Record in the Rock: What Processes Shape our Earth?
 Geology: __________________________________________________________________
_________________________________________________________________________
 Importance:
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Understanding of the ______________ that _____________ our Earth, so we can
better _________________ potential __________________
Earth’s Internal Structure:
 Characterized _____________________________________________________________
_________________________________________________________________________
 Crust is the ______________ most layer of Earth, consists of _______ types:
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Continental: __________________________________________________________
___________________________________________________________________
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Oceanic: ____________________________________________________________
___________________________________________________________________
Age of The Earth & Geologic Time
Principle of Uniformitarianism:
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The order in which __________________________________________________________
________________________________________________________________________.
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The same processes that are at work ___________ were at work in the ___________
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*The _____________ is the _________ to the __________!
Relative Dating: _________________________________________________________________
_______________________________________. We use a number of principles and laws to do this:
1. Law of Original Horizontality – ________________________________________________
________________________________________________________________________
2. Law of Superposition - ____________________
______________________________________
______________________________________
_____________________________________
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Scientist use law of superposition by using ____________ age
(something ____________ to the age of something else)
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Problem: ________________ – buried surface that represents a break in the rock record
3. Lateral Continuity- layers of sediment __________
in _________ directions when they form.
4. Law of Cross-cutting Relationships - _____
___________________________________
___________________________________
________________________________________
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5. Inclusions: _______________________(rock pieces)
_________________________________
6. Faunal Succession: _____________________
_______________________________________
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Index fossil:
__________________________________________
__________________________________________
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Correlation: matching ___________ by __________ ___________ in different places
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1st person to use correlation was ______________ _______________
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Smith & others developed the Geologic ____________ – a diagram of the
_______________ of rock ____________ in an specific area, in order of _______
Early Estimates of Earth’s Age
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Methods
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Sedimentation – estimated the total ______________ of the earth’s ______________
rocks (rate of sedimentation)
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Range from ____ million to _____ billion years
Problems
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Rate can _________ at different ___________ & ____________
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______ accurate way to measure thickness
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Started with different ___________________
2. “Salt” Method – estimated the _______ ___________ of the oceans, then _____________
it with the __________ at which salt is being _______________ to the oceans.
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Range from ____ million to _____ billion years
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Problems with Salt Method
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1. __________________ at first the oceans contained __________ water
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2. did ______ account for _____ way salt is added to or removed from the oceans
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3. Each scientist _________________ amounts of salt
3. Kelvin Method – assumed Earth was ______ ____________ rock, he measured rate of
Earth’s ______________ to _______________. Also, took into account heat coming from
within the Earth and from the ________
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Range from ______ million years to _________ million years
Problems
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No one knew about ___________________
Absolute Age Dating
Absolute Dating: Enables scientists to determine the ______________ _______________ age of
rocks and other objects
Radioactive Decay :
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Radioactive isotopes __________ ________ into other elements by _____________ radiation
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An element is defined by the number of ______________ it contains
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As the ______________of protons __________________ with each emission, the original
radioactive isotope (parent) gradually converted to a _________________ element (daughter)
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Ex: Uranium – 238, _____________, changes into Lead -206, ____________________
 Radiometric Dating
 Dating an object using _________________ isotopes
 As the _____________ of parent atoms ___________________ during radioactive decay
the number of __________________ atoms ___________________
 Rate of decay ______________ changes, but is based on elements __________ -life
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Half life: ________ it takes for ____________ of the isotope to break down into
another __________________
 Uranium 238 use to determine age of_________- ________________ things
 Carbon used to determine age of once ___________________ things
 Dendrochronology
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Dendrochronology: use _________ ______________ to determine absolute age
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Uses tree rings called ________________ rings (early & _________ season)
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The _________ of the rings depends on certain _______________ in the environment
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Trees from the __________ geographic region tend to have the same
________________ of ring width for a give span of time
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By _____________________ the ____________ in these trees scientists have
established tree ring ____________________ up to 10,000 years
 Ice Cores
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Ice Cores: they contain a record of past environmental conditions in annual __________________
of _______________ deposition
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________________ ice tends to have ___________ bubbles and ____________ crystals
than winter ice
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Ice-core chronologies study ______________ cycles and __________________
 Varves
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Varves: bands of ___________________ light and dark colored _______________ of sand, clay
and silt
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Occur with _________________ deposition of sediments around ___________ usually
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______________-sized particles in summer (________)
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Thinner, ___________-grained particles in winter (_________)
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Scientists can date cycles of glacial sedimentation over periods as long as __________ years
Calculating Half Lives:
 The time for ____________ of the ________________________ substances in a
given sample to undergo _________________.
 After one __________________ there is ___________ of original sample left.
 After two half-lives, there will be ______ of the ________ = ________ the original sample.
Example 1:
 You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years.
How many grams are left after one half-life?
How many grams are left after two half-lives?
Example 2: The half-life of iodine-131 is 8 days.
 If you start with 36 grams of I-131, how much will be left after 24 days?