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§ionnav=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/self- check_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)

 Daughter t1/2 Useful Type of Parent Range Material 4.5 238U 206Pb b.y >10 710 million 235U 207Pb m.y years Igneous 232Th 208Pb 14 b.y Rocks and 40Ar & 1.3 >10,000 Figure 8.Radioactive half- 40K Minerals life data 40Ca b.y years >10 87Rb 87Sr 47 b.y million years 100 - 5,730 Organic 14C 14N 70,000 y Material years (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

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

Sample Test Questions

Questions and Answers to follow on a separate document Content Benchmark E.8.C.1

Answers to Sample Test Questions

Questions and Answers to follow on a separate document Content Benchmark E.8.C.1

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.