A series of sudden and colossal radiation spikes in Earth’s history could stem from a series of unknown, unpredictable and potentially catastrophic cosmic events, a new study has found.
Miyake events named after the main author of the first study To describe them, the spikes occur about every 1,000 years or so and are recorded as a sudden increase in the radiocarbon content of old tree rings.
The exact cause of the sudden floods of radiation that periodically convert an additional portion of the atmosphere’s nitrogen carbon sucked up by trees remains unknown. The leading theory among scientists is that Miyake events are solar flares which are 80 times more powerful than the most powerful flare ever recorded. But a new study published in the journal Oct. 26 Proceedings of the Royal Society A: Mathematical, physical and technical sciencessuggests that the origin of the radiation bursts may be even more mysterious than first thought.
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“These giant bursts of cosmic rays, known as Miyake events, have occurred about once every thousand years, but what causes them is unclear,” the lead author said Benjamin PopeAstrophysicist at the University of Queensland, Australia, said in a statement. “We need to know more because if something like this happened today it would destroy technologies like satellites, internet cables, long-distance power lines and transformers. The impact on global infrastructure would be unimaginable.”
Each year, temperate tree species develop a new concentric ring around their trunk that adds up to indicate their age. Because trees suck carbon from the atmosphere, scientists can study the amount of radiation in the atmosphere during Earth’s recent history by measuring tree rings for amounts of the radioactive isotope carbon-14, which is produced when high-energy cosmic rays collide with atmospheric nitrogen.
Scientists have so far detected six Miyake events in tree rings, indicated by sudden, year-long jumps in levels of carbon-14 and other isotopes; these occurred in the years 7176 BC. 5410 BC. 5259 BC. 660 B.C. 774 AD and 993 AD; alongside a number of other, smaller events discovered at other times.
To investigate whether the sudden carbon-14 spikes were caused by incredibly powerful solar flares, the researchers created a simplified model of the global carbon cycle; Input tree ring data to show how carbon was produced by solar radiation and absorbed into Earth’s atmosphere, oceans, land and organisms. By comparing their atmospheric carbon timeline to the known 11-year solar cycle, the researchers expected to find that the years of the Miyake events corresponded to moments of peak solar activity.
But instead they discovered that the Miyake events did not coincide with peak solar activity and, other than the brief flashes we see as solar flares, some of the events lasted a year or two.
“Rather than a single, instantaneous explosion or flare, what we might see is some sort of astrophysical ‘storm’ or burst,” said first author Qingyuan Zhang, a mathematician at the University of Queensland, in the statement.
The intensity of these inexplicable cosmic barrages is hard to underestimate. The largest solar storm ever recorded is that of 1859 Carrington Event, which after impacting Earth sent out powerful streams of solar particles that blew out telegraph systems around the world and made auroras appear brighter than the light of the full moon as far away as the Caribbean. The storm released roughly the same energy as 10 billion 1-megaton nuclear bombs. If an equally strong flare were to hit Earth now, it would cause one “Internet Apocalypse”, Power outages and trillions in damage, scientists say. But the Carrington event was 80 times less powerful than the Miyake event of AD 774.
After raising doubts about the peaks of conventionally understood solar flares, the researchers questioned whether the Miyake events were produced by supernovae or some type of solar superflare. But even these alternative theories have holes: supernovae sometimes produce radiocarbon spikes in Earth’s atmosphere, sometimes not; Stars like ours are not known to produce flares energetic enough to trigger the Miyake events. Evidence for a solar superflare is also absent from ice core nitrate records found for the AD 774 and AD 993 events.
Venturing into the historical record yielded only two enticing references. One in the Anglo-Saxon Chronicle (a 9th-century collection of annals recounting Anglo-Saxon history) refers to a possible aurora in the form of a “red crucifix after sunset” sighted in the sky in AD 774 , but researchers think it could also have been an optical illusion known as the lunar ring. Another account from 775 AD in the Chinese chronicle Jiutangshu describes what could also have been an aurora, but its existence has not been confirmed by other records.
The researchers’ next step is to collect more tree ring and ice core data to more precisely determine the timing of the events and the isotopic mixtures they produced. But scientists’ uncertainty about what the events are or how to predict when they will occur is “very disturbing,” Pope said.
“Based on the available data, there’s about a 1% chance of seeing another one within the next decade. But we don’t know how to predict it or what damage it can cause,” added Pope. “These chances are quite alarming and lay the groundwork for further research.”
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