Oct 12, 2023 - Science

Scientists use tree rings to find evidence of largest solar storm on record

Tree rings of a buried subfossil tree in the Drouzet river.

Tree rings of a buried subfossil tree in the Drouzet River in the Southern French Alps. Photo Credit: Cécile Miramont

The largest known solar storm struck Earth more than 14,000 years ago, according to a new study of the growth rings in ancient trees.

Why it matters: The discovery illustrates the immense power of solar storms — and underscores the danger they pose today.

  • A similar storm striking Earth at present would likely knock out radio communications and satellites while causing widespread blackouts, said Tim Heaton, a professor of applied statistics at the University of Leeds and a co-author of the new study in the Philosophical Transactions of the Royal Society A journal.
  • "Extreme solar storms could have huge impacts on Earth," Heaton said, "They would also create severe radiation risks to astronauts."

How it works: Carbon-14 (C14), the rarest carbon isotope on the planet, is primarily formed by cosmic rays emitted by the Sun through solar flares and coronal mass ejections interacting with the Earth's atmosphere.

  • The radioactive carbon isotope can eventually be absorbed by living organisms — like trees, plants and animals — throughout their lifetimes.
  • Scientists use C14 levels and its radioactive decay rate to estimate how long an organism has been dead, a process called radiocarbon dating.
  • But the amount of C14 in certain organisms can also reflect how abundant the isotope was in the atmosphere and, by extension, the amount of solar activity present at a given time.
  • Trees are ideal for determining atmospheric C14 levels because they capture yearly records of Earth's past climate in their annual growth rings.

What they found: The team of scientists discovered evidence of the storm by measuring the levels of C14 in rings of ancient pine trees that lived in the French Alps more than 14,000 years ago.

  • They found a sharp increase of C14 levels precisely 14,300 years ago followed by a gradual decrease in the following years.
  • The researchers hypothesized that the abrupt spike was likely from a massive solar storm that was probably two times larger than all other major storms on record.

The intrigue: To verify their hypothesis, the researchers turned to ice cores, or cylinders of ice drilled from ice sheets and glaciers.

  • As with trees, evidence of past solar storms can be detected in ancient ice by the presence of radioactive isotopes of beryllium and chlorine, which also form when cosmic rays interact with the atmosphere.
  • They discovered the C14 spike in the trees corresponded with an unusual concentration of beryllium-10 from between 14,301 and 14,292 years ago found in a Greenland ice core.

The big picture: In recent decades, scientists, policy makers and the public have been paying increased attention to solar storms and their threat to our modern, technology-dependent way of life, Axios' Miriam Kramer reports.

  • The National Weather Service, for example, began consistently predicting space weather in the 2000s, while FEMA in recent years started creating guidance for federal agencies to prepare for, and respond to, space weather events.
  • The Sun's current solar cycle, which may peak in early 2024, is expected to be more active than previous ones based on observations from earlier this year.

Go deeper: The Sun is defying forecasts

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