View Full Version : Climate, Comets and Human History

Thursday, August 25th, 2005, 02:04 AM

Dr V.A. Gostin

School of Earth & Environmental Science

University of Adelaide

URL: http://ching.apana.org.au/~paulc/loreimpacts.html

Modern science has made major inroads into understanding the patterns and causes of climate change, and this in turn has thrown light on the evolution of human societies and on specific crises in human histories. The major factors dealt with in this report are the roles of Our Sun’s fluctuating magnetic and solar wind activity, and on our Earth’s episodic interaction with the orbit of large comet(s), whose fragmentation resulted in atmospheric dust veils and meteor storms of sufficient intensity to affect our weather over several years.

It has long been known that over the last two million years our planet has undergone major climatic (glacial) and sea-level fluctuations having periods of 23,000, 40,000, and 100,000 years, the last being the most important. These relate to Earth’s orbital oscillations that influence the amount of solar heat received by the continents in the northern hemisphere, known as the Milankovitch Cycles. The peak of the last ice age occurred around 20,000 years ago (BP), and we finally emerged out of that very cold and windy period about 11,000BP. For several thousand years until 6000BP, the global climate was a little warmer and generally wetter than today. Early agriculture and the domestication of animals occurred in several places 9-10,000 years ago, clearly aided by the climatic stability i.e. reliable seasons that contrasted with the climatic severity of the preceding ice ages.

As the ice caps continued to melt, the final rise of sea level (from –20m to the present) occurred around 8000BP; the British Isles became separated from the continent, and the North Sea plains were inundated. The rising Mediterranean waters finally burst through a narrow strait flooding what became the Black Sea around 7600BP. Memories of this event were recorded in the Gilgamesh legend preserved in Babylonian tablets and later repeated as the Biblical Flood (Ryan & Pitman, 1998). This catastrophic flooding resulted in a diaspora fleeing from the Black Sea area. Those that fled northward carried new farming and pottery techniques with them into eastern and central Europe. They may also have been the source of the proto-Indo-European language from which almost half of the world’s languages have been derived.

Around 6000BP the Earth’s polar orientation progressively changed (by precession) so that the planet experienced stronger variations in temperature. This led to stronger atmospheric and oceanic currents, and the birth of the El Nino Southern Oscillation (ENSO). This is evident from the study of lake sediments and growth rings in corals (New Scientist 22.5.99:38-41). Before 6000BP many water filled lakes existed across the Sahara. In southern Egypt west of the Nile, the originally wet, vegetated and fertile Sahara steadily dried up so that seasonal herding in that area ceased around 5800 years ago. These people probably moved eastward into the well-watered Nile Valley, and created the great Egyptian Civilization. Anthropologists like Dan Sandweiss and Kirk Maasch have noted similar peaks in cultural development around this time, in areas as diverse as Peru, North America, New Guinea highlands, China and Scandinavia (New Scientist 22.5.99:38-41). They attribute this world-wide peak in cultural innovations to people’s adaptation to changing climatic conditions and their increasing reliance on agriculture.

While the influence of solar activity on Earth’s climate has been known for many years, it has been only recently that the extent of this influence and its probable mechanisms have been elucidated. Our Sun, like most similar stars, undergoes cycles of both luminosity and magnetic activity. This magnetic activity is seen in the abundance of sunspots and in the outward sweep of magnetic fields in the solar wind. The intensity of galactic cosmic rays reaching the Earth is affected by this solar magnetic field resulting in decreased production of such isotopes as carbon-14 and beryllium-10. These isotopes have been carefully measured in many marine cores from the North Atlantic, and have been shown to be closely correlated with oceanic temperatures as measured by the abundance of iceberg rafted grains (Bond et al., 2001). Thus cooler periods are coincident with reduced solar activity and increased cosmic ray intensity. It is also possible that cosmic rays ionize atmospheric molecules they collide with, triggering cloud formation, especially at high and mid-latitudes, thus further cooling the planet (New Scientist 14.8.04:10).

