Geologic Time

Linda Kennedy, Department of Geography, UNCG, July 2011

An Introduction

Age(millions) Era Period

2 Cenozoic Quaternary

66 Tertiary

144 Mesozoic Cretaceous

208 Jurassic

245 Triassic

286 Paleozoic Permian

320 Pennsylvanian

360 Mississippian

408 Devonian

438 Silurian

505 Ordovician

570 Cambrian

4,500 Precambrian

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.

Geologic Time there’s just so much of it!

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.

To reconstruct atmospheric/climatic conditions and changes through time.

To reconstruct plant/and or animal life prevalent during the formation of rocks.

http://www.abdn.ac.uk http://news.nationalgeographic.com http://events.ucr.edu

http://dinobase.gly.bris.ac.uk

http://uts.cc.utexas.eduhttp://nsidc.org

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?

Geologic Time there’s just so much of it!

Present

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

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.

Fossil stromatolites are one of the most common forms of fossil life identified in Precambrian rocks.

http://gsc.nrcan.gc.ca/paleochron/03_e.php

http://gsc.nrcan.gc.ca/paleochron/03_e.php

http://www.eps.mcgill.edu

The Precambrian Era 4.5 billion – 570 million years ago

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.

http://ncpedia.org/symbols/rock

Rock formed during the Precambrian is a valuable resource in North Carolina

North Carolina is the nations top producer of mica, a mineral used in a variety of industries.

Mica

http://www.minfind.com

Paleozoic 9:53 – 9:56.9

The Paleozoic Era “old life” 570 – 245 million years ago

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

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

Life

The Paleozoic Era “old life” 570 – 245 million years ago

Cambrian: Trilobites & Sponges

http://www.fossilmuseum.net http://www.palaentology.geo.uu.se

Ordovician: Crinoids & Starfish http://www.oum.ox.ac.uk http://museumvictoria.com.au

Silurian: First fish & land plants http://tolweb.org http://ww.cavehill.uwi.edu

Devonian: First amphibians http://www.exploratorium.edu

Mississippian: First reptiles http://www.bluesci.org

Labidosaurus hamatus

Ichthyostega

The Paleozoic Era “old life” 570 – 245 million years ago

Rock formed during the Paleozoic is a valuable resource in North Carolina

http://www.wakestonecorp.com

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.

Mesozoic 9:56.9 – 9:58.7

The Mesozoic Era “middle life” 245 – 70 million years ago

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

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

Life

The Mesozoic Era “middle life” 245 – 70 million years ago

Triassic: early dinosaurs and turtles

Jurassic: Archaeopteryx, Stegasaurus and first flowering plant

http://www.itsnature.org http://www.askabiologist.org.uk http://news.ufl.edu

Cretaceous: T-Rex and Triceratops

http://news.bbc.co.uk http://www.nmnaturalhistory.org

http://www.impactlab.net http://www.itsnature.org

The Mesozoic Era “middle life” 245 – 70 million years ago

Deposits formed during the Mesozoic are a valuable resource in North Carolina

http://www.boggspaving.com

Sand and gravel extraction is the largest income producing mining in North Carolina.

Cenozoic 9:58.7 – 10:00

The Cenozoic Era “new life” 70 million years ago – present

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

http://www.gsi.ie

http://www.dailymail.uk.co

Mammals dominate land, human evolution occurs.

Climate ameliorates 10,000 years ago, allowing the development of agriculture and human civilization.

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

N.C. Department of Environment and Natural Resources http://portal.ncdenr.org

United States Geological Survey (USGS) http://www.usgs.gov

N.C. Geological Survey http://www.geology.enr.state.nc.us

USGS Studies in N.C. http://pubs.usgs.gov/fs/fs-033-96

Relief Map of North Carolina http://geology.com/shaded-relief/southeast.shtml

Lesson plans/Activities

Geosphere links for teachers http://nesen.unl.edu/scienceresources/linksgepsphere.asp

Resources for K-12 Earth Science Educators http://www.geosociety.org/educate/resources.htm

USGS resources for secondary schools http://education.usgs.gov/common/secondary.htm

Mining Institute http://www.mii.org