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Biological anthropologists deal primarily with the evolution of humans and primates. "Present" is academically defined as the year 1950 (the year when this term was invented).

Linguists study languages, especially their development and their function within human culture. Back dirt - The excavated, discarded material (sediment, dirt) from a site that has generally been sifted for artifacts and is presumed to be of no further archaeological significance.

In living organisms, which are always taking in carbon, the levels of carbon 14 likewise stay constant.

But in a dead organism, no new carbon is coming in, and its carbon 14 gradually begins to decay.

Back in the 1940s, the American chemist Willard Libby used this fact to determine the ages of organisms long dead.

Most carbon atoms have six protons and six neutrons in their nuclei and are called carbon 12. But a tiny percentage of carbon is made of carbon 14, or radiocarbon, which has six protons and eight neutrons and is not stable: half of any sample of it decays into other atoms after 5,700 years.

Alluvial Deposit - Soil deposited by running water, such as streams, rivers, and flood waters.

Many ancient peoples, such as the Egyptians living along the Nile, depended on annual floods and alluvial deposits to replenish the soils they were farming.

Aerial Photography - The various techniques of taking photographs of natural or cultural features from the air, using balloons, airplanes, satellites, and other sources, in order to study the features in their entirety from a top-down (bird's eye) view.

Alloys are often stronger and more durable than pure metals.

Bronze is an alloy of copper and either zinc or tin.

In the United States, anthropology is divided into four sub-disciplines: archaeology, biological/physical anthropology, cultural anthropology, and linguistics.

All the sub-disciplines study aspects of past or present humans.

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