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42 Cards in this Set
- Front
- Back
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relative dating
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determination of the age of a rock or event in relation to the age of other rocks or events
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absolute age
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the actual age of a rock or event in years
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relative dating
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determination of the age of a rock or event in relation to the age of other rocks or events
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absolute dating
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the actual age of a rock or an event in years
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principle of superposition
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inference that the bottom rock layer is the oldest and it gets younger as it goes up
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intrusion
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when magma squeezes into preexisting rocks and crystallizes
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age of intrusion
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younger in realtive age than any rock it cuts through
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extrusion
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when laval flows on earths surface and solidifies
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relative age of extrusion
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younger than any rock beneath it, but older than any rocks on top of it
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relative age of unclusion
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older than rocks it forms in
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a rock is older than ..
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any fault, joint, tilting, or fold that appears in it
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age of parts of sedimentary rock
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the sediments are older than the rock
the cement is younger than the rock |
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age of igenous rocks
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individual mineral crystals vary in age
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why
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bc they form at different temps reached by the magma as it cools or hardens over thosands or millions of years
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vein age
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younger than the rock around it
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correlation
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process that makes it pssible to show that rocks or geologic events from different places are the same or similar in age
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different ways of correlation
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1. exposed bedrock
2. similarities in rock 3. index fossils 4. volcanic ash and meteorite deposits |
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where are fossils exclusively found
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in sedimentary rocks
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why are fossils rarely found in igneous and metamorphic rocks
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bc fossils are usually destroyed by the melting of igenous rocks and by the heat and pressure associated with the formation of metamorphic rocks
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index fossils
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the fossils used in correlation
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2 conditions of a useful index fossil
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1. widespread
2. shortlived |
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correlation by volcanic ash
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in large eruptions, volcanic ash scattors over wide areas of eatrths surface, then settles among other sediments in many different environments-all volcanic is the same from the same volcano so it serves as specific age markers in rocks that can be far apart
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divions of time in order from longest to shortest
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eons, eras, periods, and epochs
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why are precambrian fossils rare and difficult to identify
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bc the earliest known life forms were small and had no hard parts
aloso, most rocks have either been buried by more recent rocks, eroded away, or converted to metamorphic rocks or magma |
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unconformities
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buired eroded surfaces
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what does an unconformity in the rock record of an area indicate?
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that at some time in its geologic history, upliift occured, which exposed the rocks to weathering and erodsion, which removed part of the rock record. later the land sunk or the sea level rose and it waas covered in water. new seidments were then depostied on the eroded land surface, producing an unconformity
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why do most unconformities show a lack of parallelism between the older rock layers and the younger rock layers
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bc the older rock layers were folded or tilted during uplift
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uniformity of process
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the pressent is the key to the past
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isotopes
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variet of elemetns
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radioactive decay
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the nuceli of atoms of many istopes are unstable, or radioacticve, and the emit particles and electromagnetic energy, chaging into atoms of other isotopes and elements
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uranium-238
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one of the most important radioacctive isoptopes used in dating rocks
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half-life
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the time required for half of the atoms in a given mass of an isotope to decay
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does anything affect a half life
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no
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radioactive dating
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estimating the absolute age of a rock sample using the halflife of a radioactive isotope along with the ratio between the amount of orginial isotope and the amount of its decay
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carbon-14 dating
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can be used to date rocks and organic remains up to approx. 70,000 yrs in age
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2 things that say extrusion came before top layer
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1. no contact metamorphism
2. top has small or no crystals |
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half-life
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the time required for half of the atoms in a given mass of an isotope to decay
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does anything affect a half life
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no
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radioactive dating
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estimating the absolute age of a rock sample using the halflife of a radioactive isotope along with the ratio between the amount of orginial isotope and the amount of its decay
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carbon-14 dating
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can be used to date rocks and organic remains up to approx. 70,000 yrs in age
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2 things that say extrusion came before top layer
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1. no contact metamorphism
2. top has small or no crystals |
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radioactive
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element that is unstable and breaks down at a fixed time
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