What about AD, BC, BCE and BP Ages?
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Before we plot up real data to compare with the theoretical decay curve, let's see how years are reported. Dates can be expressed as AD, BC, BCE (before common era), and BP (before present). The accepted way to represent C-14 ages is in terms of years BP, where the year 1950 is used as the "present." (1950 is the date that the calibration curves were established. It also predates atmospheric testing of the atom bomb, which significantly upset C12/C14 ratios in the following years.)

The time line on the right illustrates the relationship between BP and AD or BC ages. Click on the image and drag back and forth to study this relationship.

Below are descriptions of 6 samples, with known ages expressed as either AD or BC (also called BCE). Convert these dates to BP dates (using 1950 as "the present.") Also, convert the three estimates of C-14 years in the second table to BP dates.

Some materials with known age BP Age
1. Douglas Fir tree rings - excavated from a cave in Arizona. Date: 577 ± 50 years AD
2. Wood from Egyptian coffin - from the Ptolemic period based on style. Date: 200 ± 150 years BCE
3. Wood fragments from the floor of a palace in Syria - Syro-Hittite period. Date: 675 ± 50 years BCE
4. Giant Sequoia tree rings from California. Date: 979 ± 52 years BCE
5. Cedar of Lebanon fragments from funeral boat of Egyptian King Sesostris III. Date: 1843 ± 50 years BC
6. Wood from the tombs of Egyptian Kings Sneferu and Zoser. Average Date: 2650 ± 75 years BCE
Assuming this is 1999, convert these ages into BP dates. Example: an article that's 1000 years old has a BP age of 951. [BP = Age - (Today -1950) = 1000-(1999-1950) = 951]
BP Date
7. Wood from Bristlecone Pine of White Mountains, California. Age 4731 ± 75 years
8. Pleistocene mammoth bone from La Brea Tar Pits of Los Angeles, California. Age: 12,200 ± 35 years
9. Cottage roof timber from Ireland. Age: 906 ± 35 years

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