Calculating Historical Time
How do we figure out when something happened or when it existed in the past?
I study a lot of history, both professionally and for personal enjoyment, and I come across a lot of historical time periods, such as ancient and Biblical times, the medieval period, the Renaissance, the Enlightenment, the modern period, and many more. Some of these periods have a broad time span of hundreds and thousands of years. For example, Ancient Egypt can range anywhere from 3000 BC when it was founded to the time of Cleopatra in the early AD years. That’s a time span of 3000 years.
But many events and archeological items have very specific dates. For example, we know that Julius Caesar was killed on March 15, 44 BC. And we know that there was a flood or a drought or a volcano explosion in a specific year. How do we know these things? In this post, I will explore how to identify the date of historical events and archeological artifacts.
Relative vs. Absolute Dating
Dating techniques are grouped into two broad categories. Relative Dating means that dates are determined in relation to other events. For example, if there is a 20-year celebration, then you know that the original event happened 20 years ago. In the example below, you know that the great-grand-parents Max and Mary came before all the other members of the family. Meanwhile, Absolute Dating means that an item is dated through some kind of test or evaluation that tells you how old it is.
Radio Carbon Dating (Carbon-14)
Living things have chemicals made of carbon. When they die, these chemicals break down (the carbon gets lost) at a predictable rate called a “half life.” Scientists can identify the age of the item by measuring the amount of carbon that remains.
For example, if the test shows that an ancient walking stick has enough carbon to last 500 more years, and the amount of carbon is at 50%, then you can calculate the walking stick to be about 1000 years old.
It’s kind of like estimating the amount of gas in your car based on how much you have already driven. Your gas gauge shows about half, and you have driven 150 miles, so you know that you can drive a total of about 300 miles.
Radio Carbon Dating has limitations. It works only with “organic” materials that have carbon in them, so it can’t measure ancient weapons made of steel or archeological materials such as rocks. It’s also not very precise; in some cases it can estimate only to the century or decade. Also, some items may decompose faster than the half-life of that item, so the item may have dissolved before it is found, or there may be too much carbon when it is tested. The graph above shows that it takes almost 6000 years to get to 50% - that’s very slow.
Other Chemical Tests. I'm not very familiar with other types of chemical testing, but this Wikipedia page lists several of them, including amino acid testing, argon testing, iodine testing, and many others. Some of these tests can be used to identify the cause of death, especially if it is by poisoning or illness. If you know that a chemical was used in a specific year, then you can also guess the general time period it came from. For example, you know that paint with lead was not produced in the last several years.
Tree Rings
In places where there are old trees, plant biologists can count “tree rings,” which are patterns or lines inside the tree trunk. These are created by the amount of growth the tree has each year. The most recent years are on the outside, and the larger separation indicates a lot of growth in that year, which indicates good weather and plenty of water. Narrow lines show little growth and a harsher season.
Tree rings are useful for environmental knowledge, such as drought or a rainy season. They can also indicate damage such as a forest fire. These patterns in the trees can be correlated with historical events, such as a large war where the enemy set the whole countryside on fire. That damage could be memorialized in the tree, and historians can identify the exact year by counting back the number of rings.
Obviously, this method does not work in desert and grassy environments where there are only shrubs and no trees, and the tree lines can only indicate major weather patterns and damage, not historical events like who was the king or who won the battle.
How Deep in the Dirt
The land itself can indicate the historical time period. In general, the oldest archeological stuff is buried deeper, and the newest stuff is closer to the surface. As archeologists dig down, they discover older and older stuff, and they go back in time.
This method is effective for ancient territories that have been continually occupied such as Rome or Jerusalem. Newer generations build over the older generations, and archeologists can peel back the historical layers. However, this method does not work as well for locations that were abandoned or are very new. A new suburban neighborhood on top of farmland isn’t going to have any history underneath.
This method is also useful for environmental research. As with trees, the ground shows layers of historical events. Unique events such as a volcano explosion, a massive flood, or a meteor shower are indicated by a layer in the dirt. That’s because the land was covered in volcanic ash or river sediment, and then it got buried by tree leaves and other organic debris. When archeologists dig, they can see these layers and match them to historical events. The deeper it is, the older it is.
Historical Documents
Some historical time periods have a lot of official documents, and historians can learn about what happened by reading these documents. These documents include birth and death certificates, marriage licenses, sales/purchases of property, declarations of war, acts of Congress or Parliament, publications of books, newspaper stories, and many other events recorded on paper, in stone, in a personal diary, and even through a sculpture or monument. For example, the U.S. Declaration of Independence has its date on the document itself.
Unfortunately, many civilizations throughout history do not have written documents, or the documents have been destroyed, or they are written in a language we don’t understand. Many early civilizations - and even some communities today - passed their histories down verbally through song. As the story tellers died off and younger generations moved away or became more modernized, the stories got forgotten, and the history got lost.