Detailed studies of the team led by Gerard Bond of the Lamont-Doherty Earth Observatory in New York found evidence for periodic cold spells over the last 32 000 years. “Our drift-ice records contain a series of rapid, centennial-scale cycles (mostly 200-500 years) closely matching large shifts in the nuclide production rates” (Bond et al., 2001: 2132). During the last 9000 years, centennial-scale cycles are grouped into distinct, composite cycles ranging from 1000 to 2000 years.

The last five warm episodes were around 5000BP, 3600BP, 2700 to 1700BP (known as the Greco-Roman warm period), the 12thC medieval warm period, and the 20thC of global warming (thus complicating the influence of fossil-fuel burning). While average temperatures varied by only one to two degrees, the consequences for agriculture were severe in many areas including Europe (when the Thames seasonally froze over) and northern China, during the Little Ice Age of the 17th and 18thC. Greenland was settled by Europeans during the 12thC warm period, followed by a freezing climate change and death of all Europeans.

During the cooler 9thC AD Mexico was affected by severe water shortages that culminated in the severe droughts of AD810, 860 and 910. While the inhabitants were experts in water management, such extreme crises spelt the end of the great Mayan Civilization, which during the 8thC boasted a population reaching some 15 million (Haug, New Scientist 22.3.03:19).

In recent years a more accurate time scale has become available through the study of tree-rings of long-lived trees (dendrochronology). This has enabled scientists to reconstruct the growth patterns (and hence climate) of swamp oaks in Ireland and Germany, going back more than 7,000 years for that region. The bristlecone pine of California has similarly produced a climatic record reaching back an incredible 11,000 years. In their 1988 study of the Irish swamp oaks, Baillie and Munro of Queen's University, Belfast, focused on those natural events that produced the narrowest rings in many trees from different sites. Their results revealed six major periods of climatic stress: 3195BC, 2345BC, 1628BC, 1159BC, 207BC, and the latest around AD540 (Baillie, 1999; 2002). These were clearly times when there was a marked reduction in summer growth due to major atmospheric disturbance lasting five to ten years and sometimes longer. Their initial hypothesis was to attribute these to the effects of very large ash-producing explosive eruptions, similar to that of the historical 1815 explosion of Tambora volcano on Sumbawa Island in Indonesia. Only two other large eruptions are known to have occurred during the last 6,000 years: Taupo volcano in New Zealand in 180AD, and Santorini (Thera) around 1400BC. The eruption of Krakatoa in 1883 was small in comparison to the three listed above.

However, by the early 1990s Baillie considered that a volcanic interpretation was inadequate to explain such adverse conditions for many reasons including the fact that volcanic explosions had not hitherto been associated with such prolonged environmental effects (from 536 to 545AD) (Baillie 1999; 2002). The identification of similar reduced tree ring growth in trees from California, Argentina, Sweden, and Siberia, pointed to a truly unusual global weather phenomenon.

In 1990, British astrophysicists, Bailey, Clube and Napier, published their book The Origin of Comets where they indicated that the Earth must have had periodic encounters with large comets, and that one such close encounter probably occurred during the last two thousand years of recorded history, with a suggested event occurring sometime between AD 400-600, possibly from the breakup of the comet Beila. In 1995, Duncan Steel presented further research dealing with Earth’s hazardous interaction with comets and asteroids, including the possible astronomical connection with megaliths like Stonehenge. Baillie (1999) then preferred a cometary to a volcanic hypothesis as the explanation to the major tree ring events. Additional support for this interpretation has come from the discovery of cosmic dust in Swedish and Irish bogs corresponding it time to most of the tree ring events (New Scientist 14.9.02: 24).

