Your guess
How old are the neurons in an adult's cerebral cortex?
A timestamp from the Cold War
Above-ground nuclear tests almost doubled the share of carbon-14 in the Northern Hemisphere's air by 1963; it has been falling ever since. Via plants and food it ends up in the DNA of every newly formed cell. Jonas Frisén's team at the Karolinska Institute in Stockholm reads from it when a cell was born.
How long cells live
The range runs from days to an entire life. About one in ten fat cells is replaced each year.
An average that misleads
In 2005 Frisén suggested the body's cells might be only 7 to 10 years old on average – which often became “everything is new every seven years”. But an average of gut-lining cells a few days old and neurons decades old says little about any one tissue. The heart replaces fewer than half its muscle cells in a lifetime.
Deep dive
A stamp made of neutrons
Carbon-14 forms all the time high in the atmosphere: cosmic rays produce neutrons that turn nitrogen-14 into carbon-14. Atomic bombs release neutrons too. Hundreds of above-ground tests from 1945 on, stepped up after 1950, almost doubled the share of carbon-14 in the air of the Northern Hemisphere. In 1963 the United States, the Soviet Union and the United Kingdom signed a treaty banning above-ground nuclear tests. Since then the share has fallen – quickly at first, then ever more slowly: the carbon-14 spreads into the oceans and plants, and since the 1980s it has mainly been diluted by CO₂ from coal, oil and gas, which contains no carbon-14.
Continues in the app
- Why DNA of all things
- Measuring almost nothing
- A project nobody wanted
- The heart: complete at birth
- Fat: the number is fixed early
- The brain: almost everything stays
- Teeth, two sisters and a tsunami
- A tool with an expiry date
- Quiz with 4 questions
- 4 key points to keep
