C14 found wanting

10 Sep 2015

At www.scmp.com/tech/science-research/article/1856329/many-global-warming-s... ... which is the South China Morning Post, apparently read at times by Andrew - see www.bishop-hill.net/blog/2015/9/9/wrong-speed-dating.html ... and concerns a paper in Earth and Planetary Science Letters which argues C14 dating is not all it is cracked up to be. C14 dating is unreliable in context as far as global warming studies are concerned - at dates older than 30,000 years ago.

Seems like these people are catching up with archaeologists who found dating living things older than 30 to 40,000 years ago hit a buffer - and were completely unreliable. This is why Bayesian methodology was introduced, and calibration (attempting to shore up C14 dating by using other dating methods as a back up).

Actually, this is what seems to have occurred - except they were dating sediments (from a core taken from Lake Xingkai near the Sino-Russian border). It is the largest lake in NE Asia, is freshwater and fed by 23 rivers, but only 35 feet deep at the most. It probably has a glacial origin - before the Late Glacial Maximum. Samples taken from the lake were tested using C14 and optical stimulated luminescence (OSL) - and they did not agree. OSL uses light to measure the amount of free electrons trapped which enables scientists to calculate how long the samples had been kept away from sunlight - therefore estimating when it was they they fell into the lake and were buried in the bottom sediments. It is the super dating method in vogue at the moment - and no hint of anything wrong as yet. Hence, the study authors go on to imply that C14 is untrustworthy - but we all know that as a series of plateau events is common knowledge.

Willard Libby discovered C14, a radioactive isotope, could be used to date organic compounds, way back in the 1940s. His theory was that all living creatures have a constant proportion of radioactive and non radioactive carbons in their bodies because they keep absorbing these elements from the environment. When a creature dies (or any organic substance) it stops absorbing them and shed C14 at a decay rate of 50 per cent every 5700 years. The method had an inbuilt flaw as it didn't account for change in the proportion of radioactivity and non radioactivity in the environment, and if  if these did change (in the lifetime of the creature or organism) the dating would be awry.

Many things affect levels of C14, we are told, even the burning of fossil fuels in the vicinity can muddy the waters, and old carbon from volcanoes is also a problem, it would seem. The detonation of nuclear bombs in the tests of the 1950s is known to have upset C14 levels - and coronal mass ejections are another common problem (especially when the magnetosphere is reduced by the punch of a CME). It is possible that C14 levels are affected by meteors exploding in the atmosphere - the larger ones.

Anyway, it seems it was thought Xingkai Lake was formed by meltwaters during the warm interstadial event around 40,000 years ago. This date, we have noted, is the buffer zone of C14 reliability and therefore this was always possibly completely out of focus. OSL is able to kick through the buffers  and came up with a date of 80,000 years ago (for the sediments) which is twice as hoary. No wonder they were miffed.

Professor Liu Jinyi, a palaeontologist in Beijing, says C14 dating should be restricted to young samples. In geology and archaeology it usually is - but apparently not in climate studies. 

A comment at Bishop Hill says that cosmic rays and solar activity can affect C14 levels as well as changes in Earth's magnetic field (allowing greater amounts of cosmic rays to enter the earth system). Another comment says, if two methods disagree that of itself does not illuminate which one is wrong as both could be wrong - which is worth thinking about as another comment lauds the OSL methodology as it dated human footprints at Happisburgh (collapsed cliff face) to 900,000 years ago.