Comets have relatively small masses with diameters of a few kilometers (rarely 100km), made up of solid lumpy cores surrounded by various frozen gasses, ice, and complex organic compounds that evaporate during the comets passage through the inner solar system. These gasses produce a huge coma or nebulous envelope from 10,000 to 100,000km in diameter, followed by two tails that may be millions of kilometers long. The curved tail consists of dust grains and meteoroids, while a straight blue tail is made up of charged particles aligned with the flow of the solar wind (Steel, 1995: 277-279). The Earth’s encounter with cometary tails would have resulted in swarms of cometary debris raining down as meteor storms, and megaton class airbursts, like Tunguska, caused by large cometary fragments exploding in the atmosphere. Cometary debris exploding in the atmosphere or impacting into oceans could provide the dry fog or dust-veil associated with early historical records. A comet entering the Earth's magnetosphere would also trigger massive auroral displays with charged particles spiraling down magnetic lines of force. The comet would appear like a second sun, dominating the sky for months, rotating like a wheel with legs (swastika), spitting out white curved fountains, that were eventually swept back into an enormous tail that extended from horizon to horizon (Baillie, 2002).

In comparison to large volcanic eruptions, or the rare meteorite impacts that occur with little warning, comets can be seen months in advance, giving the observant humans clear signs of impending disasters. Thus the Chinese abandoned their capital in AD 534, but did not escape the terrible famines of 536-538. Indeed, many of the myths and recorded histories concerning such heavenly events, bear striking similarities with each other as recorded by the ancient scribes (Baillie 1999: 207).

Quoting the Celtic myths around the terrible events of 536-545 AD, Baillie concludes that a close encounter with a comet satisfies all the details recorded in the myths. Thus a comet can "come up in the west, it can be as bright as the sun, it can be red from the evening to morning, it can have a long mane of hair, it can appear to have three layers of hair, it can give rise to an auroral display, it can spin and look like a swastika, it can give rise to terrible showers of hail-stones, it can deliver terrible blows (if large bits of it impact the atmosphere), it can cause the Sun and Moon to go dim " (as its dust fills the Earth's atmosphere) (Baillie 2002). Such phenomena would have been most awe-inspiring and frightening to our ancestors, and any meteorites recovered from the ground could have been considered as sacred stones. Baillie recounts many ancient stories where the comet was seen as the Divine Archer - Apollo; as Archangel Michael and the evil dragon; as the Celestial Dragon (T'ien Lung) in Chinese myths; as Lugh - the Celtic comet-deity; and even heralding the death of King Arthur and Merlin, and the onset of the Dark Ages. It is intriguing to note that in the Arthurian legend "the logic also is that he probably is ... not dead, but will return." (Baillie 2002).

The likely effects of cometary encounters on agriculture-dependent societies are serious. They probably resulted in severe winters and no summers for several years, with the ensuing famines, pestilence, and the onset of a veritable "dark age". Such events could have affected, or brought about the demise of kings, Egyptian Pharoes, and Chinese Emperors. Thus the climatic events of 2354 to 2345 BC may be linked to the end of the Old Kingdom in Egypt. The 1628 to 1623 BC events may be linked to the end of the Chinese Xia dynasty, the catastrophe recorded in the Irish Annals, the Biblical plagues of Egypt and the Exodus. Similar historical catastrophes have been recorded for the 1159 to 1141 BC event, strongly recorded in Irish swamp oaks, and in acid layers in both the Antarctic and Greenland ice cores. This marked the end of the Shang dynasty, and coincided with famines at the end of King David's reign, as well as widespread destructions and burnings around the eastern Mediterranean.

While all the above listed tree-ring episodes appear to have a common link with cometary events, large volcanic eruptions such as that of Santorini (Thera) are recorded as a prominent acid layer in the Greenland ice cores. Dated at 1390 +-50 BC, the Santorini event probably also led to an environmental catastrophe involving the end of the Minoan civilization. A very large volcanic eruption is nevertheless the preferred hypothesis by David Keys (1999) for the world-wide catastrophe around 540AD. Keys locates this super-eruption as that of a proto-Krakatoa in the Sunda Straits of Indonesia. Perhaps the truth lies in the cumulative effect of volcanic and cometary events.

