Radiocarbon Dating Presentation for Benson's Students

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This is for Benson's students who missed this class. Be sure to print out the handout first. www.formontana.net/handouts.html

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Presentation Transcript

See handout :

See handout Radiometric Dating

Slide2:

Photo courtesy of the Montana Historical Society 
Figures by Gardell Christensen, 1952 
Background by Dale Livezey, 1988 
Photo by John Smart, 1988 Where is the actual place?

Slide4:

1 mile of cliff

First Peoples Buffalo Jump:

First Peoples Buffalo Jump Formerly known as Ulm Pishkun

Slide6:

Map courtesy of The Defenders of Wildlife 60-75 million bison before European Contact 40,000 Native Americans in MT east of the mtns. What two important things did Indians NOT have before 1700?

Slide7:

Over 300 bison kill sites in Montana Most are NOT buffalo “ jumps ” .

Slide11:

Bearpaw Mountains in northern Montana

Archaeologists want to know . . . :

Archaeologists want to know . . . Who used the site? (which tribes?) When did they use it? (years, seasons) How did they use it?

Slide14:

Courtesy of Canadian Museum of Civilization Corporation

Slide15:

What would be the most abundant type of evidence present at kill sites?

Slide16:

Bone Beds Projectile Points Arrowheads Spear points

Slide17:

Roasting Pits Boiling Pits Stone tools

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Used from 900 A.D. to at least 1500 A. D. How do we know?

What scientific technique can be used to establish dates?:

What scientific technique can be used to establish dates? Radiocarbon Dating One type of radiometric dating used to date materials that lived in past 50,000 years

1. What is a “radioactive isotope”?:

1. What is a “ radioactive isotope ” ? An atom with an unstable nucleus that decays (changes into something else) C-14 becomes N-14

2. C-14 has a half-life of 5,730 years. Explain what this means. :

2. C-14 has a half-life of 5,730 years. Explain what this means. Every 5,730 years half the remaining C-14 changes into N-14.

Slide22:

N-14 C-14 5,730 years after death 1/2 of the C-14 has decayed 11,460 yrs. After death After another 5,730 yrs. 3/4 of the C-14 has decayed 17,190 yrs. after death 7/8 of the C-14 has decayed 22,920 yrs. after death 15/16 of the C-14 has decayed

Half-Lives:

Half-Lives Carbon-14 . . . 5,730 years Iodine-131 . . . 8 days Potassium-40 . . . 1.25 billion years

Potassium - Argon dating (K-Ar):

Potassium - Argon dating (K-Ar) Used on rock that was formed as lava or magma hardened K-40 changes into Ar-40 Half-life is 1.25 billion years

Slide25:

3. What kinds of materials can be radiocarbon dated?

Slide26:

Bones Hides, fur Arrowheads Stone tools Bison feces Charcoal Horns Fire-cracked rock Blowfly pupa

Slide28:

Years Since Death Percentage of C-14 Remaining 40 K O 100 O 10 K 20 K 30 K 10 20 30 40 50 60 70 80 90 1-5,730 2-11,460 3-17,190 4-22,920 5-28,650 6-34,380 7-40,110

Slide29:

1. What percentage of the C-14 would be present in the bone of a wooly mammoth that died 20 kyr ago.

Finish the rest on your own.:

Finish the rest on your own.

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