How Old is My Grandmother?

25 April 2010

Question

We have a great grandmother, but we're not sure exactly how old she is. According to the Home Affairs, she was born in 1902. We strongly believe that this is not the accurate age.

How can we accurately establish in which year she was born?

Answer

We put this to Kirsty Spalding, assistant Professor in the department of cell and molecular biology at the Karolinska Institute, Stockholm, Sweden: Kirsty - There's a couple of ways you could do this, both involving a newly developed strategy which is radiocarbon dating. Essentially, because of the Cold War, there was a whole lot of above ground nuclear bomb testing and during this procedure, there was a lot of detonations which cause neutron emissions into the atmosphere. And essentially, to make the long story short, this ultimately resulted in increased levels of carbon-14 in our atmosphere. This actually occurred for some years during the period of the Cold War then they put this Test Ban Treaty out, banning all above ground nuclear bomb testing. And then the C14 levels in the atmosphere changed in a very predictable way with time so that for any given time point, the proportion of C14 to C12 represents a particular year in time. So, one way we've developed to use this strategy to look at cell turnover in the human body is to look at the DNA of cells. And by determining the proportion of the radioactive carbon-14 to the stable isotope carbon-12, we're able to say when this cell was born. And we've been applying this to different parts of the human brain and body, and actually found that there are selected regions of neurons, that's the nerve cells of the brain, that are as old as we are. And so, by taking some brain cells from this region of the brain; cortex, cerebellum for example, we're able to take out the DNA from these cells, carbon date them and they will tell us the year of birth of the individual.

Diana - But what if you don't particularly want to take a sample from a living person's brain?

Kirsty - This is perhaps a more cumbersome way to determine age. Another way that I've developed with colleagues and this actually uses the C14 to C12 ratio in tooth enamel. So in this methodology, you can take a tooth from an individual so in this case from your 100-year-old granny and depending on which tooth it is, you determine how old the enamel is and each tooth lays down the enamel at a different time point which we've decoded in a way, so we know how long it takes for each tooth to make enamel. We can figure out then from this information with carbon dating of the enamel, when the person's born and we can combine this with other methodologies to then find out when they died and how old they were when they died. So this is without a doubt the most precise way to determine the age of an individual.

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