Notes Chapter 28.1 Calculating Earth's Age
Name: ________________________________________________ Date: ______________________ Pd ____
 28.1 Understanding Earth
 Geology is the study of ________________________________________________________________________
 In 1666, Nicholas Steno (1638-87) noticed that shark’s teeth resembled mysterious stones called “tonguestones”
that were found in local rocks.
 Steno’s explanation helped him develop ideas about how rocks and fossils form.
 These ideas are used in a technique called ______________________________________________
 Relative dating _______________________________________________________________________________
 The approximate age of each layer of a rock formation can be determined by applying Steno’s idea called
superposition. As illustrated by a stack of newspapers.
 Superposition _____________________________________________________________________________
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 Original horizontality _________________________________________________________________________
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 Lateral continuity ____________________________________________________________________________
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 The idea of lateral continuity states that layers of rock are continuous unless a geologic event like a river
interrupts the layers or an earthquake offsets them.
 Another important idea, developed by Scottish geologist James Hutton (1726-97), is that
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 The idea of cross-cutting relationships ____________________________________________________________
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 Sometimes rock pieces called inclusions are contained in another rock.
 During the formation of a rock with inclusions, _____________________________________________________
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 Therefore, the inclusions are older than the surrounding rock.
 Over geologic history, many animals and plants have lived and become extinct.
 ___________________________________________________________________________________________
 The idea of faunal succession states that fossils can be used to identify the relative age of layers of a rock
formation.
 William Thompson Kelvin (1824-1907), is known for _________________________________________________
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_____________________________________________________________, meticulously calculated Earth’s age
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 Lord Kelvin’s calculation was not accurate _________________________________________________________
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 Earth’s 3 “internal” heat sources
 Original Heat – ______________________________________________________________________________
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 Friction between atoms – ______________________________________________________________________
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 Radioactive decay – ________________________________________________________________________
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 Today Earth’s age has been given by measuring the radioactive decay of uranium into lead. Absolute dating
 As techniques and evidence from tree rings and glaciers, and rock layers improved ________________________
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 28.1 The Layers of the Earth
 Earth’s surface is covered with a thin crust.
— There are two kinds of crust:
Continental Crust
continental and oceanic
Oceanic Crust
Average Thickness
Density
Oldest Known
4.28 B.Y. (Hudson Bay)
200 M.Y.
Composition
 28.1 Convection inside Earth
 The rocky material of the mantle moves in very slow convection currents.
 This movement is related to density and temperature differences in
the mantle.
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