
Gamma-ray burst 'hit Earth in 8th Century' - arethuza
http://www.bbc.co.uk/news/science-environment-21082617
======
arethuza
The Wikipedia page on the 774-774 C14 spike even mentions that there _might_
be an eye-witness account of a "red cross" in the sky:

<http://en.wikipedia.org/wiki/774%E2%80%93775_radiation_burst>

~~~
defrost
What that article tells us is that there was a 1.2% spike in Carbon-14 in 774
in Japan.

What it doesn't tell us is if that spike was local to Japan, to the Northern
Hemisphere, or was a global spike.

There are three possible reasons for an increase in Carbon-14 (and
combinations thereof); more Carbon in the upper atmosphere (either local to
the cell above Japan or more extensive), a loop in the Earth's geomagnetic
field increasing the amount of cosmic rays interacting with Carbon (with no
change in external cosmic ray levels), or an increase in the external cosmic
rays striking the Earth (with various possible extra terrestrial causes).

More data and a better understanding of the Carbon cycle are needed to move
beyond speculation.

~~~
youngerdryas
From the article:

 _In Antarctica, too, there was a spike in levels of a form of beryllium -
beryllium-10 - in the ice.

These isotopes are created when intense radiation hits the atoms in the upper
atmosphere, suggesting that a blast of energy had once hit our planet from
space.

Using tree rings and ice-core data, researchers were able to pinpoint that
this would have occurred between the years AD 774 and AD 775, but the cause of
the event was a puzzle._

~~~
defrost
There are several articles in play here, the OP BBC News article, the
wikipedia article (linked by the person I replied to and the one to which I
referred) and the primary source papers about Carbon in Japan and Beryllium in
Antartica.

My points stand, increased external cosmic rays (for whatever reason, flares /
nova / etc.) are not the only explanation for relatively low spikes in
isotopes.

~~~
youngerdryas
From the article at the bottom of the Wiki:

 _When the scientists checked the carbon-14 levels in the cedar tree rings,
though, they noticed something strange: a spike in carbon-14 corresponding to
the years 774 and 775 AD. It's normal for carbon-14 concentrations to vary a
little bit from year to year, but the normal variation is just five-hundredths
of a percent. During 774 and 775, the levels jumped by more than 1 percent --
a dramatic leap.

What kind of event would have showered Earth in the kind of radiation
necessary to make so much carbon-14? Could a supernova do it? Supernovas do
sizzle with gamma rays, which can produce carbon-14 in the atmosphere. Yet
even the supernovas that happened in 1006 and 1054 AD -- which, unlike the 774
event, were dramatic enough to catch the eyes of ancient astronomers --
weren't big enough to leave a carbon-14 fingerprint in tree rings. If it was a
supernova, it would have to be a strange one: the Invisible Man of supernovas,
incredibly powerful yet unseen.

Indeed, astronomers can still see remnants of the 1006 and 1054 supernovas
today. If a bright supernova occurred in 774, we should see a correspondingly
glaring source of X-rays and radio waves somewhere nearby -- but we don't.

Could our own sun be the culprit? Solar flares douse the atmosphere in high-
energy protons, which can also produce carbon-14. But a solar flare capable of
making enough carbon-14 to explain the tree rings would be bigger than any
solar flare ever recorded, say the scientists.

Though it is not beyond the imagination that our sun could have belched out
such a "super flare," someone on Earth would surely have noticed and made a
record of the resulting auroras, which would be unlike anything ever seen
before. And if the auroras weren't worth writing home about, surely the mass
extinction would be, as it's likely that the flare would destroy the Earth's
protective ozone layer.

Not everyone is convinced that we should rule out the solar flare option,
though. Maybe conditions were just right for a ho-hum flare to create a surge
of extremely high energy protons. Or maybe, instead of just one flare, the sun
let loose a series of smaller ones over a period of years.

Whatever happened, there are hints that it was a global phenomenon, not a
local one. Carbon-14 levels in trees from North America and Europe were
elevated around that time, too. All the way in Antarctica, layers of snow and
ice were laced with traces of another isotope made by cosmic rays,
beryllium-10. Though it's difficult to put a precise date on the sudden peak
in beryllium-10, it seems to have occurred around the same time as the
carbon-14 spike._

~~~
defrost
Yes, thank you, I read the article.

Again, an increase in cosmic ray levels striking the Earth is only one
possible cause for the observations.

Oddly enough, while no expert in the field, I did spend a decade working with
high resolution radiometric and magnetic survey equipment measuring the global
magnetic field, local and diurnal variations, ground radiation and performing
numerous high altitude stacks to plot the falloff of cosmic ray intensities
through the atmosphere. This was performed in both hemispheres and near both
poles and totalled several million line kilometres. Writing the software to
process all that data gave me a little insight into the issues and the
opportunity to work with people that had spent their careers in the field.

What the spikes tell us is that there was minor increase in isotope
production, most probably in the upper atmosphere.

Clearly this could be driven by either an increase in raw material in the
upper atmosphere (equatorial volcanic explosion is one possibility), or an
increase in cosmic ray levels within the atmosphere (variations in the global
magnetic field lines could account for that) OR an increase in the amount of
external cosmic rays (which brings us to the guesswork being expounded in the
article you so kindly quoted).

