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Reconstructing Earth's Past Climates: The HiddenSecrets of PollenAdrienne Steele a & Sophie Warny aa Louisiana State University , Baton Rouge , LA

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Reconstructing Earth’s Past Climates:The Hidden Secrets of Pollen

Adrienne Steele and SophieWarnyLouisiana State University,Baton Rouge, LA

ABSTRACT Palynology is the study of fossil pollen and spores, and thesetiny grains can provide fundamental information about past climates on Earth.Among their many unique and useful properties, pollen and spores are com-posed of some of the most chemically resistant organic compounds found innature. They are also produced in vast quantities and are unique to the specificplant from which they originate. All these features make them ideal to recon-struct past climates from both recent history as well as from the ancient past.The purpose of this activity is to get students familiar with palynology and howscientists study climate change. It is based on real palynological data acquiredfrom Antarctic cores obtained recently from the ANDRILL and SHALDRILdrilling campaigns. In order for students to understand this research and itsimportance, they will separate and identify pollen and spores from a simulatedcore sample in which different species of plants are represented as differentcolors of glitter. Students will compare the types and abundance of pollen andspores found in each layer of the core sample and research the climate prefer-ences of the types of plants recovered in order to reconstruct the past climatesof Antarctica.

KEYWORDS biology, climate, data analysis, Eocene, geology, Miocene, Oligocene, pollen

INTRODUCTIONAn ancient mystery awaits us underneath thousands of meters of ice,

water, and rock. The clues to unraveling this mystery are hidden in tinymicrofossils that have been buried in sediments for millions of years.The study of these fossil pollen and spores is called palynology (pro-nounced \pal-uh-NOL-uh-jee\), and these tiny grains can provide fun-damental information about past climates on Earth. Pollen and sporesare particularly useful for the reconstruction of past climates because

• They are composed of some of the most chemically resistant organic com-pounds found in nature. Their outer wall is remarkably resistant to microbialattack, to temperature and pressure from burial underground, and to aciddigestion.

• They are produced in vast numbers.

Address correspondence to AdrienneSteele, Louisiana State University,College of Science, 336 Hatcher Hall,Baton Rouge, LA 70803, USA. E-mail:alopez@lsu.edu

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• They are unique to a specific plant, so scientists canmake ecological and environmental inferences aboutthe area where they were found.

• The majority of pollen and spores produced traveland settle rapidly due to their small size. They areubiquitous in all environments where plants growbut can also be found offshore if carried by rivers,and to a lesser extent, by wind.

The following activity is based on the latestpalynological data from the SHALDRIL (SHAL-low DRILling) and ANDRILL (ANtarctic geologicalDRILLing) projects, which obtained sediment coresfrom Antarctica that date back to the Eocene epochas many as 56 million years ago (Ma). This contrastsfrom existing palynological activities that use pollendata from much younger lake sediments (less than20,000 years old) and are thus limited to climate re-construction for the recent past (e.g., Henderson, Hol-man, and Mortensen 1993). This proposed activity isthe only palynological activity focusing on the Antarc-tic continent. In order for students to understand on-going Antarctic research and its importance, they willseparate and identify pollen and spores from a simu-lated core sample in which different types of pollengrains are represented as different colors of glitter. Fineglitter is used in order to more accurately represent thesize of the pollen grains and the general abundance ofthese grains recovered from sediment cores. Studentswill separate the glitter in their sediment samples usingmethods meant to simulate how palynologists extractpollen from ancient cores (e.g., dissolution and siev-ing). Last, students will reconstruct the past climates ofAntarctica by comparing the types and abundance ofthe “pollen” found in each layer of the core sample us-ing statistical analyses, thus improving their math andanalytical skills.

This activity meets several objectives in all threeof the dimensions in A Framework for K–12 ScienceEducation (National Research Council 2011). Planningand conducting investigations, using mathematicsand computational thinking, analyzing and inter-preting data, and communicating information areimportant scientific practices stressed in this newframework, and all are emphasized in this lesson plan.Crosscutting concepts such as systems and models,stability and change, and patterns are also clearlyrepresented through this activity. The third dimensionof the Framework consists of the core disciplinary ideas.

