The Rock Record

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Ch. 21
The Rock Record
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Uniformitarianism the processes that act on the
Earths surface today are the same as the
processes that have acted on the Earths surface
in the past
James Hutton
The present is the key to the past
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relative age
age of anything compared to the age of something
else

• doesnt indicate actual date of occurrence

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Rules for determining relative age by using
relatvie time
law of superposition in undisturbed rock, the
older rocks will be at the bottom and the
youngest rocks will be at the top
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law of cross-cutting relationshipsan igneous
rock cutting through another rock is younger than
the rock it has cut-cross
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law of included fragments pieces of one rock
found in another rock must be older than the rock
in which they are found
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unconformity
break in the geologic rock record
Contorted rock, hard to determine relative age
(Copiapo, Chile)
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• nonconformity when stratified rock rests upon
  unstratified rock

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• Noncomformity
• Granite formed
• 2. Granite exposed by erosion
• 3. Beds 1-3 deposited

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• angular unconformity boundary between horizontal
  and tilted layers of rock

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• Angular Unconformity
• Beds 1-6 deposited
• 2. Beds 1-6 tilted
• 3. Erosion
• 4. Beds 9,10 deposited

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• disconformityboundary between layers of rock
  that have not been deposited continuously

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• Disconformity
• Beds 1,2 deposited
• 2. Erosion
• 3. Beds 5, 6, 7 deposited

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• absolute age identifies actual age of a rock
  layer
• if actual time of two events is known, the length
  of time between two events can be calculated

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fossil remains or evidence of living things
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(1) original remains the actual, unchanged
remains of the organism are preserved
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(a) frozen in ice
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(b) preserved in amber(tree sap that has hardened
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(c) mummification
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(2) replaced remains soft parts of the organism
have disappeared and been replaced by minerals
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petrification
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(3) molds and casts of the original organism (4)
trace fossils evidence of life other than
remains of an organisms activities and/or
appearance
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(a) footprints
(c) tracks, trails, burrows, borings
(b) imprint
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coprolites fossilized dung or waste materials
from ancient animals
T-Rex Carnivore Coprolite (8 lbs.)
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gastroliths fossilized stone found within the
digestive system of a dinosaur or other reptile
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• index fossil fossils found exclusively in rock
  record of a particular geologic age
• must have (4) characteristics
• (1) must be easily recognizable
• (2) must be widespread in occurrence
• (3) must be limited in time
• (4) must be found in large numbers with the rock
  layer

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• geologic time scale summary of major events of
  the Earths history preserved in the rock record
• the history of the Earth is divided by major
  changes in the Earths surface, climate and/or
  species

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Eras largest segment of time (1) Precambrian (2)
Paleozoic- ancient life (3) Mesozoic- middle
life (4) Cenozoic- recent life Eras are
divided into Periods, Periods are divided into
Epochs
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• theory of evolution theory that organisms change
  over time and new organisms are derived from
  ancestral types
• theory proposed by Charles Darwin