How do you use nitrogen to determine the radioactive age of a fossil?
To determine the radioactive age of a fossil using nitrogen, one needs to apply a dating technique called radiocarbon dating or carbon-14 dating. Here's how it works:
1. Understand the concept: Radiocarbon dating relies on the fact that radiocarbon (carbon-14) is constantly being formed in the atmosphere by cosmic rays interacting with nitrogen gas. This newly formed carbon-14 then combines with oxygen to create carbon dioxide (CO2), which mixes into the carbon cycle and is taken up by plants during photosynthesis.
2. Plant consumption: Fossils usually contain organic material from the plants or animals that were alive at the time of their formation. Plants absorb carbon dioxide from the atmosphere and incorporate it into their tissue through photosynthesis. Thus, the carbon-14 is introduced into the organism's system.
3. Stable carbon ratio: While an organism is alive, it maintains a consistent ratio of carbon-14 to stable carbon isotopes (carbon-12 and carbon-13). This ratio is generally the same as that in the atmosphere.
4. Death and decay: When an organism dies, it no longer takes in carbon dioxide and the carbon-14 starts to decay. Carbon-14 has a half-life of approximately 5,730 years, meaning that after this time, only half of the original carbon-14 content remains.
5. Measurement: To determine the age of the fossil, a small sample is taken from it. This sample is typically organic material such as bone, collagen, or wood. The process involves extracting the carbon from the sample and measuring its carbon-14 ratio compared to a standard known as the "modern standard."
6. Calibration: The measured carbon-14 ratio is then compared to a calibration curve, which takes into account variations in the amount of carbon-14 in the atmosphere over time. This helps to determine the age of the fossil by estimating how many half-lives have passed since the organism's death.
It is worth noting that radiocarbon dating is most effective for fossils up to around 50,000 years old. Beyond this point, the carbon-14 levels become too low to accurately measure.