In many civilizations, historical documents (and entire ethnic populations) were destroyed through acts of war, such as with the burning of the ancient Library at Alexandria, which was believed to contain the most important knowledge of the time. And some documents are not reliable. People forge wills and property deeds, and they write scandalous stories about their opponents. Sometimes, historians have only a small portion of a document, and they must try to figure out what the rest would have said.
Historical Artifacts
As with documents, the date is sometimes stamped on a historical artifact. This often happens with coins, such as this Liberty Dollar golden coin from 1861. Or, the coin could have been issued in celebration of a war or other historic event. If we know the date of that event, we can identify the date of the coin as well.
Rulers often issue commemorative portraits, sculptures, monuments, churches, and gifts for similar reasons - important military victories, weddings, coronations, etc. If we know when these events happened, we can also identify the date of the coin.
Historians can also identify the time of the historical artifact by identifying what it shows. Sculptures and coins of emperors and generals were probably issued during their lifetime or immediately after; historians can identify the time of the artifact by comparing it to the historical record.
Relationships to Family and Other Events
In many situations, historians know when one person lived, and they can make comparisons to other people. For example, they may not know the exact years when unimportant kings ruled, but they can figure out that it was somewhere in between the rule of two great kings. The less important rulers get organized in time by comparison to the famous rulers.
Historians can also arrange people in time through family relationships by comparing them to parents and grand-parents or to their children and grand-children, especially if they have indicators in their name such as “junior” or “Henry the Fifth.” It’s like building a family tree.
Historical events can be organized like this too. Historians may know when an important event such as a battle, a coronation, a birth, or a death happened, and they can estimate when another event happened by comparison. For example, they can estimate the date of a battle based on the date of a peace treaty.
In practice, this gets very complicated because there are thousands of historical events, and each event needs to come before or after another event. It’s like a jigsaw puzzle of historical dates.
Artistic or Cultural Style
Historical artifacts from different time periods and different cultures look different. Historians can identify these artistic and cultural styles, and they can figure out what time period the artifact is from.
This is often done with pottery. Pottery from older Greek civilizations looks different than newer ones. The older pottery on the left has only geometrical patterns, while the newer pottery on the right has more sophisticated artwork with mythological figures such as Achilles. As you can see, ancient Greek artisans got better and more sophisticated with their pottery and artwork over time. When historians analyze pottery pieces, they can identify the time and culture.
As cultures move across continents, they also bring their unique artistic style, and these are clues for who lived in what territories during what specific times.
Language
Different cultures have different languages, and historians can use language differences to identify the cultures of a certain area. In Ancient Roman times, people in northern Italy probably spoke Latin, but later on the Germanic tribes invaded and took over the area, and the language probably became more Gallic or Germanic. Historians who find a Gallic or Germanic or Latin document will know which culture and which time period it came from.
Language also changes over time, and historians can identify the date of a document based on how old the language is. For example, an ancient document written in ancient Latin has a different language than a medieval document written in church Latin about 500 or 1000 years later. The Latin of Ancient Rome is also different from the Italian of modern Rome. Today, you can definitely tell if a story was written by Chaucer, Shakespeare, or Charles Dickens. They all wrote in English, but their English is very different.
Language differences also indicate that cultures have a common history and are drifting apart. When cultures live close together and interact with each other, they have many shared words, and old “root” words are the same. For example, the root word for “mother” is “mater,” and this is the same in many European languages. Today, American and English speakers say “the weekend,” while French and Italian speakers say “la weekend.” This similarity shows that these cultures interact with each other.
But different cultures have different words for the same thing, and that shows that the cultures live separately or far apart. Historians use this information to identify when cultures drifted apart and migrated to somewhere else, and this knowledge can help them identify the time period of an artifact.
Combined Methods
Historians don’t have to rely on a single method for determining the age of an historical artifact. Instead, they use several methods together to create a story that is reinforced with many pieces of evidence.
For example, a piece of pottery can be identified in time by how deep it is buried in the ground. Then, its artistic style and its language can be dated to a particular culture and a particular time period. The chemicals on the pottery and the paint can be carbon dated. Perhaps there is also a replica of the item in a modern museum, or maybe a writer from the same historical time period described the same pottery in a play or in a song as it was used by a famous warrior such as Achilles.
Thank you for being a part of Lirim’s Learning Club. If you enjoyed reading this post, but have not subscribed to the newsletter, consider joining. (It’s free, and you can unsubscribe at any time. New posts will be sent directly to your email.)
My name is Lirim Neziri, and I am an educator and a writer. I love to read and learn, and this newsletter (which I call Lirim’s Learning Club) lets me share interesting things I am learning. I write about History, Literature, Writing, Education, Technology, Leadership, and Personal Productivity. Please join my learning adventure.