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69 Cards in this Set
- Front
- Back
Pre-existing rocks are broken down into smaller particles by
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unloading
thermal expansion frost wedging |
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In temperate and polar regions, the accumulation of talus slopes at the base of steep, rocky cliffs is most often attributes to
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Frost wedging
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The production of tabular slabs of rock caused by unloading of material overlying igneous bodies is known as
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Sheeting
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In the accumulation of particles in a talus slope, which of the following influences moves particles to their resting place
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Gravity
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Mechanical weathering is a significant factor in the breakdown of rocks. Which of the following factors enhances the effectiveness of further weathering as particles are created
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increased surface area of the particles
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The chemical weathering process known as oxidation would be most effective in the breakdown of
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Pyroxenes
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The chemical weathering process known as dissolution is most effective in the breakdown of which of the following minerals?
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Calcite
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During hydrolysis, ions and clay minerals are produced by the decomposition of
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Feldspars
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The Hawaiian Islands contain active volcanoes and are known for nutrient-rich soils and lush vegetation. What is the most powerful explanation for this
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1)Abundant rainfall
2)Minerals in the volcanic rock produce clay minerals as weathering by products 3)volcanic rocks contain minerals susceptible to hydrolysis |
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Sand dunes are typically dominated by quartz grains and very little other mineral matter. Why does this selection occur?
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Quartz is extremely resistant to all forms of chemical weathering.
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The formation of sedimentary rock requires
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Weathering and erosion of pre-existing rocks
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Which agents is capable of moving sediment from the site of formation to the site of deposition?
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ice, waves, wind, running water
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What is an example of a sedimentary rock composed of solid masses of inter grown crystal?
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rock salt
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you find a sedimentary rock that has all its flat particles aligned in parallel. From this you can infer that
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the particles have been compacted
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Sedimentary rocks that exhibit the inter growth of crystal masses are generally formed by
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chemical weathering
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Which two minerals are most common in detrital sedimentary rocks
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clay minerals and quartz
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What is the most abundant chemical sedimentary rock in Earth's crust?
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Limestone
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Working in the field, you find a rock that contains rounded fragments that are greater than 2 mm in diameter. What would you call this rock?
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conglomerate
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The geologic laboratory where you work received a sample for analysis that is composed of calcite that includes many microscopic fossils of marine organisms and reacts with acid. What name would identify this rock?
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Chalk
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Sediments
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Sediment:
Rock and mineral fragments. Shells. Mineral precipitates. Cemented into rocks. |
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Earth’s external processes
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Weathering – the physical breakdown and chemical alteration of rock at or near Earth’s surface
Physical - Mechanical breakage and disintegration. Chemical - Decomposition by reaction with water. Erosion – the physical removal of material by mobile agents such as water, wind, ice, or gravity |
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Jointing
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Deep crustal rocks are hot and under high pressure.
At the surface, crustal rocks cool and expand. Igneous plutons crack in onionlike “exfoliation” layers. These layers break off as sheets that slide off of a pluton. |
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Chemical Weathering
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Reaction with water disintegrates many minerals.
Maximized under warm and wet conditions. Tropical weathering is intensive. Turns rock into heavily decomposed material Chemical weathering is virtually absent in deserts.Dissolution Some minerals (halite, calcite) dissolve. |
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Hydrolysis
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Water breaks cation bonds in silicate minerals. Yields…
Dissolved cations. Alteration residues. Clay minerals. Iron oxides (rust). |
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Chemical Weathering
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Oxidation
Rusting is a familiar example.Hydration Absorption of water into a mineral structure. Results in a volume increase (expansion). |
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Biological Weathering
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Organisms often important chemical weathering agents.
Plant roots. Fungi. Lichens. Bacteria. Organic acids attack minerals |
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Weathering Feedbacks
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Weathering processes often work as a positive feedback.
Physical weathering speeds chemical weathering. How? An increase in surface area accelerates chemical attack. Chemical weakening increases surface area via breakage. |
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Soil
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Soil is a combination of mineral and organic mater, water, and air
That portion of the regolith (rock and mineral fragments produced by weathering) that supports the growth of plantsFactors controlling soil formation Parent material Time Climate (temperature and precipitation) Plants and animals Slope |
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The soil profile
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Soil forming processes operate from the surface downward
Vertical differences are called horizons – zones or layers of soil |
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The process of compaction, cementation and hardening of these sediments is termed
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lithification
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Sedimentary Rocks
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Sediments are the building blocks of sedimentary rocks.
