A Glossary - Paleontological Research Institution

cGlossaryCanadian Shieldthe stable core of the North Americancontinental landmass, containing someof the oldest rocks on Earth. The shieldhas experienced very little tectonic activity(faulting or folding) for millions of years. Asthe stable cores of all continents, shields areoften covered by layers of younger material.capstone, caprocka harder, more resistant rock type thatoverlies a softer, less resistant rock. Theharder rock typically helps to control the rateof erosion.See also: erosioncarbonate rocksrocks formed by accumulation of calciumcarbonate, often made of the skeletons ofaquatic organisms such as corals, clams,snails, bryozoans, and brachiopods. Theseorganisms thrive in warm, clear shallowwaters common to tropical areas, thereforemodern carbonate rocks are observedforming in places such as the Florida Keysand the Bahamas. They are also one ofthe dominant rock forms of the bottom ofthe ocean, where sediments form from theskeletons of planktonic organisms such asforaminifera.Carbonate rocks include limestone anddolostone.See also: brachiopod, bryozoan, dolostone,foraminifera, limestoneCarboniferousa geologic time period that extends from359 to 299 million years ago. It is dividedinto two subperiods, the Mississippian andthe Pennsylvanian. By the Carboniferous,terrestrial life had become well established.The name Carboniferous means "coalbearing," and it is during this time that manyof today's coal beds were formed.The Carboniferous is part of the Paleozoic.See also: coal, geologic time scale,Mississippian, Pennsylvanian, Paleozoic242

GlossaryCenozoiccthe geologic time period spanning from66 million years ago to the present. TheCenozoic is also known as the age ofmammals, since extinction of the largereptiles at the end of the Mesozoic allowedmammals to diversify.The Cenozoic includes the Paleogene,Neogene, and Quaternary periods.See also: geologic time scale, Mesozoic,Neogene, Paleogene, Quaternarycephalopoda marine invertebrate animal belongingto the Class Cephalopoda in the PhylumMollusca, and characterized by a prominenthead, arms and tentacles with suckers, andjet propulsion locomotion.Cephalopods are swimming predators withbeak-shaped mouthparts. The shells ofcephalopods range from long straight conesto spirals, but some have internal shells orno significant shell at all, like the octopus.The group includes belemnites, ammonoids,nautilus, squid, and octopuses.A mass extinction between the Cretaceousand Paleogene eliminated many varieties ofcephalopods.See also: Cretaceous, mass extinction,Paleogenechalcedonya crystalline silicate mineral that occurs in awide range of varieties.See also: mineral, silicachalka soft, fine-grained, easily pulverized, whiteto-grayish variety of limestone, composed ofthe shells of minute planktonic single-celledalgae.See also: limestone243

cGlossarychemical fossilschemicals produced by an organism thatleave behind an identifiable record in thegeologic record. Chemical fossils providesome of the oldest evidence for life onEarth.See also: fossilchemical reactiona process that involves changes in thestructure and energy content of atoms,molecules, or ions but not their nuclei.See also: energycherta sedimentary rock composed ofmicrocrystaline quartz. It is often found asnodules or concretions in limestone andother marine sedimentary rocks. As theserocks form, water moving through themtransports small amounts of silicon dioxidethat accumulate into clumps of microscopiccrystals. The resulting rocks are extremelyhard and have no planes of weakness.For thousands of years, humans exploitedthese qualities, breaking chert nodules intoblades and other toolsSee also: concretion, nodule, sedimentaryrock, silica, quartzchlorastrolitea variety of pumpellyite with a distinctive“turtleback” pattern created by itsinterlocking green crystals.See also: pumpellyiteCincinnati Archan uplifted region that existed betweenthe Illinois Basin, the Michigan Basin, andthe Appalachian Basin during the lateOrdovician and Devonian. It stretched fromsoutheastern Ontario all the way to northernAlabama.See also: Appalachian Basin, Devonian,Illinois Basin, Michigan Basin, Ordovician,upliftclasperan anatomical structure used by sharks formating.See also: shark244

