Dating:

Published November 5th, 2000 - 02:00 GMT

Dating methods used for geosciences cover events that occurred from hundreds to thousands of millions of years ago.  

 

Many stable, radiogenic or cosmogenic isotopes in the natural environment are used to provide absolute or relative dates.  

 

Different geological samples and environments require different dating techniques. For example, radiocarbon dating by accelerator mass spectrometry is used for organic materials from about 250-45,000 years old.  

 

The range of carbonaceous materials includes textiles, antiques, fine art, and archaeological artefacts. 

 

Accelerator mass spectrometry measures particles of high atomic mass such as beryllium-10, aluminium-26, chlorine-36, silicon-32, and other cosmogenic isotopes for geological dating and tracing.  

 

Beryllium and aluminium isotopes are particularly useful for dating surface rocks up to ten million years old, and the ages of rocks, and lake, river, and harbour sediments from the last 1000 years are estimated by lead-210 dating. 

 

Silicon-32 is useful for dating soils, groundwater and ice, and groundwater may also be dated and traced using tritium, which helps to define the resource. 

 

Potassium and argon isotopes are common in all igneous rocks and their proportions can date rocks and minerals that formed more than a million years ago.  

 

Proportions of rubidium to strontium isotopes are valuable dating techniques for materials older than ten million years. 

 

Isotopes of uranium have complicated radioactivity, and several dating methods are available for rocks and minerals older than one million years. 

( gns.cri.nz )  

 

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