The origin of…Half-life

“I think money is due for some sort of collapse. People are going to realize that money has a half-life, like radioactive elements.” Douglas Coupland

Post 40 Half-life

Half-life is often used to measure how long it takes for a radioactive element to lose its radioactivity and to date fossils. It is the time it takes for one half of a radioactive element to decay into a daughter isotope. Ernest Rutherford first used the term in 1907 when he discovered the principle.
As radioactive isotopes decay, they lose their radioactivity and develop into a new element, the daughter isotope. By measuring the ratio the amount of the original element to the daughter isotope, scientists can determine how many half-lives the element already has experienced and calculate the age of the element.

So, to calculate the age of a human skeleton you can do the following. As soon as a living organism dies, it stops taking in new carbon. The best elements to calculate the age of a human bone are carbon-12 and carbon-14. As the dead organism decays, the carbon-14 is not replaced, but decays with its half-life of 5,700 years. The amount of carbon-12 remains the same. So, when looking at the ratio of carbon-12 to carbon-14 and comparing it to the ratio in a living organism, you can define the age of the dead organism. Because of its half-life of 5,700 years, carbon-14 is only useful to date back fossils up to 60,000 years old.
Other radioactive elements used to date fossils are Potassium-40 (half-life of 1.3 billion years), Uranium-238 (half-life of 4.5 billion years), Thorium-232 (half-life of 14 billion years) and Rubidium-87 (half life of 49 billion years).

There is also the concept of biological half-life, which is the time it takes for a substance to lose half of its activity. For example, the half-life of morphine in the human body is 2 to 7 hours, water 9-14 days days and Polonium 30 to 50 days.

Half-life:
1. the time required for half of something to undergo a process as:
a. the time required for half of the atoms of a radioactive substance to become disintegrated
b. the time required for half the amount of a substance (as a drug, radioactive tracer, or pesticide) in or introduced into a living system or ecosystem to be eliminated or disintegrated by natural processes
2. a period of usefulness or popularity preceding decline or obsolescence (source: Merriam Webster).

The English word half comes from Old English half, halb (Mercian), healf (W. Saxon), side/part, not necessarily of equal division (original sense preserved in behalf), from Proto-Germanic *halbas, something divided, perhaps from Proto Indo European (s)kel-, to cut. The word life comes from Old English life, existence/lifetime/way of life/condition of being a living thing/ opposite of death, from Proto-Germanic *libam, continuance/perseverance, from Proto Indo European *leip-, to remain/persevere/continue/stick/adhere.
Dutch halverings comes from half and has the same origins as the English half. Tijd comes from Middle Dutch tijt, time/period/season, from Proto-Germanic *tīdi-, probably from Proto Indo European *dih2-ti, to divide.
Spasish periodo comes from Latin periodus, period, from Greek periodos, from peri, around, and hodos, road/trip. The word semi, comes from Latin semi, half, and desintegración comes from the words des, meaning a reversal, and ingegración, which is compiled of the prefix in, a negation, tangere, to touch/reach, and the suffix ción, action/effect.
Italian emivita, is composed of emi, a Greek prefix meaning half, and vita, from Latin vita, life.

Half-life in other languages:
Dutch: de halveringstijd (or halfwaardetijd)
Spanish: el periodo de semidesintegración
Italian: l´emivita (or tempo di dimezzamento)

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