Glossaryclaycthe common name for a number of veryfine-grained, earthy materials that becomeplastic (flow or change shape) when wet.Chemically, clays are hydrous aluminumsilicates.See also: silicacleavagea physical property of minerals. Cleavageoccurs when a mineral breaks in acharacteristic way along a specific plane ofweakness.Mica and graphite have very strongcleavage, allowing them to easily break intothin sheetsSee also: graphite, mica, mineralclimatea description of the average temperature,range of temperature, humidity,precipitation, and other atmospheric/hydrospheric conditions a regionexperiences over a period of many years(usually more than 30). These factorsinteract with and are influenced by otherparts of the Earth system, including geology,geography, insolation, currents, and livingthings.The climate of a region represents theaverage weather over a long period of time.See also: weatherclimate changeSee global warmingcoala combustible, compact black or darkbrown carbonaceous rock formed bythe compaction of layers of partiallydecomposed vegetation.By far the greatest abundance of coal islocated in strata of Carboniferous age.See also: Carboniferous245

cGlossarycold frontthe boundary between the warm air andthe cold air moving into a region. At thisboundary, denser, colder air moves in,making the less dense, warm air rise. Thisdisplaced warm air cools as it rises becauseair pressure decreases with increasingheight in the atmosphere. As the air cools,it becomes saturated with water vapor, andcondensation begins to occur, eventuallyleading to dramatic rainstorms.color (mineral)a physical property of minerals. Color isdetermined by the presence and intensity ofcertain elements within the mineral.See also: mineralcolor (soil)a physical property of soils. Soil color isinfluenced by mineral content, the amount oforganic material, and the amount of water itroutinely holds. These colors are identifiedby a standard soil color chart called theMunsell chart.See also: soilcommoditycompression,compressional forceconcretiona good for which there is demand, but whichis treated as equivalent across all markets,no matter who produces it.a force acting on an object from all ormost directions, resulting in compression(flattening or squeezing). Compressionalforces occur by pushing objects together.a hard, compact mass, usually of sphericalor oval shape, found in sedimentary rockor soil. Concretions form when mineralsprecipitate around a particulate nucleuswithin the sediment.See also: mineral, sedimentary rock, soil246

Glossaryconglomerateca sedimentary rock composed of multiplelarge and rounded fragments that havebeen cemented together in a fine-grainedmatrix. The fragments that make up aconglomeerate must be larger than grains ofsand.See also: sand, matrix, sedimentary rockconifera woody plant of the division Coniferophyta.Conifers bear cones that contain theirseeds.Conservation of Energya principle stating that energy is neithercreated nor destroyed, but can be alteredfrom one form to another.See also: energycontact metamorphisma metamorphic rock that has been alteredby direct contact with magma. Changesthat occur due to contact metamorphism aregreatest at the point of contact. The furtheraway the rock is from the point of contact,the less pronounced the change.See also: magma, metamorphismconvectionthe rise of buoyant material and the sinkingof denser material. In the mantle, variationsin density are commonly caused by themelting of subducting materials.See also: mantle, subductionconvergent boundaryan active plate boundary where two tectonicplates are colliding with one another.Subduction occurs when an oceanic platecollides with a continental plate or anotheroceanic plate. If two continental platescollide, mountain building occurs.See also: active plate boundary, platetectonics, subductioncoppera ductile, malleable, reddish-brown metallicelement (Cu).Copper is used extensively as wiring in theelectrical industry as well as in alloys suchas brass and bronze.247

cGlossarycratonthe old, underlying portion of a continentthat is geologically stable relative tosurrounding areas. The portion of a cratonexposed at the surface is termed a shield,while that overlain by younger layers is oftenreferred to as a platform.A craton can be thought of as the heart of acontinent—it is typically the oldest, thickest,and most stable part of the bedrock. It isalso usually far from the margins of tectonicplates, where new rock is formed and olddestroyed. This rock has usually beenmetamorphosed at some point during itshistory, making it resistant to erosion.See also: metamorphismCretaceousa geologic time period spanning from 144to 66 million years ago. It is the youngestperiod of the Mesozoic. The end of theCretaceous bore witness to the massextinction event that resulted in the demiseof the dinosaurs."Cretaceous" is derived from the Latin word,“creta” or “chalk.” The white (chalk) cliffs ofDover on the southeastern coast of Englandare a famous example of Cretaceous chalkdeposits.See also: chalk, geologic time scale, massextinction, Mesozoiccrevassea deep crack in an ice sheet or glacier,which forms as a result of shear stressbetween different sections of the moving ice.See also: glacier, ice sheet248

