Hello everyone and welcome back to Seeker+!
I’m your host, Julian Huguet.
And as your host, it is my duty to dig into really cool topics and see what I can find
for you.
Dig, get it, because we’re talking about archaeology.
I’m sorry, my duty as your host is also to supply the nonstop puns.
I don’t make the rules here.
So archaeology - we’re going to talk about some of the coolest discoveries made recently
in the field and get into the insane futuristic technology that is completely revolutionizing
the field.
Because archaeology often gets overlooked in the big science headlines, but it’s literally
the study of everything we know about humans of the past.
And it takes a lot of careful investigation, insight and plenty of creativity to interpret
the things that we’ve left behind.
So before we get into all that, I want to answer a couple of big “hows” related
to what archaeology is and what it actually entails.
Like how do archaeologists know where to dig?
How do they know how old things are?
How do they know what is a significant finding and what might be something unimportant?
Ultimately the goal of archaeology is to find out about historic humans and their lives.
To answer questions about how they lived, what they ate, did for fun, what they believed
in, and how they communicated.
But beyond just facts about the past, archaeologists are tasked with interpreting them to gain
a deeper understanding of why some communities flourished and some failed.
That, and to keep golden idols and crystal skulls out of reach of the bad guys (cue Indiana
Jones theme).
So how does this all go down?
Well, the field of archaeology is based around something called the archaeological record.
Think of it as the big book of time chronicling who lived where and what they were up to.
Unlike a lot of other sciences that involve hands-on experiments and interactions with
living people, archaeology is forced to rely on found objects and evidence of activity.
Which can make it tricky to find concrete answers.
This archaeological record is made up of all the things people have left behind.
It’s their trash, their tools, their buildings, and even their bones.
So that’s step one in archaeology 101.
Collect and observe the stuff.
Step 2 - organize the stuff.
So once you’ve found the evidence of previous humans, all of it can be sorted into categories.
There are artifacts.
Which is a term you’ve probably heard before but it officially means a simple object that
shows modification or workmanship by a human.
As opposed to a natural or untouched object.
So think arrowheads or dishes.
Then there’s ecofacts.
Gotta love it when the etymology is that clear.
Artifacts..
Ecofacts..
Ecofacts are unmodified biological remains related to human use.
A good example of ecofacts would be animal bones or plant residue from human food preparation.
But charcoal from fires would qualify too.
And then we have features.
That’s the bigger stuff and this category includes non-portable human objects like walls
or fire pits.
These still scream - hey a human was here and this is proof.
But they’re bigger than an artifact.
And lastly you zoom all the way out and you have the archaeological site where all of
this stuff is found.
Great.
So once you’ve established what evidence of past humans exists and that it belongs
in the archaeological record, the next logical question is when.
When in the record should we place all this so that it starts to make sense in context?
This is where archeology starts to get really cool and sciencey.
Let’s say that you’re digging a new foundation in your backyard and you find a piece of sweet-looking
pottery.
How would an archaeologist know if it was evidence of some ancient civilization or just
a crusty old mug from the early 2000s?
Luckily there are some immediate rules of thumb that you can use before you have to
break out the heavy tech.
First up, we have the law of superposition.
Now when I think about superposition, my mind immediately jumps to quantum mechanics.
But in archaeology, the law of superposition is a much more approachable idea.
It says that layers of sediment are formed in order so that the layer at the bottom is
the oldest and the layer at the top is the youngest.
Pretty straightforward.
Old dirt at the bottom, new dirt on the top.
This is the same with geology.
So if you found this piece of pottery pretty deep in the ground, it’s likely to be a
lot older than if you found it near the surface.
This is called relativity dating.
If you know how old the surrounding rock layer is, or the dates of other objects found in
the same layer, that gives you a bit more information.
But there’s an even more accurate way to go known as chronometric or absolute dating
which relies on physical or chemical measurements.
In the mid 20th century, chemistry professor Willard Libby figured out that organic materials
could be dated by measuring the decay of the radioactive isotope carbon-14.
Side note: Libby had previously worked on the Manhattan project, so this massive leap
forward for archaeological analysis is an interesting offshoot from all that bomb research.
Although ironically the testing of nuclear weapons later on distorted the scale used
in dating archaeological objects because of the artificially high background levels of
carbon-14 that it caused.
I digress!
So how does a radioactive measurement mean that we can figure out how old archaeological
stuff actually is?
It works like this.
Radiocarbon dating uses isotopes of Carbon to date samples.
An isotope is just a variation of an element that has the same number of protons but different
numbers of neutrons.
This means that the isotopes have different masses.
The more neutrons, the more mass it’s going to have.
So you can have Carbon, and have these versions of it that are a little bit different from
each other.
The atomic mass is indicated in the number of the isotope.
Carbon-12 has six protons and six neutrons.
Carbon-13 has 6 protons and 7 neutrons.
These are both considered stable isotopes.
But if the nucleus gets too heavy, like with Carbon-14 where there are 8 neutrons to the
6 protons, then the isotope is unstable meaning that it will disintegrate or decay over time
by emitting radiation.
Ok bear with me, we’re getting back to the cool Indiana Jones jungle dig discovery stuff
shortly.
But you better believe he would be a huge fan of radiocarbon dating.
Radiocarbon or Carbon-14 is made in the atmosphere - this is a process that involves nitrogen
and cosmic radiation and it is eventually oxidized into 14-CO2.
Then this mixes with the 12-CO2 that is also in the atmosphere.
This mixture is then taken in by plants through photosynthesis.
It’s important to note here that all plants take in the same ratio of 14-carbon to 12-carbon
as the atmosphere.
When the plant, animal, or person dies, it’s cut off from the carbon cycle, creating a
time-capsule of sorts with a steadily decaying carbon-14 count.
When the plant, animal or person dies, the radiocarbon will start to decrease and decay.
And this process happens regardless of temperature or chemical interactions.
It takes about 5730 years for half of the atoms in carbon-14 to decay.
This is called the half-life of the isotope.
Scientists can measure the amount of carbon-14 left over and gauge how long ago the plant
or animal or human died.
Most absolute dating techniques use this radioactive decay method, but there are some others out
there that depend on other phenomena and are specific to unique materials.
Notably, one of my favorites is dendrochronology which you probably know as the study of tree
rings to see how old a tree is and what those years were like.
Or my other favorite - geezernology - where you can tell how old your grandpa is based
on the height of his belt.
Using multiple time scales like this is a good way to gut check the dates that an archaeologist
gets and make sure that it’s as accurate as possible.
In the next episode of this Seeker+ series on archaeology, we’re going to talk about
some incredible recent archaeological findings and dive into the conversation about whether
it’s okay to dig up humans of the past in the first place.
Let me know if there’s a topic you think I should cover in this podcast and I’ll
see you next time.