Ancient Trees Hold Record of Mysterious Cosmic Event

By Sophie Bushwick | June 4, 2012 1:36 pm

tree rings

A tree’s rings mark both its age and the local environmental conditions, which allows researchers to track historical changes in an ecosystem. But tree rings can also encode signals from beyond Earth: Ancient trees in the Northern Hemisphere have preserved a radioactive souvenir from a 1200-year-old burst of cosmic rays.

Using tree rings, researchers have collected 3,000 years worth of data on the presence of the radioactive carbon isotope carbon-14 in the atmosphere. When examining the ebb and flow of carbon-14 over time, Japanese researchers noticed an increase during the 8th and 9th centuries CE. They decided to look at that period in detail by studying the yearly concentrations of carbon-14 in Japanese cedar trees. The cedars revealed a 1.2 percent carbon-14 spike that lasted less than a year between 774 and 775 CE, which corresponded with similar spikes in North American and European trees. This peak, twenty times the amount of variation normally caused by the sun’s fluctuations, resulted from a short-term burst of cosmic rays. But where did those rays come from—a supernova, a solar flare, or some other source?

Carbon-14 can form when gamma rays, spewed from a supernova, hit the Earth’s atmosphere. But any supernova big enough to cause the spike in radioactive carbon would have also been bright enough for contemporary astronomers to observe, as they did with two 11th-century blasts. The hypothetical carbon-14-producing supernova would have been even brighter than the 11th century ones, which were too weak to create any carbon-14.

A solar flare could have made carbon-14 by shooting protons at Earth, but to produce a peak the size of the one the tree rings recorded, the solar flare would have to have been a “super flare,” large enough to destroy significant amounts of ozone, causing easily visible auroras, and causing mass extinctions.

So while the source of the cosmic rays is still unknown, the space signals recorded in trees could one day help researchers solve this astronomical puzzle. Plus, it’s just cool.

Image courtesy of codersquid / flickr

CATEGORIZED UNDER: Environment, Space
  • TC

    Our current carbon 14 testing procedures measure the rate of decay based on current carbon 14 levels on earth. What this article is saying then is that our current conclusions based on our testing is completely wrong. If the carbon 14 levels were different in the past than they are now, all of our past timelines will need to be revised. ALL of them!

  • Chris

    Gamma rays can’t transmute elements unless they have the right energy to break apart something heavier, but the odds are incredibly low. High energy particles hitting the atmosphere will produce neutrons that hit nitrogen and will produce carbon-14 and a proton.

  • paolo

    try searching in the Egyptian papyri, perhaps find the explanation.

  • Hoobie

    Would any evidence of this event be reflected in ice core samples – which go back much further than 1200 years.

  • TheCritic

    I move to have Robert Rhodes comment stricken from the record on the basis that it is made out of sheer idiocy.

    To be productive in the comments section, it would probably be more beneficial to just leave your own political bias out of the discussion, especially when referring to scientific matters. If not done, then all of your speculation becomes instantly tinged with bias and, therefore, useless.

  • James1st

    And I agree that the Rhodes comment should be removed. Why give this person any outlet for his/her political views?
    The article was very good.

    • Veronique Greenwood

      My goodness, apologies for that getting through. Removed.

  • Bruce

    I somewhat disagree with TheCritic. I, as a Christian, have many friends who believe in creationism. While I don’t, vociferously, I think it’s good to know your opposition. that said, this may be the wrong space to do it.

    Otherwise, I find this fascinating!

  • jcr

    I don’t think this introduces any significant error in carbon dating. The jump is stated to be 1.2%, and based on a half life of 5730 years the level of carbon 14 drops 1.2% in 70 years. Because the decay is exponential, the 70 year error is the same whether you are dating something 1,000 or 30,000 years old.

  • m

    The only thing I dont like is this “CE” business. I mean really – political correctness has gone totally berserk.

    What about a collision? Could the element have been produced that way?

  • amphiox

    What this article is saying then is that our current conclusions based on our testing is completely wrong. If the carbon 14 levels were different in the past than they are now, all of our past timelines will need to be revised. ALL of them!

    No it doesn’t. At MOST is would make C14 dating suspect, but C14 dating only applies to up to 50 000 years ago. None of the other methods of dating are affected by this in any way at all.

    And the very fact that scientists were able to identify and date this spike in C14 levels means that they can also calibrate whatever effect it may have on C14 dating and account for it.

    Furthermore, the accuracy of C14 dating can and has been cross-checked against other methods of dating, including the use of tree rings.

  • John Roth

    The amount of C14 in the atmosphere is quite variable in different eras. See the topic Calibration in the Wikipedia article; many researchers give uncalibrated dates precisely because of the problems in turning them into calibrated dates.

  • Daniel J. Andrews

    Amphiox has it right. There is a C14 calibration chart that determines levels of C14 over time. They use tree rings, lake varves, and ice cores (at least three independent means of checking how levels vary over time). This information is used to add correction factors to C14-derived dates. A good introductory book on this is Nature’s Clocks: How Scientists Measure the Age of Almost Everything (comes in both e-book and hard copy format).

  • Iain

    Aliens, they’d had enough of us and that was part of the residue of their thrusters on maximum boost.

  • paublus-americanus

    @Iain—-no it is not leaving, it is in the arrival. As they come in they de-celerate, in doing this at first they are very high speed, high delta v, so a pulse as they burst their beam earthwards in slowing down to get here. Sort of like the jets used landing on the lunar surface. At high delta, the particles from their dielectric wall accelerators, pulse beams of mega-watt particles which are doppler shifted into the gamma. Hoo-boy we get fried taters free.

  • Kurt Cagle

    I can think of a few possibilities. The first is to question the dating of the 11th century references. Chronology systems in the late middle ages were far from exact, and there were in fact several different systems that were in use in various parts of Europe during that era. The second possibility is that the gamma burst producer in question may have produced radiation well above the visible part of the spectrum (certain X-Ray bursters in particular come to mind). One other possibility might have been a reasonably large meteor, especially if it was carbonaceous. If it had come down over the Northern Pacific, Siberia or North America, for instance, the resulting explosion might have vaporized a high enough concentration of C14 to be picked up by trees, especially if the meteor was an air burst. The fact that the concentration seemed to be primarily in the northern hemisphere is perhaps telling here as well, as there would be relatively little circulation between the hemispheres in the event of a disrupted meteor. Finally, vaporizing in any of those regions it would not have been visible to observers in Europe.


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