Geologic Time
An Introduction
Linda Kennedy, Department of Geography, UNCG, July 2011
Geologic Time
there’s just so much of it!
Earth is how old?
Our planet formed approximately 4.5
billion years ago (4,500,000,000).
Geologists divide this immense length
of time into progressively smaller
(and more manageable) units of time
using fossils, radiometric dating, and
rock sequences.
We will discuss the major
characteristics of the Precambrian,
Paleozoic, Mesozoic, and Cenozoic
eras.
Age (millions)
Era
Period
2
Cenozoic
Quaternary
66
144
Tertiary
Mesozoic
Cretaceous
208
Jurassic
245
Triassic
286
Paleozoic
Permian
320
Pennsylvanian
360
Mississippian
408
Devonian
438
Silurian
505
Ordovician
570
Cambrian
4,500
Precambrian
Geologic Time
there’s just so much of it!
History written in stone
Evidence from rocks allows geologists:
To identify the geological processes
that resulted in the formation of
each rock.
http://www.abdn.ac.uk
http://news.nationalgeographic.com http://events.ucr.edu
To reconstruct plant/and or animal life
prevalent during the formation of rocks.
http://dinobase.gly.bris.ac.uk
To reconstruct atmospheric/climatic
conditions and changes through time.
http://uts.cc.utexas.edu
http://nsidc.org
Geologic Time
there’s just so much of it!
It is very difficult for humans to
conceptualize a time frame as
large as 4,500,000,000 years.
To help we will imagine that
Earth formed at 9:00 am this
morning and it is now only10:00
am. What has occurred on
planet Earth during the past
hour?
Present
The Precambrian Era
4.5 billion – 570 million years ago
Precambrian
9:00 – 9:53
The Precambrian Era
4.5 billion – 570 million years ago
Most of the past hour – 53 minutes –is known as the Precambrian era. Earth’s
crust formed at approximately 9:01 but much of it has been recycled or altered
from it’s original state (metamorphosed).
Precambrian rock in North Carolina is located in the western portion of the state,
in the Blue Ridge Mountains and includes granites, gneisses, and schists.
Granite is magma that cooled deep in the crust and schist and gneiss are
examples of rocks that have been heated and pressurized, altering their original form.
Life during the Precambrian included single-celled, and simple
multi-celled organisms.
The Precambrian Era
4.5 billion – 570 million years ago
Banded iron is believed to have formed when oxygen
released by blue green algae combined with iron present
in ancient ocean waters to form iron oxide precipitates
that settled to the ocean floor.
Stromatolites are dome shaped mineral
formations built by microbes.
They continue to survive today in the waters
around Australia.
http://www.eps.mcgill.edu
http://gsc.nrcan.gc.ca/paleochron/03_e.php
http://gsc.nrcan.gc.ca/paleochron/03_e.php
Fossil stromatolites are one of the
most common forms of fossil life
identified in Precambrian rocks.
The Precambrian Era
4.5 billion – 570 million years ago
Rock formed during the Precambrian is a valuable
resource in North Carolina
Mount Airy, Surry Co. The world’s largest open faced granite mine.
The granite formed when magma cooled deep in the crust. Overlying
rock has since been eroded away, exposing the granite.
Mica
http://ncpedia.org/symbols/rock
North Carolina is the nations
top producer of mica, a
mineral used in a variety of
industries.
http://www.minfind.com
The Paleozoic Era
“old life” 570 – 245 million years ago
Paleozoic
9:53 – 9:56.9
The Paleozoic Era
“old life” 570 – 245 million years ago
If all of Earth’s geologic history is represented by one hour then the Paleozoic
era occurred between 9:53 am and 9:56.9 am.
The Paleozoic is characterized by the development of diverse sea life and the
emergence of the first land plants, first insects, first amphibians, and first
retiles. The end of the Paleozoic is marked by a mass extinction of life on Earth.
Rocks formed during the Paleozoic are located in a SW-NE trending belt in
central North Carolina, and are characterized by intrusive and extrusive
volcanic rocks, and metamorphosed sedimentary deposits.
