Overview
Two of the most important questions in archaeology are “when”? and “where”? Accurate dating is essential to document changes in human behavior over time. It is necessary to be able to place things and events in a framework of time and geographic space to know what happened, when, and where; in other words, the order in which things happened. Only after when and where something happened, and by creating a chronology or a sequence of events, can archaeologists understand the past. As the archaeologist Mortimer Wheeler (1890-1976) said, “Chronology is the backbone of archaeology: not the entire skeleton, but nothing less than the backbone.”
Archaeological dating methods fall into two general categories, relative or absolute.
Relative dating methods provide an indication of the age of an item in relation to other materials. These methods rely on stratigraphic position or association – context – to determine that an object is of approximately the same age or younger or older than something else. An example of a relative association is: the Oldowan industry is older than the Levallois stone tool industry. Bow and arrow hunting technologies are a younger (or more recent development) than spear hunting technologies.
Relative dates: dates expressed relative to one another instead of in absolute terms. For instance, earlier, later or more recent.
Absolute dating methods are used to assign a specific, calendar age to an object or event in years B.P. (before the present), B.C. (before Christ), A.D. (anno Domini), B.C.E. (before Common Era), or C.E. (Common Era) calendar years, or another conventional system. For example, the Fourth Egyptian Dynasty lasted from 2680 to 2565 B.C. The Roman Colosseum was constructed between A.D. 70 and 82. The Battle of Gettysburg took place on July 1-3 in A.D. 1863. “Absolute” does not mean that the date is perfect. Instead, “absolute” means that the date is given in years according to our calendar.
Absolute date: a date expressed as specific units of scientific measurement, such as days, years, centuries, or millennia. Absolute determinations attempt to pinpoint a discrete, known interval in time.
A calendar is a system for classifying and organizing time into repeatable and predictable units. Calendars operate in both the past and the future for recording history and scheduling activities. A day is the smallest unit of calendrical time; the measurement of fractions of a day is referred to as timeskeeping and involves hours and minutes. The earliest evidence for an awareness of time comes from 15,000 years ago during the Upper Paleolithic, when seasons of the year (and perhaps the phases of the moon) were recorded in art and systems of notation. By 3000 B.C. the Sumerians in Mesopotamia were using a lunar calendar that divided the year into 30-day months and split each day into 12 equal periods. Today, there are approximately forty different calendars in use around the world. The most common among these is the Gregorian calendar. The Gregorian calendar was installed by Pope Gregory in A.D. 1582. The calendar was originally created for religious purposes to calculate the dates for the moveable feasts of Christian ritual. The Gregorian calendar is a solar calendar and is based on a cycle of 400 years of 146,097 days; each year has an average of 365.2425 days. The 12 months of the year have a fixed order and an unequal number of days. Years are counted both forward (A.D.) and backward (B.C.) from the birth of Christ. There are two types of years. A common year is 365 days; a leap year of 366 days occurs once every four years (with a few exceptions).
Calculating Time
The calendrical references (B.C./A.D., B.P., etc.) used in archaeology vary based on the period, region, and culture one is investigating. As we continue to survey the archaeological record in this class you will see variations in the way time is referenced. This activity will help you learn how to identify the archaeological time references and to accurately switch between timescales in a meaningful way.
Datum
All measuring devices and scales – including calendars – use a datum point. A datum is the starting point from which things are measured. A calculator, ruler, car odometer, etc. all use a datum of 0.
Example of a ruler and its 0 datum:
Calendrical and chronological time scales, which measure time, also use a datum. For example: the datum for the B.C./A.D. timescale is 0, while the datum for the B.P. timescale is 1950 A.D. Read on to learn why these datums differ.
Example of the B.C./A.D. timeline and its 0 datum:
Timescales & Date Abbreviations
There are four major timescales used to provide absolute/calendrical dates in archaeology, all of which link to the Gregorian calendar.
