Post on 16-May-2015
Geologic History
F SSILS
WHAT ARE FOSSILS?
the remains or trace of a once the remains or trace of a once living thing, usually preserved in living thing, usually preserved in
sedimentary rocksedimentary rock
F SSILS- How are they formed?
ALIVE
F SSILS
DEAD ANDDECAYING
F SSILS
HARD PARTSLEFT BEHIND
Hard parts are the bonesor the shells of an organism
F SSILS
BURIAL ANDFOSSILIZATION
FOSSILIZATION OCCURS WHENMINERALS REPLACEANY ORGANIC MATERIALTURNING IT INTO A FOSSIL (ROCK)
F SSILS
FOSSIL
F SSILSTYPES OF FOSSILS
IMPRINTS
Occur when leaves andOccur when leaves and
feathers leave an feathers leave an
impression in mud that impression in mud that
later hardens into rock.later hardens into rock.
F SSILSTYPES OF FOSSILS
ORGANISMS GET TRAPPEDIN HARDENING TREE SAPAND ARE PRESERVED ASFOSSILS
AMBER
F SSILSTYPES OF FOSSILS
ICE
SOME ORGANISMSMAY BE PRESERVED ASFOSSILS IN ICE
F SSILSTYPES OF FOSSILS
TAR
ANIMALS GET TRAPPED IN TAR PITS AND THEIR REMAINS GET PRESERVED- LA BREA TAR PITS INCALIFORNIA
F SSILSTYPES OF FOSSILS
PETRIFIED WOOD
PETRIFICATION OCCURSWHEN MINERALSDISSOLVED IN GROUNDWATER GRADUALLYREPLACE THE ORIGINALTISSUES OF PLANTS ANDANIMALS
F SSILSWHAT DO FOSSILS TELL US?
APPEARANCEAND ACTIVITIESOF PAST LIFE
FOSSIL TEETH GIVEUS CLUES AS TOWHAT THE ANIMALATE
F SSILSWHAT DO FOSSILS TELL US?
SPECIES HASEVOLVED ORCHANGED
F SSILSWHAT DO FOSSILS TELL US?
EARTH’S PASTCLIMATES
NYS
458 MILLION YEARS AGO 250 MILLION YEARS AGO
FOSSIL CORAL = WARM CLIMATE
GE LOGIC TIME
The geologic time scale is based on the
FOSSIL RECORD
LARGETIME
UNITS
SMALLTIME
UNITS
EON
ERA
PERIOD
EPOCH
GE LOGIC TIME
Geologic History of NYS- ESRT p. 8 & 9
Precambrian Eon
Archean Proterozoic
Phanerozoic Eon
GE LOGIC TIME
Geologic History of NYS- ESRT p. 8 & 9
Precambrian Eon
Archean Proterozoic
Phanerozoic Eon
Cenozoic Era Mesozoic Paleozoic
GE LOGIC TIME
Phanerozoic Eon
Cenozoic Era
Quarternary
Period
Mesozoic Paleozoic
Neogene Paleogene
GE LOGIC TIME
Cenozoic Era
Quarternay
Period
EARLY LIFE ON EARTH
Neogene Paleogene
Pleistocene Holocene
GE LOGIC TIMEGE LOGIC TIMEWhy are the sections of geologic time separated
this way?
Major Extinctions Major Climate
Change
Appearance Of new
life
GE LOGIC TIME- Model of Geologic Time
Scale
Name of Era/Eon Millions of Years Ago
Duration Percent of Earth’s History
Cenozoic
Mesozoic
Paleozoic
Precambrian
0 to 65
65 to 251
251 to 544
544 to 4600
65 my
186 my
293 my
4056 my
1.4%
4%
6.4%
88.1%
RELATIVE DATING
What is relative dating?
Determining the age of something compared to
something else
NO NUMBER IS NEEDED!!THIS IS JUST LIKESAYING:
Trilobites are olderthan dinosaurs
Dinosaurs are olderthan mastodonts
We do this to determine howold rock layers are…
RELATIVE DATING
Rules for
Sequencing:LAW OF SUPERPOSITION:
In undisturbed sedimentary rock the oldest layer is on the bottom, youngest on
topYOUNGEST
OLDEST
RELATIVE DATING
Rules for
Sequencing:
FAULTING:
A fault is younger than the layers it
cuts across
Duh!!! Don’t the rock layers need to be therein the first place?
