Scientists Say: Decay

This word refers to the breakdown of material

When the old fruit on your counter starts to rot, it is undergoing decay. Another kind of decay happens inside unstable, or radioactive atoms.

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Decay (noun, verb, “dee-KAY”)

The word “decay” can be a verb or a noun. The verb means to break down. The noun is the process or product of that breakdown.

In the life sciences, decay usually refers to a process also known as rot. Rotting fruit in the compost bin is undergoing decay. So is a tooth that has a cavity. When a living thing dies, its tissue becomes food for decomposers. These organisms include worms, insects and microbes. They break down big molecules in the dead matter into simpler compounds. Such decay products include carbon dioxide and water. Living things can then use those compounds to grow. But not all materials decay easily. Plastic, for instance, is hard for microbes to digest. As a result, most plastic trash is long-lasting.

In the physical sciences, decay also describes a breakdown of matter. But this breakdown happens on a much smaller scale. In fact, it happens to individual atoms. It is called radioactive decay. This kind of decay happens to unstable forms, or isotopes, of chemical elements. Examples include carbon-14 and uranium-238. In radioactive decay, an unstable atom spits out smaller particles. That process transforms the atom from an unstable isotope into a stable one.

An unstable, or radioactive, isotope always decays at the same rate. That rate is measured in terms of a “half-life.” An isotope’s half-life is how long it takes for half of the unstable atoms in a sample to decay. Some half-lives are mere seconds. Others are billions of years. Knowing an isotope’s half-life can help date objects — such as old rocks or bones — that contain the isotope.

In a sentence

The decay of radioactive uranium recently helped date some of the world’s oldest cave art, found in Indonesia.

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Maria Temming is the assistant editor at Science News for Students. She has bachelor's degrees in physics and English, and a master's in science writing.

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