Transcript Geological Time Scale [ B. Frueger – Colby ]

Founders of Historical Geology
Charles Darwin 1809-1882
Evolution – organisms changed through time
Individuals with variations most favorable in existing
environment had best chance of survival
Passed these traits on to next generation
Natural Selection
Also recognized by Alfred Russell Wallace
Neither knew the mechanism, do you?
Founders of Historical Geology
Charles Darwin 1809-1882
Origin of Species – 1859
Documented two things:
1. Evolution occurred
2. Natural selection was
active & how it worked
Organic evolution became the
guiding principle of
paleontological and biological
research
Founders of Historical Geology
North American Notables
William McClure 1763-1840
Produced the first geologic
map of the US
Founders of Historical Geology
North American Notables
Amos Eaton
1776-1842
Taught “hands on” geology at Rensselaer School (RPI)
Took long field trips
Father of American geology
Studied New England region
Founders of Historical Geology
North American Notables
Louis Agassiz
1807-1873
Recognized that massive ice sheets
once covered North
America
First to hint at “ice ages”
Stated that glacial deposits did not
accumulate during Biblical flood
Founders of Historical Geology
North American Notables
James Hall 1807-1873
First director of NY State
Geological Survey
Founders of Historical Geology
North American Notables
James D. Dana 1813-1895
Published Manual of Geology
System of Mineralogy
Founders of Historical Geology
North American Notables
John Wesley Powell
Director of USGS
First to traverse Grand
Canyon by boat
(1869)
Union officer in Civil War
Lost arm at Shiloh
1834-1905
Founders of Historical Geology
North American Notables
Othniel C. Marsh 1831-1899 Yale
Edwin D. Cope 1850-1897 Penn
Both vertebrate paleontologists
Exploited fossil beds of western
United States
No cooperation between two
Founders of Historical Geology
North American Notables
George Otis Smith
Director of USGS 1907-1930
Colby graduate, 1893
1871-1944
Time and Geology
The fundamental interest in geology is to put rocks
in order time wise
Geologists try to establish a GEOCHRONOLOGY
Steno, Hutton, Smith etc
tried by use of superposition, fossil succession
As science advanced we used radiometric techniques.
Time and Geology
Smith and contemporaries used
RELATIVE GEOLOGIC DATING techniques
In relative dating, no reference to actual time
Time and Geology
ACTUAL OR NUMERICAL DATING tries to assign
numbers in terms of years to events.
Generally based on radiometric decay of unstable
elements
Expresses actual age of rocks or events
Time and Geology
GEOLOGIC TIME
SCALE
Subdivisions of Time
Eons
Eras
Periods
Epochs
None last equal intervals of
time.
Based on events.
Time and Geology
Subdivisions of Time
EON
Largest subdivision of
Geologic Time Scale
Four Eons recognized
Phanerozoic
Proterozoic
Archean
Hadean
Precambrian
Time and Geology
Precambrian
Subdivisions of Time
Phanerozoic Eon
0.544 byBP – present
Includes most sedimentary rocks and
history of life
Proterozoic Eon
2.5-0.544 byBP
Mostly crystalline rocks
Archean Eon
3.9-2.5 byBP
Oldest preserved rocks
Hadean Eon
4.6–3.9 billion years before present (byBP)
No geologic record
Time and Geology
Subdivisions of Time
Phanerozoic Eon
Three major subdivisions:
ERA
Cenozoic Era (recent life)
65 myBP-present
Mesozoic Era (middle life)
250-65 myBP
Paleozoic Era (ancient life)
544-250 myBP
Time and Geology
Subdivisions of Time
Paleozoic Era
7 major subdivisions:
PALEOZOIC
PERIODS
Permian
Pennsylvanian Carboniferous
Mississippian
Devonian
Silurian
Ordovician
Cambrian
Time and Geology
Subdivisions of Time
EPOCH
Periods are subdivided into
EPOCHS
Quaternary Period
Holocene Epoch
Pleistocene Epoch
Tertiary Period
Pliocene Epoch
Miocene Epoch
Oligocene Epoch
Eocene Epoch
Paleocene Epoch
Time and Geology
Subdivisions of Time
Units on the Geologic Time Scale represent actual increments
of time = GEOCHRONOLOGIC UNITS
Actual rock units formed or deposited during these intervals
are CHRONOSTRATIGRAPHIC UNITS
Geochronologic Units
Eon
Era
Period
Epoch
Age
Chron
Chronostratigraphic Units
Eonathem
Erathem
System
Series
Stage
Zone
Time and Geology
Subdivisions of Time
Geochronologic units have the same names as
Chronostratigraphic units
Jurassic Period
=
Jurassic System
Time and Geology
Subdivisions of Time
Geologic Time Scale
Organized using fossil succession, superposition
Then the units could be correlated
Resolution of Geologic Time Scale still taking place today