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.
An age determination technique in which the amount of light energy released in a pottery sample during heating gives a measure of the time elapsed since the material was last heated to a critical temperature.
The older a piece of pottery, the more light produced.
These ages are also consistent with the faunal and microfaunal.
The north African site of Jebel Irhoud contains one of the earliest directly dated Middle Stone Age assemblages, and its associated human remains are the oldest reported for H. The emergence of our species and of the Middle Stone Age appear to be close in time, and these data suggest a larger scale, potentially pan-African, origin for both.
For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years.
However, by itself a fossil has little meaning unless it is placed within some context.
Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.
Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.
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.These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth's surface is moving and changing.