Glossarycrinoidca marine invertebrate animal belongingto the Class Crinoidea of the PhylumEchinodermata, and characterized by ahead (calyx) with a mouth on the top surfacesurrounded by feeding arms. Severalgroups of stemmed echinoderms appearedin the early Paleozoic, including crinoids,blastoids, and cystoids.Crinoids have 5-fold symmetry and featheryarms (sometimes held off the sea floor on astem) that collect organic particles from thewater. The stems, the most often preservedpart, are made of a series of stacked discs.Upon death, these stems often fall apartand the individual discs are preservedseparately in the rock.The crinoid's feathery arms make it looksomething like a flower on a stem. Thus,crinoids are commonly called “sea lilies,”although they are animals, not plants.See also: echinodermcross-beddinglayering within a bed in a series of rockstrata that does not run parallel to theplane of stratification. Cross-beds form asflowing water or wind pushes sedimentdowncurrent, creating thin beds thatslope gently in the direction of the flow asmigrating ripples. The downstream slopeof the ripple may be preserved as a thinlayer dipping in the direction of the current,across the natural flat-lying repose of thebeds. Another migrating ripple will form anadditional layer on top of the previous one.249

cGlossarycrustthe uppermost, rigid outer layer of the Earth,composed of tectonic plates. Two typesof crust make up the lithosphere. Oceaniccrust is denser but significantly thinner thancontinental crust, while continental crust ismuch thicker but less dense (and thereforebuoyant).When continental crust collides with oceaniccrust, the denser oceanic crust will bedragged (subducted) under the buoyantcontinental crust. Although mountains arecreated by these oceanic/continental crustcollisions due to the compression of the twoplates, much taller ranges are producedby continental/continental collisions. Whentwo buoyant continental crusts collide, thereis nowhere for the crust to go but up! Themodern Himalayas, at the collision site ofthe Asian and Indian plates, are a goodexample of very tall mountains formed by acollision between two continental crusts.See also: active plate boundary,compression, lithosphere, subductionCryogeniana geologic period lasting from 850 to 635million years ago, during the Precambrian.During this period, the Earth was subject toa 200-million-year-long ice age.See also: ice age, Precambriancrystal forma physical property of minerals, describingthe shape of the mineral's crystal structure(not to be confused with cleavage). Amineral might be cubic, rhomboidal,hexagonal, or polyhedral.See also: cleavage, mineralcyanobacteriaa group of bacteria, also called "blue-greenalgae," that obtain their energy throughphotosynthesis.cyclothemalternating sequences of marine and nonmarine sedimentary rocks, usually includingcoal, and characterized by their light anddark colors.See also: coal250

Glossarydegrade (energy)dthe transformation of energy into a formin which it is less available for doing work,such as heat.See also: energydensitya physical property of minerals, describingthe mineral's mass per volume.See also: mineralderechoa set of powerful straight-line winds thatexceed 94 kph (58 mph) and can oftenapproach 160 kph (100 mph). Thesepowerful windstorms can travel over400 kilometers (250 miles) and causesubstantial wind damage, knocking downtrees and causing widespread poweroutages. The lightning associated with theseintense storms can cause both forest firesand house fires.Derecho is the Spanish word for "straightahead."See also: windDevoniana geologic time period spanning from 419 to359 million years ago. The Devonian is alsocalled the "age of fishes" due to the diversityof fish that radiated during this time. Onland, seed-bearing plants appeared andterrestrial arthropods became established.The Devonian is part of the Paleozoic.See also: geologic time scale, Paleozoicdiamonda mineral form of carbon, with the highesthardness of any material. Most naturaldiamonds are formed at high temperatureand pressure deep in the Earth's mantle.See also: hardness, mantle, mineral251

dGlossarydinosaursa group of terrestrial reptiles with a commonancestor and thus certain anatomicalsimilarities, including long ankle bones and erectlimbs. All of the large reptile groups , includingthe dinosaurs, disappeared at or before themass extinction at the end of the Cretaceous.See also: Cretaceous, mass extinctiondolomitea carbonate mineral, consisting of calciummagnesium carbonate (CaMg(CO3)2).Dolomite is an important reservoir rock forpetroleum, and also commonly hosts largeore deposits.See also: mineral, ore, petroleumdolostonea rock (also known as dolomitic limestoneand once called magnesian limestone)primarily composed of dolomite, a carbonatemineral. It is normally formed whenmagnesium bonds with calcium carbonate inlimestone, forming dolomite.See also: dolomite, limestonedouble refractionthe result of light passing through a materialthat splits it into two polarized sets of rays,doubling images viewed through thatmaterial. For example, a single line on asheet of paper will appear as two parallellines when viewed through a clear calcitecrystal.See also: calcite, mineral252