Important concepts in the Earth, life, and physical sci-ences are also addressed through these activities, suchas climate change and the Earth’s history, evolutionand diversity, and interactions of matter. A completeversion of this activity with extensions and step-by-step instructions can be downloaded from this Website:http://www.geol.lsu.edu/warny/SophieWarnyWebsite/Bio.html.

BACKGROUNDThe fossil record indicates that the climate has con-

tinuously changed over time throughout Earth’s his-tory. For example, time periods such as the Last IceAge (Wurmian) and the Age of Dinosaurs were dras-tically different climatically. Because many plants areknown to live in particular habitats with specific tem-perature and rainfall patterns, paleobotanists can makeinferences about past climates based on the plants thatwere living at a geologic or archaeological site at thattime. For example, if evidence of an abundance of cactiis found in an area, it can be inferred that the climatewas hot and dry, but if gigantic ferns are found alongdinosaur bones, it implies that the climate at that timewas hot and humid.

How do paleobotanists know what types of plantslived in a past environment? Fossils of leaves and trunkswould provide excellent clues, but the leaves or trunksare not often found because they decay and, if sedi-mentary conditions are right, the organic material turnsinto oil, gas, or coal after being buried for millions ofyears. Since pollen and spores are very resistant to de-cay, produced in great abundances, and morpholog-ically unique to each plant, palynologists can isolateand identify the pollen and spores found in sedimentcores taken from lakes, riverbeds, and coastal sea beds.Pollen is deposited in the sediments in layers, with theoldest layers found at the bottom and the newer layerson top—–this is known as the law of superposition (seeTedford and Warny 2006, for a related activity on thistopic). Geologists have been coring the Earth’s surfacelayers for centuries to learn about past environments.As mentioned earlier, a thorough Internet search willprovide a few examples of activities that use pollendata from more recent lake sediments (e.g., Henderson,Holman, and Mortensen 1993), but the latest frontierto study is Antarctica. To delve further into the pastclimates of this continent, a consortium of scientistsand drillers, along with educators and students from

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FIGURE 1 ANDRILL SMS sediment cores showing layers ofrocks sampled from the Ross Sea, Antarctica (color figure avail-able online).

several countries, formed the ANDRILL project (http://andrill.org), which drilled a sediment core 1,200 m longfrom beneath the McMurdo Ice Shelf. The ANDRILLsediment cores pictured in Figure 1 show layers ofMiocene-age rocks that were sampled from below theRoss Sea. Prior to that, the SHALDRIL project drilledin the Antarctic Peninsula; Figure 2 is an artistic ren-

FIGURE 2 SHALDRIL drilling operations from the RV/IB N.B.Palmer, cutting into the Eocene-age sediments (artwork by A. Foxand S. Warny) (color figure available online).

TABLE 1 Comparison of the ANDRILL and SHALDRIL Projects

ANDRILL SHALDRIL

Geography McMurdo Ice Shelf Antarctic PeninsulaDrilling method From boat

(ice cutter)From platform on ice

shelfAge of core

sedimentsMiocene Eocene, Oligocene,

Miocene,Plio-Pleistocene

References Warny et al. 2009;Feakins, Warny,and Lee 2012

Anderson et al. 2011;Warny and Askin2011a, 2011b

dering of this drilling operation. A comparison of theseprojects is shown in Table 1.

Once a sediment core is obtained, it is sampled everymillimeter, centimeter, meter, and so forth, dependingon the time frame a palynologist is studying. Somelake cores are examined every millimeter to look foryearly changes, whereas a large core such as from theANDRILL project may be sampled only every five me-ters to look at changes on a millennial scale over mil-lions of years. Each sample is dissolved in strong acids(HCl and HF) to remove unwanted particulates suchas sand and mud, washed with distilled water, and runthrough sieves to concentrate microscopic fossils. Ifneeded, a flotation technique can be used to separateparticles of the same size but of different weights. Theresidues left over—–mostly composed of palynomorphs,e.g., pollen, spores, dinoflagellate cysts—–are mountedon microscope slides and examined under high magni-fication to identify the types of pollen grains and spores.The relative abundance of each type of palynomorphis charted on a pollen diagram to look for patterns ofchange over time.

