Britain has an unparalleled studied record of fossil-rich terrestrial sediments from the Quaternary, a period that includes relatively long glacial episodes – known as the Ice Age --interspersed with shorter ‘interglacial’ periods where temperatures may have exceeded present day values.

However, too often the interglacial deposits have proved difficult to link to global climatic signals because they are just small isolated exposures, often revealed only by quarrying.

Using amino acid racemization ( transformation of one half of molecules of an optically active compound into molecules having exactly the opposite configuration, with complete loss of rotatory power because of statistical balance between equal numbers of dextro- and levorotatory molecules) as the new method is called, it will be possible to link climatic records from deep sea sediments and ice cores with the responses of plants and animals, including humans, to climate change over the last three million years.  The research is published in the latest issue of Nature.

The new method was developed by (left)  Dr Kirsty Penkman, of theDepartment of Chemistry, alongside Prof. Matthew Collins ( right) of the Department of Archaeology at York, and measures the the extent of protein degradation in calcareous fossils such as mollusc shells. 

It is based on the analysis of intra-crystalline amino acids – the building blocks of protein - preserved in the fossil opercula (the little ‘trapdoor’ the snail uses to shut itself away inside its shell) of the freshwater gastropod Bithynia.  It provides the first single method that is able to accurately date such a wide range of sites over this time period.

Dr Penkman said: "The amino acids are securely preserved within calcium carbonate crystals of the opercula. This crystal cage protects the protein from external environmental factors, so the extent of internal protein degradation allows us to identify the age of the samples.  In essence, they are a protein time capsule.

“This framework can be used to tell us in greater detail than ever before how plants and animals reacted to glacial and interglacial periods, and has helped us establish the patterns of human occupation of Britain, supporting the view that these islands were deserted in the Last Interglacial period.”

In a close collaboration with palaeontologist Dr. Richard Preece (left) in the Department of Zoology at the University of Cambridge, the study examined a total of 470 fossil remains from 71 sites in the UK and three on continental Europe.

The method proved highly reliable with more than 98% of samples yielding useful results, resulting in the largest British Pleistocene geochronological programme.

Professor Collins said: "When we started this work 11 years ago, we thought it was going to be relatively straightforward to identify a good material for dating, but the first 3 years of research on shells showed that the stability of the mineral itself was vital. The tiny trapdoor of a snail proved to be the key to success."

Dr Preece adds: “Luckily, fossil opercula are common in Quaternary sediments around the world, so the new technique can be used to build regional Ice Age chronologies everywhere, giving it enormous international scope”.

Vital to the study were the inter-disciplinary collaborations with Quaternary scientists, the core team of which involved researchers at the Department of Geography, University of Durham; Institute of Archaeology and Antiquity, University of Birmingham; Institute of Archaeology, University College London; the Netherlands Centre for Biodiversity, Leiden and the Department of Palaeontology, The Natural History Museum.

The analyses were funded by English Heritage, Natural Environment Research Council and the Wellcome Trust. The research is a contribution to the Ancient Human Occupation of Britain (AHOB) project funded by the Leverhulme Trust.

FOOTNOTE: Pleistocene snail survivors

This Ice Age snail was known only in fossils until examples were discovered alive in 1972. The species persists on steep slopes in Iowa and Illinois where cracks in the limestone act as cool-air vents. Naturally air-conditioned at 15° to 50°F, these micro-habitats mimic Pleistocene conditions, but logging and erosion threaten change.

This is a true relict species, left over from an age when glaciers dominated North America. Today it can survive only in vents in the sides of a few hills in the Midwest. Hot air literally kills it, so moving these animals, even for a few minutes, is out of the question. The entire photo set up consisted of a flash, a macro lens, and a piece of white plastic stuck in a cracked rock. That they're the size of a pencil lead adds to the fun of trying to photograph them. - Courtesy: Joel Sartore.