Public Release:  NPL and SUERC calibrate a 'rock clock'

This will help geologists temporally dissect Earth's history more faithfully

National Physical Laboratory

New research by the National Physical Laboratory (NPL) and the Scottish Universities Environmental Research Centre (SUERC) will improve the accuracy of estimates of the time of geological events. The work centres on the calibration of one of the world's slowest clocks, known as the 'argon-argon clock'.

The 'argon-argon clock' works by measuring the ratio of the amount of radioactive potassium in a sample of rock to the amount of its decay product, argon. As scientists already know the half-life of this radioactive decay (1.25 billion years), it can be used to date rocks back to the time of the formation of the Earth, 4.5 billion years ago. The older a rock is, the more potassium has decayed and the more argon is found in the rock.

The effect of the new research varies from one rock type to another, but could mean up to a 1.2 per cent difference in a rock's age from the original calculation.

"One per cent change in the accuracy of an age doesn't sound like a lot, but when aiming for 0.1 per cent precision through geological time it is a very significant breakthrough," said Darren Mark at the SUERC, who worked with NPL on the research.

"For example, this will help with establishing eruptive histories and predicting the future behaviour of young volcanoes, such as the inhabited British overseas territory Tristan da Cunha in the South Atlantic Ocean."

The discovery came about as part of an unrelated NPL research project to measure the Boltzmann Constant. The Boltzmann Constant links the magnitude of a degree Celsius to the amount of energy held by the molecules of a substance.

To measure the Boltzmann researchers needed to build the world's most accurate thermometer which works by measuring the speed of molecules in argon gas. But to understand their results they had to measure the isotopic composition of their samples of argon gas. After searching the world for collaborators, NPL enlisted the help of Darren Mark and Fin Stuart of the Natural Environment Research Council's Argon Isotope Facility (AIF). Darren and Fin are the 'parents' of ARGUS - the most accurate mass spectrometer for argon isotope measurements in the world.

During the course of their research, they came across an unexpected result. The measurements they made using ARGUS were so precise that they allowed the team to draw conclusions about the isotope distribution of atmospheric argon. This is used to calibrate noble-gas mass spectrometers and so is responsible for the calibration of all 'argon-argon' dating that takes place throughout the world.

The results show that Alfred Nier, a great American physicist of the 1950s, was slightly in error with his measurements of argon. The data revealed that the correct measurement was achieved in 2006 by researchers in South Korea and North America.

"This work shows the power of precision measurement," said Michael de Podesta, who led the research efforts at NPL. "Many people think precision measurement is just about adding another decimal place to a number. But it's far more exciting than that. It's more like getting a sharper lens on a camera. It allows us to see the world more clearly and, when we look closely, we are never quite sure what we will find."

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About NPL

The National Physical Laboratory (NPL) is one of the UK's leading science facilities and research centres. It is a world-leading centre of excellence in developing and applying the most accurate standards, science and technology available.

NPL occupies a unique position as the UK's National Measurement Institute and sits at the intersection between scientific discovery and real world application. Its expertise and original research have underpinned quality of life, innovation and competitiveness for UK citizens and business for more than a century:

• NPL provides companies with access to world leading support and technical expertise, inspiring the absolute confidence required to realise competitive advantage from new materials, techniques and technologies

• NPL expertise and services are crucial in a wide range of social applications - helping to save lives, protect the environment and enable citizens to feel safe and secure. Support in areas such as the development of advanced medical treatments and environmental monitoring helps secure a better quality of life for all

• NPL develops and maintains the nation's primary measurement standards, supporting an infrastructure of traceable measurement throughout the UK and the world, to ensure accuracy and consistency.

http://www.npl.co.uk

About SUERC

SUERC, The Scottish Universities Environmental Research Centre, is a collaborative research facility operated jointly under a Consortium agreement between the University of Glasgow and Edinburgh University. It hosts five Natural Environment Research Council (NERC) Facilities that are available to UK scientists through competitive application to the relevant Steering Committees. The SUERC Accelerator Mass Spectrometer Laboratory is recognised by NERC as a suitable facility to undertake NERC-funded science.

SUERC's mission is to perform, stimulate and support high quality basic, applied and strategic research, within the Scottish University community and beyond, in the Earth, Environmental and Biomedical Sciences through development and maintenance of high-end analytical facilities, inter-disciplinary exchange and collaborative interaction. SUERC provides a focus in Scotland for high quality research through its own research programme and by assisting partner universities successfully to bid for research grants and deliver research outputs. Through teaching and training, SUERC contributes to the future supply of highly able scientists.

http://www.gla.ac.uk/departments/suerc/

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