Give Me Knowledge, So I May Have Kindness For All

Plains Indians

Telling Time GeologicallyDanny M. Vaughn, Ph.D., CMS

Age of the Earth

4.6 billion years

Hoba meteorite, Namibia.

Lunar boulder, Apollo 17, December, 1972.

Oldest Rocks on Earth

Acasta GneissYellowknife Region, Northwest Territories, CanadaDated 4.03 billion years

Oldest Mineral Crystals:Zircon w/in Jack Hills Conglomerate,Western Australia

Oldest Fossils on Earth

Stromatolites (Blue-green algae) Precambrian Period (Archean Eon)

A Perspective of Geologic Time

Telling Time

Relative datingComparing two or more rocks,

structures, or events to determine which is older & which is younger.

Numerical (absolute) datingDetermining how long ago (in years) a particular rock or structure formed or

geologic event occurred.

Principles of Relative Dating

Principle of:• Uniformitaria

nism• Original

horizontality• Superposition• Cross-cutting

relationships• Inclusions• Faunal succession

“The presentis the key to

the past”

Principles of Relative Dating

Principle of:• Uniformitarianism• Original

horizontality• Superposition• Cross-cutting

relationships• Inclusions• Faunal succession

Which Way Is Up?

Applying superpositi

on

The Lazy Person Is Apt To Be EnviousOmaha

Principles of Relative Dating

Principle of:• Uniformitariani

sm• Original

horizontality• Superposition• Cross-cutting

relationships• Inclusions• Faunal

succession

Principles of Relative Dating

Principle of:• Uniformitarian

ism• Original

horizontality• Superposition• Cross-cutting

relationships• Inclusions• Faunal

succession

Principles of Relative Dating

Principle of:• Uniformitarianism• Original

horizontality• Superposition• Cross-cutting

relationships• Inclusions• Faunal

succession

CambrianTrilobite

PennsylvanianBrachipods

FossilsWhat are they?

FossilsHow do they

form?

UnconformitiesGaps in the geologic record

separatingrocks of different ages.

Nonconformity Angular unconformityDisconformity

Unconformities

Nonconformity Angular unconformityDisconformity

Nonconformity Angular unconformityDisconformity

Unconformities

Angular Unconformity

UnconformitiesExample from the Grand

Canyon

Correlation of Rock

Formations

Correlation of Key Beds

Volcanic ash.Which of the two layers are oldest?How do you know?

Other Types of Relative Dating

Weathering Rinds & Soils

Geologic Time Scale

Great People Are Usually Destroyed By Those Who Are

Jealous Of ThemSioux

Absolute Dating

Isotope dating

Parent Isotope

Daughter Isotope + Decay Particle + Energy

Radioactive Decay

Types of Radioactive Decay

• Alpha decay• Beta decay• Electron

(beta) capture

Radioactive Decay: An unstable atomic nucleus loses energy by emitting ionizing particles & radiation.

Radiation: A process in which energy emitted (in all directions) by one body travels through a medium or space ultimately absorbed by another body.

Uranium 238 (AN92)to Thorium 232 (AN90)

1 electron expelled,K40 (AN19) to Ca40 (AN20)

expelled

Nucleus captures an electron from energy level. Joins proton in nucleus. K40 (AN19) to Argon 40 (AN18).

Half-LifeThe time it takes for half of the

parent isotope to decay into a daughter isotope

Major Isotopes Used for Isotope Dating

Carbon-14 Dating

Other Types of Numerical Dating

Fission-track dating

Dendrochronology

Varve Chronology

Lichenometry

Surface-Exposure Dating

Combining Relative & Numerical Dating

Recreating Geologic History

Extinctions

UnconformitiesExample from the Grand

Canyon

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