Researchers can find out how long ago something died using radiocarbon dating. Bones and teeth from animals and humans, as well as artefacts made out of wood, fabric or paper are just some of the objects that can be aged using this process.
This dating method works by measuring the ratio of different isotopes of carbon in a sample using a particle accelerator, such as the ANTARES accelerator at ANSTO.
There are three main isotopes of carbon on earth. The carbon-12 isotope makes up 99% of all carbon on earth, carbon-13 accounts for almost 1%, and carbon-14 is found in trace amounts.
Carbon-12 and carbon-13 are both stable isotopes, but carbon-14 is unstable and is radioactive.
Carbon-14 is continually produced in the upper atmosphere as neutrons, which are by-products of cosmic rays, and is then absorbed by nitrogen atoms. Carbon-14 atoms react with oxygen to form carbon dioxide, and carbon-14 is incorporated into the food chain when plants use carbon dioxide for photosynthesis.
Living things contain carbon-14 and carbon-12 in a ratio that is the same as in the atmosphere at the time. When the organism dies, the ratio of carbon-14 to carbon-12 decreases, as carbon-14 decays and is no longer incorporated into the organism.
Radiocarbon dating can date samples up to 50,000 years old. Samples older than that contain so little carbon-14 that the dating process is inaccurate.
Interesting fact: The carbon-14 bomb spike |
Above-ground nuclear weapons testing in the 1950s and 1960s resulted in a dramatic increase of carbon-14 in the atmosphere. This is known as the carbon-14 bomb spike. Nuclear tests released lots of neutrons into the atmosphere. Some of these neutrons hit nearby nitrogen atoms, turning them into atoms of carbon-14. Living organisms contain the same ratio of carbon-14 to carbon-12 as the atmosphere. This meant that animals and plants living in the 1950s and 1960s contained much higher amounts. The carbon-14 bomb spike has helped researchers to date Antarctic mosses (pictured above), trees and may be useful for dating human remains, such as teeth, to help identify victims of homicide or mass disasters. |
Published: 24/02/2012