Continuous cores, sometimes taken to the bedrock below, allow the sampling of an ice sheet through its entire history of accumulation.
Because there is no melting, the layered structure of the ice preserves a continuous record of snow accumulation and chemistry, air temperature and chemistry, and fallout from volcanic, terrestrial, marine, cosmic, and man-made sources.
Clay and rocks contain magnetic minerals and when heated above a certain temperature, the magnetism is destroyed.
If there has been significant change in the temperature during the time in which the object is buried, the result is flawed.
Other problems of contamination have occurred, so the technique is not fully established.
Other methods include: coin dating, seriation, and amino-acid racemization.
The methods have varying applications, accuracy, range, and cost.
The date on a coin is an absolute date, as are AD 1492 or 501 in which the proportion of carbon isotopes is counted directly (as contrasted with the indirect Geiger counter method) using an accelerator mass spectrometer.
The method drastically reduces the quantity of datable material required.Actual samples of ancient atmospheres are trapped in air bubbles within the ice. CATEGORY: feature DEFINITION: A pattern of parallel ridges resulting from the plowing of strip fields in medieval and later open field systems.The fossilized remains of ancient plowmarks are a common sight in England, having the appearance of long, rounded parallel ridges with alternating ditches., in which figures in solar years (often with some necessary margin of error) can be applied to a particular event.Unless tied to historical records, dating by archaeological methods can only be relative -- such as stratigraphy, typology, , fluorine and nitrogen test, and radiometric assay.Aspartic acid is the compound most often used because it has a of 15,000-20,000 years and allows dates from 5,000-100,000 years to be calculated.