Back to the 775AD event ... the Chinese broadside

24 Jan 2014

At Nature Science Reports 4:3728 (DOI:10.1038/srep03728) - download the four page article at ... Yi Liu et al 'Mysterious abrupt C14 increase in coral contributed by a comet' - the work has the support of the National Science Foundation of China and concerns geochemistry as well as asteroids and comets. Received by Nature on the 6th of November 2013 and published 16th January 2014 - queries to weidongsun [at] gig [dot] ac [dot] cn

A large and sudden increase in C14 around AD773 was documented in coral skeletons from the South China Sea. It increased suddenly and remained at a high level for some 4 months during the winter, increased slightly and then dropped back down over the next 2 months, forming a spike of 45 per cent higher in late spring, followed by two smaller spikes. The C14 anomaly coincides with an historic comet crossing very close to the atmosphere of the Earth, if not actually impacting with the upper atmosphere, on 17th January AD773. Comas of comets are known to have high levels of nitrogen by weight and are exposed to cosmic radiation in space. Hence, they may be expected to contain highly elevated C14 and C12 in comparison with the atmosphere of the Earth. A significant impact of C14 by comets may have contributed to the fluctuation of C14 in the atmosphere throughout Earth's history.

We've had the giant solar flare and the supernova theories for the AD773-5 event - now we have the coma of a passing comet. Western scientists wouldn't dare to suggest such a radical idea - as they would very quickly be diagnosed as a quack. This has the backing of the Chinese Academy of Sciences - they are being serious. The fact it is published by Nature must make the eyes of Mike Baillie water - as he has been left at the edge by suggesting comets played a role in the historical past.

The abundance of C14 varies over time and this is generally attributed to variations in the Earth's magnetic field, solar activity, and changes in the solar cycle (quoting the Encyclopedia of Quaternary Science). A large and sudden increase of C14 was reported from a tree ring study in Japan, dated 774/5. Their modelling showed that the atmospheric levels of C14 must have jumped over the course of no longer than a year, corresponding to an increase ten times larger than the average production level from galactic cosmic rays and 20 times larger over two eleven year solar cycles. The measured levels were too high for a solar flare or a local supernova event. The Chinese describe these alternative explanations as a highly energetic radiation burst (a proton storm from a giant solar flare), a major comet impacting upon the face of the Sun, or floods of y-rays from a supernova. Such high levels of radiation, it is thought, might also cause mass extinctions - and none of these occur around AD773. However, by looking at historical records, no super flare occurred (not then or within the last few thousand years).

Doubt was then cast on the veracity of the original Japanese study - they must have got it wrong (the usual disbelief kicked in). A simulated carbon cycle model suggested the length of the event was over estimated - but the key issue is still the elevation of the C14 import. Based on modelling, the tree ring record could be explained by a spike that lasted less than one year but due to the annual resolution of the C14 data they could not pinpoint the duration in greater detail. The Chinese researchers chose to look at corals rather than tree rings, taken from a reef, where they could achieve half annual resolution sampling.

The abrupt increase by 45 per cent in just two weeks requires a radiation intensity 100 times stronger than the previous estimation for the event - which is staggering. It is well established that a comet collided with the atmosphere of the Earth coming from the direction of the constellation of Orion (or Shen in traditional Chinese astronomy), they say, on 17th January AD773, the 7th year of Emperor Dai Zong of the Tang dynasty. The phenomena lasted less than one day and had an accompanying coma that stretched across the whole sky. Dust rain in the day time before the comet implies a considerable amount of cometary material was added to the atmosphere assuming the two events are related. Celestial observations were especially significant to the emperors of China, and this included the Tang dynasty. They were carefully recorded and this particular event was recorded in several different official archives in China, including by the royal celestial officer in Chang'an (now Xi'an), the capital of the Tang. It is possible it resulted in the sudden sharp increase in C14 (and continues by exploring the chemistry of meteorites and rocks etc).

Coincident with the C14 increase there was a 30 per cent increase in the decadel Beryllium 10 flux from Dome Fuji, from AD755-785, which has been attributed to a burst of high energy y-rays (in the Monthly Notes of the Royal Astronomical Society 430 pages 32-36). 10Be is another cosmogenic isotope formed through spallation of nitrogen or oxygen which often co-varies with C14 imports. It has long been recognised that C14 and 10Be in the Earth's atmosphere varied dramatically throughout the history of the Earth and was previously solely attributed to cosmic radiation. Comets might well have contributed to some of these events, on an epsodic periodicity.

Wow. I always thought the Chinese might come up with the goodies - is this just the beginning?