~~~
edmccard
I'm no expert either, but I was under the impression that the paleomagnetic
record is pretty good for at least the last thousand years. So a magnetic
variation which could cause a 20-times-normal variation in the production of
carbon-14 (from 5/100 of a percent to 1 percent) would have left some
evidence?

Likewise for volcanic explosions, especially considering the narrow time
scale; enough material was pumped into the atmosphere to cause that 20-fold
increase in variation, but its effects were gone in a year or less?

Anyway, I know that mainstream science reporting is not the best, but just
because scientists don't explicitly say "we've considered alternate
explanations and found them less likely" doesn't mean they haven't done that.

~~~
defrost
From the wikipedia account, assuming it's accurate;

> The 774–775 carbon-14 spike was an increase of 1.2% in the carbon-14 content
> of tree rings during the years AD 774 or 775, which was about 20 times
> higher than the normal rate of variation.

A somewhat convoluted way of saying that the _increase_ was only 1.2%, but
this was an uncommon variation (a spike) as most of the time (year to year)(?)
variations where 20 times smaller.

Without delving into the mechanics of possible transfer functions and
localised concentration for other reasons and just going for a simple linear
coupling ... this could simply mean that 1.2% more material was raised up or
that 1.2% more cosmic rays were being let through ... and that this unusual
(like an eruption, like field lines hiccuping, like a flare or a nova) as
"normally" you see a much smaller variation in isotope levels.

Now the paleomagnetic record isn't continuous and year by year globally
complete, it's formed from spot observations of the magnetic orientation at
ground level in rock flows as they cooled. Inference of field strength at
ground level from this is difficult, and inference from that to field
orientation a few kilometers overhead is, umm, akin to reading tea leaves.

The IGRF (International Geomagnetic Field) is a richly structured and
constantly fluctuating 3D beast that pulses on a daily basis and can only be
coarsely approximated with confidence over five year intervals (the spherical
harmonics used for this are fun).

> but just because scientists don't explicitly say "we've considered alternate
> explanations and found them less likely" doesn't mean they haven't done
> that.

A moot point as nor does it mean they have; what we have is mainstream
reporting on the speculations of those scientists that are hypothesizing on
the assumption that increased isotope production was caused by an increase in
external cosmic ray levels. There are possibilities that arise from the
assumption of no such increase that are equally interesting and have similar
probabilities (ie equally difficult to quantify)

------
panacea
I've always been saddened by the fact that we're so far away from other large
cosmological entities that it's almost guaranteed that we'll never venture
beyond our solar system and visit other stars.

The flipside to this, is that we appear to live in a bit of a 'The Shire' and
the distances mean we don't have to deal with stars going supernova or showers
of meteors raining down on our heads with any sort of meaningful frequency.

However, I'm equally fascinated and overjoyed at just how much looking around
at the wider Universe we're managing to get done considering that, relatively
speaking, our window of observation as a species is akin to a polaroid
snapshot from a infinitesimally small fraction of this period.

~~~
arethuza
"it's almost guaranteed that we'll never venture beyond our solar system"

I like to think that it's almost guaranteed that we _will_ venture beyond our
solar system - it might take hundreds or years (or maybe thousands) but, in
one form or another, we'll get there.

[I suspect that transporting big lumps of meat about probably isn't the way
ahead - travelling in an uploaded form seems far more likely (e.g. Greg Egan's
_Diaspora_ ).]

~~~
panacea
A pessimistic way of thinking (apologies for my disposition on this
entrepreneurial board) is that the odds of being born into an era with the
highest population ever to live, are just that: the highest probability.

That we're going to solve the energy crisis, and that this era isn't a brief
spike in human population, burning at breakneck speed through the very finite
'windfall' of exploiting found reserves of fossil fuels seems unlikely.

~~~
guard-of-terra
But someone born in ancient Rome could say the same thing about an era with
the highest population.

But we now know there's more to mankind than Rome.

------
clux
Speculative non-article..

From the last paragraph:

He said: "A solar proton event and a short gamma-ray burst are both possible
explanations, but based on the rates that we know about in the Universe, the
gamma-ray burst explanation is about 10,000 times less likely to be true in
that time period."

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KwanEsq
As it is slightly ambiguous in the article, yes the Professor Adrian Melott
quoted in the last two paragraphs is one of the authors of the previously
mentioned solar flare hypothesis paper.

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teeja
BBC's headline is completely misleading; the researchers state that a solar-
flare is a much likelier cause. There needs to be a science journalism bar
exam.

------
__--__
Interesting article, but I'm more interested in what effect (if any) a gamma-
ray burst would have had on the people and animals who were exposed to it.
Does anyone have any ideas or theories?

