Chronometric dating techniques are based on

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.

Other problems of contamination have occurred, so the technique is not fully established.

Many new techniques are being developed and tested.

CATEGORY: technique DEFINITION: Borings taken from the Arctic and Antarctic polar ice caps, containing layers of compacted ice, useful for the reconstruction of paleoenvironments and paleoclimatology and as a method of .

Clay and rocks contain magnetic minerals and when heated above a certain temperature, the magnetism is destroyed.

Upon cooling, the magnetism returns, taking on the direction and strength of the magnetic field in which the object is lying.

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