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Today, radiometric dating is considered a very reliable dating method, and the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself.
Carbon is the basic building block of organic compounds and is therefore an essential part of life on earth.
Carbon (meaning all three isotopes) is absorbed by living organisms, and continuously replenished during their life cycle. Radiocarbon dating was developed in the 1950s, with Willard Libby receiving the 1960 Nobel Prize in chemistry for the use of 14C to determine age in archaeology, geology, geophysics and many other branches of science.
Three rings variations: 1 - first year of growth, 2 - rainy season (thiker ring), 3 - dry season (narrower ring), and 4 - a scar from a forest fire.
The dendrochronology involves obtaining a horizontal cross-section of the main trunk of a tree and analysing the visible rings caused by the natural plant growth. Many prehistoric cavern paintings dating up to 30,000 years ago, have been investigated using radiocarbon dating, because the materials used are mostly of organic origin. The tree-ring technique is useful for calibrating the 14C method up to about 11,000 years.
During their lifetime, corals absorb the uranium (with a half life of 245.5 years) present in the seawater but they do not absorb the thorium (230Th). However, thorium is also radioactive and decays (half life 75,380 years) into other elements via a long decay chain, finally ending with lead, which makes the dating process a little more complicated. Pierre and Marie Curie noted that some glass containers in their laboratory gained intense colour when hit by radiation, and that these colours disappear with simultaneously emission of light when the material is heated. It was shown that the intensity of the emitted light is directly proportional to the radiation that the mineral has received. This technique has many applications - such as the dating of heated flint, pottery and ceramics of prehistoric periods. Above: radon radiation gives a blue tint to a glass recipient from Pierre and Marie Curiea€?s laboratory.
Below: Skeletons of a woman and of a child dated by thermoluminescence to be 92,000 years old.
The K-Ar method is well suited to study volcanic activity, and given that 40K has a half-life of 1.3 billion years, the method is used in geochronology to date periods ranging from 106 to 109 years back. An interesting story is how Rb-Sr dating helped to determine the origin of the king Yax K’ uk Mo, who founded the dynasty that ruled the Mayan city of CopA?n (presently in Honduras) for 400 years. In the 8th century, a modest village in Mesoamerica by the name of CopA?n (located in present-day Honduras) became one of the most important Mayan cities. At the time, Teotihuacan was at its height, the largest city in pre-Colombian Mesoamerica of the valley of Mexico.


The Yucatan peninsula where king Yax K’ uk Mo lived and died is made mostly from marine sediments. Strontium is chemically close to calcium and can replace it in enamel and dentin of the teeth and in the bones. Which isotopic systems are most useful for radiometric dating and what are the limitations of each? What is the Concordia, how is it used, and what information can be obtained from discordant dates?
Carbon is only absorbed by living organisms (or rather things that were alive at some time) such as wood or fossils so it can’t be used to date stone or pottery for example, and the method is accurate only for objects up to about 60,000 years old.
These rings result from the change in growth speed through the seasons of the year, with each ring usually marking the passage of one year in the life of the tree. In September 1991 two mountain hikers discovered the body of a man sticking half-way out from the ice in a mountainous region of the Alps. The analysis of cereals found in the bowels as well as of minerals in the hair led to the conclusion that A–tzi was coming from south Tyrol when trapped by snow and ice.
After the corals die, the Uranium decays into 230Th, which accumulates in their skeleton. The U-Th method can be used to date subjects with ages ranging between 10,000 and 500,000 years. Recent studies have shown that lead can be produced via neutron capture and may not have originated from uranium decay. Many crystalline materials such as some minerals have this property of emitting light when heated.
Thus, thermoluminescence can be used for dating objects that have been exposed to cosmic rays or to radiation from the ground, since the doses depend on the object's age. The other Sr isotopes (A = 84, 86, 88) are stable, so strontium is a useful tracer for the age and rubidium content in rocks, and has also been used to date lunar samples. Oxygen enters the body through the water supply, and rain from clouds near the ocean is richer in 18O than the rain from clouds that have travelled far inland. Instead, it was concluded than the he spent his early years near Tikal and moved later to CopA?n.
Because radioactive elements have various half-lives, there are numerous different methods that apply to different timescales.
14C is produced by cosmic rays in the atmosphere and then distributed in nature (93% in the ocean, 5% in the biosphere and 2% in the atmosphere). This means that the flux of cosmic rays impinging on the atmosphere varies, and therefore so does the 14C production rate.


This technique works best in temperate climates where the seasons differ more markedly, and, obviously, one can only date back a few hundred years as very old trees are rare. The iceman, later nicknamed A–tzi after the mountain range where he was found, might have died more than 4000 years ago.
When translated into the calibrated age with the help of tree-rings technique curves, A–tzi appears to be about 650 years older.
He had eaten porridge of einkorn (a type of wheat), vegetables and meat recently before his death. Three hundred years after this discovery, scientists have learned how to explain this effect. Artisans from CopA?n depicted Yax K’ uk Mo with Teotihuacan trappings, apparently indicating the king's origins and association with Teotihuacan.
The valley of Mexico is made of volcanic rocks, and there the variation is larger, while at Teotihuacan, the value is lower (0.7046). Thus a person's tooth enamel bears the isotopic signature of the food and water of their early childhood country, isotope ratios in dentin and bones reflect their later whereabouts.
Among the best-known techniques are radiocarbon dating, uranium-lead dating and potassium-argon dating.
By measuring how much 14C is left undecayed at a given moment in time, one can work out how long ago the organism has died. Moreover, by analysing the isotopes of carbon and oxygen in the teeth and bones of the iceman, the researchers were able to differentiate the country of his early childhood from that where he lived later. When the material is exposed to high energy radiation, the electrons in the material move into an excited state. With the 87Rb - 87Sr method it is possible to date materials aged between 10 million and 10 billion years.
We also know that he was a 45 year old man with shoulder length, dark, wavy hair and he had blue eyes.
In some minerals, this energy is then trapped inside due to defects in the crystal lattice. But when the crystal is heated, the electrons can drop into the lower energy shells, emitting a photon at each such transition. Enamel mineralises when the tooth grows in the childhood, dentin as bones form continuously during the life.



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