The worldwide significance of the 2354-2345BC events was highlighted in the Second SIS Cambridge Conference held in July 1997 called "Natural Catastrophes During Bronze Age Civilizations - Archaeological, geological, astronomical & cultural perspectives". In the conference proceedings, Benny Peiser (Abstract O-7) showed that his survey of some 500 excavation reports and research papers indicated a pattern of abrupt glacial, eustatic, lacustrine, fluvial, pedological and geomorphic changes at around 4250 +/- 250 cal BP in many areas around the world. In addition, the majority of sites and cities of the first urban civilizations in Asia, Africa and Europe appear to have collapsed at around the same time. Most sites in Greece (~260), Iberia (~70), Mesopotamia (~30), the Indian subcontinent (~230), China (~20), Persia (~50) and other areas, show signs of natural calamities and/or rapid abandonment. Peiser concludes that close cometary encounters provide the best explanation for such global catastrophic effects, and associated ecological and social disasters.

To conclude, it is clear that the progress of civilization has been intermittent and that humans have had to face many hazardous natural events that have celestial origins: from the periodic pulsations of our Sun's magnetic activity, to the oscillations and precession of our orbit, and to the millennial close encounters with large comets. All have severely affected our human lives and well-being. We should avoid believing that the present-day celestial peace is set to continue. Rather, we have become aware of just how precarious and precious is our continuing existence on this planet.

Dr V.A. Gostin - victor.gostin@adelaide.edu.au


Bond G. and others 2001. Persistent Solar influence on North Atlantic climate during the Holocene Science 294, Dec 7, 2001,pp 2130-2136.

Bailey M.E., Clube S.V.M., and Napier W.M. 1990. The Origin of Comets. Pergamon Press, London.

Bailey M.E., Palmer T., and Peiser B.J. 1997. Natural Catastrophes during Bronze Age Civilisations – Archaeological, geological, astronomical & cultural perspectives. Second SIS Cambridge Conference, Fitzwilliam College, Cambridge University, 11-13 July 1997.

Baillie M. 1999. Exodus to Arthur. - Catastrophic encounters with comets. Batsford, London, 272pp.

Baillie M. 2002. Tree-ring chronologies,…and stories from myth. www.celt.dias.ie/publications/tionol/baillie02.pdf

Keys D. 1999. Catastrophe. An investigation into the origins of the modern world. Century, U.K. (also Arrow Books, 2000) 509pp.

Ryan W. and Pitman W. 1998. Noah’s Flood. Simon & Schuster, U.S., 319pp.

Steel D. 1995. Rogue Asteroids and Doomsday Comets. John Wiley & Sons. 308pp.

Gorm the Old
Thursday, August 25th, 2005, 04:13 PM
Excellent ! This comet-débris hypothesis makes much more sense than the original Milankovitch hypothesis which attributed large-scale changes in the annual temperature of the Northern and Southern hemispheres exclusively to orbitally-induced changes in the distance between the Earth and Sun and in the obliquity of the Ecliptic. The Milankovitch hypothesis would have required that glaciations alternate in the Northern and Southern Hemispheres, which they did not. Southern Hemisphere glaciation, however, would be inhibited by the greater abundance of water, with its high specific heat, in the Southern Hemisphere, The comet débris hypothesis retains the orbital aspects of the Milankovitch hypothesis but adds the far more effective mechanism of obscuration of sunlight by suspended cometary débris, a mechanism which has been observed to be effective following major volcanic eruptions. The point is also made, though not emphasized, that the interpretation of the present episode of global warming is complicated by the operation of natural phenomena which obscure the effects of human activity. I have made this point to my students and other groups many times. Until we know the natural causes of global warming and refrigeration, we cannot, with confidence, know how much of it to attribute to human activity.