| Tikalon Blog is now in archive mode.
An easily printed and saved version of this article, and a link
to a directory of all articles, can be found below: |
|
This article |
| Directory of all articles |
Tree Rings
July 30, 2012
For the past thirty years, my
family has been
protecting the environment in one small way. Every year, we harvest our own
Christmas tree from a local
Christmas tree farm. How is this good for the environment? First, it eliminates the manufacture and transportation of the
artificial tree we would buy in its place. The manufacture includes
toxic and non-
biodegradable materials, and the long distance transport (usually from
China) involves a
fossil fuel burn.
A
natural tree sequesters carbon from the
atmosphere while it grows and provides a
habitat for wildlife. The tree we cut each year is replaced by another that's planted on the farm, so the process is
sustainable. Sure, our tree is discarded afterwards, but its
decomposition in a
landfill takes a lot longer than the time it took to grow, so there really is a net carbon sequestration.
When our
children were younger, we would save a disk-shaped slice from the
tree stump as a record of the tree. We would count the
growth rings,a method of finding the age of a tree, and we would look for wide rings and narrow rings indicative of better and worse growing seasons. We were practicing
dendrochronology, the scientific method of dating using tree rings.
Left image, a slice from the 1990 Gualtieri Christmas tree. The rings are hard to see after 22 years, but Christmas trees are generally eight years old when cut. Right image, growth rings of a tree in Pacific Spirit Regional Park, Vancouver, by Lawrence Murray, via Wikimedia Commons)
Since humans use a lot of
wood, there's a record of
climate embedded in many
dwellings. There's even an inverse method, called
dendroarchaeology, by which you can date a structure by looking at the growth rings in its wood. You just do a
cross-correlation of the ring patterns in the wood with an historical record of growth rings, and out pops your date.
Tree growth rings have more information than what's present in their width. The
14C isotope of carbon holds clues to their age and environment. An increase in
14C concentration can be the result of a
radiation event, such as a
solar flare, or
cosmic rays. One interesting example of such a
14C excess is reported in a recent article in
Nature by
scientists at the
Solar-Terrestrial Environment Laboratory and the
Center for Chronological Research,
Nagoya University,
Japan.[1-4]
The Japanese scientists measured the
14C concentration in the growth rings of
cedar trees from 750
AD to 820 AD with an ultimate resolution of a single year. They found that
14C increased by a phenomenal 1.2% for the years 774-775, much larger than any affect caused by solar radiation. These results are consistent with coarser resolution measurements for
North American and
European trees.[1] Also in concurrence are
10Be measurements for
Antarctic ice cores at the same time.[4]
14C is produced when cosmic rays transform
14N to
14C.[2] This reaction is fuel to a lesser extent by natural solar radiation, and this enables
14C dating, since the isotope is replenished continually. The annual variation in solar production of
14C is just 0.05%, or a twentieth of that seen for the 774-775 time period.[3-4]
The one problem with this observation, however, is that there are no dramatic signs, such as
auroras, recorded in
human history that mark this event. One scenario, a nearby
supernova explosion, appears to be ruled out. Two supernovas, one in
1006, and the
1054 supernova that caused the
Crab Nebula, were observed on
Earth, and even these were too small to cause a spike in
14C.[2-3] Both of these supernovas were visible, even in
daytime skies, for a period of weeks.[3]
Composite image of the Crab Nebula, NGC 1952. This image combines visible, infrared and X-ray images by various NASA telescopes.
