Carbon-14

Carbon-14, also called radiocarbon, is a radioactive isotope of carbon. An isotope is a version of an element with a different number of neutrons. While most carbon on Earth is stable, carbon-14 is unstable. Its atomic nucleus contains 6 protons and 8 neutrons. This instability means it undergoes a process called radioactive decay. Carbon-14 is a cosmogenic nuclide, meaning it is created by cosmic rays from space. It exists in very small amounts compared to other types of carbon.

The creation of carbon-14 begins high in the Earth's atmosphere. Cosmic rays enter the atmosphere and create neutrons through various transformations. These neutrons then strike nitrogen atoms in the upper troposphere and stratosphere. This specific reaction turns the nitrogen into carbon-14. Most of this new carbon quickly forms carbon monoxide. This then oxidizes to become radioactive carbon dioxide. This gas mixes throughout the atmosphere within weeks. It also dissolves into the oceans, though at a slower rate.

Carbon-14 follows a specific cycle through living things. Plants absorb atmospheric carbon dioxide during photosynthesis. Animals then consume these plants, incorporating the carbon into their own bodies. Because of this, the level of carbon-14 in a living organism roughly matches the level in the atmosphere. However, once an organism dies, it stops taking in new carbon. The carbon-14 already present begins to undergo beta decay. During beta decay, a neutron turns into a proton. This process releases an electron and an electron antineutrino. The carbon-14 eventually becomes the stable isotope nitrogen-14.

This decay happens at a predictable rate known as a half-life. The half-life of carbon-14 is 5,700 years. This means that after 5,700 years, half of the original carbon-14 will have decayed. Scientists use this steady decline to perform radiocarbon dating. This method can determine the age of organic materials up to about 60,000 years old. To get accurate dates, researchers compare samples to known data. They use tree-ring data, called dendrochronology, to calibrate results up to 10,000 years. They can also use cave deposits, known as speleothems, to look back 45,000 years.

The history of radiocarbon dating is tied to important scientific breakthroughs. In 1949, Willard Libby and his colleagues developed the technique at the University of Chicago. They pioneered the use of carbon-14 to date archaeological and geological samples. This work was so significant that Libby was awarded the Nobel Prize in chemistry in 1960. Before this, dating ancient organic remains was much more difficult. Today, scientists use advanced tools like accelerator mass spectrometry. This method counts every carbon-14 atom in a sample. It is much faster and works on tiny samples, such as individual plant seeds.

Human activities have also changed the amount of carbon-14 in our world. Between 1955 and 1980, many countries conducted open-air nuclear testing. These tests nearly doubled the concentration of carbon-14 in the Northern Hemisphere. This created a massive increase known as a bomb spike.

Scientists can actually use this spike for "bomb-pulse dating." This allows them to determine the exact birth year of an individual by testing tooth enamel or the lens of the eye. Interestingly, carbon-14 from these tests has even been found in the Mariana Trench.

Carbon-14 is also useful for studying the Earth's environment and history. Scientists use it to see if carbon is being released from peatlands due to climate change. They also use it to study ancient solar activity through Miyake events. These are large spikes in carbon production caused by extreme solar events. For example, a massive event occurred around 12,350 BCE. Furthermore, the lack of carbon-14 in fossil fuels helps scientists track pollution. Since fossil fuels are millions of years old, they have no remaining carbon-14. By measuring carbon-14 levels, researchers can see how much fossil fuel combustion is affecting the atmosphere.