Close to the end of the last ice age there was a sudden disappearance of many mammalian species which some paleontologists say was the most severe since the disappearance of the dinosaurs 65 million years ago. In North America 95 percent of the megafauna became extinct, these being predominantly mammals having body weights greater than 25 to 50 kilograms. But even small animals were affected, as in the disappearance of 10 genera of birds.
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| Close up of coronal loops over a solar flare made with the TRACE spacecraft in 2005 [Credit: NASA/TRACE] |
Although North America was most affected, it had a severe impact also in Europe, Siberia, and South America. The cause of the extinction has long remained a mystery. Theories that have been put forth have ranged from overkill by North American paleolithic hunters to the impact of a large comet or swarm of meteors. But all have been shown to have serious flaws.
Now, Starburst Foundation researcher Dr. Paul LaViolette has found evidence that this mysterious die-off may have had a solar flare cause. In his paper published this week in the journal Radiocarbon, LaViolette concludes that a super sized solar proton event (SPE) impacted the earth about 12,900 years ago (12,837± 10 calendar years BP). He notes that this date roughly coincides with that of the Rancholabrean termination, a time boundary beyond which the numbers of extinct megafaunal remains are found to sharply decline.
Solar proton events, blasts of energetic solar cosmic ray particles that are shot out with the eruption of a solar flare, can arrive with little advance notice, traversing the 93 million mile distance from the Sun to the Earth in a matter of hours. They are usually followed some days later by a slower moving solar wind plasma shock called a coronal mass ejection. They have been observed to occur from time to time in past decades, but none in modern times have been strong enough to pose a serious ground-level radiation hazard.
LaViolette carefully studied data spanning the onset of the Younger Dryas cold period near the end of the ice age during which there was a progressive long-term rise in the atmosphere’s radiocarbon concentration. Although some of this 14C rise was due to changes in the ocean’s carbon reservoir due to deep ocean circulation, a large part of it was believed to be due to a real rise in atmospheric radiocarbon concentration.
Studying radiocarbon data from the Cariaco Basin ocean sediment core drilled off the coast of Venezuela, he found that, at certain times in the course of this rise, radiocarbon concentration shot up sharply. The two largest 14C spurts to occur in the 4000 year Cariaco record occurred in particular during the first three centuries of this early YD period. The Cariaco Basin varve chronology dated these events at 12,837 years BP and 12,639 years BP.
Interestingly, they were separated by 198 ± 9 years, or nine Hale solar cycle periods. This interval also matched the 200-year de Vries solar cycle period which is believed to be one of the most prominent of the Sun’s solar cycle periods. This was the smoking gun that indicated that these spurts very likely had a solar cause. And, there were two other notable 14C spurts of lesser magnitude that preceded the 12,837 years BP event, each separated from the other by three Hale solar cycle periods.
The radiocarbon increase of the two largest 14C spurts was comparable to that produced by a SPE at least 125 times stronger than the hard spectrum SPE that occurred in February 1956. Extrapolating upward from that event, LaViolette estimates that the 12,837 years BP extinction level SPE would have delivered over a two day period a radiation dose of from 3 to more than 6 Sieverts, lethal dose (LD-100) for most mammals being in the range of 3 – 8 Sieverts. Hence it could have been a principal cause of the final termination of the Pleistocene megafauna and even of several genera of smaller mammals and birds.
The upper range of his estimate is a very conservative projection based on the assumption that the SPE would have been strong enough to overpower the Earth’s protective magnetic field sheath allowing the full intensity of the solar cosmic ray barrage to directly contact the Earth’s atmosphere and induce an intense shower of cosmic ray secondaries. The 1956 SPE was observed to produce a 1 percent decline in geomagnetic field intensity, so a super SPE over two orders of magnitude more intense would likely have completely overpowered the Earth’s field.
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| Ice core from the Northern Greenland ice sheet. [Credit: J. White/INSTAAR] |
LaViolette was also able to find the place where this solar event appears to be registered in the Greenland ice core record. He did this by matching up the Cariaco Basin climatic profile with that of the GISP2 Summit, Greenland ice core. He found that a very large magnitude acidity spike was formed on this 12,837 years BP date, found in the ice record at a depth of 1708.65 meters and that it also was associated with high nitrate ion concentration peaks, both of which were the highest in the Younger Dryas portion of the ice record. This depth also corresponds with a rapid rise in the core’s concentration of beryllium-10. All of these, ice acidity, nitrate ion concentration, and 10Be deposition rate, are good indicators that the Earth had experienced a sudden influx of cosmic rays at that time.