The Paleozoic Era
“old life” 570 – 245 million years ago
Life
Age
(millions)
Period
Organism
286-245
Permian
Reptile diversity explodes
320-286
Pennsylvanian
Large scale coal formation in swamps
360-320
Mississippian
Land plant diversity explodes, first flying insects, first
reptiles
408-360
Devonian
First insects (flightless), first amphibians
438-408
Silurian
First fish and land plants
505-438
Ordovician
Starfish and crinoids appear
570-505
Cambrian
Explosion of marine life – bivalves, sponges, trilobites,
jellyfish, coral
The Paleozoic Era
“old life” 570 – 245 million years ago
Mississippian:
First reptiles
http://www.bluesci.org
Devonian:
First amphibians
http://www.exploratorium.edu
Labidosaurus hamatus
Ichthyostega
Silurian:
First fish &
land plants
Ordovician:
Crinoids &
Starfish
http://www.oum.ox.ac.uk
http://museumvictoria.com.au
Cambrian:
Trilobites &
Sponges
http://www.fossilmuseum.net
http://www.palaentology.geo.uu.se
http://tolweb.org http://ww.cavehill.uwi.edu
The Paleozoic Era
“old life” 570 – 245 million years ago
Rock formed during the Paleozoic is a valuable
resource in North Carolina
Metamorphic, sedimentary
and igneous rocks of
Paleozoic age are quarried
throughout North Carolina,
including the High Point area,
for use in a variety of
construction projects.
http://www.wakestonecorp.com
The Mesozoic Era
“middle life” 245 – 70 million years ago
Mesozoic
9:56.9 – 9:58.7
The Mesozoic Era
“middle life” 245 – 70 million years ago
The Mesozoic era occurred between 9:56.9 am and 9:57.8 am. During
this brief 1.8 seconds, the dinosaurs came and went, and the first birds
and mammals emerged. The end of the Mesozoic, like the Paleozoic
before it, was marked by a mass extinction.
Mesozoic rocks occur principally in southeastern North Carolina, and are
characterized by sedimentary deposits of sandstone, shale, and clays.
The Mesozoic Era
“middle life” 245 – 70 million years ago
Life
Age
(millions)
Period
Organism
144-66
Cretaceous
First flowering plants, T-Rex, Triceratops, Dteranodon
208-144
Jurassic
Dinosaurs grow large: Stegasaurus, Archaeopteryx
245-208
Triassic
Reptiles dominate land – crocodiles, turtles and early
dinosaurs emerge
The Mesozoic Era
“middle life” 245 – 70 million years ago
Cretaceous: T-Rex and Triceratops
http://www.impactlab.net
Jurassic:
Archaeopteryx,
Stegasaurus and
first flowering
plant
http://www.itsnature.org
http://www.askabiologist.org.uk
http://www.itsnature.org
http://news.ufl.edu
Triassic: early dinosaurs and turtles
http://news.bbc.co.uk
http://www.nmnaturalhistory.org
The Mesozoic Era
“middle life” 245 – 70 million years ago
Deposits formed during the Mesozoic are a valuable
resource in North Carolina
Sand and gravel
extraction is the
largest income
producing mining
in North Carolina.
http://www.boggspaving.com
The Cenozoic Era
“new life” 70 million years ago – present
Cenozoic
9:58.7 – 10:00
The Cenozoic Era
“new life” 70 million years ago - present
It is only during the last 1.3 seconds that the first human ancestor appeared,
ice ages occurred, and modern man evolved.
Unconsolidated sands and clays of the Coastal Plain date to the Cenozoic era.
The Cenozoic Era
“new life” 70 million years ago – present
Climate ameliorates 10,000 years
ago, allowing the development of
agriculture and human civilization.
http://www.gsi.ie
Mammals dominate land,
human evolution occurs.
http://www.dailymail.uk.co
The Cenozoic Era
“new life” 70 million years ago – present
Deposits formed during the Cenozoic are a valuable
resource in North Carolina
Aurora, N.C. Phosphate mine.
North Carolina is the nations second
largest producer of phosphate. North
Carolina and Florida account for 95% of
the total phosphate produced
in the U.S.
http://www.wazengineeriing.com
Resources
General
Lesson plans/Activities
N.C. Department of Environment and Natural Resources
http://portal.ncdenr.org
Geosphere links for teachers
http://nesen.unl.edu/scienceresources/linksgepsphere.asp
United States Geological Survey (USGS)
http://www.usgs.gov
Resources for K-12 Earth Science Educators
http://www.geosociety.org/educate/resources.htm
N.C. Geological Survey
http://www.geology.enr.state.nc.us
USGS resources for secondary schools
http://education.usgs.gov/common/secondary.htm
USGS Studies in N.C.
http://pubs.usgs.gov/fs/fs-033-96
Mining Institute
http://www.mii.org
Relief Map of North Carolina
http://geology.com/shaded-relief/southeast.shtml