# 8.5: Activity 4 - Dating Conversions

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Amanda Wolcott Paskey and AnnMarie Beasley Cisneros
Cosumnes River College and American River College

Historical dates are expressed as AD (Anno domini—“in the year of the Lord”), BC (Before Christ), BCE (Before Common Era), BP (Before Present), and YA (years ago). This exercise gives you an opportunity to practice making basic conversions of dates from conventions commonly used outside of scientific disciplines (AD/BC or BCE and YA) to BP, the most accepted form used in science.

## BC, BCE, AD→ BP Conversion

Convert the following ages into BP dates using these formulas:

$1950 – AD date = BP 1950 + BC/BCE date = BP$

Example: California redwood tree rings excavated from the Northwest coast and dated as 755 ± 40 years AD equals 1195 ± 40 BP.

1. Charcoal from a fire along the northern California coast: Dated 150 ± 80 years BCE =

1. Tule reed fragments, possibly from a canoe, from California: Dated 560 ± 20 years BCE =

1. Mediterranean cypress tree rings from Iran: Dated 979 ± 53 years AD =

1. A woven net fragment made from yucca and milkweed: Dated 1251 ± 60 years BC =

1. Woven sagebrush sandals from Fort Rock Cave, Nevada: Average date 10,981 ± 50 BCE =

## Years Ago (YA) → BP Conversion

Using the current calendar year, convert the YA ages into BP dates using the following formula:

$BP = Age – (Current year – 1950)$

Example: In 2020, an item date of 1,000 YA converts to 930 BP.

1. A wooly mammoth tusk found in an ice patch in the Canadian Rockies: Age 20,800 ± 650 YA =

1. Papyrus scrolls from Egypt: Dated 1,500 ± 35 YA =

1. A blanket wrapped around an Incan mummy: Age 450 YA =

1. Redwood planks from a house on the Pacific Northwest Coast: Age 800 ± 75 YA =

1. A dog’s skull found at the site of a former village: Dated 8,700 ± 250 YA =

1. What does the “±”in the dates refer to? Why would a very small ± number and a very large ± number be unlikely?

1. Why is it important to consistently use a single dating convention?