Amino acid time capsule

An amino acid time capsule could help scientists link climatic records from deep sea sediments and ice cores with the response of plants and animals in the Quaternary period in Britain.

A freshwater snail shell (top) and the opercula (bottom) Credit Dr Richard Preece

Researchers from the University of York have developed a new method called amino acid racemisation which measures the extent of protein degradation in calcareous fossils, like the freshwater snail. It analyses the intra-crystalline amino acids preserved in the fossil opercula – the trapdoor the snail uses to shut itself away inside its shell.

“The amino acids are securely preserved within calcium carbonate crystals of the opercula,” said Dr Kirsty Penkman from the department of chemistry. “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.”

The method is the result of over a decade of collaborative study with Professor Matthew Collins from the department of archaeology. Collins said they thought identifying a good material for dating would be straightforward, but research showed the stability of the mineral was vital.

“The tiny trapdoor of a snail proved to be the key to success,” Collins said.

The pair analysed 470 fossil remains from 71 sites in the UK and three on continental Europe with palaeontologist Dr Richard Preece from the department of zoology at the University of Cambridge. Their method proved highly reliable with more than 98% of samples yielding useful results.

“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,” said Preece.

The method – published in Nature – is a refinement of the 40-year-old technique of amino acid geochronology. It will be used to see how plants and animals survived in different conditions in the period.

“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,” said Penkman.