Miyake event
A Miyake event is an observed sharp enhancement of the production of cosmogenic isotopes by cosmic rays. It can be marked by a spike in the concentration of radioactive carbon isotope   in tree rings,  and  in ice cores, which are all independently dated. At present, five events are known (7176 BCE, 5259 BCE, 660 BCE, 774 CE, 993 CE) and four (12,350BCE, 5410 BCE, 1052 CE, 1279 CE) need independent confirmation. This data shows that Miyake events are rare, occurring roughly once per 1–2 millennia. There is strong evidence that Miyake events are due to extreme solar particle events. They are likely related to super-flares discovered on solar-like stars. Some events might have taken seemingly longer than one year; they can still be consistent with a solar origin, or they might be indicative of other scenarios. The biggest Miyake event so far discovered occurred in 12,350 or 12,349BCE, according to the analysis of ancient tree rings found in the French Alps. For this study, an international team of researchers measured radiocarbon levels in ancient trees on the eroded banks of the Drouzet River, near Gap, France, in the Southern French Alps. This newly identified 14,300-year-old storm is roughly twice the size of the Δ increase for more recent 774CE and 993CE events, but the strength of the corresponding solar storm is not yet assessed. A Miyake event occurring in modern conditions might have significant impacts on global technological infrastructure such as satellites, telecommunications, and power grids. Discovery 
The events are named after the Japanese physicist Fusa Miyake, who as a doctoral student was the first one to identify these radiocarbon spikes and published with co-authors the results in 2012 in the journal Nature. The investigation at that time found a strong  increase in the annual rings of Japanese cedars for the years 774/775. The event of 775 was independently discovered, using the low-resolution IntCal data. In 2013, Miyake and co-authors published the discovery of another, similar radiocarbon spike in the years 993/994. In December 2013, Miyake received her Doctor of Science degree from Nagoya University. Time benchmark
After a Miyake event is well-studied and confirmed, it can serve as a reference time benchmark, a "year-stamp", enabling more precise dating of historical events. Six diverse historical occurrences, from archaeological sites to natural disasters, have thus been dated to a specific year, using Miyake events as benchmarks and counting tree rings. For example, wooden houses in the Viking site at L'Anse aux Meadows in Newfoundland were dated by finding the 993 CE Miyake event and then counting tree rings, which showed that the wood is from a tree felled in 1021 CE. References

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See also
 Carrington Event
 Coronal mass ejection
 Dendrochronology
 Solar flare
 Solar storm
 Geomagnetic storm

Geomagnetic storms
Astrophysics
Geophysics
Stratigraphy
Dendrology