Ancient tree ring radiocarbon increases do not coincide with the solar cycle. 
Trees add rings to their trunks as they grow. 
Scientists analyse the chemical makeup of these rings.
Scientists can find out more about the past of the environment.

Tree rings can keep a snapshot of the Earth and its surroundings at various times in addition to being a fantastic record of a tree's existence. Australian researchers have now discovered evidence of massive radiation storms that periodically saturate the earth yet their origin is still unknown.

Less than a day after astronomers discovered massive solar flares, Earth experienced the strongest geomagnetic storm ever recorded in 1859. Telegraph systems shorted out, and fires even started in telegraph stations. 

It wasn't the first, it won't be the last, and it might not even be the most powerful, but it was close. Natural records found in tree rings indicate that an event roughly ten times stronger than what the Sun is capable of creating occurred around the year 774 CE. In fact, six significant radiation increases known as Miyake events over the past 10,000 years or so.

There is a high likelihood that it would take years for our enormous power grids and communication networks to recover if anything similar occurred now. So, in order to better understand them, scientists at the University of Queensland looked into the past occurrences of Miyake events to determine their strength and when they took place in relation to the Sun's regular cycles.

The researchers created a system to evaluate and model the global carbon cycle over the past 10,000 years using a vast amount of available data on tree rings from around the world. They were specifically searching for carbon-14, a radioactive isotope created when cosmic radiation interacts with the Earth's atmosphere.

As the tree grows, it absorbs this and stores the information in its rings. Large radiation storms from space can be indicated by sudden, rapid rises in carbon-14 levels. As a result, the scientists made an unusual and somewhat unsettling discovery.

Since Miyake events are typically thought to be huge solar flares, they anticipated finding them concentrated around the solar maximum, the Sun's 11-year cycle's most active period. Contrary to expectations, this wasn't the case, and in some instances, the symptoms appeared to linger longer than normal for flares. For instance, an event in 663 BCE appeared to last three years, whereas one in 5480 BCE increased over a full ten years.

The study's first author, Qingyuan Zhang, stated, 'We've proven they're not connected with sunspot activity, and some actually survive one or two years.' What we might be seeing is an astronomical 'storm' or outburst as opposed to a single instantaneous explosion or flare.

Supernovae, gamma ray bursts, and magnetar outbursts are further possibilities, however the team claims there is currently no evidence for any of these in the sky. For reference, the Crab Nebula, which was a supernova that occurred in 1054, is still seen today.