### How is Carbon Dating Used to Identify Age of a Thing?

Carbon dating, also known as radiocarbon dating, is a method used to determine the age of organic materials, such as wood, paper, and fabrics. It is based on the fact that carbon, a radioactive isotope of carbon, decays at a constant rate over time. By measuring the amount of carbon-14 in a sample, scientists can determine how long ago the material was alive or in use.

Carbon dating works by measuring the ratio of carbon-14 to carbon-12 in a sample. Carbon-14 is a radioactive isotope of carbon that is produced in the upper atmosphere by cosmic rays. It is present in small amounts in the environment and is absorbed by plants during photosynthesis. When plants or animals die, they stop absorbing carbon-14, and the carbon-14 in their bodies begins to decay at a constant rate.

To determine the age of a sample using carbon dating, scientists first need to measure the amount of carbon-14 and carbon-12 in the sample. This is typically done using a device called a mass spectrometer, which can measure the amount of carbon-14 and carbon-12 in a sample with a high degree of accuracy. The ratio of carbon-14 to carbon-12 in the sample is then compared to the ratio of carbon-14 to carbon-12 in the atmosphere, which is known to be constant over time.

Using the known decay rate of carbon-14, scientists can then calculate how long it has been since the material was alive or in use. This age is expressed in years before present (BP), with "present" being defined as 1950. For example, a sample with a carbon-14 to carbon-12 ratio that is half of the ratio in the atmosphere would be considered to be about 7,000 years old, because half of the carbon-14 in the sample would have decayed in that time.

In conclusion, carbon dating is a method used to determine the age of organic materials by measuring the ratio of carbon-14 to carbon-12 in a sample and comparing it to the ratio in the atmosphere. By using the known decay rate of carbon-14 and a device called a mass spectrometer, scientists can calculate the age of a sample in years before present.