Scientists 'see' ghosts

Other than helping to identify the victims of a tsunami, terrorist attack or other disaster, the new method could also find other uses, such as tracking down the source of tumours in the body or even studying how organs are regenerated.

Proteins called lens crystallines form in the eye in our early years and remain essentially unchanged. The age measurement method comes as an unusual byproduct of atomic weapons tests that took place in the atmosphere half a century ago. The carbon isotope that the explosions produced has declined year by year, providing a kind of watch to determine a victim's birth dates by looking into the lens of the eye.

Now, by measuring the amount of the carbon isotope C-14 trapped in the eye lens, scientists at the Universities of Copenhagen and Aarhus report in the journal PloS One that they can now establish, with relatively high precision, when a person was born, a useful tool for forensic scientists with which to date an unidentified body.

The reason that the isotope level can be used this way is that it is incorporated into the body in the first two years of life to build tiny transparent proteins, which allow light to pass through the eye so that we can see.

These special proteins, known as lens crystallines, remain essentially unchanged for the rest of our lives and is the only tissue in the human body apart from dental enamel to remain unchanged throughout life. advertisementBy comparing the yearly record of the content of the C-14 in the atmosphere with the content of C-14 in the lens crystallines of the eye, scientists can accurately date a person's year of birth - providing they are born after 1950. The technique uses a nuclear particle accelerator to determine the amount of C-14 in as little as one milligram - thousandth of a gram - of lens tissue and will be valid for a minimum of a century, until the Carbon-14 in the atmosphere finally returns to normal levels.

The method may also offer scientists a more precise means of dating bodies than checking the C-14 content in teeth, since teeth take between six and eight years to develop.

Associate Professor Niels Lynnerup from the Department of Forensic Sciences explains that this method, which he says is "extremely accurate, almost to the precise year of birth" also has other applications: "We think that carbon dating of proteins and other molecules in the body could be used to study when certain tissues are generated or regenerated. This could, for example, be applied to cancer tissue and cancer cells.