MATERIALS• 1 L graduated cylinder or other tall container to make

a sample sediment core• Sand (use coarse sand that will sink, such as play sand

sold at hardware stores)• Salt• Dark brown sugar (in a color easily distinguished

from the sand)• Coarse grain sugar, such as “raw sugar”• Fine glitter in six colors: red, green, gold, blue, pur-

ple, and black (colors can be substituted as long asthey look different enough to visually distinguish—–

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e.g., gold and silver are very reflective and are hard totell apart under a microscope)

• Sandwich bags with zip closure• Measuring spoons: 1 tbsp., 1 tsp., 1/2 tsp., 1/4 tsp.• Deep pans or other containers for separating the glit-

ter from substrate (one per group of students)• Glass slides and cover slips (at least three for each

group of students)• Fine mesh sieves, kitchen strainers, and/or filter paper• Warm water• Plastic knives or other flat instruments• Black construction paper• Graph paper• Dissecting scope or video microscope

PREPARATIONBefore understanding how pollen and spores are

used to reconstruct past climates, students need anappreciation of the diversity of these grains. Just likehuman fingerprints, each species of flowering plant hasa specific pollen morphology that is unique. By exam-ining the physical characteristics of pollen and spores,palynologists can identify the specific plant from whichthe pollen or spores arose. It is recommended to beginthis activity by familiarizing students with the conceptof how palynologists categorize pollen grains by size,shape, ornamentation, and aperture (i.e., characteris-tics of the pollen wall, such as furrows and pores). Adiversity of pollen and spore morphologies is shownin Figure 3. To explore differences in pollen, have stu-dents observe real pollen by viewing the anthers of liveflowers with dissecting scopes or handheld video micro-scopes. For example, Figures 4 and Figure 5 show thedifferences in shape, size, and ornamentation of lily andhibiscus pollens, respectively. To further extend student

FIGURE 3 Diversity of pollen morphologies (color figure avail-able online).

FIGURE 4 Image of lily pollen taken with the 200× lens of theScope-on-a-Rope (color figure available online).

understanding of pollen and how it is transmitted, yourclass can collect airborne pollen. Smear glass slides witha thin layer of petroleum jelly and place them outsidefor a day or two. These slides can be examined usinga microscope to look for any pollen grains that werecollected. This simple experiment will teach studentsabout “pollen rain” and show how pollen grains aretransported by the wind from local flowers; this activ-ity is most productive if done in the spring or earlysummer.

Once students have a basic understanding of themorphological differences in pollen and spores, theyare ready to conduct their own investigations on a sim-ulated core. This simulated core consists of four layersthat reflect the actual core that was recently acquired

FIGURE 5 Image of hibiscus pollen taken with the 200× lens ofthe Scope-on-a-Rope (color figure available online).

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TABLE 2 Recipes to Make Each Layer of the Simulated Core Sample

Eocene Oligocene MioceneSand Salt Brown sugar

Amounts and colors of glitterto add to each layer

Red 1 tsp. (25%) —– —–

Green 1 tsp. (25%) 1/4 tsp. (10%) —–Gold —– 1/4 tsp. (10%) 1/4 tsp. (40%)Blue —– 1/4 tsp. (10%) 1/4 tsp. (40%)Purple 1 tsp. (25%) 1/2 tsp. (35%) A pinch (10%)Black 1 tsp. (25%) 1/2 tsp. (35%) A pinch (10%)

by the SHALDRIL program off the Antarctic Penin-sula. These four layers are as follows: Eocene, ∼55 to34 million years ago; Oligocene, ∼34 to 23 millionyears ago; Miocene, ∼23 to 5 million years ago; andPlio-Pleistocene, ∼5 million years ago to almost thepresent. Each layer is made up of a different “substrate”so that the layers are visually distinguishable; suggestedsubstrates that work well are sand, salt, and differenttypes of sugar, as listed in Table 2. The substrates usedin these layers will react to dissolution by water and/orsieving in the same way that real substrates (e.g., sand,mud) would react to dissolution by acid and sieving.This provides a perfect analogue to what real palyno-logical processing entails and furthers the students’ un-derstanding of this field of study. Have your studentstest whether the “substrate” materials will dissolve inwarm water (to simulate the HCl or HF acid digestionprocess that dissolves carbonates and silicates), if theywill sink in water (to simulate the floatation technique),and/or if a sieve will be needed to isolate the “pollen.”

