the geologic timescale a calendar of geologic time
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Modern Geologic Time Scale
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
Four Eons of Geologic Time
Modern Geologic Time Scale
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
“Hidden Eon”
“Ancient Eon”
“Earlier Life”
“Visible Life”
Modern Geologic Time Scale
Pa
leo
zoic
Ordovician
Cambrian
Silurian
Devonian
Mississippian
Pennsylvanian
Permian
Me
so
zoic
Triassic
Jurassic
Cretaceous
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Ce
no
zoic
Te
rtia
ry
Holocene
Qu
at.
Pal
eoge
neN
eoge
ne
540
510
439
408
360
323
290
245
208
146
57
35
23
5
1.6
.01
0
Ca
rb.
Quat. = QuaternaryCarb. = Carboniferous
Ma
65RIP
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
Eons
Modern Geologic Time Scale
Pa
leo
zoic
Ordovician
Cambrian
Silurian
Devonian
Mississippian
Pennsylvanian
Permian
Me
so
zoic
Triassic
Jurassic
Cretaceous
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Ce
no
zoic
Te
rtia
ry
Holocene
Qu
at.
Pal
eoge
neN
eoge
ne
540
510
439
408
360
323
290
245
208
146
57
35
23
5
1.6
.01
0
Ca
rb.
Quat. = QuaternaryCarb. = Carboniferous
Ma
65RIP
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
Eras
Modern Geologic Time Scale
Pa
leo
zoic
Ordovician
Cambrian
Silurian
Devonian
Mississippian
Pennsylvanian
Permian
Me
so
zoic
Triassic
Jurassic
Cretaceous
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Ce
no
zoic
Te
rtia
ry
Holocene
Qu
at.
Pal
eoge
neN
eoge
ne
540
510
439
408
360
323
290
245
208
146
57
35
23
5
1.6
.01
0
Ca
rb.
Quat. = QuaternaryCarb. = Carboniferous
Ma
65RIP
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
Periods
Modern Geologic Time Scale
Pa
leo
zoic
Ordovician
Cambrian
Silurian
Devonian
Mississippian
Pennsylvanian
Permian
Me
so
zoic
Triassic
Jurassic
Cretaceous
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Ce
no
zoic
Te
rtia
ry
Holocene
Qu
at.
Pal
eoge
neN
eoge
ne
540
510
439
408
360
323
290
245
208
146
57
35
23
5
1.6
.01
0
Ca
rb.
Quat. = QuaternaryCarb. = Carboniferous
Ma
65RIP
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
Epochs
What records the passing of geologic time?
• Formation of rock layers
• Sediments are deposited over time in layers.
• Each layer traps and records information about the time during which it formed.
• Sedimentary layers are analogous to the pages that compose the book of Earth History.
East Devonshire
Problem - how do you determine the order in which rock layers formed?
At a single place, layers can be ordered using the law of Superposition.
oldest
less old
even less old
younger
youngest
tim
e
Primary
Secondary
Transitional
Tertiary
Diluvial
post-Diluvial
circa 1790
Flood Gravels
Layers composed of unconsolidated sediment
Rock layers with abundant fossils
Partly crystalline rock layers with sparse fossils
Crystalline rock
Earth History, 1700’s
SE Coast of England
Within a local region, rock layers can be correlated on the basis of their lithology (physical characteristics) to define a geologic system.
NW Coast of France
Primary
Secondary
Transitional
Tertiary
Diluvial
post-Diluvial
circa 1790
Parisian gypsum beds
London clay
alluvium
Sicilian strata
English chalk
Oolites
Lias
New Red Sandstone
Muschelkalk - TriasMagnesian Limestone
Coal Measures
Mountain Limestone
Old Red SandstoneDevonshire strata
Wenlock Limestone
Welsh Greywackes
Parisian chalk
Jura Mt. strataPerm strata
circa 1820
gravels
Crystalline (metamorphic) strata
British Isles Continental Europe
GeologicSystems
Correlation - the matching-up of rock layers between different places.
• We can put local rock layers in the correct time order because we can see how they are stacked on each other.
• We can use the physical features of rock layers to correlate them into a regional system.
• The Problem: How can we correlate different regional
systems so that they are in the correct time order if we can’t directly match their layers?
Great Britain Continental Europe
?
?
How can we correlate different systems if the layers cannot be correlated based on their physical features?
Smith made the first large scale geologic map showing the distribution and order of rock layers in Great Britain.
In his work as a surveyor, Smith noticed that the rock layers seemed to contain a unique sequence of fossil species that appear and disappear through time.
Even when the rocks look different, the sequence of fossils is always the same.
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Unique interval of time
Exists
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• Once a particular regional system was formally named and its fossils described, other regional systems with the same fossils were correlated to it and given the same name.
• The original system names thus came to stand for particular intervals of geologic time.
Geologic Systems and Geologic Time
• For example, the Jurassic System was originally named for the rocks and fossils of the Jura Mountains between France and Switzerland.
• Now the Jurassic Period refers to the time interval during which the fossil species of the Jurassic System lived.
• Any rock layers with these fossils can be identified as Jurassic in age.
Geologic Systems and Geologic Time
Primary
Secondary
Transitional
Tertiary
Diluvial
post-Diluvial
Parisian gypsum bedsLondon clay
alluvium
Sicilian strata
English chalk
Oolites
Lias
New Red Sandstone Muschelkalk - Trias
Magnesian Limestone
Coal Measures
Mountain Limestone
Old Red Sandstone Devonshire strata
Wenlock Limestone
Welsh Greywackes
Parisian chalk
Jura Mt. strata
Perm strata
circa 1790 circa 1870
Modern Time Scale
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Precambrian
Quaternarygravels
Crystalline (metamorphic) strata
British Isles Continental Europe
How do we assign sedimentary layers to their correct place in time?
• fossils• each time interval in Earth history is defined by a
unique set of species that existed at that time.• Species evolve, live for a short time, and go extinct.• The same species never evolves twice (extinction is
forever).• Evolution provides a “biological calendar” that
geologists use to keep track of time.• Fossils allow us to put the individual scenes from Earth
history into the correct order to tell the full story.
Modern Geologic Time Scale
Pa
leo
zoic
Ordovician
Cambrian
Silurian
Devonian
Mississippian
Pennsylvanian
Permian
Me
so
zoic
Triassic
Jurassic
Cretaceous
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Ce
no
zoic
Te
rtia
ry
Holocene
Qu
at.
Pal
eoge
neN
eoge
ne
540
510
439
408
360
323
290
245
208
146
57
35
23
5
1.6
.01
0
Ca
rb.
Quat. = QuaternaryCarb. = Carboniferous
Ma
65RIP
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
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