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The clock of life science

Have you ever wondered how scientists an archaeological dating?

First of all start by saying that the purpose of archaeological research is to establish scientifically the history and framework dating of the finds from the excavation.

Think what a mess it would be if we could not dating an object just found out: it would be devoid of interest.

What, then, means finding a date? It means give it a calendar date (eg, Caravaggio painted the "Rest on the Flight into Egypt" in 1594).

It also means establishing a time frame in which an event has occurred (eg, the last phase of reconstruction of Pompeii took place between 62 AD - the date of the earthquake - and 79 AD - the date of the eruption) .

The main difficulties relate primarily to dating prehistoric remains, as for they do not have data from historical documents, literary and numismatic and these findings can be attributed approximate age, a "chronology."

natural clock

Scientific methods of dating are based on the fact that some substances and (bone, wood, textile fibers, seeds, charcoal) , widely distributed in nature, behave as natural watches, that are transformed chemically and physically in time, according to strict rules and constant speed, then these changes can be measured to determine absolute dates.

CARBON NOBEL

One such method is known as a method of carbon-14 (it also writes 14 C) , or radiocarbon, which was conceived and developed between 1945 and 1955 by the American chemist Willard Frank Libby , that this discovery won the Nobel Prize in 1960 .

Carbon 14 is a radioactive isotope carbon found in nature. All living organisms continually exchange carbon with the atmosphere through the processes of respiration (animals) and photosynthesis (plants).

After the death of these processes end and this exchange does not happen anymore because when the body dies ¹⁴ C begins to decrease is no longer new in the life processes and that this turns into nitrogen (N).

therefore a measure the level of carbon 14 in organic remains allows a calculation of the age of the remains.

the half-life

^{The decay of 14 C} happens on a regular basis. The time for half of the atoms of decay is called half-life (time in which his half turns into nitrogen).

Libby indicated as half-life 5568 years, given that modern research has changed in 5,730 years . Considered as the percentage of ¹⁴ C in the atmosphere were to remain constant over time and how this concentration were to move uniformly in living organisms by carbon dioxide. For example, plants in the process of photosynthesis they absorb carbon dioxide, they are consumed by herbivores, which in turn are eaten by carnivores. Only the death of the animal or plant ceases taking ¹⁴ C, and its concentration, the first constant begins to decrease due to radioactive decay.

Knowing the rate of decay of ¹⁴ C and measuring the amount remaining than remaining in the sample, one can determine the age of death, and therefore, less ¹⁴ C is present, the finding is more ancient. 

The major advantage is that this method can be adopted everywhere, provided organic material is available, but the rapid decay of carbon makes the application of this method is limited to the dating of objects between the ages of 50,000 and 100 years (although with modern techniques and sophisticated, it is sometimes possible to extend the ' time about 70,000 years), it remains too old would make no ¹⁴ C, since this is now completely fallen in nitrogen.

The dates obtained by this method are always accompanied by an estimate of uncertainty due to counting errors, the percolation of water (water-soaked sites may also dissolve the organic materials and deposit them, changing the isotopic composition ), and other situations that make inaccurate measurements.

Anna Picchi