Scapa 7Th Grade Science Vocabulary - Biological Change Over Time

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Fossil

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Remains, imprints, or traces of prehistoric organisms that can tell when and where organisms once lived and how they lived.

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Cast

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A type of body fossil that forms when crystals fill a mold or sediments wash into a mold and harden into rock.

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Mold (fossil definition)

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A type of body fossil that forms in rock when an organism with hard parts is buried, decays, or dissolves, and leaves a cavity in the rock.

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Carbon (or carbonaceous film)

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An organism outline of a fossil. It is a type of fossil found in any rock when organic material is compressed, leaving a thick carbon film

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Petrified

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To cause to become stiff or stonelike

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Trace Fossil

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Trace fossils (also called ichnofossils or lebenspuren) are the evidence of animal's activity. Unlike molds and casts which are evidence or replicas of skeletal remains or body impressions, trace fossils are sedimentologic or lithologic disturbance from an animal's (or plant's) activity such as resting, locomotion, or feeding.

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Index Fossil

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The fossil remains of an organism that lived in a particular geologic age, used to identify or date the rock or rock layer in which it is found.

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Relative Age

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The approximate age determination of rocks, fossils or minerals made by comparing whether the material is younger or older than other surrounding material. Relative age is estimated according to stratigraphic and structural relationships, such as superposition, and by fossil content, since the relative ages and successions of fossils have been established by paleontologists.

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Absolute Age

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The measurement of age in years. The determination of the absolute age of rocks, minerals and fossils, in years before the present, is the basis for the field of geochronology.

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Principle of Superposition

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Steno's principle that, in the case of undeformed, flat-lying strata,younger layers are deposited atop older ones, such that the top layer is youngest and underlying layers increase in age with depth.

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Principle of Cross-Cutting Relations

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The scientific law stating that a pluton (or intrusive rock) is always younger than the rock that surrounds it

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Angular Unconformity

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Four basic steps create angular unconformities. In step one, sediment weathered from land and carried to the sea accumulates on the sea floor and over millions of years turns to rock layers. Then the collision of plates, giant sections of the earth's crust that constantly shift, lift and tilt the layers until the layers rise above sea level and then weather and erode. They erode for millions of years until the edges of the tilted layers become a flattened plane (a "peneplain" is a broad land surface flattened by erosion). Finally, in step four, sea level rises or land sinks. Sediments wash down, forming new horizontal layers that cover the submerged, tilted layers. These four steps could take hundreds of millions of years to complete.

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Natural Selection

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The process in nature by which, according to Darwin's theory of evolution, only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations while those less adapted tend to be eliminated.

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Disconformity

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A type of unconformity in which the rock layers are parallel.

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Unconformity

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A boundary separating two or more rocks of markedly different ages, marking a gap in the geologic record.

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Nonconformity

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Disconformities form in steps. In step one, sediments collect on an ocean floor (or perhaps on the bed of a large lake). They compact and become rock layers. In the second phase, sea level falls or the sea floor rises to expose the layers to weathering and erosion. The main difference in the formation of disconformities and angular unconformities lies in this second step. As the layers of the future disconformity rise above sea level, they remain horizontal—no tilting occurs. If they tilt in this step, they later form an angular unconformity. Then, in step three, the land subsides or sea level rises, and new sediments collect on the older, still horizontal, layers.

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Artificial Selection

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Human intervention in animal or plant reproduction to ensure that certain desirable traits are represented in successive generations.

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Evolution

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A gradual process in which something changes into a different and usually more complex or better form.

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Geologic Time Scale

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Division of Earth's history into time units based largely on the types of life-forms that lived only during certain periods

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Eon

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An indefinitely long period of time; an age.The longest division of geologic time, containing two or more eras.

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Era

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Second longest division on geologic time scale; is subdivided into periods and is based on major worldwide changes in types of fossils.

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Period

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A unit of time, longer than an epoch and shorter than an era.

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Epoch

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A unit of geologic time that is a division of a period.

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Precambrian Time

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Of or belonging to the geologic time period between Hadean Time and the Cambrian Period, often subdivided into the Archean and Proterozoic eras, comprising most of the earth's history and marked by the appearance of primitive forms of life.

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Paleozoic Era

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Of, belonging to, or designating the era of geologic time that includes the Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian periods and is characterized by the appearance of marine invertebrates, primitive fishes, land plants, and primitive reptiles.

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Mesozoic Era

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Of, belonging to, or designating the era of geologic time that includes the Triassic, Jurassic, and Cretaceous periods and is characterized by the development of flying reptiles, birds, and flowering plants and by the appearance and extinction of dinosaurs.

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Cenozoic Era

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Of, belonging to, or designating the latest era of geologic time, which includes the Tertiary Period and the Quaternary Period and is characterized by the formation of modern continents, glaciation, and the diversification of mammals, birds, and plants.