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In 2011 Paul A. LaViolette published a paper in the journal Radiocarbon (vol. 53, no. 2, pp. 303 to 323) titled “Evidence for a Solar Flare Cause of the Pleistocene Mass Extinction.” He argues that a massive solar proton event killed off many large mammals at the start of the Younger Dryas, about 12,900 years ago.
Did a Massive Solar Flare Cause the Pleistocene Megafauna Extinction?
LaViolette proposes that one super-sized solar proton event (SPE), or several, struck around 12,837 calibrated years before present (cal yr BP). An SPE is a burst of high-energy protons thrown out by the Sun. In his view it delivered heavy radiation to Earth’s surface and helped bring the Pleistocene megafauna to an abrupt end, above all in North America.
He builds the case from sediment records, ice cores and radiation estimates. It stands apart from the usual explanations of human hunting, climate shifts or a comet impact.
LaViolette sums up the dose such an event could deliver.
A SPE of this magnitude would have been large enough to deliver a lethal radiation dose of at least 3–6 Sv to the Earth’s surface…
Paul A. LaViolette, "Evidence for a Solar Flare Cause of the Pleistocene Mass Extinction," Radiocarbon 53(2), 2011, p. 303 (abstract), short excerpt for review and study
Main Evidence from Radiocarbon Records
The Cariaco Basin sediment core off Venezuela shows a sharp rise in atmospheric radiocarbon (^14^C). Excess ^14^C rose by 65 per mil (‰) during the first 200 years of the Younger Dryas. Per mil means parts per thousand.
The core dates distinct spurts at 12,973, 12,904, 12,837 and 12,639 cal yr BP, each ± 10 years. The spurts at 12,837 and 12,639 are the largest in the record. The first shows a 20‰ rise between two successive 8-year sampling intervals.
The spurts are spaced by multiples of the Hale solar cycle of about 22 years. LaViolette reads this pattern as solar activity, a time when the Sun was throwing off super-sized coronal mass ejections. Lunar rock studies by Zook and colleagues found that solar cosmic-ray intensity was about 50 times today’s level around 16,000 years ago, falling to 15 times by 12,000 years ago.
Evidence from Greenland Ice Cores
The GISP2 ice core from Greenland shows a ^10^Be peak that matches the 12,837 cal yr BP ^14^C spurt. ^10^Be forms when cosmic rays strike the atmosphere, so the match points to an SPE rather than a change in Earth’s magnetic field.
An acidity spike at 1708.65 m depth lines up with the same date. It carries high nitrate (NO₃⁻) and ammonium (NH₄⁺) levels. High nitrate is a sign of cosmic-ray ionization, and high ammonium a sign of global fires.
Nitrate is also depleted within the layer. LaViolette takes this as a sign that the snow surface sat under intense UV for a long time, after cosmic rays destroyed the polar ozone layer.
Radiation Dose and Lethal Effects
LaViolette compares the event with the SPE of February 1956. That event raised atmospheric ^14^C by only 0.16‰ and delivered a fluence of about 10^9 protons/cm². Fluence is the number of particles passing through each square centimetre.
The 20‰ rise at 12,837 cal yr BP implies an event at least 125 times stronger, on the order of 1.25 × 10^11 protons/cm². His abstract rounds this to about 1.3 × 10^11.
With a hard spectrum, meaning more very high-energy protons, such an event could have given animals at sea level about 3 Sv over 50 hours, and in his estimate substantially over 6 Sv. LD-100, the dose that kills all exposed animals, spans 3 to 8 Sv for most large mammals. A partial collapse of the magnetosphere would have raised the dose further.
He notes that events this large are not unusual by astronomical standards. Superflares of 10² to 10^7 times the energy of the 1956 flare have been seen on nearby sun-like stars.
Timing and Link to Extinctions
The 12,837 cal yr BP event falls within the Rancholabrean termination, dated about 12,883 ± 60 cal yr BP, and LaViolette places it immediately after the end of the Clovis culture (12,880 to 12,840 cal yr BP). It also sits inside the window of 12,950 to 12,750 cal yr BP that he gives for the extinction in the first 200 years of the Younger Dryas.
The “black mat”, a dark sediment layer in the American Southwest often linked to megafauna remains, is younger. LaViolette argues it reflects changes that came after the SPE.
Additional Impacts
The high ammonium levels point to widespread wildfires, which would have cut the food supply of plant eaters. A rapid warming followed, visible in the oxygen isotope record.
LaViolette also suggests the SPE partly collapsed the magnetosphere and released dust held in orbit around Earth. In his view this accounts for the scattered nanodiamonds and other markers found in sediments, which do not show the even spread a comet impact would leave.
Comparison to Other Theories
LaViolette argues that human overkill does not explain why the extinction also struck Europe and Siberia, or why 10 genera of birds vanished at the same time. Some also argue that earlier climate cycles in the Pleistocene did not cause mass extinctions of this kind (unchecked).
The comet impact idea, he says, has no identified crater. Citing Melott and colleagues (2010), he adds that a comet of the proposed size should have left a nitrate signal far larger than any seen in the GISP2 ice. Its extraterrestrial markers are disputed and could come from cosmic dust instead.
What LaViolette Proposes to Test
LaViolette concludes that an SPE at 12,837 cal yr BP, with a fluence of about 1.3 × 10^11 protons/cm², brought lethal radiation, ozone loss, wildfires and a release of dust, and that this led to the megafauna extinction. Several events may have added to the effect.
He proposes testing the idea by analysing the GISP2 layer at 1708.65 m for a ^10^Be spike and for platinum group elements. These would confirm a cosmic-ray influx and the fall of orbital dust.
The idea remains debated in paleoclimate and extinction research. For a rival cosmic cause of the same period, see Could the Taurid Meteor Shower Have Caused the Great Flood?, and for the wider dates, the 26,000 year timeline.
