1. Examining Sources
How do archaeologists investigate ancient cultures?

2. The Formation of Record
The archaeological record of a site is sealed within layers of earth over hundreds and thousands of years.
Wind and rain may destroy buildings and artifacts, soil may cover the site, trees and brush may grow over the remains.

3. The Formation of Record Continued
Centuries later, signs of a site might be brought back to the surface of the earth through erosion, animals digging in the ground, or people clearing land for farming, building, or other purposes.
 The ruins above were unearthed in Athens, Greece when the local subway was under construction.

4. The Formation of Record Continued
Archaeologists can then examine the surface of a site and can begin to piece together the archaeological record.
In most cases, evidence remains buried in layers of earth and archaeologists must dig up the remains of the past through the process of excavation.

5. The Excavation of a Site
Once a site has been located, archaeologists carefully remove the earth, layer by layer.
They divide the surface of the site into squares with grids.
As they dig, they carefully record the exact location of every object they find.

6. The Excavation of a Site Continued
The study of the remains that are found in various layers of soil and rock is called stratigraphy.
Studying the layers themselves, as well as the artifacts, can give archaeologists clues about how the archaeological record was formed at different periods in history.

7. The Excavation of a Site Continued
In general, archaeologists believe that the deepest layers are the oldest. However, this may not always be true.
Over time, earth and artifacts may shift due to earthquakes or human disturbances.
Archaeologists must then use other techniques to date the layers and the objects found in them.

8. Dating
Archaeologists use two methods to find out how old an artifact might be:
Cultural Dating
Scientific Dating
 No, no, no... not THAT kind of dating!

9. Cultural Dating
Archaeologists use cultural dating when they compare objects they find with information they already have.
To find the date of a Roman coin, for example, you might review research from written sources that share information about the history of Roman coins.

10. Absolute Dating
With absolute dating, archaeologists decide the age in years of an object.
Finding the date of a Roman coin, for example, is an example of absolute dating.

11. Relative Dating
However, archaeologists cannot always find out exactly how old an object is.
Sometimes they can only determine whether an artifact is older or newer than other objects. This is called relative dating.
Pottery in an important tool in relative dating.

12. Scientific Dating
Some ancient objects can be dated more accurately by analyzing them in a lab.
The oldest form of scientific dating, in use since the 1700s, is called dendrochronology, or tree-ring counting.

13. Radiocarbon Dating
Radiocarbon dating is the most important scientific development in dating techniques.
In radiocarbon dating, the radioactive carbon within an object is measured to determine the age of the object.
Radiocarbon dating can only be used to date the remains of once-living things, such as wood or bones.

14. Radiocarbon Dating Continued
How does it work?
Every living thing absorbs carbon from the atmosphere. A small amount is radioactive. When a plant or animal dies, it stops absorbing carbon. The radioactive carbon absorbed when it was alive begins to decay at a known rate.

15. Radiocarbon Dating Continued
Archaeologists have figured out methods of measuring the amount of radioactive carbon left in things like bones and wood. Using this information, they can figure out when a plant or animal died. They can even figure out how long ago the tree used to make an artifact lived.

16. Radiocarbon Dating Continued
Radiocarbon dating has helped solve a lot of mysteries, like the Tollund Man, but it is not perfect.
Radiocarbon dating will not work on objects less than 1,000 years old or more than 60,000 years old.
Pollution can also negatively impact the accuracy of a sample.

17. Reconsidering the Past
As different archaeologists examine the archaeological record, they come to different conclusions about its meaning.
Take a look at the 10,000 year old cave painting from Lascaux, France. What do you see?

18. Finally…
Archaeologists must use ALL the evidence they can gather to interpret the archaeological record, from using radiocarbon dating to examining written records.
As new techniques and tools become available to archaeologists, they will continue to interpret and reinterpret the evidence in a never-ending process!

19. Let’s Review!
Our essential question: How do archaeologists investigate ancient cultures?
Put the following steps in proper order:
Cultural or scientific dating
Reinterpreting the evidence
The formation of record
Excavation of the site

20. How would you date these objects
How would you date these objects? Absolute, Relative, or Radiocarbon Dating?
A wooden Egyptian sarcophagus
Ancient Roman coins
Ancient Greek pottery
Ancient Egyptian mummy