Radiocarbon Dates

Enough of babies, skiing and the Apprentice - I figure it is time for some science on the blog. Time to present the radiocarbon dates from last spring's Olga Lakes Survey. WARNING - FOR MATURE AUDIENCES ONLY.

Archaeologists use various methods to date what they find. But the best method is probably radiocarbon analysis. Basically this method relies on measuring the ratio of radioactive carbon (C14) to stable carbon (C12) in a sample of organic carbon, usually charcoal. Living organic objects incorporate carbon into their organic structure at a fixed, known ratio between C14 and C12. But once they die the radioactive carbon 14 decays and turns back into Carbon 12. Thus with time a sample has less and less C14 in it. The half life of C14 is about 5700 years - so if you have half the expected carbon 14 in a sample then the sample dates to about 5700 years old. Archaeologists use this method to date what they find. Only problem is that it is expensive - about 400 dollars a date. No cheap dates in archaeology!

Anyway, last week I was excited to finally get back the results of the samples from Olga Lakes that we sent in for analysis. One of the dates from a sample taken from the black layer in the profile seen in two of the pictures above dated to around 6100 years ago. The black layer is actually charcoal and it probably represents the floor of a tent where a group of intrepid Alutiiq people lived while they visited Upper Olga Lake to fish for salmon and trout. This is the earliest evidence for Alutiiq people fishing on the inland lakes of Kodiak. We knew that at that time they were fishing at the mouths of rivers, but we had not found any sites older than about 5400 years on the inland stretches of these lakes and rivers. Now we know Alutiiq people were using the interior areas of kodiak far earlier than previously suspected.

In the top photo Mark and Catherine are collecting charcoal from a test pit. We generally dug these pits into the hearths of old houses to collect charcoal samples. In this way we were able to date many of the old villages that we found while on survey. All of the villages we found were less than 1500 years old. It seems that prior to that date the Alutiiq just visited the inland lakes to catch fish and then take it back to their villages on the coast. They did not build inland villages until relatively recently (last 1500 years).

In a little over a month I will be returning to the Olga Lakes to finish our survey and to excavate a 1000 year old house. We know it's a thousand years old because we already radiocarbon dated it;-). Patrick