Potassium Argon Dating

8/11/2019 Potassium Argon Dating

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Potassium-Argon Dating


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A radioactive counting technique used to datethe age of geological formations which are

associated with fossil remains of early hominidsites from rocks as old as 2 billion years old and

as recent as 100, 000 years old.


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Based on the steady but very slow decay of the

radioactive potassium-40 isotope to the inertgas argon-40 isotope in igneous/volcanic rocks.

Fossils are not dated but the rocks thatsurrounds them assuming they are of the same

age as of the rock.


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The rock layers above and below the fossil aredated using K-Ar dating to get a minimum andmaximum age of the fossils sandwiched

between the two layers.


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RocksRocks that can be used in this process are:

1. Igneous rocks

2. Volcanic Rocks

3. Volcanic Ash (hardened)

*Most resistant to later argon diffusion are: biotite, muscovite, sanidine

*Other possible igneous/metamorphic rocks: Hornblende, anorthoclase, plagioclase, leucitnepheline, phlogopite, and lepidolite


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1. Argon is inert.

-does not chemically react with other elements

2. Argon is a gas.

-it just bubbles up when it is present in the liquid, flowing lava

-it escapes from the rock when it is heated in very high temperatures


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When lava flows over the land, the naturally occurring argon gas is drivexcessive/intense heat. (no more argon gas inside)

As the lava cools and hardens into a rock (crystallization), it becomes a closystem which traps the argon-40 gas that will form from the decay ofpotassium-40 inside the rock.

The formation of the rock which also drives off any naturally occurring aformerly present sets the radioactive clock to zero .


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1. Samples are collected and thcrushed.

2. Treatment of Hydrofluoric aremove remaining atmospherifrom the sample.

3. Sample is heated to extract isolate the argon gas into a sepcontainer

4. Gases are then monitored ansubjected to mass spectrometryspectrographic analysis.


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Ratio of Potassium-40 and Argon-40 atoms


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Has a wide range of time.

Can be used to date rocks that are associated with fossils that lived a very long time befo

Very useful for dating artifacts that are found near volcanic areas.


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o It can only be used to date sites buried by volcanic formations.

o It is rarely possible to achieve an accuracy of better than 10% .

o It can only be used with rocks that contained no argon gas when they were formed.

o Possible contamination of atmospheric argon gas.

o Possible loss of argon gas after formation of rocks.

o Rocks to be used should not have gone through a heating-recrystallization process after initial formation.

o Standard deviations resulting from this method are very large.

o Expensive.


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-volcanic area (volcanic tuff beds)-9 miles and 350 feet deep site-excavated by Louis and Mary Leakey (mid- fossils of Austrolopithecus (Paranthropus) Homo habilis, Homo erectus- Achulean and Oldowan stone tool assembl-almost 2 million years of occupation-bones of about 1.75 million years of age


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-determination of age of tuffs associated with early hominid finds extending thechronology of human existence back further than 2 million years

-association of lava with human settlements in East Africa- Australopithecus of age 4.5 million years

-stone flakes and chopping tools of age 2.6 million years

-earliest date for human artifacts

-Homo erectus -bearing levels dated by Berkeley scientists-1.8 million years (laser-fusion technique)


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http://anthro.palomar.edu/time/time_5.htm

http://archserve.id.ucsb.edu/courses/anth/fagan/anth3/Courseware/Chronology/09_Potassiuon_Dating.html

http://www.creation-science-prophecy.com/K-Ar-dating.htm https://www.khanacademy.org/science/cosmology-and-astronomy/life-earth-universe/measu

age-tutorial/v/potassium-argon-k-ar-dating

https://www.khanacademy.org/science/cosmology-and-astronomy/life-earth-universe/measuage-tutorial/v/k-ar-dating-calculation

http://archaeology.about.com/od/oterms/g/olduvai.htm http://www.boneandstone.com/articles/detrich_04.html

http://australianmuseum.net.au/Homo-habilis

Potassium Argon Dating

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