When a living thing dies, its body stops working, and a body that has died does not start working again. Every living thing, plant and animal alike, dies at some time. When a person dies, they no longer breathe, eat or sleep; beyond that, people and families believe different things about what death means, and that is a question to bring to the grown-ups in yours. The changes in a dead body begin almost at once: microbes living inside an animal's body start breaking it down almost immediately after it dies.
Insects are among the first to arrive at a dead animal, and as they eat, they help move nutrients into the soil. Blowflies are thought to double the rate at which a dead animal breaks down, and burying beetles coat a carcass in chemicals that suppress bacteria and repel ants. Many germs on a dead animal cannot survive passage through a vulture's highly acidic gut, so scavenging can reduce the spread of disease. A 1979 study estimated that vultures in Serengeti National Park, Tanzania ate about 14 million kilograms of meat a year, more than all the mammal meat-eaters there combined. That single figure shows how much work the scavengers of one park perform.
Composting turns decay into something a thermometer can follow. It lets tiny microorganisms break down materials like leaves and food scraps into compost, which feeds soil. Those microorganisms use carbon and nitrogen to grow and reproduce, water to digest materials, and oxygen to breathe, and a well-kept backyard compost pile can reach 130 to 160 degrees Fahrenheit. Worms can be counted, too. Of about 9,000 species of earthworms, only seven suit worm composting, and those worms eat about 25 percent of their weight each day.
On the deep sea floor, a dead whale becomes a long experiment in timing. This is called a whale fall. Scavengers eat the soft parts in a matter of months, and then different animals arrive; in shallow oceans a whale fall may vanish within a year or two, yet in deep water a skeleton can feed animals for years, even decades. Whale carcasses in Monterey Canyon are expected to decompose in under 10 years, while whale carcasses studied off Southern California may last 50 to 100 years. Microbes live off chemical energy from sulfides released as the bones decay, and they form the base of ecosystems for as long as the food lasts.
Bone-eating worms make an acid that dissolves the hard outer layer of whale bone, and Osedax worms are a foundation species for whale falls, not just another weird deep-sea animal. Each of the studied whale falls followed a different sequence of community development, with different key species. About four months after a whale died on Davidson Seamount, its carcass was crawling with octopuses, eelpouts, worms, grenadiers and crabs. And a whale fall found in 2009 off Canada was watched for over a decade, with tube worms still living on its jaw bone.
Trees keep their own ledger. Trees typically grow one ring each year, so each ring is one year of growth, and a wide ring means a year with plenty of moisture while a very narrow ring can mean a dry year. In spring the wood cells are large with thin walls and look light, and growth slows by late summer as the thicker-walled cells look darker. The ring pattern over a tree's whole life shows the climate it grew in, and scientists plotted ring widths to build the first chronologies, which let them mark exact calendar dates for each ring. NOAA's paleoclimatology archive holds the world's largest public collection of tree ring data, from more than 5,000 sites on six continents (as of November 2026).
Counting the rings of the long-lived requires care. A quahog clam grows a new ring on its shell each year: wide rings mean food-rich years and narrow rings mean years with less food. A clam called Ming was 507 years old when it died in 2006, and as of November 2026 it was the longest-lived single animal, not a colony, ever found. Its growth rings had become too compressed to count easily, so scientists counted in the hinge ligament and checked the age with methods including carbon-14. As of November 2026, the longest-lived non-colonial animal ever found is a quahog clam, Arctica islandica. Galapagos tortoises, by comparison, can live to be over a hundred years old, and one at the San Diego Zoo lived to an estimated 150.
Aging a shark takes a different tool. Usual ways of aging a species look at calcified tissue, so researchers used radiocarbon dating of eye lenses to find the average age. A study of 28 female Greenland sharks suggested an average lifespan of at least 272 years, and two of the sharks were estimated to be roughly 335 and 392 years old. A 2016 study made the Greenland shark the longest-lived vertebrate known as of November 2026. Because females are thought to mature at lengths above 4 meters (13 feet), the study put them at least 156 years old when they mature.
The method behind that shark estimate is worth understanding. Living things take in carbon-14 from the air, and when they die they stop taking it in, so the carbon-14 in them slowly changes into other atoms. Scientists estimate how long ago a living thing died by counting the carbon-14 atoms that remain. Carbon-14 has a half-life of about 5,730 years: half the atoms in a sample change into other atoms in that time. Radiocarbon dating works on anything that used to be alive, up to about 60,000 years old, but it does not work on rocks. Around 50,000 years ago only about 0.1 percent of the original carbon-14 is left, so about 10 half-lives is the limit of any radioisotopic dating method. Willard Libby proposed carbon dating in the journal Physical Review in 1946 and won the 1960 Nobel Prize in chemistry for it.
Most dead plants and animals decay or get eaten, so only some become fossils. A fossil often starts when a dead plant or animal is buried quickly by mud, sand or ash. Soft parts rot away and hard parts such as bones, teeth and shells are left behind. The layer of sediment protects remains from the elements, scavengers and even oxygen, and over time the mud and sand harden into rock, while water full of minerals soaks into the remains and can turn bones to stone. By far the most common fossils are those of shelled invertebrates, and fossils of land plants and animals are much scarcer than fossils of animals that lived in water. Fossils of soft tissue form only in special cases that often need rapid burial and low oxygen.
Most of what does not become a fossil is eaten or decays, and what decays helps make soil. Humus is dark, nitrogen-rich soil matter that forms when plant and animal matter decay, and it holds nutrients for plants. Soil organic matter acts like a sponge and can hold up to 90 percent of its weight in water, then release most of it. As organic matter decomposes, nutrients are cycled from organic forms into forms plants can take up. Dead wood does this slowly: it often takes several decades for a nurse log to decay completely. Death, measured this way, is a ledger kept in rings, isotopes and bones. If thinking about death raises questions or sad feelings, a parent, a teacher, a school counselor or another grown-up you trust can talk it through with you.
Words to know
- microbes: tiny living things
- carcass: dead animal body
- radiocarbon: carbon-14 dating
- chronologies: dated ring records
- sediment: settled mud, sand
