calcium carbonate -- n. A white compound, CaCO3, that occurs naturally as marble, chalk, limestone, and calcite. It is used by many marine invertebrates, such as corals and echinoderms, and by protists, such as coccolithophorids, to construct their exoskeletons. Calcium carbonate, in the form of calcite, is also incorporated into the eggshells of amniotes, except for turtles whose eggs are composed of aragonite (CaCO3 + magnesium).
caliche -- n. A sedimentary deposit commonly made of calcium carbonate and formed from the leaching of minerals from the top layers of soil. Caliche deposits characterize arid and semi-arid environments.
Canadian Shield -- n. A broad area of Precambrian rock that covers most of Canada, from the Great Lakes to the Arctic Ocean and from Labrador to Northwest Territories. It forms the center of the original North American craton (Laurentia) around which the rest of the continent was added.
carbon film -- Thin layer of carbon remains of past life found in sedimentary rocks.
carbonate -- n. A mineral composed mainly of calcium (Ca) and carbonate (CO3) ions, may also include magnesium (Mg), iron (Fe) and others. n. Rock or sediments derived from debris of organic materials composed mainly of calcium and carbonate (e.g., shells, corals, etc.) or from the inorganic precipitation of calcium (and other ions) and carbonate from solution (seawater). For example, limestone or dolomite. carbonate platform - n. A broad (hundreds of meters), flat, shallow submarine expanse of carbonate rock, more common in the early-middle Paleozoic. carbonate bank – n. A narrow (tens of meters), fairly flat, shallow, submarine plateau of carbonate rock, more common from the middle-late Paleozoic to the present, e.g., the Bahama Banks.
carnivore -- Literally, an organism that eats meat. Most carnivores are animals, but a few fungi, plants, and protists are as well.
cataphyll -- In cycads, a scale-like modified leaf which protects the developing true leaves.
Cathaysian terranes -- n. A set of small landmasses that developed in tropical to subtropical latitudes on the eastern side of Pangea during the Permian and Triassic, includes modern North China (Sino-Korea), South China (Yangtze), Eastern Qiangtang, Tarim, and Indochina.
cathodoluminescence -- n. An analytical technique used in geology and paleontology to analyze the different minerals in a sample, or diagenetic history of a sample how crystals grew, were deformed, and were replaced. A beam of electrons is fired at a sample to produce visible light, which can then be used to interpret the mineralogical and diagenetic history of the sample.
cell -- Fundamental structural unit of all life. The cell consists primarily of an outer plasma membrane, which separates it from the environment; the genetic material (DNA), which encodes heritable information for the maintainance of life; and the cytoplasm, a heterogeneous assemblage of ions, molecules, and fluid.
cell cycle -- Complete sequence of steps which must be performed by a cell in order to replicate itself, as seen from mitotic event to mitotic event. Most of the cycle consists of a growth period in which the cell takes on mass and replicates its DNA. Arrest of the cell cycle is an important feature in the reproduction of many organisms, including humans.
cell wall -- Rigid structure deposited outside the cell membrane. Plants are known for their cell walls of cellulose, as are the green algae and certain protists, while fungi have cell walls of chitin.
cellulose -- carbohydrate polymer of the simple sugar glucose. It is found in the cell walls of plants and green algae, as well as dinoflagellates. Cellulose is the most abundant compound on earth that is manufactured by living things.
chaetae -- Stiff bristles characteristic of annelids.
character -- Heritable trait possessed by an organism; characters are usually described in terms of their states, for example: "hair present" vs. "hair absent," where "hair" is the character, and "present" and "absent" are its states.
chela -- The claw of an arthropod.
chelicera -- The first pair of appendages of a chelicerate arthropod. Originally a short clawed appendage, the chelicerae of many arachnids are highly modified for feeding; in spiders, for instance, they are modified into poisonous fangs.
chert -- Hard, dense sedimentary rock, composed of interlocking quartz crystals and possibly amorphous silica (opal). The origin of the silica is normally biological, from diatoms, radiolaria or sponge spicules. Synonymous with flint.
chlorophyll -- n. The green-colored pigment that absorbs light during photosynthesis, often found in plants, algae, and some bacteria; it includes a porphyrin ring, and often has a long hydrophobic tail. More info?
chordate -- n. An animal with a notochord (a cartilaginous rod that extends the length of the body), dorsal hollow nerve cord (a fluid-filled tube that runs the length of the body), gill slits or pouches, and a tail at some stage in its life cycle.
