Over the years, other secondary radiocarbon standards have been made.Radiocarbon activity of materials in the background is also determined to remove its contribution from results obtained during a sample analysis.
Once the organism dies, however, it ceases to absorb carbon-14, so that the amount of the radiocarbon in its tissues steadily decreases.
The carbon-14 method was developed by the American physicist Willard F. It has proved to be a versatile technique of dating fossils and archaeological specimens from 500 to 50,000 years old.
The method is widely used by Pleistocene geologists, anthropologists, archaeologists, and investigators in related fields.
The radiocarbon age of a certain sample of unknown age can be determined by measuring its carbon 14 content and comparing the result to the carbon 14 activity in modern and background samples.
The principal modern standard used by radiocarbon dating labs was the Oxalic Acid I obtained from the National Institute of Standards and Technology in Maryland. Around 95% of the radiocarbon activity of Oxalic Acid I is equal to the measured radiocarbon activity of the absolute radiocarbon standard—a wood in 1890 unaffected by fossil fuel effects.