Transcript SuperPosition - Science A 2 Z

Geologic Time
Super what??!?!
Superposition: Younger rock layers are
on top of older rock layers.
 Used with the other principles of
stratigraphy to study rock layers and
layering.
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 Stratigraphy : “Branch of geology concerned with the
study of the formation, composition, ordering in time, and
arrangement in space of stratified rocks.” – USGS
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Nicolaus Steno (1669)
http://stloe.most.go.th/html/lo_index/LOcanada8/801/2_en.htm
Principles of Stratigraphy
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superposition - in a vertical sequence of sedimentary or
volcanic rocks, a higher rock unit is younger than a lower
one. "Down" is older, "up" is younger.
horizontality - rock layers were originally deposited close
to horizontal.
Original lateral extension - A rock unit continues laterally
unless there is a structure or change to prevent its
extension.
cross-cutting relationships - a structure that cuts another
is younger than the structure that is cut.
inclusion - a structure that is included in another is older
than the including structure.
"uniformitarianism" - processes operating in the past were
constrained by the same "laws of physics" as operate
today
http://www.talkorigins.org/faqs/dating.html :
Inclusion
Cross
Cutting
Original
lat. Ext.
Animations
Disconformity :
http://duedall.fit.edu/wholeearth/PHysica
l%20geology%20animations/0012.swf
 Geologic history
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http://www.wwnorton.com/college/geo/earth2/c
ontent/chapter_12/animations.asp#12_1
Rock Layer Formation
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Sedimentary: igneous rock that is
broken down by weathering into fine
particles. Compressed over time by it’s
own weight and weight of layers above
Rock Layer Formation
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Igneous: formed from liquid hot magma
that cools above or below the earths
surface.
Were are fossils found
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Sedimentary rock -- yes, Most fossils are found in
sedimentary rocks as an animal dies it get’s buried by
sediment , perhaps along a river or lake bed, and the organic
parts of the animal are replaced by minerals in the
water/sediment that
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Igneous rock -- nope, Fossils aren’t found in
igneous rock because remember that igneous rock starts out
as molten lava and if an animal were to be covered by it then
it would melt or burn away.
How old are fossils?
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2 Generic Methods:
 Absolute
○ Several methods.
○ (radiometric) Measurement of the decay rate
of isotopes.
 Carbon 14 : 5730 years Dates organic material
 Potassium – Argon : 50,000 to 2 billion years ago
Dates volcanic material
 Relative
○ Uses igneous rock above or below
sedimentary rock to determine age.
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Which layers are
Sedimentary/Igneous?
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Which layers are
older?
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S: 1,2,3,4,5,7,8,11,12
I: 10,8,6
1 - 12
What is a possible
history for this area?
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1-5 area was covered by an
ocean
7 - Oceans recede, area
appears to be covered by
large amounts of plant life
9 small to mid size animals
appear
11,12 larger animals
appears
Resources
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http://www.usgs.gov/
http://jersey.uoregon.edu/~mstrick/AskGeoMan/geoQuerry13.ht
ml
Wiki Sedimentary -http://en.wikipedia.org/wiki/Sedimentary_rock
http://www.talkorigins.org/faqs/dating.html
http://www.pbs.org/wgbh/evolution/library/03/3/l_033_01.html
http://pubs.usgs.gov/gip/geotime/time.html <- curvy geotime
http://www.kidsgeo.com/geology-for-kids/0030-geologictime.php
http://stloe.most.go.th/html/lo_index/LOcanada8/801/3_en.htm
“Geology an introduction to physical geology” , Chernicoff &
Whitney, ISBN 0-13-147464-1 , Page 20
 “Geology an introduction to physical geology” , Chernicoff &
Whitney, ISBN 0-13-147464-1 , Page 234
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