Founders of Historical Geology

Charles Darwin 1809-1882

Evolution – organisms changed through time

Individuals with variations most favorable in existingenvironment had best chance of survival

Passed these traits on to next generation

Natural SelectionAlso 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 theguiding principle of paleontological and biologicalresearch

Founders of Historical Geology

North American NotablesWilliam McClure 1763-1840

Produced the first geologic map of the US

Founders of Historical Geology

North American NotablesAmos Eaton 1776-1842

Taught “hands on” geology at Rensselaer School (RPI)Took long field tripsFather of American geologyStudied New England region

Founders of Historical Geology

North American NotablesLouis Agassiz 1807-1873

Recognized that massive ice sheetsonce covered North America

First to hint at “ice ages”Stated that glacial deposits did notaccumulate during Biblical flood

Founders of Historical Geology

North American NotablesJames Hall 1807-1873

First director of NY StateGeological Survey

Founders of Historical Geology

North American NotablesJames D. Dana 1813-1895

Published Manual of GeologySystem of Mineralogy

Founders of Historical Geology

North American NotablesJohn Wesley Powell 1834-1905

Director of USGSFirst to traverse Grand

Canyon by boat(1869)

Union officer in Civil WarLost arm at Shiloh

Founders of Historical Geology

North American NotablesOthniel C. Marsh 1831-1899 YaleEdwin 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 NotablesGeorge Otis Smith 1871-1944

Director of USGS 1907-1930Colby graduate, 1893

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 etctried by use of superposition, fossil succession

As science advanced we used radiometric techniques.

Time and GeologySmith and contemporaries used

RELATIVE GEOLOGIC DATING techniques

In relative dating, no reference to actual time

Time and Geology

ACTUAL OR NUMERICAL DATING tries to assignnumbers 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

EonsEras

PeriodsEpochs

None last equal intervals oftime.

Based on events.

Time and Geology

Subdivisions of Time

EONLargest subdivision of Geologic Time Scale

Four Eons recognized

PhanerozoicProterozoicArcheanHadean

Precambrian

Time and Geology

Subdivisions of Time

Phanerozoic Eon0.544 byBP – presentIncludes most sedimentary rocks and

history of lifeProterozoic Eon

2.5-0.544 byBPMostly crystalline rocks

Archean Eon3.9-2.5 byBPOldest preserved rocks

Hadean Eon4.6–3.9 billion years before present (byBP) No geologic record

Pre

cam

bri

an

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:

PERIODS

PermianPennsylvanianMississippianDevonianSilurianOrdovicianCambrian

Carboniferous

PA

LE

OZ

OIC

Time and Geology

Subdivisions of Time

EPOCH

Periods are subdivided intoEPOCHS

Quaternary PeriodHolocene EpochPleistocene Epoch

Tertiary PeriodPliocene EpochMiocene EpochOligocene EpochEocene EpochPaleocene Epoch

Time and Geology

Subdivisions of Time

Units on the Geologic Time Scale represent actual incrementsof time = GEOCHRONOLOGIC UNITS

Actual rock units formed or deposited during these intervalsare CHRONOSTRATIGRAPHIC UNITS

Geochronologic Units Chronostratigraphic Units Eon Eonathem Era Erathem Period System Epoch Series Age Stage Chron Zone

Time and Geology

Subdivisions of Time

Geochronologic units have the same names asChronostratigraphic 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