Flashcards for the Record of Time
Topics 4-5:  Chronometric Techniques
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The study of annual growth-rings of trees, usually for the purpose of chronometric dating logs and, subsequently, human remains and artifacts found in association with them.

dendrochronology or tree-ring dating

A chronometric dating method based on the fact that the magnetic north and south poles periodically reverse. A permanent record of these reversals can be found in the thermoremnant magnetism of volcanic rock deposits. When fossils are found sandwiched between such volcanic layers, they can be dated by association--i.e., a minimum and a maximum age can be assigned.

Paleomagnetic dating (or geomagnetic reversal time scale dating or geomagnetic polarity time scale dating)

A chronometric dating method based on the fact that amino acids progressively change to mirror image forms following the death of an organism--i.e., from L-amino acid to D-amino acid forms.

amino acid racemization dating

Magnetic fields that are altered or formed in atoms of iron by heat in excess of 1100°F. (600°C.). Such fields line up with the magnetic field of the Earth at the time of the exposure to a high temperature. They will remain oriented to that direction indefinitely despite the fact that the true position of magnetic north wanders over thousands of miles around the rotational north pole and even reverses with the magnetic south pole over longer periods of time.

thermoremnant magnetism

The point on the northern extremity of the earth where the axis of rotation is located. Compared to the magnetic north pole, this one is relatively stable.

rotational north pole

A term referring to techniques for chronometric dating based on known half-lives of particular isotopes or the rate of other cumulative changes in atoms resulting from radioactivity. Examples include electron spin resonance, fission track, potassium-argon, radiocarbon, and thermoluminescence dating.

radiometric dating

A radiometric dating method based on the fact that potassium-40 in volcanic rock decays into argon-40 and calcium-40 at a known rate. Chronometric dates are determined by measuring the amount of argon-40 in a sample.

potassium-argon dating (K-Ar dating)

A radiometric dating method based on the fact that the amount of carbon-14 steadily decreases in all organisms after death. This technique is used to provide chronometric dates for organic materials such as bone, shell, wood, and charcoal.

radiocarbon dating (carbon-14 dating)

The process by which plants, algae, and some bacteria use energy from sun light to create new organic molecules out of carbon dioxide and water.

photosynthesis

The amount of time for half of the atoms of a radioactive element in a sample to decay, or fission. The reduction in the number of atoms follows a geometric scale.

half-life

A dating technique using a research instrument primarily employed in physics to accelerate streams of charged subnuclear particles to high velocities in order to sort and analyze them. This technique is now also used to count individual carbon isotope atoms for radiocarbon dating. The advantage of this technique over the conventional radiocarbon method is that it requires a far smaller sample size and can potentially provide dates going back to around 100,000 B.P.

accelerator mass spectrometer dating (AMS dating)

A radiometric dating method based on the fact that when trace amounts of uranium-238 decay, there is a release of highly energy-charged alpha particles which burn narrow tracks, or damage trails, through glassy materials like obsidian (i.e., volcanic glass).

fission track dating

A radiometric dating method based on the fact that background radiation causes electrons to separate from their atoms and become trapped in the crystal lattice of minerals. When heated to high temperatures, the trapped electrons are released and they give off energy in the form of light. The characteristic of that light is measured to determine the age of the sample. This technique is mainly used to date pottery and rock that previously had been in an intense fire.

thermoluminescence dating (TL dating)

A radiometric dating method based on the fact that background radiation causes electrons to separate from their atoms and become trapped in the crystal lattice of minerals. This progressively alters the magnetic field of the material at a predictable rate. The magnetic field of the atoms in a sample is measured to determine the age. This technique is employed primarily to chronometrically date calcium carbonate in limestone, coral, teeth, and egg shells.

electron spin resonance dating (ESR dating)

Any of two or more forms of an element that differ in terms of atomic mass but have the same atomic number--for example, carbon-12 and carbon-14.

isotope