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60 Cards in this Set
- Front
- Back
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Petrified
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when minerals replace the remains and they become rock.
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Mold
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when the shell remains and the contents dissolve (hollow).
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Cast
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when the mold becomes filled with minerals that are not a part of the original organism
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How can an organism be preserved completely intact?
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If the organism is surrounded by ice or tar. This is very rare.
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Relative Dating
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looks at where the fossil is located to determine its age relative to other fossils. This works only if the area has been undisturbed.
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Absolute Dating
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uses radioactive elements near the fossil to determine the actual age of the fossils.
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How can scientists calculate the age of the fossil/s buried nearby?
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By determining the age of radioactive element.
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How is the absolute age of the fossils estimated?
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By dating associated igneous rock and lava flows.
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What is the Geologic Time Scale?
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The dating of all fossils is included and divides the time that earth has existed into 4 eras.
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Eras are divided into what?
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Periods
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What are periods?
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Based on common events in that time period.
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James Hutton
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Proposed that most geologic processes happen very slowly. Geologists sort Earth's history into a seuence of events.
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When did the earth form?
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4.6 billion years ago
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Relative Age
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Position in that sequence; older or younger than nearby layers
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Absolute Age
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Numerical Age can be determined through analysis of the products of radioactive decay. Reading the layered rocks.
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Layered rocks contain clues about what?
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Past environments at/near surface.
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Sequence and relative ages provide what?
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basis for reconstructing Earth's history.
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The study of strata is called?
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stratigraphy
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Most sediment is laid down where?
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in the sea, in shallow waters, or in streams.
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Each new layer is laid how?
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horizontally over the older ones.
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Law of Original Horizontality
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sediments are deposited in strata that are horizontal or nearly horizontal.
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Unconformity
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break or gap in sequence
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Angular unconformity
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older strata deformed and cut off by erosion before younger layers were deposited across them.
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Disconformity
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irregular surface of erosion between parallel strata; no tilting; hard to recognize, because the strata above and below are parallel.
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Nonconformity
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strata overlie igneous or metamorphic rock.
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Significance of Unconformities
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Evidence of former sea floors uplifted by tectonic forces and exposed to erosion. Later tectonic forces depress the surface. The surface, in turn, becomes a site of deposition of sedimentary.
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Stratigraphic Classification
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The basis of rock stratigraphy is the formation. A collection of similar strata that are sufficiently different from adjacent groups. Basis of physical properties they constitue a distinctive, recognizable unit that can be used for geologic mapping over a whole area.
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Correlation
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comparing different places to see if thye are the same geo time and processes
Determining the relative ages of exposed areas. Uses standard geo times scale to establish ages. Index fossils are useful for this. If a distinctive index fossil is recognizable at an outcrop, a rapid and reliable means of correlation is available. |
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The Geologic Column and the Geologic Time Scale 19th Century
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geologists assembled a geologic column. Composite column containing, in chronological order, the succession of known strata, fitted together. Based of fossils or other evidence of relative age.
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What did the discovery of radioactivity provide?
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The needed method to measure the age of Earth accurately.
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Isotopes
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Different kinds of atoms of an element that contain different numbers of neutrons. Most isotopes are stable and do not change.
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Radioactive Isotopes
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Instability within a nucleus. Transform spontaneously to a nucleus of a more stable isotope of a different chemical element.
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Radioactive Decay
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When a radioactive isotope transforms to a nucleus of a more stable isotope of a different chemical element.
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Radioactive decay varies among?
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Isotopes
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How is radioactive decay measured?
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in half-lives, amount of time needed for number of parent atoms to be reduced by one half
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Freezing (refridgeration)
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Best means of preservation of ancient materials. Rare-continually frozen from death till discovery. Mammoths and wooly rhinoceros found in ice from Alaska and Siberia. Specimens with flesh, skin, and hair intact have been found.
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Drying (desication)
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Mummified bodies. Soft tissues preserved if completely dried. Discovered in arid parts.
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La Brea Tar Pits
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famous for Plestocene fossils. Asphalt is an excellent preservative.
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Amber (unaltered preservation)
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Insects, spiders, and even small lizards have been found, nearly perfectly preserved in amber.
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Carbonization (distillation)
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Plant leaves, and some soft body parts of fish, reptiles, and marine invertebrates decompose and leave behind only the carbon. This carbon creates an impresssion in the rock out lining the fossil, sometimes with great detail.
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Molds and Casts are what?
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Molds and casts of organisms which have dissolved or rotted away, leaving only a trace of their existence. They are the types of fossils where the physical characteristics of organisms have been impressed onto rocks. Buried or trapped in mud, clay, or other materials which hardened around them-leaving molds of the organism.
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What are the two types of molds?
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Internal and external
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Permineralization (petrifacation)
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mos common, minerals fill the cellular spaces and crystalize. Shape of the orgianl plant or animal is preserved as rock. Sometimes the orginal material is dissolved away leaving the form and structure but none of the organic material.
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Fossils
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Preserved remains or traces of an organism that lived in the past.
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What are the eras?
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Precambrian, Palaeozoic, Mesozoic, Caenozoic
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What periods are in Palaeozoic era?
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Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian
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What periods are in the Mesozoic era?
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Triassic, Jurassic, Cretaceous
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What periods are in the Caenozoic era?
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Paleocaene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene
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What happened in the Precambrian era?
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Began with the formation of the earth 4.6 billion years ago. Bacteria appeared 3.5 billion years ago, followed by algae and fungi.
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What happened in the Cambrian period?
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Sponges, snails, clams, and worms evolve.
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What happened in the Ordovician period?
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First fish evolved and other species become extinct.
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What happened in the Silurian period?
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Land plants, insects, and spiders appear.
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What happened in the Devonian period?
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Amphibians evolve, and cone-bearing plants start to appear
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What happened in the Carbonferous period?
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Tropical forests appear and reptiles evolve.
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What happened in the Permian period?
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Seed plants become common and insects and reptiles become widespread. Sea animals and some amphibians begin to disappear.
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What happened in the Triassic period?
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Turtles and crocodiles evolve and dinosaurs start to appear.
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What happened in the Jurassic period?
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Large dinosaurs roam the world. First mammals and birds appear.
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What happened in the Cretaceous period?
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Flowering plants appear, mammals become more common, dinosaurs become extinct.
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What happened in the Tertiary period?
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First primates appear and flowering plants become the most common.
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What happened in the Quaternary period?
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Humans evolve and large mammals like the wooly mammoth become extinct.
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