Each layer except for the Plio-Pleistocene has a spe-cific ratio of different colors of glitter to simulate thepollen and spores found in that time period. The totalamount of glitter in each layer is meant to representthe overall plant abundance through time observed inthe real Antarctic sediments by Warny and colleagues(Warny and Askin 2011a, 2011b; Anderson et al. 2011),and the mixtures of different colors of glitter in eachlayer serve as an example of general plant diversity.These ratios do not precisely reflect actual data, butrather, present a simplified version of the real Antarcticdata representing climate change over geological time.Use Table 2 to make each of these layers, dividing theminto sandwich bags. Make enough for each group of stu-dents in your class to get one specific layer. Prepare anextra bag of each layer in order to make the sample core.Use a graduated cylinder or other tall vessel to create

the sample core in order to allow students to compareand identify their sample. Starting with the oldest layer(Eocene), fill the bottom of the cylinder with a bag ofthe sand mixture. The next layer will consist of the saltmixture, followed by the brown sugar mixture, and fin-ishing with a layer of raw sugar at the top to representthe Plio-Pleistocene layer (Figure 6).

PROCEDUREThis activity takes two to three class periods. First,

give each group of students one of the core layers. Aftercomparing their sample with the simulated core, theyshould begin formulating a plan to separate the pollenfrom the substrate. This can be done using large pans,strainers, sieves, and/or filter paper (Figure 7). Give stu-dents one class period to perform their pollen extrac-tions. Remind them that their goal is to collect as muchof their pollen grains as possible. (You may choose to

FIGURE 6 Sample core showing the four layers representingthe different time periods with approximate ages in Ma. (Note thatthe last 11,700 years of deposition [Holocene] are not discussedin this article.) (color figure available online).

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FIGURE 7 Students separate glitter from the substrate usingfilter paper (color figure available online).

give each group a sample of the Plio-Pleistocene layeras well or simply illustrate to the whole class that it doesnot contain any glitter.) Since it would be nearly impos-sible to identify and count every grain of pollen fromtheir sample, the collected glitter should be placed on asheet of graph paper or some sort of grid for samplingpurposes (Figure 8). Leave the glitter to dry overnight.

On the next class day, after the glitter is dry, studentscan begin to analyze their samples. They will first needto mix the glitter well and to spread it evenly on thegrid so that a sample taken from one part of the gridcan be used to extrapolate the data for the rest of thesample. The extrapolation will reinforce the students’math skills, but it will also serve as an analogue toreal-case research, because scientists usually study onlya fraction of the sediment available and large-scaleextrapolation of results are always necessary. Depend-ing on how much pollen was present, students willchoose how many squares of the grid from which tocollect (Figure 9). Instruct students to prepare at leastthree slides of glitter from their sample. To make slides,place a tiny drop of water onto a slide, scrape a portion

FIGURE 8 A group of students places their collected glitter ona grid for sampling (color figure available online).

of glitter off the grid with a flat implement, then tapit over the droplet of water to deposit glitter and topwith a cover slip (Figure 10). Depending on how muchof the grid was sampled, students will need to calculatethe percentage of pollen they are going to analyze. For

FIGURE 9 Glitter sampling method developed by a group ofhigh school students (color figure available online).

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FIGURE 10 Slides made from glitter collected in the Eocenelayer (color figure available online).

FIGURE 11 Glitter slide from the Eocene layer taken with the30× lens of the Scope-on-a-Rope (color figure available online).

FIGURE 12 Glitter slide from the Oligocene layer taken with the30× lens of the Scope-on-a-Rope (color figure available online).