Sediments are diverse, as are the rocks made from them. 4 classes: Clastic – Made from weathered rock fragments (clasts). Biochemical – Cemented shells of organisms. Organic – The carbon-rich remains of plants. Chemical – Minerals that crystallize directly from water |
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Clastic Sedimentary Rocks
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Clastic sedimentary rocks reflect several processes.
Weathering – Generation of detritus via rock disintegration. Erosion – Removal of sediment grains from rock. Transportation – Dispersal by wind, water, and ice. Deposition – Accumulation after transport stops. Lithification – Transformation into solid rock. |
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Clastic Sedimentary Rocks
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Lithification – Transforms loose sediment into solid rock.
Burial – More sediment is added onto a previous layer. Compaction – Overburden weight reduces pore space. Clast (grain) size – The average diameter of clasts. Range from very coarse to very fine. With increasing transport, average grain size decreases. |
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Clastic Sedimentary Rocks
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Angularity and sphericity – Indicate degree of transport.
Grain roundness and sphericity increases with transport. Well-rounded – Long transport distances. Angular – Negligible transport. |
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Clastic Sedimentary Rocks
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Sorting – The uniformity of grain size.
Well-sorted – Uniform grain size. Poorly sorted – Wide variety of grain sizes. |
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Biochemical and Organic Rocks
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These are sediments derived from living organisms.
Biochemical limestone – Made from CaCO3 shell remains. Carbonate grains accumulate in the “carbonate factory.” Warm (tropical and subtropical). Normal-salinity marine water. Oxygenated. Shallow. Clear. |
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Biochemical and Organic Rocks
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Organic rocks – Made from organic carbon.
Coal – Altered remains of fossil vegetation. Accumulates in lush tropical wetland settings. Requires deposition in the absence of oxygenComprised of minerals precipitated from water solution. Evaporites – Created from evaporated seawater. Evaporation triggers deposition of chemical precipitates. Examples include halite (rock salt) and gypsum. |
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Sedimentary structures
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Large scale features of sedimentary rocks
Generated by a variety of processes and reflect environmental conditions Occur at very different scales, from less than a mm (thin section) to 100s–1000s of meters (large outcrops); Microforms (e.g., ripples) Mesoforms (e.g., dunes) Macroforms (e.g., bars) |
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Bedding and lamination
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Sedimentary rocks generally have bedding or stratification
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Graded Bedding
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Some beds show an upward gradual decrease in grain size, known as graded bedding
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Bedforms
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Small-scale alternating ridges and troughs
Current ripple marks water or wind currents flowing in one direction asymmetric profiles Wave-formed ripple marks result from the to-and-fro motion of waves symmetrical |
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Current Ripple Marks
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The internal structure shows small-scale cross-beddingCan tell you the direction and strength of the current by the size of the ripple, you will find asymmetric ripples for example such as beach side, or sand dunes, because the wind direction is always changing and the strength of the winds may also change to create an asymmetric profile.
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Wave-Formed Ripples
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Ripples are More Symmetrical because the waves move back and forth to create the ripples…
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Mud Cracks
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When clay-rich sediments dry, they shrink and crack into polygonal patterns bounded by fractures called mud cracksalong a lakeshore
or a river flood plain or where mud is exposed at low tide along a seashore |
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Biogenic Sedimentary Structures
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Biogenic sedimentary structures include
tracks burrows trails Extensive burrowing by organisms is called bioturbation |
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Bioturbation
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U-shaped burrows
Vertical burrows |
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What are metamorphic rocks?
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“morphos” is Greek for form“meta” is Greek for changemetamorphism means
“change of form” |
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Introduction
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Protoliths (parent rock) undergo pronounced changes in…
Texture. Mineralogy. Due to change in physical or chemical conditions. Burial. Tectonic stresses. Heating by magma. |
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Metamorphism
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Metamorphism occurs in the solid state.
