- Hi, I'm Sean Romo, senior staff archaeologist
with the Jamestown Rediscovery Foundation,
and I'm here today with director of archaeology
David Givens.
Now, we're out here at Historic Jamestown,
practicing social distancing.
You can see that we're about six feet away.
And we're going to talk to you today a little
bit about radiocarbon dating
as part of our ongoing series,
"Dig Deeper," at Jamestown.
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- So Dave's going to explain a little bit
of the science behind radiocarbon dating.
- Well, one of the things that archaeologists
love to do
is to date the deposits
they're working on, right?
Date a skeleton, date a specific layer,
and one of the ways
that we can do that with chemistry,
or science in chemistry,
is to look at the ratio of carbon-12 and carbon-14
that's sequestered in a material.
Now, carbon-14 and carbon-12
are naturally in our environment.
They're formed in the upper atmosphere
when a nitrogen molecule is bombarded
by particles from the sun,
and that forms radioactive carbon-14
and stable isotope carbon-12.
Now, the different between the two is that
carbon-12 is very stable,
of course, and decays at a very slow rate,
and carbon-14, being radioactive, is unstable,
and decays with a half-life of 5,730 years.
Now, that allows the archaeologists,
if you send a sample
out to a lab, to get a date back
in which the carbon-12
and the carbon-14 are decaying
and giving you a ratio
where a clock starts and then begins
to decay over time.
So in the lab, they can read that and then
give you a rough estimate of the date.
- So radiocarbon dating is another tool
in the archaeologist's arsenal
for figuring out when a feature
or a deposit dates to,
or even an artifact, since we can date directly
human bone,
charcoal fragments, oyster shells,
and other organic things.
Now, today, we actually went out
and sampled charcoal
from an archaeological feature
that we have recently discovered
so that we could send it out
to get radiocarbon dating.
And we do the sampling
in a very specific way,
because we don't want to contaminate
the charcoal sample
or the bone or whatever else
we're pulling from a feature.
So first thing we do, wear gloves.
That way, none of the oils
or other material on your skin
can get onto the artifact
and potentially deposit new carbon.
Then, we clean off our tools.
So we'll use a trowel,
spray it off with distilled water,
and then wipe it off with a neutral wipe like
a non-bleached paper towel.
That will make sure that there's nothing adhering
to our tools that might get into the sample.
The next thing we do is we scrape away
a little bit of the overlying soil
so we can make sure that our sample
has not been exposed
to the air or the environment
to get new carbon deposited.
We want to make sure it is just what was there
when the sample went into the ground
in the first place.
So then we'll dig out that little piece of
charcoal or animal bone or what-have-you,
and we'll put it into a piece of tinfoil,
seal it up really tightly,
and then put it into a plastic bag.
Once that is labeled, we'll send it on down
to our friends
Beta Analytic in Florida,
and they'll test that sample for us
and then get back to us very quickly.
- Now, the reason that we don't carbon date
everything that we come across
is that as you move forward in time,
it gets less accurate.
And the reason is because that carbon ratio
between 12 and 14 is less and less.
And so often, here at Jamestown, 
because of the stratigraphy--
in other words, the layer,
the layers of history cake that are out here
are so tightly dated for us in comparison
to the historic documents
that we don't often need carbon dating
to give us
plus or minus, say, 20 years, which is often
the case with carbon dating.
As you go back in time thousands of years,
20 years isn't going to make that much
of a difference,
but here at James Fort, if I want to know
that this house is 1619
or this skeleton was buried in 1627,
that makes a big deal.
And I already know within a few years
of what I'm looking at.
So this is a very unique case in which we
have a carbon-rich feature
that we'd like to just pin down to at least
within a 30-year time period.
- Yeah, one of the things we really want
to see with this
is does it go with a European household,
a colonial household, or is it far older?
Does it date to an earlier
Native American occupation
that could have been before the colonists
arrived at Jamestown?
And radiocarbon dating will tell us that.
- Now, with this segment of "Dig Deeper,"
I think the theme
that we wanted to get out for this segment
is that archaeology is science.
And we use the biggest tools
to get the job done right.
And sometimes it's sending things
off to a lab,
and sometimes it is
out shoveling in the hot sun,
but it takes a large range of activities,
labs, and things like that,
a big sort of multi-national, multi-international
team, as it were, to solve our mysteries.
And although today, again,
we're practicing social distancing
and the coronavirus has shut us down,
we can do things like what we did today, 
sample carbon.
You have to wear a mask and gloves
and things like that
and send it off to a lab, and it doesn't really
affect our process of archaeology out here.
So we'll continue to make these videos 
for you guys,
letting us know what we're up to,
and we appreciate your support.
- Thanks for watching.
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