FIGURE 13 Glitter slide from the Miocene layer taken with the30× lens of the Scope-on-a-Rope (color figure available online).

example, if they collected all the glitter from twosquares of a 36-square grid, they are examining about6% of the sample (2 divided by 36). Use a dissectingscope or a handheld video microscope to view theslides. Figures 11–13 are images taken at 30 × of threeslides representing each layer of the core (Eocene,Oligocene, and Miocene, respectively). Students mayuse the worksheet provided in this lesson to recordtheir pollen counts, or they may simply record theirmethods and results into their lab notebooks. Anexample of a completed student worksheet is shownin Figure 14. (This activity was piloted by two highschool classes.) Notice that this group’s results closelymirror the actual percentages of glitter colors that wereprepared by the teacher!

FIGURE 14 Example of a completed student worksheet.

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TABLE 3 Glitter Key to Identify Plants Found in the DifferentLayers of the Sample Core

Glitter color Plant Genus Plant common name

Red Laevigatosporites Tree fern similar toCyatheaceae today

Green Proteacidites Angiosperm similar toProteaceae today

Gold Coptospora Bryophyte similar tomosses today

Blue Colobanthus Angiosperm calledpearlwort

Purple Nothofagus Beech tree, which is anangiosperm

Black Podocarpidites Gymnosperm similar topodocarps today

After the pollen counts have been completed, dis-tribute the pollen key (Table 3). Students should con-duct research on each type of plant found in their sam-ple for information about its ecology and climate pref-erences. For instance, the red glitter is a type of tree fernthat lives in tropical and subtropical forests and cloudforests, whereas the blue glitter is a pearlwort, which is amoss-like plant that is the southernmost dicot and canwithstand snow cover for several months of the year.Each group’s results and conclusions should be sharedwith the whole class in order to make overall conclu-sions regarding the changes in climate observed fromthe data taken from this core sample. This can also leadto discussions about sampling and replication in scien-tific studies. A graphic representation of the possibleresults is shown in Figure 15.

FIGURE 15 Example bar graph representing the percentagesof each plant species found in the three layers of the core sample(color figure available online).

CONCLUSIONSThis activity is based on real data that was obtained

from two drilling campaigns: the SHALDRIL and AN-DRILL projects. Drill cores and seismic data acquiredduring two cruises (SHALDRIL I and II) in the north-ernmost peninsula region yielded a record that indicatesprogressive cooling and associated changes in terrestrialvegetation over the course of the past 37 million years(Warny and Askin 2011a, 2011b; Anderson et al. 2011).The data from the ANDRILL cores showed the samecooling trend except for one brief warming period inthe Middle Miocene (Feakins et al. 2012; Warny et al.2009). This cooling trend occurred as a product ofseveral events. First, as Antarctica separated from theGondwana supercontinent and moved farther and far-ther south, the continent became isolated. A cold cur-rent, called the circumpolar current, developed aroundthe Antarctic continent. This strong current started toblock the warm currents that develop in the equatorialregion, preventing these from warming the southern po-lar region; Antarctica has become progressively colderever since. This cooling is exacerbated by other factors,one of them being the albedo feedback mechanism.As the continent became colder, ice sheets developed.These white surfaces reflect solar radiation, thereby re-ducing the amount of heat absorbed from the sun.Forests are excellent at trapping heat, but they gradu-ally disappeared due to the encroaching ice sheets thatformed as the climate cooled.

Although glaciation began in higher elevations inAntarctica in the Late Eocene (approximately 37–34Ma), the transition from a more temperate climateto a dynamic, polythermal ice sheet started in theOligocene and was fully in place during the Miocene.The “warmest” location in Antarctica, the northern-most peninsula, was overridden by an ice sheet in theEarly Pliocene (approximately 5.3–3.6 Ma); therefore,this area became devoid of plants at this time. If anyplants survived in isolated regions of the peninsula, noevidence has been discovered yet. Today, just a fewplants survive in coastal regions of Antarctica, whichare mainly cold-tolerant bryophytes. The opening ofocean passageways and the associated establishmentof circumpolar circulation locked Antarctica into itsfrozen state, where it remains today.