It doesn’t include weathering and melting. Metamorphics often look totally unlike protoliths. |
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Metamorphic Character
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Metamorphic rocks have distinctive properties.
Unique minerals – Some that are only metamorphic. Staurolite, Kyanite, Sillimanite, etc. Unique foliation – A planar fabric from aligned minerals. |
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Agents of Metamorphosis
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Three primary “agents” can metamorphose rock
Heat (Temperature – T). Pressure (P). Differential stress. Hydrothermal fluids (chemically activeby changing the chemistry, mineralogy, and/or structure of the rocks, without melting them |
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Heat (Temperature)
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Metamorphism occurs as the result of heat.
Temperature (T) ranges between 200oC and 850oC. The upper T limit is…melting. It varies based upon rock mineral composition and water content. Sources of heat. The geothermal gradient. Magmatic intrusions. Compression. |
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Pressure (P)
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P increases with depth in the crust.
270 to 300 bars per km. Metamorphism occurs mostly in 2 to 12 kbar range. T and P both change with depth. Mineral stability is highly dependent upon T and P. This stability can be graphed on a “phase diagram.” Changes in T and P lead to changes in minerals |
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Differential Stress
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Pressure that is greater in one orientation.
A commonplace result of tectonic forces. |
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Hydrothermal Fluids
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Hot water with dissolved ions and volatiles.
Hydrothermal fluids facilitate metamorphism. Accelerate chemical reactions. Alter rocks by adding or subtracting elements. Hydrothermal alteration is called metasomatism. |
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Types of Foliated Rocks
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Slate – low grade change from shale
Schist = high grade change from shale Gneiss = high grade change from shale/sandstone or granite/rhyolite |
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Non-foliated Rocks
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Don't have planes, have no preferred orientation, not subjected to any directed pressure
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Determining geological ages
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Relative age dates – placing rocks and events in their proper sequence of formation
Numerical dates – specifying the actual number of years that have passed since an event occurred (known as absolute age dating) |
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Principles of relative dating
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Law of superposition
Developed by Nicolaus Steno in 1669 In an undeformed sequence of sedimentary rocks (or layered igneous rocks), the oldest rocks are on the bottom |
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Principles of relative dating
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Principle of original horizontality
Layers of sediment are generally deposited in a horizontal position Rock layers that are flat have not been disturbed Principle of cross-cutting relationships Younger features cut across older feature |
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Principles of relative dating
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Inclusions
An inclusion is a piece of rock that is enclosed within another rock Rock containing the inclusion is younger |
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Principles of relative dating
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Unconformity
An unconformity is a break in the rock record produced by erosion and/or nondeposition of rock units |
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Absolute-Dating Methods
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Radioactivity is the spontaneous decay of an atom’s nucleus to a more stable form
Radioactivity provides geologists with a powerful tool to measure absolute ages of rocks and past geologic events |
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Atoms: A Review
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The nucleus of an atom is composed of
protons – particles with a positive electrical charge neutrons – electrically neutral particles with electrons – negatively charged particles – outside the nucleus |
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Isotopes: A Review
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Atomic mass number
= number of protons + number of neutrons The different forms of an element’s atoms with varying numbers of neutrons are called isotopes |
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Radioactive Decay
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Some isotopes are unstable. They undergo radioactive decay, releasing particles and energy.
Radioactive decay is the process whereby an unstable atomic nucleus spontaneously transforms into an atomic nucleus of a different element |
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Half-Lives
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The half-life of a radioactive isotope is the time it takes for one half of the atoms of the original unstable parent isotope to decay to atoms of a new more stable daughter isotopeThe length of half-lives can vary from less than one billionth of a second to 49 billion years!
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Radioactive Decay
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In radioactive decay, during each equal time unit (half-life), the proportion of parent atoms decreases by 1/2
Example: If a rock has a parent/daughter ratio of 1:3 and the half-live is 57 million years, how old is the rock 25% means it is 2 half-lives old. the rock is 57my x 2 =114 million years old. |
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Determining Age
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By measuring the parent/daughter ratio and knowing the half-life of the parent which has been determined in the laboratory geologists can calculate the age of a sample containing the radioactive element
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