu/fosrec/ScotchmoorTime.html.
4. Relative Age Dating pictures and clips
Class zone has a site that explains relative age dating with pictures of rock strata and
animated clips. The following link takes you to a page (Step 1) containing images of our
dynamic Earth. Below the pictures are questions for discussion. “Steps” at the bottom of the
page link to additional topics directly related to this benchmark such as; 2) story in the rock,
3) principle of superposition, 4) principle of original horizontality, 5) folded layers, 6)
principle of cross-cutting relationships, 7) faulted layers, 8) unconformity, 9) analyzing
sequences, 10) formation of an unconformity, and 11) stratigraphy and structural geology.
To access this resource go to
http://www.classzone.com/books/earth_science/terc/content/investigations/es2903/es2903pag
e01.cfm
5. Fossils found in specific Geologic Times
“Here you can journey through the history of the Earth, with stops at particular points in time
to examine the fossil record and stratigraphy.”
To examine portions of geologic time and examine fossils found within specific time periods
go to, http://www.ucmp.berkeley.edu/exhibits/geologictime.php.
6. Information about geologic history on a middle school level
The “Classroom of the Future” site has great information about geologic history written at a
middle-school level. The site is full of articles about the age of the Earth, geologic time, and
the fossil record with activities to match.
For more information go to
http://www.cotf.edu/ete/modules/msese/earthsysflr/geotime.html.
7. Rock Cycle Information
The University Corporation for Atmospheric Research (UCAR) produced a wonderful site
with rock cycle information at three levels (Beginner, Intermediate, and Advance). The site
is rich with animation and teaching materials in both English and Spanish.
For more information go to
http://www.windows.ucar.edu/tour/link=/earth/geology/rocks_intro.html.
8. Relative Age Dating Activities
The University Corporation for Atmospheric Research (UCAR) also has a site about relative
age dating. In this site the students work in groups to understand relative age dating through
modeling sedimentary rock formation and layers.
For more information and a student handout go to
http://www.windows.ucar.edu/tour/link=/teacher_resources/teach_strata.html
9. Activities that explain the importance of fossils
“Learning from the Fossil Record” is a web site with teaching materials and student
activities. The site explains the importance of fossils and the need for science literacy.
The site also links activities to the National Science Standards for each grade level. To begin
exploring this site visit
http://www.ucmp.berkeley.edu/fosrec/
10. Radioactive Decay activities
The Lesson Plans Page has an activity for grades 7-9 to model radioactive decay with paper
and scissors. The site offers an analogy that students can easily understand and use to
understand radiometric (absolute age) dating.
For further information go to
http://www.lessonplanspage.com/ScienceModelRadioactiveDecay79.htm
11. A computer based activity on Radioactive Decay
An applet (computer modeling program) for modeling radioactive decay can be a useful tool.
The model shows students how the radioactive decay curve and graph are produced and how
the half-life affects the time it takes for the parent material to breakdown.
To use the applet go to http://lectureonline.cl.msu.edu/~mmp/applist/decay/decay.htm.