Carbon Dating Process?

The basis of radiocarbon dating is simple: all living things absorb carbon from the atmosphere and food sources around them, including a certain amount of natural, radioactive carbon-14. When the plant or animal dies, they stop absorbing, but the radioactive carbon that they've accumulated continues to decay.

Dating techniques used by scientists-

* Age of rocks

* Fossils

* Artifacts

(1) Relative Dating, method tell only one sample is older or younger than another.

(2) Absolute dating method provide an approximate date in year.

(3) Carbon is one of the chemical element on the Earth.

(4) All carbon atom have a nucleus containing six protons and 99% of these also countoin six neutrons.

6 Proton + 6 Neutron = Carbon 12

(5) C12 and C13 are stable, but C14 is not.

(6) In any given mass of C-14, half of them will decay in 5730 years.

■ Dating techniques are procedures used by scientists to determine the age of rocks, fossils, or artifacts

■ Relative dating methods tell only if one sample is older or younger than another; absolute dating methods provide an approximate date in years

■ The latter have generally been available only since 1947.

■ Many absolute dating techniques take advantage of radioactive decay, whereby a radioactive form of an element decays into a non-radioactive product at a regular rate

■ Others, such as amino acid racimization and cation-ratio dating, are based on chemical changes in the organic or inorganic composition of a sample

■ Radiocarbon dating is a method that gives age estimates for carbon-based materials that originated from living organisms

■ Carbon is one of the many chemical elements on Earth

■ Carbon, along with hydrogen, nitrogen, oxygen, phosphorus, and sulfur, is a building block of biochemical molecules of life {fats, proteins, hormones etc.)

■ All carbon atoms have a nucleus containing six protons, and 99% of these also contain six neutrons. The 6 proton + 6 neutron atoms are said to have a mass of 12 and are referred to as "carbon-12"

■ What about other 1%? Their nuclei contain either seven or eight neutrons in addition to six protons. They have masses of 13 and 14 resp. and are referred to as "carbon-13" and "carbon-14." {isotopes)

■ 14C varies from 0.0000000001% {one part per trillion) down to zero

At Death

100% of C-14

5730 Year

50% of C-14

11460 Year

25% of C-14

17190 Year

12.5 of C-14

Maximum dating process is upto 50-70000 years and minimum is 100 years.

Dating Processes

Relative Dating Absolute Dating

Seriation Amino Acid Racimization
Faunal Dating Cation Ratio
Pollen Dating Redio active Decay
stratigraphy Tree rings

Relative dating determines if one sample is older or younger than another but does not provide an age in years.

1. Stratigraphy- is the study of layers of rocks or the objects embedded within those layers. Assumption is that deeper layers were deposited earlier, and thus are older, than more shallow layers. The sequential layers of rock represent sequential intervals of time.

2. Seriation-is the ordering of objects according to their age. Example: finding the chronological order of American Indian pottery styles in the Mississippi Valley. (How was it done? By analyzing their abundances through time, by counting the number of pieces of each style of the artifact in each stratigraphic layer and then graphing the data)

3. Faunal Dating is the use of animal bones to determine the age of sedimentary layers or objects such as cultural artifacts embedded within those layers. Works best if the animals belonged to species, which evolved quickly, expanded rapidly over a large area, or suffered a mass extinction.

4. Pollen Dating (Palynology) - Each year seed-bearing plants release large numbers of pollen grains, resulting in a "rain" of pollen that falls over many types of environments. Pollen that ends up in lakebeds or peat bogs is the most likely to be preserved, and a pollen chronology can be made by noting which species of pollen were deposited earlier in time (residue in deeper sediment or rock layers, than others). Pollen zones are translated into absolute dates by the use of radiocarbon dating.

Absolute dating tells how old a specimen is in years, and is carried out in a laboratory. Absolute dates must agree with dates from other relative methods in order to be valid.

1. Amino Acid Racemization requires a smaller sample than radiocarbon dating, and has a longer range, extending up to a few hundred thousand years. It has been used to date coprolites (fossilized feces) as well as fossil bones and shells. These specimens contain proteins embedded in minerals such as calcium.

2. Cation-Ratio dating dates rock surfaces such as stone artifacts and cliff and ground drawings. It can be used to obtain dates that would be unobtainable by more conventional methods such as radio-carbon dating. The principle is that the cation ratio (K+ + Ca2+)/Ti4+ decreases with increasing age of a sample.

3. Thermoluminescence dating is useful for determining the age of pottery. Electrons from quartz and other minerals in the pottery clay are bumped out of their normal positions (ground state) when the clay is exposed to radiation. It covers the time interval between radiocarbon and potassium-argon dating, or 40,000 - 2,00,000 years.

4. Tree-Ring dating is dendrochronology, and based on the fact that trees produce one growth ring each year. Narrow rings grow in cold and/or dry years, and wide rings grow in warm years with plenty of moisture. The rings form a distinctive pattern, which is the same for all members in a given species and geographical area. It has a range of 1 - 10,000 years or more.

5. Radioactive Decay dating is a group of related methods for absolute dating of samples, including Potassium-Argon Dating, Radiocarbon Dating and Uranium Series Dating.

1. Potassium-Argon Dating - When volcanic rocks are heated to extremely high temperatures, they release any argon gas trapped in them. As the rocks cool, argon-40 (40Ar) begins to accumulate. Argon-40 is formed in the rocks by the radioactive decay of potassium-40 (40K). The amount of40Ar formed is proportional to the decay rate (half-life) of40K, which is 1.3 billion years. In other words, it takes 1.3 billions years for half of the40K originally present to be converted into40Ar. This method is generally only applicable to rocks greater than three million years old, although with sensitive instruments.

2. Radiocarbon Dating - Radiocarbon is used to date charcoal, wood, and other biological materials. The range of conventional radiocarbon dating is 30, 000- 40, 000 years, but with sensitive instrumentation this range can be extended to 70, 000 years. Radiocarbon (14C) is a radioactive form of the element carbon. It decays spontaneously into nitrogen-14 (14N). While a plant or animal is alive, the ratio of14C/12C in its body will be nearly the same as the14C/12C ratio in the atmosphere. When the organism dies, however, its body stops incorporating new carbon. The ratio will then begin to change as the14C in the dead organism decays into14N.

3. Uranium Series Dating - Uranium series dating techniques rely on the fact that radioactive uranium and thorium isotopes decay into a series of unstable, radioactive "daughter" isotopes; this process continues until a stable (non-radioactive) lead isotope is formed. The daughters have relatively short half-lives ranging from a few hundred thousand years down to only a few years. The "parent" isotopes have half-lives of several thousand million years. This provides a dating range for the different uranium series of a few thousand years to 500, 000 years. Uranium series have been used to date uranium-rich rocks, deepsea sediments, shells, bones, and teeth, and to calculate the ages of ancient lake beds. The two types of uranium series dating techniques are daughter deficiency methods and daughter excess methods.

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