Question of the Week

How Old is My Grandmother?

Sat, 24th Apr 2010

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Mike Mohali, Pretoria asked:

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?


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. Old lady from Zacatecas, Mexico 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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BRValsler, Thu, 15th Apr 2010

Thanks Ben, Didn't see this QotW when I heard the show and couldn't resist the mummy joke... mountaineirc1969, Sun, 18th Apr 2010

Aren't all our cells replenished every 5 years so carbon dating might be hard. Make it Lady, Tue, 20th Apr 2010

The way carbon dating works is that a living thing absorbs carbon 13, an isotope of carbon that is radioactive. When that living thing dies it stops breathing (plants breath too) and thus stops absorbing carbon 13. You can then test for the amount of carbon 13 in the dead tissue and find out about how long it's been dead (within several thousand years so this would not work for the police investigating a murder), I'm assuming granny's still breath so carbon 13 dating would not work anyway. mountaineirc1969, Wed, 21st Apr 2010

Ask her what historical events she remembers. I remember watching Skylab fly over but I don't remember the Apollo 11 landing. I was born December 1969 so was on my way that July but was only half baked......

If she remembers the Battle of Jutland then she's at least 96. Why would a sea battle be named after some "land"?

Not sure you can accurately tell a person's age from a physical examination as different people age at different rates. But it's worse than that as the same person ages at different rates at different times as well. Also what you are exposed to can make you age differently too. Aging is really really complex. The only way to avoid it it to die, and once you're dead it's hard to do anything else. People get all bothered if dead people get up and start doing things. mountaineirc1969, Wed, 21st Apr 2010

Wouldn't this only tell us who was born after 1945? If a person born before 1945 is still alive today we can assume they lived through the entire era of nuclear testing, so logic would dictate that all of these people would have the same level of carbon 14 relative to where they lived. So a person born in 1915 living in Portland, Or would have very smiler levels to someone born in 1944 living in Portland. mountaineirc1969, Thu, 29th Apr 2010

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