Ancient bones — how old?

22 01 2021

Radiocarbon (14C) dating was developed by Nobel-Prize winning chemist Willard Libby, and has become the predominant method to build chronologies of ancient populations and species using the Quaternary fossil record. I have just published a research paper about 14C dating of fossil bone reviewing the four standard chemical pretreatments of bone collagen to avoid sample contamination and generate accurate fossil ages: gelatinization, ultrafiltration, XAD purification and hydroxyproline isolation. Hydroxyproline isolation is perceived as the most accurate pretreatment in a questionnaire survey completed by 132 experts from 25 countries, but remains costly, time-consuming and not widely available. I argue that (1) innovation is urgently required to develop affordable analytical chemistry to date low-mass samples of collagen amino acids, (2) those developments should be overseen by a certification agency, and (3) 14C users should be more conceptually involved in how (much) 14C chemistry determines dating accuracy. Across the board, scientific controversies like the timing of Quaternary extinctions need not be fuelled by inaccurate chronological data.

Megafauna bones from the Quaternary fossil record. Top: excavation of a partial skeleton of a short-faced kangaroo Procoptodon browneorum at Tight Entrance Cave (Western Australia) [1]: these bones are close to the limit of radiocarbon (14C) dating in a geological context 43000 to 49000 years old. Middle: metacarpal of the extinct horse Hippidion cf. devillei from Casa del Diablo (Peru) 14C dated at 11980 ± 100 years before present (BP) (CAMS-175039) following XAD purification of collagen gelatin [2]. Bottom: collection of skeletal remains of (mostly) red deer Cervus elaphus from El Cierro Cave (Spain) 14C dated at 15520 ± 75 years BP on ultrafiltered gelatin (OxA-27869 and OxA-27870 average) [3].

Scientists have widely been interested in the present and future state of biodiversity. Ecologists (the main audience of this blog) have also looked into the past with pioneering investigations addressing the composition of ancient forests and the origins of agriculture in layers of fossil pollen accumulated in lake sediments [4]. But it took us decades to see the fossil record as a useful tool (combining biological, geochemical and molecular techniques) to answer basic ecological questions. Some of those questions are critical for conserving today’s biodiversity [5, 6]: for example, when did human impacts on ecosystems become global or what extinct species have best tolerated past environmental change and what that means to modern species? [7].

The study of (pre)historic biological events relies one way or another on our ability to time when a certain animal, human, or plant occurred and what environmental conditions they experienced, and relies on concepts borrowed from archaeology (past human activity), palaeontology (fossils), palaeocology (species responses to past environments), and geochronology (age of fossils and/or their geological context). Among the range of chronological methods available to date biological and cultural samples [8], radiocarbon (14C) dating has become the most important for dating bones aged modern to late Quaternary (last ~ 50,000 years). Hereafter, ‘bone’ comprises antler, bone, ivory and teeth. 14C dating of bones is appealing at least for four reasons: 

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When did it go extinct?

11 01 2012

It was bound to happen. After years of successful avoidance I have finally succumbed to the dark side: palaeo-ecology.

I suppose the delve from historical/modern ecology into prehistory was inevitable given (a) my long-term association with brain-the-size-of-a-planet Barry Brook (who, incidentally, has reinvented his research career many times) and (b) there is no logic to contend that palaeo extinction patterns differ in any meaningful way from modern biodiversity extinctions (except, of course, that the latter are caused mainly by human endeavour).

So while the last, fleeting days of my holiday break accelerate worringly toward office-incarceration next week, I take this moment to present a brand-new paper of ours that has just come out online in (wait for it) Quaternary Science Reviews entitled Robust estimates of extinction time in the geological record.

Let me explain my reasons for this strange departure.

It all started after a few drinks (doesn’t it always) discussing the uncertainties associated with the timing of megafauna extinctions – you might be aware that traditionally there have been two schools of thought on late-Pleistocene extinction pulses: (1) those who think there were mainly caused by massive climate shifts not to dissimilar to what we are experiencing now and (2) those who believe that the arrival of humans into naïve regions lead to a ‘blitzkrieg‘ of hunting and overkill. Rarely do adherents of each stance agree (and sometimes, the ‘debate’ can get ugly given the political incorrectness of inferring that prehistoric peoples were as destructive as we are today – cf. the concept of the ‘noble savage‘). Read the rest of this entry »