I've used some of the world's great telescopes to search for planets and study stars. Our team has recently looked at Earth's forests in order to understand the universe.
We studied the radioactive signatures left in tree rings around the world to find out if there have beenradiation storms over the past 10,000 years.
"solar superflares" are not the culprit, but the true cause remains a mystery.
There is a history in tree rings.
Nitrogen atoms are turned into carbon-14 by high-energy radiation. The radiocarbon goes through the air and the oceans, into the ocean and into you and me, as well as into animals and plants.
It is a blessing to archaeologists. Carbon-14 can be used as a clock to measure the age of organic samples when it decays back into nitrogen after being created.
This is of equal value to the astronomer. Cosmic rays are high energy particles that go back thousands of years.
Earth and the sun have magnetic fields that protect them from the rays of the stars. When the magnetic fields are less strong, more Cosmic rays reach Earth.
The 11-year cycle of the sun's magnetic field and the reversals of Earth's magnetic field are explained by the rise and fall of carbon 14 levels in tree rings.
The Miyake events took place.
We can't explain the events that are recorded in tree rings. A spike in the radiocarbon content of tree rings was discovered by Fusa Miyake. Several years' worth of rays must have arrived at once because it was so large.
More teams have joined the search and the evidence from the tree ring has been uncovered.
There has been a revolution in archaeology. Finding one of these short, sharp spikes in an ancient sample pins its date down to a single year, instead of decades or centuries of uncertainty.
The exact year of the first European settlement in the Americas can be found in the 993 AD event.
Huge radiation pulse could happen again.
The Miyake events are a mystery in astronomy.
How do you get such a large amount of radiation? There are a lot of papers that blame comets, supernovae, and other things.
The most popular explanation is that Miyake events are solar superflares. The biggest recorded in the modern era was the Carrington event of 1859, which was 50 times more energetic.
It would ruin power grids, telecommunications and satellites. A 1% chance per decade is a serious risk.
Data is noisy.
In order to pull out the intensity, timing, and duration of Miyake events, our team at UQ had to sift through all the tree ring data.
To do this we had to develop software to solve a system of equations that model how radiocarbon filters through the entire global carbon cycle and to work out what fraction ends up in trees in what years.
The first systematic study of all the published data on Miyake events has just been released. Open source modeling software has been released.
There are storms of flares on the sun.
Between one and four ordinary years' worth of radiation can be delivered in one go. It was thought that trees closer to Earth's poles recorded a bigger spike, but our research shows this is not the case.
In the sun's activity cycle, these events can arrive at any time. The peak of the cycle is when solar flares occur.
The spikes seem to take longer than they can be explained by the carbon cycle. It's possible that the events can take longer than a year, which is not expected for a giant solar flare, or that the growing seasons of the trees are not as long as previously thought.
The sun is the most likely culprit. Our results show that we're seeing something more like a storm of solar flares.
We need more data to figure out what happens in these events. We need more tree rings to get this data.
This is science in many different ways. I think about telescopes that are clean and precise, but it's hard to understand the Earth.
More information: Qingyuan Zhang et al, Modelling cosmic radiation events in the tree-ring radiocarbon record, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences (2022). DOI: 10.1098/rspa.2022.0497 Journal information: Proceedings of the Royal Society AUnder a Creative Commons license, this article is re-posted. The original article is worth a read.
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