New dating technique with sand grains

November 15, 2002

In a Technology Foundation STW project at the University of Groningen, researchers have successfully determined how long ago a number of sand grains were last exposed to sunlight. The dating method is useful for mapping the transport of sand along the coast. Forensic science may also benefit from this technique.

Sand that is deposited along the coast contains the mineral zircon (zirconium silicate). Zircon is often 'contaminated' with the trace elements uranium and thorium. The impurities emit alpha radiation and this damages the crystal structure of the zircon sand grains. The longer the irradiation period the greater the damage to the mineral. However, sunlight or heating to several hundred degrees Celsius repairs the damage. Beach sand which lies on the surface will therefore exhibit little damage, whereas sand which lies deeper will exhibit more.

In a Technology Foundation STW project under the leadership of Prof. H.W. den Hartog, researchers from the University of Groningen have developed a method to measure the damage in zircon and thus to determine the age of sand sediments. Carefully selected zircon sand grains are heated, thereby repairing the damage in the zircon. This is associated with the emission of visible light (thermoluminesence). The greater the amount of damage repaired, the greater the intensity of the light emitted. Zircon grains from old sentiments which were last exposed to sunlight a long time ago, will have been irradiated by alpha radiation for longer and will therefore exhibit much damage and thus produce much light.

Only zircon grains which are transparent are suitable for the dating method. These do not absorb the light from the thermoluminesence. The researchers developed a new selection installation to select these 'zircon jewels' from the zircon fraction in the sand, in which coloured and sometimes dark grains with much irreparable damage occur. An electrical technique separates ideal, clear, electrically non-conducting zircon grains from unsuitable, dark and coloured, electrically conducting zircon grains which disrupt the dating process.

Using zircon it might in future be possible to date sand grains with ages up to 100,000 years. The method can be used worldwide, because zircon occurs in almost all sediments. The researchers suspect that all sediments aged at least one year or more can be dated. In addition to this there are promising possibilities for forensic dating research. Using this technique the scene of a crime can be dated. For example, in the case of illegal dumping or if detectives are looking for information about the moment at which objects were buried.

The researchers have already tested the method. They took a 175-year-old sand sample from the Zwanenwater dunes on Ameland (The Netherlands). The zircon dating method gave an age of 177 years.
Further information can be obtained from Prof. H.W. den Hartog (Laboratory for Solid State Physics, University of Groningen), tel. +31(0) 50 3634789, fax +31 (0)50 3634879, e-mail

The research was funded by the Netherlands Organisation for Scientific Research (NWO).

Netherlands Organization for Scientific Research

Related Sunlight Articles from Brightsurf:

This white paint keeps surfaces cooler than surroundings, even under direct sunlight
Scientists have developed a white paint that cools below the temperature of its ambient surroundings even under direct sunlight.

Radiative cooler that cools down even under sunlight
POSTECH-Korea University joint research team develops a non-energy consuming radiative cooling material.

Can sunlight convert emissions into useful materials?
A team of researchers at the USC Viterbi School of Engineering has designed a method to break CO2 apart and convert the greenhouse gas into useful materials like fuels or consumer products ranging from pharmaceuticals to polymers.

Breakthrough technology purifies water using the power of sunlight
A research team, led by Australia's Monash University, has been able to transform brackish water and seawater into safe, clean drinking water in less than 30 minutes using metal-organic frameworks (MOFs) and sunlight.

Study: A plunge in incoming sunlight may have triggered 'snowball earths'
Global ice ages may have been triggered by sharp declines in incoming sunlight, research finds.

Study: Reflecting sunlight to cool the planet will cause other global changes
Study finds reflecting sunlight to cool the planet will weaken extratropical storm tracks, causing other global changes.

How iron carbenes store energy from sunlight -- and why they aren't better at it
Photosensitizers absorb sunlight and pass that energy along to generate electricity or drive chemical reactions.

NTU Singapore scientists convert plastics into useful chemicals using sunlight
Chemists at Nanyang Technological University, Singapore (NTU Singapore) have discovered a method that could turn plastic waste into valuable chemicals by using sunlight.

Sunlight degrades polystyrene much faster than expected
Polystyrene persists in the environment for millennia, according to some international governmental agencies.

Sunlight degrades polystyrene faster than expected
A study published by researchers at Woods Hole Oceanographic Institution (WHOI) shows that polystyrene, one of the world's most ubiquitous plastics, may degrade in decades or centuries when exposed to sunlight, rather than thousands of years as previously thought.

Read More: Sunlight News and Sunlight Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to