Furthermore LaViolette noticed that nitrate ion concentration did not peak in coincidence with the acidity peak, as is observed to be the case in ice records of contemporary SPEs. Instead, nitrate ion reached a peak on either side of the acidity spike and produced a conspicuous trough at the time of the spike. This suggested to him that the SPE had been so intense that its stratospheric ions were able to destroy the polar ozone layer and allow solar UV to penetrate the atmosphere which in turn would have photolytically dissociated the nitrate ions in snow deposited at that time.
The NOx gas so released would then have diffused to deeper levels where it would have recombined to form nitrate ions, thus displacing the nitrate peak. Once the ozone layer had reestablished itself, the precipitating nitrate ions would have been allowed to build up once again and produce the other flanking nitrate peak. The breadth of the nitrate trough indicated that polar regions were being exposed to UV for a period of several years. If the stratospheric ozone layer was significantly depleted also at mid latitudes, which seems likely, it would have posed an additional hazard to animal life, exacerbating the radiation hazard due to the SPE.
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| Nitrate ion concentration in relation to two acidity peaks in the GISP2 ice core [Excerpted from LaViolette, 2011] |
LaViolette also reports that the 12,837 years BP acidity spike coincides with an abrupt climatic cooling and interprets this as an expected consequence of solar cosmic ray exposure. That is, the impact of the solar proton event and its direct contact with the Earth’s atmosphere would have generated high concentrations of condensation nuclei in the stratosphere which would have had a cooling effect on climate.
He noted that this proposed super SPE also occurred midway between two very warm climatic intervals separated from one another by about one solar cycle period. The warming that followed this event was one of the most pronounced climatic oscillations of the entire Younger Dryas with polar temperatures briefly reaching levels of warmth characteristic of the Alleröd interstadial. He notes that aridity associated with this period of unusual climatic warmth must have contributed to the occurrence of wildfires since high ammonium ion concentrations coincide with each of these warm intervals, ammonium ion being a recognized wildfire indicator. He notes that hazards associated with these fires as well as the associated destruction of food supplies and habitats would have also contributed to the megafaunal termination.
LaViolette reasoned that given that this ice age super SPE was large enough to substantially disturb and possibly even temporarily collapse the geomagnetic field, large amounts of extraterrestrial dust residing in the circumterrestrial dust sheath would likely have been jettisoned into the stratosphere. This could account for the sporadic reports of an extraterrestrial debris-rich layer said to overlie the remains of extinct megafauna in early YD sediments and could also explain the discovery of a nanodiamond-rich layer found in Greenland ice correlating with the time of this event. However, the amount of this deposited material would likely have varied considerably from one place to another which could explain why these indicators are not always found.
This ET debris layer was initially cited by a group of scientists led by Berkeley scientist Richard Firestone as evidence that the Pleistocene mammals were wiped out by an impacting comet. But among the most serious objections to the comet theory is the absence of the nitrate ion signature which should have been present in the ice record if an impact and ensuing fireball had occurred at that time. If present, it should have been quite obvious since it would have been 105 times higher than the highest levels seen in the ice age portion of the Greenland ice record.
Also many paleontologists believe that the mass extinction did not occur all at once in a solitary extinction event, as the comet impact theory had proposed, but rather transpired over a few thousand years. The solar proton event hypothesis allows for a more progressive extinction episode by allowing the occurrence of multiple extinction level episodes. The early YD events, though, being among the most severe, would have precipitated the final phase of this demise.
LaViolette is doubtful that a super SPE of such a large magnitude is likely to occur in the near future. He points out that the reason why it occurred at the end of the ice age is because the Sun for several millennia had at that time been in a highly active flaring state, behaving similar to a T Tauri flare star. He attributes this elevated solar activity to the presence in the solar system of high concentrations of interstellar dust which at that time were being driven inward by a wind of galactic cosmic rays. Background information about this dust incursion theory may be found in his Ph.D. thesis, his book Earth Under Fire, and in various papers he has published.
One question that arises is how would paleolithic man have survived this event. LaViolette’s book Earth Under Fire, which he first published in 1997 and later updated in 2005, relates stories and ancient legends from around the world describing how the Earth had once been burned by the Sun, an event that was said to have brought about a world conflagration and even caused genetic mutations in animals. Some legends describe how survivors took shelter for several days in a cave or underground dwelling. LaViolette believes that there may be much truth to these stories and that evidence found in the geologic record may cause us to regard them in a whole new light.
Paleontologists note that Clovis paleoIndian campsites in North America suddenly terminate at one point and LaViolette notes that this Clovis end date either immediately preceded or coincided with the date of the 12,837 years BP super SPE. Although a new paleoIndian civilization resurfaced some centuries later, these new findings raise the question as to whether this super SPE may have been the cause of the disappearance of the Clovis civilization.