Cimmerian terranes -- n. An archipelago of small landmasses that developed in tropical and subtropical latitudes on the eastern side of Pangea during the Triassic, blocks that comprised it include modern Turkey, Iran, Afghanistan, Tibet, and Malaysia; also called Cimmeria.
clade -- A monophyletic taxon; a group of organisms which includes the most recent common ancestor of all of its members and all of the descendants of that most recent common ancestor. From the Greek word "klados", meaning branch or twig.
cladogram -- A diagram, resulting from a cladistic analysis, which depicts a hypothetical branching sequence of lineages leading to the taxa under consideration. The points of branching within a cladogram are called nodes. All taxa occur at the endpoints of the cladogram.
clast -- n. An individual grain or constituent of a rock; clastic- adj. Describes a rock or sediment composed mainly of fragments of preexisting rocks or minerals that have been transported some distance from their place of origin, e.g., sandstone, shale.
clitellum -- In annelids, a swelling of the body towards the head of the animal, where the gonads are located. Both oligochaetes and leeches have a clitellum.
cnidocyst -- The "stinging cell" of a cnidarian.
coelom -- Fluid-filled cavity within the body of an animal; usually refers to a cavity lined with specialized tissue peritoneum in which the gut is suspended. The structure and development of the coelom is an important character for recognizing major groups of animals.
coenocytic -- Condition in which an organism consists of filamentous cells with large central vacuoles, and whose nuclei are not partitioned into separate compartments. The result is a long tube containing many nuclei, with all the cytoplasm at the periphery.
colonial -- Condition in which many unicellular organisms live together in a somewhat coordinated group. Unlike true multicellular organisms, the individual cells retain their separate identities, and usually, their own membranes and cell walls.
columella -- A small column of tissue which runs up through the center of a spore capsule. It is present in hornworts, mosses, and some rhyniophytes.
compound eye -- Found in many but not all arthropods, a compound eye is composed of a large number of small, closely packed simple eyes (ommatidia), each with its own lens and nerve receptors.
compression -- Fossil formed when an organism is flattened (compressed) and a thin film of organic material from its body is left in the rock.
concretion -- n. A hard, rounded mass, commonly of silica, calcite, dolomite, iron oxide, pyrite, or gypsum, that formed within a rock from the precipitation of these minerals around a nucleus, such as a leaf, bone, shell, or fossil, and ranging in diameter from centimeters to meters.
conglomerate -- A coarse-grained sedimentary rock, with clasts larger than 2 mm.
consumer -- Any organism which must consume other organisms (living or dead) to satisfy its energy needs. Contrast with autotroph.
continental crust -- The Earth's crust that includes both the continents and the continental shelves.
continental margin -- n. The ocean floor from the shore of continents to the abyssal plain.
continental rise -- n. Part of the continental margin; the ocean floor from the continental slope to the abyssal plain. The continental rise generally has a gentle slope and smooth topography.
continental shelf -- n. The part of the continental margin from the coastal shore to the continental slope; usually extending to a depth of about 200 meters and with a very slight slope, roughly 0.1 degrees; includes conetinental and oceanic sediments down to the ocean floor.
continental slope -- n. Part of the continental margin; the ocean floor from the continental shelf to the continental rise or oceanic trench. Usually to a depth of about 200 meters. The continental slope typically has a relatively steep grade, from three to six degrees.
contractile vacuole -- In many protists, a specialized vacuole with associated channels designed to collect excess water in the cell. Microtubules periodically contract to force this excess water out of the cell, regulating the cell's osmotic balance.
core -- That portion of the interior of the Earth that lies beneath the mantle, and goes all of the way to the center. The Earth's core is very dense, rich in iron and the source of the magnetic field.
cotyledon -- n. The "seed leaves" produced by the embryo of a seed plant that serve to absorb nutrients packaged in the seed, until the seedling is able to produce its first true leaves and begin photosynthesis; the number of cotyledons is a key feature for the identification of the two major groups of flowering plants.
Cretaceous Western Interior Seaway -- n. The epicontinental sea that formed as marine waters from the north spread over North America from around 130 to 70 million years ago (Ma), at its peak in the Middle Cretaceous (~ 90 Ma) it extended from present-day Utah to the Appalachians and from the Arctic to the Gulf of Mexico; also refered to as the Western Interior Seaway
crust -- n. The outermost layer of the Earth, varying in thickness from about 10 kilometers (6 miles) below the oceans, to 65 kilometers (about 40 miles) below the continents; represents less than 1 percent of the Earth's volume.
cuticle -- 1) In animals, a multilayered, extracellular, external body covering, usually composed of fibrous molecules such as chitin or collagen, and sometimes strengthened by the deposition of minerals such as calcium carbonate. 2) A waxy layer which seals the outer surface of land plants, helping to retain moisture.
cytoskeleton -- Integrated system of molecules within eukaryotic cells which provides them with shape, internal spatial organization, motility, and may assist in communication with other cells and the environment. Red blood cells, for instance, would be spherical instead of flat if it were not for their cytoskeleton.