RELATIVE DATING
Rules for
Sequencing:
IGNEOUS INTRUSION:
An igneous intrusion is younger than the
rock layers it penetrates
Remember igneous rocks form from magma. An igneous intrusion is when magma seeps up in between rock layersand hardens to form rock.
RELATIVE DATING
Rules for
Sequencing:
CONTACT METAMORPHISM:
The contact metamorphism is younger than the
layers it cuts through
When the magma seeps up between rock layers it is very hot and it bakes the rocks around it. The surrounding rocks do not melt but are metamorphosed.
Duh again!!!! If there were no rock layers there then there wouldn’t be anything to turn into metamorphic rock.
RELATIVE DATING
Rules for
Sequencing:
Unconformity
A “missing” layer of rock. buried erosional surface.
Rocks were deposited, erosion occurred at the surface and then new rock was deposited.
RELATIVE DATING
Rules for
Sequencing:
TILTING:
Tilting or folding of rock layers is
younger than the layers it affects
Relative Dating Instructions
Relative Time:Ages of events are placed in order of
occurrence.
No exact date is identified. Ex. WWI and WWII
"I am the second child in my family."
Law of Uniformitarianism
• "The present is the key to the past."
• or what we see now has almost certainly happened before and therefore can be used for interpreting the past.
Original Horizontality- Rocks are usually deposited flat and level.
• You would say– “Deposition of”
sandstone, limestone, shale, etc.
– This applies to sedimentary rocks ONLY
The law of cross-cutting relationships—an igneous rock is younger than the rocks that it has intruded into. This also applies to faults.
You would say— “Igneous intrusion” or faulting/folding.
4. Faulting3. Deposition of Shale2. Deposition of Sandstone1. Deposition of Limestone
Sequence 1: Uplift & Erosion
• Any time folding or tilting occurs• UPLIFT will occur• If there is uplift – EROSION will
occur
Unconformity
• A “gap” in the rock record where erosion or non-deposition occurred.
• You must include this as a separate step in the sequence of events.
•Layers are formed according to superposition.
Here’s How It Works!Here’s How It Works!
•Something happens to uplift the area- (folding, faulting, etc).
•Erosion wears away the uppermost layers
•Area submerges (or sinks) and deposition begins again.
Other Guidelines for figuring out a sequence:
• Sedimentary rocks are usually formed under water.
• Weathering and erosion usually happen above water (on dry land).
Practice Sequencing
• Turn to page 7 in your notes.
• We will complete #1 together.
• Complete #2-#6 for homework, we will go over them tomorrow.
Practice Sequencing #3
8._________________________
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Practice Sequencing #4
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3._________________________
2._________________________
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Practice Sequencing #5
7._________________________
6._________________________
5._________________________
4._________________________
3._________________________
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Practice Sequencing #6
7._________________________
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Rock Correlation
• Want to know what happened in Earth history in widely different locations?
• Rock correlation -- hooks up rocks that look alike
– The key bed – a particular strata that is very distinctive
– Fossil correlation -- hooks up rocks that formed at the same time and relies on the following:
• index fossils • Rock type (color and composition)
Rock Correlation:
Matching up outcrops at different locations
Volcanic TimeMarkers
Index Fossils
Rock layers have:Same color, and
composition
Outcrop 1 Outcrop 2 Outcrop 3 Outcrop 4
Correlating Rock Layers
Index Fossils
Short Lived
Wide Spread
Absolute Age
Examples
--65 Million Years Ago --1990
What is absolute age?
Identifies the exact date of an event
How can we figure it out?
Radio Active decay
Radioactive(parent element):
Atom with anunstable nucleus
that decays
Radioactive(parent element):
Atom with anunstable nucleus
that decays
Carbon 14: CarbonDating
Used to date organic remains(woods, bones) no older than
50,000 years
Half-Life:
Time it takes for ½ of a radioactive element
to decay into a stableelement
Is NOT affected by:
Heat Pressure
Mass
Daughter Element:
Stable element, productof radioactive decay