B.C./A.D. (before Christ/anno Domini): This scale uses the references in the Gregorian calendar. B.C. refers to the time “before Christ”. A.D. refers to “anno Domini” (Latin for “year of the Lord”) which denotes time after the birth of Christ. This timescale was not used until the spread of Christianity through Europe. It became the predominant timescale only after European colonization across many regions. Datum is 0 and symbolically represents “the year Christ was born”. Everything before datum is B.C., everything after datum is A.D.
B.C.E./C.E. (before Common Era/Common Era): This timescale is the same as above, however, it replaces the B.C./A.D. references with the abbreviations of more generalized, non-religious-based, terminology. B.C.E. refers to the time “before the Common Era”. C.E. denotes time “during the Common Era”. Essentially, B.C.E. aligns with B.C., and C.E. aligns with A.D. Datum is 0 and marks the year in between the end of B.C.E. and the transition to C.E. Everything before datum is B.C.E., everything after datum is C.E.
B.P. (before the present): This scale was developed in coordination with radiocarbon dating, an absolute dating method. Radiocarbon dating relies on the ratio of different isotopes of carbon within the atmosphere and the regular decay of the isotope carbon-14 (14C). Atomic-bomb testing in the mid-twentieth century drastically altered the ratio of different carbon isotopes within the atmosphere, so the datum in the B.P. timescale is equivalent to the year A.D. 1950 (in the Gregorian calendar). In other words, A.D. 1950 is considered “present” in the “before the present” reference. B.P. – before the present – literally means before A.D. 1950. Thus, 1800 B.P. means 1800 years before the present, or 1800 years before A.D. 1950. The B.P. timescale counts backwards, so the year 1 B.P. is equivalent to A.D. 1949, 50 B.P. is equivalent to A.D. 1900, 100 B.P. is equivalent to A.D. 1850, and so on. There is no “after the present reference” in this timescale as anything more recent than A.D. 1950 is considered to be of historical rather than archaeological nature.
ya (years ago), ka (kilo annum, thousand years ago), or mya (million years ago): These references are used to assign a general, more approximate rather than specific, date to events that occurred a very long time ago. For example, the entry of humans into the New World during the Pleistocene (Ice Age) is thought to have occurred by about 15,000 ya (years ago), or 15 ka, which is equivalent to about 14,929 B.P. and approximately 13,000 B.C.
Calculations
Because calendrical references vary in archaeology, researchers – and students – must learn to accurately switch between timescales in a meaningful way. In order to compare a B.P. reference to a B.C./A.D. reference, for example, one must first place the two references into the same timescale. This takes a bit of simple math.
First note that the B.C./A.D. and B.C.E./C.E. timescales are offset from the B.P. timescale by 1,950 years. In other words, the difference between the B.C./A.D., B.C.E./C.E. datum (0) and the B.P. datum (A.D. 1950) is 1,950 years. Therefore, to convert the dates to the same timescale one would either need to add or subtract the difference.
How to convert B.C./A.D. and B.C.E./C.E. dates to B.P. dates:
B.C. to B.P. calculation:
B.C. date + 1950
For example: 1000 B.C. + 1950 = 2950 B.P. (i.e. 2,950 years before the present or 2,950 years before A.D. 1950)
A.D. to B.P. calculation:
1950 – A.D. date
For example: 1950 – 1000 A.D. = 950 B.P. (i.e. 950 years before the present or 950 years before A.D. 1950)
B.C.E. to B.P.:
Same as the B.C. to B.P. calculation
C.E. to B.P.:
Same as the A.D. to B.P. calculation
How to convert B.P. dates to B.C./A.D. and B.C.E./C.E. dates:
When converting a B.P. date to the other timescales, always subtract the B.P. date from its own datum (A.D. 1950). A positive result is equivalent to an A.D. or C.E. date, and a negative result is equivalent to a B.C. or B.C.E. date.
For example: 1000 B.P.
1950 – 1000 B.P. = 950
The positive result indicates the converted date falls within the A.D. and C.E. range so the answer is 950 A.D. or 950 C.E.
