Dating Rocks and Fossils Using Geologic Methodsabsolute dating: Determining the number of years that have elapsed since an event occurred or the specific time when that event occurred atomic mass: The mass of an isotope of an electron, based on the number of protons and neutronsatomic nucleus: The assemblage of protons and neutrons at the core of an atom, containing almost all of the mass of the atom and its positive chargedaughter isotope: The isotope that forms as a result of radioactive decayelectrons: Negatively charged subatomic particles with very little mass; found outside the atomic nucleuselectron spin resonance: Method of measuring the change in the magnetic field, or spin, of atoms; the change in the spin of atoms is caused by the movement and accumulation of electrons from their normal position to positions in imperfections on the crystal structure of a mineral as a result of radiation. Chemical substances that cannot be split into a simpler substancesfault: A fracture in a rock along which movement occursgeomagnetic polarity time scale: A record of the multiple episodes of reversals of the Earth's magnetic polarity that can be used to help determine the age of rockshalf- life: The amount of time it takes for half of the parent isotopes to radioactively decay to daughter isotopesindex fossil: A fossil that can be used to determine the age of the strata in which it is found and to help correlate between rock unitsisotopes: Varieties of the same element that have the same number of protons, but different numbers of neutronsmagnetic field: A region where lines of force move electrically charged particles, such as around a magnet, through a wire conducting an electric current, or the magnetic lines of force surrounding the earthmagnetism: The force causing materials, particularly those made of iron and other certain metals, to attract or repel each other; a property of materials that responds to the presence of a magnetic fieldnormal polarity: Interval of time when the earth's magnetic field is oriented so that the magnetic north pole is approximately in the same position as the geographic north poleneutrons: A subatomic particle found in the atomic nucleus with a neutral charge and a mass approximately equal to a protonoptical stimulating luminescence: Dating method that uses light to measure the amount of radioactivity accumulated by crystals in sand grains or bones since the time they were buriedpaleomagnetism: Remanent magnetization in ancient rocks that records the orientation of the earth's magnetic field and can be used to determine the location of the magnetic poles and the latitude of the rocks at the time the rocks were formedparent isotope: The atomic nucleus that undergoes radioactive decaypolarity (magnetic polarity): The direction of the earth's magnetic field, which can be normal polarity or reversed polaritypotassium- argon (K- Ar) method: Radiometric dating technique that uses the decay of 3. K and 4. 0Ar in potassium- bearing minerals to determine the absolute ageprinciple of cross- cutting relationships: Any geologic feature that cross- cuts across strata must have formed after the rocks they cut through were deposited. Fossil species succeed each other in a definitive, recognizable order and once a species goes extinct, it disappears and cannot reappear in younger rocks.
Layers of strata are deposited horizontally, or nearly horizontally, and parallel or nearly parallel to the earth's surface. In an undeformed sequence, the oldest rocks are at the bottom and the youngest rocks are at the top. Positively charged subatomic particles found in the nucleus of an atom radioactivity (radioactive): An unstable isotope spontaneously emits radiation from its atomic nucleusradioactive decay: The process by which unstable isotopes transform to stable isotopes of the same or different elements by a change in the number of protons and neutrons in the atomic nucleusradiocarbon dating: Radiometric dating technique that uses the decay of 1. C in organic material, such as wood or bones, to determine the absolute age of the materialradiometric dating: Determination of the absolute age of rocks and minerals using certain radioactive isotopesrelative dating: Rocks and structures are placed into chronological order, establishing the age of one thing as older or younger than another reversals (magnetic reversals): Changes in the earth's magnetic field from normal polarity to reversed polarity or vice versa reversed polarity: Interval of time when the earth's magnetic field is oriented so that magnetic north pole is approximately in the same positions as the geographic south polestrata (singular: stratum): Distinct layers of sediment that accumulated at the earth's surface. The study of strata and their relationshipsthermoluminescence: Dating method that uses heat to measure the amount of radioactivity accumulated by a rock or stone tool since it was last heated. Plate Tectonics Theory Lesson - You. Ancient Egypt was a civilization of ancient Northeastern Africa, concentrated along the lower reaches of the Nile River in the place that is now the country Egypt.
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