The data acquired and conclusion made by studentsshould mirror these main findings discovered from theaforementioned research:

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1. Tropical and subtropical angiosperms dominatedAntarctica in the Early Eocene. This time periodalso contains the highest volume of plants due tothe warmer climate conditions.

2. A mosaic of southern beech and conifer-dominatedwoodlands as well as some tundra plants occupiedthe region during the Oligocene, illustrating thecooling of the climate in Antarctica.

3. By the Miocene epoch, only localized pockets oftundra vegetation existed, showing an even moredrastic cooling of the continent. There was a lowerdiversity of plants and fewer plants in general, as ev-idenced by the smaller volume of pollen recovered.

4. No pollen is recovered in the Plio-Pleistocene layer,as the Antarctic Peninsula was completely coveredin ice and inhospitable for plant life. Although a fewplants survive today on the continent, they are sorare that the few pollen and spores produced are lostin the sedimentary record.

ASSESSMENT• The student worksheet provided in the Appendix can

be used to ascertain students’ understanding of theactivity. Lab notebooks can also be used for them torecord their extraction plan, results, and conclusions.

• In order to improve students’ written and oral com-munication skills, they should write a report and/ordo a class presentation to relay their results and con-clusions about what the climate was like in the timeperiod represented by the sample they analyzed.

• Students should also be directed to synthesize theresults from all groups to create an overall picture ofhow the climate changed over the time periods thatwere sampled in the core. This can also be done asoral and/or written presentations.

REFERENCESAnderson, J. B., S. Warny, R. A. Askin, J. S. Wellner, S. M. Bohaty,

A. E. Kirshner, D. N. Livsey, A. R. Simms, T. R. Smith, W. Ehrmann,et al. 2011. Progressive Cenozoic cooling and the demise of Antarc-tica’s last refugium. Proceedings of the National Academy of Science108(28): 11299–11726.

Feakins, S. J., S. Warny, and J.-E. Lee. 2012. Hydrologic cycling overAntarctica during the Middle Miocene warming. Nature Geoscience5: 557–560.

Henderson, S., S. R. Holman, and L. L. Mortensen, eds. 1993.Global climates—–Past, present, and future. Washington, DC:United States Environmental Protection Agency.

National Research Council. 2011. A framework for K–12 science educa-tion: practices, crosscutting concepts, and core ideas. Washington,DC: National Academies Press.

Tedford, R., and S. Warny. 2006. Layer-cake Earth. Science and Children44(4): 40–44.

Warny, S., and R. A. Askin. 2011a. Last remnants of Cenozoic vegeta-tion and organic-walled phytoplankton in the Antarctic Peninsula’sicehouse world. tectonic, climatic, and cryospheric evolution of theAntarctic peninsula, ed. J. B. Anderson and J. S. Wellner, 167–192.Washington, DC: American Geophysical Union.

Warny, S., and R. A. Askin. 2011b. Vegetation and organic-walled phy-toplankton at the end of the Antarctic greenhouse world: A two-step cooling. Tectonic, climatic, and cryospheric evolution of theAntarctic peninsula, ed. J. B. Anderson and J. S. Wellner, 193–210.Washington, DC: American Geophysical Union.

Warny, S., R. A. Askin, M. J. Hannah, B. A. R. Mohr, J. I. Raine, D. M.Harwood, F. Florindo, and the SMS Science Team. 2009. Pa-lynomorphs from a sediment core reveal a sudden remarkablywarm Antarctica during the Middle Miocene. Geology 37: 955–958.

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APPENDIX: STUDENT WORKSHEET

Name ___________________________________ Date ___________

Time period represented by your sediment layer _________________________

Glitter Color Slide #1

glitter count Slide #2

glitter count Slide #3

glitter count Total

glitter count Percent of total glitter

Red

Green

Gold

Blue

Purple

Black

TOTAL 100%

How many squares did you sample from the grid? _____________________________

What percentage of the grid did you sample? _________________________________

Use the percentage of the grid that you sampled and the total glitter count from that portion to estimate how much total glitter was in your core sample.

______________________________________________________________________

How much glitter was collected in the Plio-Pleistocene layer? Explain what this means.

_____________________________________________________________________

_____________________________________________________________________

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