Image credits: NASA/ESA/J.Hester & A.Loll (optical); NASA/JPL-Caltech/R.Gehrz (Infrared); NASA/CXC/J.Hester (X-ray)
(Via Wikimedia Commons))
One possibility is that the source erupted in
southern skies, and it was not observed; however, its
remnant would have been detected by now.[2-3]
Roger of Wendover, a
thirteenth century English chronicler, wrote about events, such as signs in the sky after
sunset (auroras), that might indicate a
solar flare.[3-4]
Daniel Baker, a
space physicist at the
Laboratory for Atmospheric and Space Physics of the
University of Colorado (Boulder, Colorado) thinks that a solar flare is possibility;[2] while
Igor Moskalenko, an
astrophysicist at
Stanford University, is quoted in the
Daily Mail as saying, "I cannot imagine a single flare which would be so bright... It may be a series of weaker flares over the period of one to three years."[3]
In the midst of all this uncertainty is an hypothesis by Jonathon Allen, a
biochemistry major at the
University of California at Santa Cruz, who decided to
Google historical references for those dates.[5-6] The historical record is sparse, but he did find a mention of an event for 744 in the
Anglo-Saxon Chronicle, a history of
England written in the
ninth century. An online version of this Chronicle was available from the
Avalon Project hosted by
Yale University.[6]
"Her oðywde read Cristes mæl on heofenum æfter sunnan setlgange..."[7]
"This year also appeared in the heavens a red crucifix, after sunset..."[8]
The red color may indicate that the object is hidden behind
interstellar dust clouds[5-6] Its appearance at sunset would put the object's location too near the
Sun to be observed easily.[6]
Portion of the first page of the Anglo Saxon Peterborough Chronicle, c. 1150. This is one of a number of annals that are collectively known as the Anglo-Saxon Chronicle. (Via Wikimedia Commons))
References:
- Fusa Miyake, Kentaro Nagaya, Kimiaki Masuda & Toshio Nakamura, "A signature of cosmic-ray increase in ad 774–775 from tree rings in Japan," Nature, vol. 486, no. 7402 (June 14, 2012), pp. 240-242.
- Richard A. Lovett, "Mysterious radiation burst recorded in tree rings, Nature News, June 3, 2012.
- Eddie Wrenn, "Mystery over the giant cosmic explosion of 774AD, which has left absolutely no trace - except deep within the bark of two cedar trees," Daily Mail (UK), June 4, 2012.
- Jessica Griggs, "Vast cosmic event leaves record in ancient trees," New Scientist, June 3, 2012.
- Eddie Wrenn, "Does a single report of a 'red cross in the skies' over Britain in AD774 prove a supernova exploded in the heavens?," Daily Mail (UK), June 29, 2012.
- Richard A. Lovett, Supernova Could Have Caused Mysterious 'Red Crucifix' in the Sky in A.D. 774," Scientific American, June 27, 2012.
- Tony Jebson, The Anglo-Saxon Chronicle We Site, December 5, 2006.
- The Anglo-Saxon Chronicle : Eighth Century, Lillian Goldman Law Library, Yale University
Permanent Link to this article
Linked Keywords: Family; environmentalism; protecting the environment; Christmas tree; Christmas tree farm; artificial Christmas tree">artificial tree; toxic; biodegradation; biodegradable; material; China; fossil fuelvcombustion; burn; tree; carbon sequestration; atmosphere of Earth; habitat for wildlife; renewable resource; sustainable; decomposition; landfill; child; children; tree stump; growth rings; dendrochronology; Pacific Spirit Regional Park; Vancouver; Lawrence Murray; Wikimedia Commons; wood; climate; dwelling; dendroarchaeology; cross-correlation; carbon-14; 14C; isotope of carbon; radiation; solar flare; cosmic ray; Nature; scientist; Solar-Terrestrial Environment Laboratory; Center for Chronological Research; Nagoya University; Japan; Cedrus; cedar tree; Anno Domini; AD; North America; Europe; 10Be; Antarctic; ice core; aurora; history of the world; human history; supernova; supernova explosion; SN 1006; SN 1054; 1054 supernova; Crab Nebula; Earth; daytime; Crab Nebula, NGC 1952; visible light; infrared; X-ray; Chandra; Hubble; Spitzer; celestial sphere; southern sky; supernova remnant; Roger of Wendover; thirteenth century; historians of England in the Middle Ages; English chronicler; sunset; solar flare; Daniel Baker; space physicist; Laboratory for Atmospheric and Space Physics; University of Colorado (Boulder, Colorado); Igor Moskalenko; astrophysicist; Stanford University; Daily Mail; biochemistry; University of California at Santa Cruz; Google Search; Google; Anglo-Saxon Chronicle; England; ninth century; Avalon Project; Yale University; cosmic dust; interstellar dust cloud; Sun; Anglo Saxon; Peterborough Chronicle; Anglo-Saxon Chronicle.