GlossaryDriftless Aread–ea region that did not experience glaciation,located in parts of southwestern Wisconsin,eastern Minnesota, and northeastern Illinoisand Iowa. This region is known as theDriftless Area since it lacks glacial deposits,which are collectively called drift. Glaciersare known to have reached all sides of theDriftless Area at various times throughoutthe Quaternary Ice Age, but are not knownto have completely encompassed the areaat any time.The Driftless Area is also called thePaleozoic Plateau.See also: glacier, ice agedrumlina teardrop-shaped hill of till that was trappedbeneath a glacier and streamlined in thedirection of the flow of the ice movingover it. The elongation of a drumlin is anexcellent clue to the direction of flow duringan ice sheet’s most recent advance.See also: glacier, tilldynamic metamorphismSee regional metamorphismearthquakea sudden release of energy in theEarth’s crust that creates seismic waves.Earthquakes are common at active plateboundaries.See also: active plate boundary, seismicwavesechinodermsmembers of the Phylum Echinodermata,which includes starfish, sea urchins,and crinoids. Echinoderms have radialsymmetry (which is usually five-fold), anda remarable ability to regenerate lost bodyparts,See also: crinoidedrioasteroidsan extinct class of echinoderm that had asimple, cushion-shaped body and five arms.See also: echinoderm253

eGlossaryeffervesceto foam or fizz while releasing gas.Carbonate minerals will effervesce whenexposed to hydrochloric acid.See also: carbonate rock, mineralefficiencythe use of a relatively small amount ofenergy for a given task, purpose, or service;achieving a specific output with less energyinput.See also: energyenergythe power derived from the use of physicalor chemical resources. Everything we dodepends upon energy - without it therewould be no civilization, no sunlight, nofood and no life. Energy moves peopleand goods, produces electricity, heatsour homes and businesses, and is usedin manufacturing and other industrialprocesses.energy carriera source of energy, such as electricity, thathas been subject to human-induced energytransfers or transformations.See also: energyEntisolsa soil order; these are soils of relativelyrecent origin with little or no horizondevelopment. They are commonly foundin areas where erosion or deposition ratesoutstrip rates of soil development, such asfloodplains, mountains, and badland areas.See also: erosion, horizon, soil, soil orders254

Glossaryerosionethe transport of weathered materials. Rocksare worn down and broken apart into finergrains by wind, rivers, wave action, freezingand thawing, and chemical breakdown.Over millions of years, weathering anderosion can reduce a mighty mountainrange to low rolling hills. Some rocks weardown relatively quickly, while others canwithstand the power of erosion for muchlonger. Softer, weaker rocks such as shaleand poorly cemented sandstone andlimestone are much more easily worn thanhard, crystalline igneous and metamorphicrocks, or well-cemented sandstone andlimestone. Harder rocks are often leftstanding as ridges because the surroundingsofter, less resistant rocks were morequickly worn away.See also: igneous rock, metamorphic rock,sedimentary rock, weatheringerratic, glacial erratica piece of rock that differs from the typeof rock native to the area in which it rests,carried there by glaciers often over longdistances.Erratics are often distinctive becausethey are a different type of rock than thebedrock in the area to which they’ve beentransported. For example, boulders andpebbles of igneous and metamorphicrocks are often found in areas where thebedrock is sedimentary; it is sometimespossible to locate the origin of an erraticif its composition and textures are highlydistinctive.See also: glacier, igneous rock,metamorphic rock, sedimentary rock255

e–fGlossaryeskera sinuous, elongated ridge of sand andgravel. Most eskers formed within ice-walledtunnels carved by streams flowing beneatha glacier. After the ice melted away, thestream deposits remained as long windingridges.Eskers are sometimes mined for their wellsorted sand and gravel.See also: glacier, gravel, sandeukaryotesorganisms with complex cells containinga nucleus and organelles. Protists and allmulticel

Acadian mountain-building events. The crust was downwarped as a result of the colliding plates, and the basin was later filled with an inland sea. See also: crust, inland basin, inland sea, plate tectonics aquifer a water-bearing formation of gravel, permeable rock, or sand that is capable of