Tag Archives: obsidian hydration dating

Valentine’s Day Archaeology Style

Everyone likes to bring up radiocarbon dating for this Hallmark day of love. There’s other kinds of dating we archaeologists use too!

We’ve also got…
Obsidian hydration dating
Tree ring dating (dendrochronology)
Type dating (seriation)
Potassium-Argon dating

The list goes on, my friends! I’m sure you’ve heard the joke “Archaeologists will date any old thing.” It’s true. As a group, we looooove to get dates. Dates are closer to concrete answers. We may never have absolute answers, but we really like to get close to them if possible.

Here at TOA, we have Origer’s Obsidian Laboratory. Guess what we do there? Yep, it’s an obsidian dating service. Flakes and projectile points alike flock to our lab to get a date. We cut, grind, and slip pieces of obsidian between glass to read hydration bands. Go check out our Lab’s page to learn more.

Tree ring dating helps calibrate the ever-so-glamorous carbon dating system. Most people have at the very least heard of radiocarbon dating, but few knew that the simple act of counting tree rings helps calibrate something so obviously scientific.

Dating by types, known as seriation, is a form of relative dating that compares items based on where they fit into the known order of manufacture. I assure you, it has nothing to do with dating your Aunt Sally. Let’s say you’ve three projectile points that are from the same site, but shaped differently and found at different levels. You can correlate their age to the type based on the levels they came from (assuming the site is undisturbed of course). That’s thanks to the law of superposition, which tells us that the top level is the youngest and things get older as we go down into the ground. Once you know the seriation for projectile points (or any other type of artifact) in an area, you can perform this type of relative dating!

Potassium-Argon dating is used on fossilized human remains. It isn’t done much around here, but is popular elsewhere. In practice, it’s much like radiocarbon dating since it deals with measuring the product of an isotope’s decay in relation to its half-life.

So there you have it, folks. A brief look at some other forms of archaeological dating!



A note on Paisley Caves

Paisley Oregon is known for a couple of things; their annual mosquito festival, and Paisley Caves. With the co-operation and support of the Bureau of Land Management, the University of Oregon has built an international team of scientists to study the archaeology within the caves. Origer’s Obsidian Laboratory has been working with this team since 2005. This summer we returned to the caves to work on on-going research regarding obsidian hydration in cave environments.

For those who haven’t heard of Paisley Caves, it’s a pretty exciting site. Several finds in the site suggest some of the earliest human occupation in North America. What has probably received the most publicity are western stemmed projectile points and coprolites that have human DNA dating to about 13,200 calendar years ago.

Our involvement has been in looking at the obsidian from the site. More specifically, we are exploring the issue of how the cave environment influences the development of hydration bands. Our original analysis provided some counter-intuitive results; for example the interiors of the caves were typically cooler at noon than at midnight. Why? The caves face generally west, and get little sun before mid-day. From noon until sunset they get full exposure and the rock absorbs heat. From sunset, through the night the heat is radiated into the caves from the rock, pretty neat.

Our current research is geared at understanding what happens in the caves in three dimensions. We have deployed about 100 temperature sensors to establish what the temperature is doing at various depths, and from the front of the caves to the back. With those data we will be able to see what is happening with the temperature, which will help us understand the hydration measurements, which will help understand the dating of the deposits in the cave.

Many thanks to Dr. Dennis Jenkins of the University of Oregon for allowing us access to the work site during his field schools. That kindness has saved us hours, and given us a chance to meet his amazing students, who work cheerfully through some tough and demanding circumstances.