How to date a Russian cave lion
The oldest bone sample to be reliably carbon dated is 61,000 years old. Viviane Richter reports.
In the summer of 2008, a resident of the Russian village of Anyuisk stumbled upon a stack of bones submerged in the muddy waters of the Malyi Anyui River. The bones made up the first near-complete skeleton of the now-extinct cave lion Panthera leo spelaea found in Russia.
The bones also came with preserved strands of hair and a curved claw – the first ever found for the species that roamed between 300,000 and 10,000 years ago. For millennia the remains were frozen in river sediment dating from the Pleistocene era. They were sufficiently preserved to allow researchers from the National Alliance of Shidlovskiy “Ice Age” to piece together the lion’s morphology. But to find out when the lion died, the Russians contacted Vladimir Levchenko at the Australian Nuclear Science and Technology Organisation (ANSTO).
So how does one date an ancient lion?
Carbon atoms come in different varieties. The typical carbon nucleus contains six protons and neutrons, but some have an extra neutron or two, producing carbon-13 and the radioactive carbon-14. Eventually, carbon-14 decays into the stable carbon-13 and carbon-12 isotopes. Working out ratios of the radioactive and stable carbons tells you the age of the sample. But the older the sample the less carbon-14 remains, and what is left becomes harder to find.
Most labs are only able date carbon back to 50,000 years ago, but ANSTO’s super-sensitive, low background accelerator mass spectrometry facility can pick up tiny amounts of radioisotopes – comprising a quadrillionth of the total atoms in a sample. That’s the equivalent of finding one ant out of all the ants on Earth.
ANSTO chemist Fiona Bertuch extracted collagen from the lion’s bones. She extracted the carbon from the collagen, the claw and hair samples and processed it into black graphite powder. Each powder sample was then placed inside a particle accelerator and turned into a particle beam, enabling Levchenko to count the radioactive carbon atoms as they hit a detector. From their isotope ratios, he calculated the age of the lion’s bone and claw to be a little more than 61,000 years old – making it the oldest bone sample to be reliably carbon dated. The work was published in Quaternary Science Reviews.
But the jury’s still out on whether the hairs belong to the same lion. ANSTO’s isotope ratios date them at around 28,700 years old. But this date could have been skewed by contaminants. The lion’s hairs are hollow in order to trap air and insulate the animal against the cold. Microbes could have crept in long after the lion died, adding a younger stock of carbon-14. Levchenko plans to dissolve the hair’s keratin to remove contaminants and get a more accurate date. If the hair does belong to the skeleton, this lion wore a stylish honey-copper coat.