Radiocarbon dating is used to determine the age of carbon-bearing material by measuring its radiocarbon, the radioactive isotope carbon-14 (with six protons and eight neutrons). Invented by Willard Libby in the late 1940s, the method soon became a standard tool for archaeologists. Radiocarbon is constantly created in the atmosphere, when cosmic rays create free neutrons that hit nitrogen. Plants take in carbon, including radiocarbon, through photosynthesis, and after an animal or plant dies, it stops exchanging carbon with its environment. Half of the radiocarbon decays every 5,730 years; the oldest dates that can be reliably measured by radiocarbon dating are around 50,000 years ago. Atmospheric radiocarbon was reduced starting in the late 19th century by fossil fuels, which contain little detectable radiocarbon, but nuclear weapons testing reversed that trend, almost doubling it by 1963. Accelerator mass spectrometry has become the method of choice for radiocarbon dating; it can be used with samples as small as plant grains. Libby received the Nobel Prize for his work in 1960.

Read more: https://en.wikipedia.org/wiki/Radiocarbon_dating

_______________________________ Today's selected anniversaries:

1663:

King Charles II of England granted John Clarke the Rhode Island Royal Charter, described by one historian as "the grandest instrument of human liberty ever constructed." https://en.wikipedia.org/wiki/Rhode_Island_Royal_Charter

1709:

Great Northern War: Peter I of Russia defeated Charles XII of Sweden in Poltava, effectively ending Sweden's role as a major power in Europe. https://en.wikipedia.org/wiki/Battle_of_Poltava

1808:

Joseph Bonaparte approved the Bayonne Statute, a royal charter intended as the basis for his rule as King of Spain during the Peninsular War. https://en.wikipedia.org/wiki/Bayonne_Statute

1947:

After various news agencies reported the capture of a "flying disc" by U.S. Army Air Force personnel in Roswell, New Mexico, the military stated that what was actually recovered was debris from an experimental high-altitude surveillance weather balloon. https://en.wikipedia.org/wiki/Roswell_UFO_incident

2011:

Space Shuttle Atlantis was launched in STS-135, the final mission of the U.S. Space Shuttle program. https://en.wikipedia.org/wiki/STS-135

_____________________________ Wiktionary's word of the day:

maw: 1. The upper digestive tract (where food enters the body), especially the mouth and jaws of a ravenous creature. 2. Any great, insatiable or perilous opening. https://en.wiktionary.org/wiki/maw

___________________________ Wikiquote quote of the day:

Bring me your children hither. … Unto this twain, man-child and womanchild, I give the passion of this element; This seed of longing, substance of this love; This power, this purity, this annihilation. Let their hands light the altar of the world. 'T is yours forever. I have brought it home!   --William Vaughn Moody https://en.wikiquote.org/wiki/William_Vaughn_Moody