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”

"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.”

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

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)

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

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

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

Wood, charcoal Cloth (Shroud of Turin, etc.) Bone and antler Peat, organic-bearing sediments Marine and fresh-water shell Carbonate deposits –Caliche (CaCO 3 ) UA has a GREAT Radiocarbon lab 14 C (Radiocarbon dating) Dates Organic Stuff (not rocks)

Radiocarbon Dating 14 C is formed in the upper atmosphere through the effect of cosmic ray neutrons upon 14 N. The reaction is: 14 N + n 14 C + 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

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

Think ratios--- ½, ¼, etc.

Variations atmospheric 14 C 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 14 C Dating Errors

Andrew Ellicott Douglass Astronomy 1894: Flagstaff to build Lowell Observatory Sunspots a lifelong interest – impact on Earth climate?

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

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? Douglass

Long Chronologies SW: 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

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

Outside Activity: Skeleton Plotting Access through our course web page 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

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

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

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