1 / 26

Tree-Ring and Radiocarbon Dating in Archaeology

Learn about the techniques of tree-ring and radiocarbon dating in archaeology to accurately date artifacts and understand ancient history. Join the group meetings at the Tree-Ring Lab and RadioCarbon Lab. Due date for the activity is Feb 3rd. Reading material on dating lecture provided.

johnsongary
Download Presentation

Tree-Ring and Radiocarbon Dating in Archaeology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 1/27 notes Group 1: Meet at Tree-Ring Lab 9:30 (west stadium 104) Group 2: Meet at RadioCarbon Lab 9:30 (Physics & Atmo Main Lobby) • Start tree-ring crossdating activity today • Due next Thurs Feb 3 • Reading for dating lecture • E Haury: HH-39: Recollections of a Dramatic Moment in Southwestern Archaeology • Focus on “bridging the gap”

  2. "Everything which has come down to us from heathendom is wrapped in a thick fog; it belongs to a space of time we cannot measure. We know that it is older than Christendom, but whether by a couple of years or a couple of centuries, or even by more than a millenium, we can do no more than guess.”Rasmus Nyerup, 1802 • Emil Haury: Recollections … (Reading) • “… descriptions of ruins, study of pots and pans, and efforts to recreate ancient history were sterile without a valid sense of time.”

  3. Dating Terms • Precision • Accuracy • Labels-- • 500BC • 2500b.p. • but AD 2008

  4. Know what is being Dated ! • Dated Event • Tree-ring growth • Decay of element/death of organism • Movement of magnetic pole • Target Event • Building construction • Site occupation • Last use of fireplace (hearth)

  5. Dating Techiques: • Relative– (before, after, earlier, later) • Stratigraphy (think layer cake; Grand Canyon) • Seriation– Changes in style (think changes in car bodies; video games, etc) Both used extensively in Southwest—but must be “calibrated” against some known date

  6. Dating Techniques (Pertinent to SW) • Absolute: • Radiometric • Archaeomagnetic—burned things 500B.C. • 14C for recent organic material: 35,000 bp both– calibrated with Dendrochronology— • Dendrochronology • Trees, about the last 2000 years • Crossdating: outside activity #1 • Due Tuesday

  7. Archaeomagnetic Dating Hearths, Burned clay walls, etc. (not movable objects) N Pole (geographic) N Pole (Magnetic) Southwest Year From: Michaels, J. 1973

  8. 14C (Radiocarbon dating) Dates Organic Stuff (not rocks) • Wood, charcoal • Cloth (Shroud of Turin, etc.) • Bone and antler • Peat, organic-bearing sediments • Marine and fresh-water shell • Carbonate deposits • Caliche (CaCO3) UA has a GREAT Radiocarbon lab

  9. Radiocarbon Dating • 14C is formed in the upper atmosphere through the effect of cosmic ray neutrons upon 14N. The reaction is: 14N + n 14C + p (Where n is a neutron and p is a proton) • The radiocarbon method is based on the rate of decay of the radioactive or unstable carbon isotope 14

  10. Carbon • 12C: stable, 98.9% of all Carbon • 13C: stable, 1.1% of all Carbon • 14C: radioactive, ~1 x 10-10 % of all Carbon

  11. Think ratios--- ½, ¼, etc.

  12. 14C Dating Errors • Variations atmospheric 14C production • Natural– over time due to solar • Post bomb • Postdepositional contamination • percolating groundwater • incorporation of older or younger carbon • contamination in field or laboratory • Determination of half-life • Now 5730 ± 40 years

  13. Andrew Ellicott Douglass • 1867 - 1962 • Astronomy • 1894: Flagstaff to build Lowell Observatory • Sunspots a lifelong interest – impact on Earth climate?

  14. 1906: Tucson as UA Professor of astronomy, physics, geography, dean, acting president • Founder of LTRR - 1938 • 1929: Natl. Geog. Magazine: • Secrets of the SW Solved by Talkative Tree Rings

  15. Douglass • 1904: observed a ring pattern in Flagstaff sawmill logs • 1904, 1902, 1899, 1896, 1894, and 1891 were narrow • Compared, confirmed other Flagstaff trees– oral history • Flagstaff chronology • 1911: Prescott trees confirmed the pattern • Climate caused? Solar variation?

  16. Long Chronologies • SW: 2000-3000 years • Bristlecone pine of West: • Oldest tree known was 4900 years old • Chronology now at 8700 years • Europe: • Oak chronologies at ~10,000 years • Composed of short segments

  17. The 2nd Radiocarbon Revolution (1960s) Another GREAT discovery at the UA

  18. Outside Activity: Skeleton Plotting • Access through our course web page http://www.ltrr.arizona.edu/skeletonplot/ introcrossdate.htm • Read explanatory pages • Try skeleton plotting for yourself • When you succeed: • alt-print screen • Edit-Paste (or Paste Special) into a word document • Fill in page with text: • Insightful observations on crossdating • MUST HAVE: Your plot, Master plot, Answer box (begin/end year), comments • Due next Tuesday 2/2

  19. Some Tips Answer box • Your homework should look like this– paragraph here , blah, blah core Master Plot Your plot WARNING: Easy to cheat, Easier to See if you cheated!!!

  20. Steps: Plotting Mark ONLY small rings on graph paper From bottom up

  21. Steps: Looking at the Master Align Your graph paper with the Master so Every Ring Matches

More Related