What is a half-life?
Quick Answer
A half-life is the time it takes for half of the atoms in a radioactive sample to decay. It ranges from fractions of a second to billions of years.
The Full Story
Radioactive atoms are unstable and decay at random, but a large group decays at a predictable rate. After one half-life, half the original atoms remain; after two, a quarter; after three, an eighth. Carbon-14 has a half-life of about 5,730 years, which makes it useful for dating once-living materials up to around 50,000 years old. Uranium-238 has a half-life of about 4.5 billion years, close to the age of Earth. The term is also used in medicine for how long it takes the body to remove half of a drug.
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Suggested video title for this topic:
"Nature's stopwatch — how half-lives let us date bones, rocks and the Earth itself."