Expanding amino acid dating

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Geologists take samples at a site
Geologists take samples at a Russian site dating to the Plio-Pleistocene (5 million-12,000 years ago).

How should we date material that is millions of years old? Looking at the predictable rates of the breakdown of proteins from an organism found in fossils is one possibility, and a technique that goes well beyond the range of radiocarbon dating. This amino acid dating (or amino acid racemisation) was first developed in the 1960s, but in those early years one complication was that some of the fossils studied had lost some of their original protein, and were affected by various environmental factors. Later work, however, found that a protein trapped within the crystals of biominerals (called the intra-crystalline fraction) served as a more reliable biological time capsule.

Kirsty Penkman, a researcher at the University of York, was recognised as a Laureate in this year’s Blavatnik Awards for Young Scientists for her work in this field. She has been using amino acid racemisation to date molluscs, egg shells, and corals up to 3 million years old. Penkman has been able to apply this analysis to tooth enamel too, which allows direct dating of mammals, including humans. The long expanse of time covered by amino acid dating is an important one for understanding the evolution of animals, humans, and early tool technologies against the backdrop of big swings in the climate, from cool glacial to warm interglacial periods.

Kirsty Penkman identifies fossil shells for analysis in the lab
Kirsty Penkman identifies fossil shells for analysis in the NEaar lab at the University of York.

‘In Europe we have this incredibly rich fossil record, but one of the big problems is that it is very challenging to date,’ Penkman said. ‘We’re just starting a big new project to date hundreds of sites across Europe, all the way to Russia. Some of these sites were studied by gentleman archaeologists 200 years ago, and their material has been archived and is sitting in museums. Now we can go back and date that material to give us a beautiful, unparalleled archive of climatic changes related to the archaeology.’

Temperature has a big impact on the rate of the reactions as proteins break down, so it is important to first understand a region’s temperature history before using amino acid racemisation for widespread dating. When and where it is warmer, the reactions happen much faster, leading to more precise dates, but across a shorter period; while in cool periods and regions, the reactions are slower, giving less resolution but a longer time range.

Studies so far have been clarifying timelines that can be used to address questions about the contemporaneity of different Lower Palaeolithic technologies and the early inhabitation of certain areas.

The breakdown of the proteins happens at a slower rate in tooth enamel too, so sampling this material can give an even longer time range, important for studying early human evolution. An ongoing project is now analysing African material from the last 4 million years; the results (still to come) may add further details to the timeline of hominin evolution in Africa.

At the moment, the dating work is carried out in a specialist lab, but the future may see this change. Penkman explained, ‘We want to really reduce the amount of material that we’re using, especially for human samples. We’re working on something called lab-on-a-chip technology, which is technology miniaturising the analytical preparations, enabling them to be performed on a chip the size of a credit card. If it’s successful, then we’ll be able to move away from analyses being undertaken at a specialist lab, and instead enable dating to be undertaken in the countries where these finds are being excavated, and even potentially in field-stations at the excavations.

‘Being able to do that really democratises the technology and the data, rather than them remaining very European- and North American-centric, which is what a lot of dating work is at the moment. It’s going to be really challenging, though. It even might not work, but we’re going to try.’

Further information
For updates on Wisdom Teeth, the project that is dating dental enamel from Africa to refine our understanding of evolution, visit https://sites.google.com/york.ac.uk/wisdom-teeth.
For updates on EQuaTe, the project dating the Palaeolithic in Europe, visit https://sites.google.com/york.ac.uk/equate.

This article appears in issue 101 of Current World ArchaeologyClick here for more information about subscribing to the magazine.

All images: K Penkman

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