For example: 3000 B.P.
1950 – 3000 B.P. = -1,050
The negative result indicates the converted date falls within the B.C. and B.C.E. range so the answer is 1050 B.C. or 1050 B.C.E.
Investigate the following events in human history and consider their chronology in relation to each other. Calculate the dates of the events in multiple calendrical timescales and put the events in order, from oldest to most recent.
Task 1
Create a table with six columns and seventeen lines. Title the first line of each column in the following way:
Example of the table you will create for this activity.
Event B.C. or A.D. Date B.C.E. or C.E. Date B.P. Date
Calculations
Show your work
Sequence Order
Task 2
Using your textbook and other reliable resources, conduct a bit of research on the dates of the following events.
Humans reach Australia
Wheat first domesticated
Humans reach North America
Dogs first domesticated
Great Pyramids of Giza built
Stonehenge built
Sumerian cuneiform invented
Columbus arrives in the New World
United States Declaration of Independence signed
Start of the Common Era
Quin era Great Wall of China
Ming era Great Wall of China
Battle of Little Big Horn
BP timescale datum
Humans reach Europe
Homo sapiens sapiens (AMHs) emerge in Africa
Task 3
Place the events into your table – one event per line. Enter the date you found from researching the event into the corresponding column. For example: if you learned construction began on the Roman Colosseum in A.D. 70, you would enter the date into the B.C. or A.D. Date column.
Example of the activity table.
Event B.C. or A.D. Date B.C.E. or C.E. Date B.P. Date
Calculations
Show your work
Sequence Order
Example:
Construction of the Roman Colosseum begins
A.D. 70
Task 4
Convert the remaining dates for each event and place the results in the corresponding columns. Note that you must also show your work for any calculations that are made. Provide the exact calculations. Do not round off your results. For example: if you learned construction began on the Roman Colosseum in A.D. 70, you would enter the date into the B.C. or A.D. column, and then convert and enter the dates and calculations into the B.C.E. or C.E. column and the B.P. column.
Example of the activity table.
Event B.C. or A.D. Date B.C.E. or C.E. Date B.P. Date
Calculations
Show your work
Sequence Order
Example:
Construction of the Roman Coliseum begins
A.D. 70 C.E. 70 1880 B.P. 1950 AD – 70 AD = 1880 BP
Task 5
After the dates have been calculated and entered, compare all of your events and place them in sequential order, starting with #1 and ending with #16. Enter the number for each event into the Sequence Order column of your table.
Example of the activity table.
Event B.C. or A.D. Date B.C.E. or C.E. Date B.P. Date
Calculations
Show your work
Sequence Order
Example:
Construction of the Roman Coliseum begins
A.D. 70 C.E. 70 1880 B.P. 1950 AD – 70 AD = 1880 BP 6
Task 6
Create a simple* timeline that represents the passage of time and place the events in sequential order, starting with the earliest (oldest) event and progressing to the latest (most recent) event. Note that the timeline may only use one timescale – either B.C./A.D. or B.C.E./C.E. or B.P.
The timeline must include the following elements:
A marked datum point that corresponds with your chosen timescale.
Labelled B.C. and A.D. sections or B.C.E. and C.E. sections, if you chose to use one of these timescales.
The name of each event.
The date of each event. All of the event dates must be uniform across your timeline. In other words, if you chose to create a B.P. timeline, then all of the dates must be converted and labelled using the B.P. reference.
*Note: This timeline will include a lot less information than the annotated versions you constructed for the Paleolithic Periods. That is perfectly fine! It’s a simple timeline – you are not being asked to include more information, such as annotations and photos.
Format
The activity may be typed or hand-written. If you choose to turn in a hand-written document, it may be submitted as a high-resolution JPEG image, or scanned and submitted as a PDF. Typed versions must be submitted in one of these CANVAS friendly formats – Microsoft Word, WordPerfect, Adobe PDF, JPEG, Rich Text Format (RTF), or Google Docs (submitted via the Google Drive tab).
