Death of living tissue, usually within a limited area.

Cells die naturally after a period of time, but may also die as a result of injuries, infections, or cancer. Burns produce necrosis, and the bedsores suffered by nursing-home patients are a form of necrosis. The dreaded condition known as gangrene, in which the dying tissue turns black or green, is another form. When untreated, the dying cells release substances that lead to the death of surrounding cells, so untreated necrosis can lead to death. Treatment usually requires the removal of the *necrotic* tissue, and in severe cases can even involve amputating a limb.

The practice of *necromancy* goes back as far as the ancient Assyrians and Babylonians and has continued through all the centuries since. In the Middle Ages it became associated with black magic; condemned by the church, it had to be practiced secretly. In Europe a necromancer might work in a remote graveyard at night, standing within a magical circle he had drawn to shield himself from the anger of the spirits. The grave of a person who had died suddenly or violently might be plundered for its body parts; the unused energy these were believed to contain made them valuable in the *necromantic* ceremony. But body parts aren't essential to necromancy, which is now practiced by channelers, mediums, and shamans, and even by groups of amateurs sitting around a Ouija board.

A cemetery, especially a large, elaborate cemetery of an ancient city.

With its *-polis* ending, meaning “city” (see POLIS/POLIT), a *necropolis* is a “city of the dead.” Most of the famous necropolises of Egypt line the Nile River across from their cities. In ancient Greece and Rome, a necropolis would often line the road leading out of a city; in the 1940s a great Roman necropolis was discovered under the Vatican's St. Peter's Basilica. Some more recent cemeteries especially deserve the name necropolis because they resemble cities of aboveground tombs, a necessity in low-lying areas such as New Orleans where a high water table prevents underground burial.

An autopsy, especially one performed on an animal.

Human autopsies are generally performed either to determine the cause of death or to observe the deadly effects of a disease for research or education purposes. Autopsies may be necessary when tracking an epidemic; they're also performed to discover whether a death might actually have resulted from murder, and if so, what evidence it might reveal that could help catch the murderer. Animal necropsies are actually more common than human autopsies, since a farmer with livestock is always concerned that whatever killed one animal not pose a threat to the others.

Of or relating to the earliest period of the Stone Age, characterized by rough or chipped stone implements.

Since *lithos* means “stone” in Greek, the name Paleolithic was given to the older part of the Stone Age. The first known period of human culture, the Paleolithic actually covers almost all of human history, from the first use of stone tools around 2.5 million years ago until the invention of agriculture around 10,000 years ago. For almost all that time, humans used the very crudest of stone tools, produced by chipping away flakes of stone in order to make an edge for an ax or knife. Near the end of the period, animal bones and antlers were being used for tools, especially pointed tools, and sculpted figures and cave art were being produced. The Paleolithic gave way to the Mesolithic (“Middle Stone Age”) period, with its tools made of polished stone, wood, and bone.

(1) The study of ancient writings and inscriptions. (2) Ancient writings.

The world's oldest literature dates from about 4,000 years ago, from the land known as Sumer (now southern Iraq). Early writing took the form of pictographs, very simple pictures that first represented things or ideas and later came to represent actual words. The first actual alphabet, in which each character represents a sound, appeared in the same general region about 500 years later. But writing developed in very different ways in different parts of the world, and 1,000 years later, when Europeans first arrived in the New World, alphabetic writing still wasn't being used anywhere in the Americas. Decoding some ancient languages has proven to be a huge task for *paleographers*, and determining the age and the source of a piece of writing can pose major challenges.

A science dealing with the life of past geological periods as known from fossil remains.

Until the 1820s, hardly anyone even suspected that dinosaurs had ever existed. In the years since, paleontology has sought to discover the entire history of life on earth, from the era of single-celled organisms up into the human era. *Paleontologists* continue to make remarkable discoveries, such as that a huge meteorite that fell in the Gulf of Mexico wiped out the dinosaurs —all except the birds, the only surviving dinosaurs. “Radiometric dating” can reveal the age (often tens of millions of years) of a rock or fossil or a tiny grain of pollen by measuring how much its radioactive elements have disintegrated. The study of molecules of DNA, RNA, and proteins has also become important for dating. Paleontologists often consult with geologists searching for oil, gas, and coal deposits, since all these “fossil fuels” were formed from plant and animal remains.

The era of geological history, ending about 248 million years ago, in which vertebrates and land plants first appeared.

The Greek root *zo-* means “animal,” so names such as Paleozoic were invented to refer to a period in the development of animal life. For geologists, the Paleozoic era is followed by the Mesozoic (*meso-* meaning “middle”), which is followed by the Cenozoic (*cen-* meaning “recent”). Eras are huge stretches of time; geologists break eras down into smaller “periods” and “epochs.” Thus, the Paleozoic ends with the Permian period, the Mesozoic ends with the Upper Cretaceous epoch, and the Cenozoic ends with the Holocene epoch—the epoch in which we are living. The Paleozoic era produced the first fish, the first land plants, the first insects, and the first amphibians and reptiles; the dinosaurs, birds, and mammals had to wait for the Mesozoic.