Dendrochronology and Radiocarbon Dating in Anthropology Lab 5

Anthropology 204 Lab # 5 – Absolute Dating Grace Tucker, Clarissa Hurtado, Brandon Smith Part 1: Dendrochronology – Organizing Tree Rings Take a look at the four trees from the first table. They came: • Sample 1: From a living tree from the Cedarville Forest, July 1993 • Sample 2: From a tree from the Cedarville Christmas Tree Farm • Sample 3: From a log found near the main trail in Cedarville Forest • Sample 4: From a barn beam removed from Cedarville Hollow Put the tree ring samples in order – it’s probably easier to cut them out to do this. Fill out this table Sample Year tree was cut Year growth began 1 31 years 1962 2 28 years 1962 3 39 years 1949 4 28 years 1942 1. What years are represented by this data? The years that are represented by this data are 1962,1949, and 1942. Take a look at the four trees from the second table. They came from a group of trees from the “ghost forests” of Willapa Bay Washington. They seem to have been killed when their roots were submerged in brackish (salty) water from a tsunami that we’re tryin g to date. Take a look at these trees and see if you can date that tsunami. The first sequence above is the master sequence for the zone. Fill out this table Sample Year tree died Year growth began 1 1700 1685 2 1700 1682 3 1700 1676 4 1700 1685 2. What year was the tsunami that killed these trees? How did you figure it out? The tsunami killed the tress in 1700s. What we did to figure this out was align each sample with the pattern between 1685 and 1715 and counted backwards to figure out

the year. Part 2: Dendrochronology – Interpreting Data I’ve given you dendrochronology data from multiple buildings at the southwestern site of Mesa Verde. Like Chaco Canyon, there are multiple buildings that may not have been built at the same time. 3. What dates were the trees used for Spruce Tree House cut down? Be sure to get them all. The years the trees were cut are 4. What’s the earliest date Spruce Tree House could have been built? Why did you pick that number? 5. What dates were the trees used for Cliff Palace cut down? Be sure to get them all. 6. What’s the earliest date Spruce Tree House could have been built? Why did you pick that number? 7. The trees used for Square Tower (Sq. Tower) vary greatly. How many years are there between the oldest and youngest tree used in that building? What might explain that difference?

8. What would you guess is the earliest building represented here? What makes you say that? Part 3: Radiocarbon dating Here are some radiocarbon dates from areas around Mesa Verde. Each group that shares a site number comes from a single area. Remember that BP is standardized with 1950 as “present” so we don’t have to worry about what year the tests were done. Fill out the table, giving the range for one standard deviation (68%) and two (95%) for each site. Then answer the following questions. 9. For the first site (5MT10594), do you think these represent a single short phase of occupation or multiple? What makes you think that? I believe that it is a single short phase of mutiple, due to the fact there are multiple reports/record of site 5MT10594. 10. Which of these sites is the oldest? Beta-201368 11. Over what years does occupation at Mesa Verde as a whole probably range, based on these dates? I believe it from the years 760-1600s 12. For the youngest site, do the carbon dates overlap at the 95% probability level? If so, by how much? How about at the 68% probability level? If so, by how much? (1 point) I don’t believe that the youngest site carbon overlaps, at either 68% or 95%.

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Table 1 Data: Table 2 Data: Student core samples

Radiocarbon Dates from Mesa Verde

Lab Number Date_BP Site Number 68% Range 95% Range Beta-75286 1080±50 5MT10594 Beta-75282 1240±60 5MT10594 Beta-75283 920±60 5MT10594 Beta-75285 1030±60 5MT10594 Beta-75284 1240±70 5MT10594 Beta-201369 760±40 5MT123 Beta-201370 880±40 5MT123 Beta-201368 800±60 5MT123 Tx-3883 1680±60 5MT2854 Tx-3884 1620±60 5MT2854 Tx-3877 2000±60 5MT2858 Tx-3878 1660±60 5MT2858 Tx-3879 1660±70 5MT4614 Tx-3880 1590±90 5MT4614

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