Scientists have new theory on ice age

Lawrence Journal-World ^ | 12/29/2003 | Alea Smith

[U S Army EOD]

So nature has it own neutron bomb.

[VadeRetro]

Article FULLY explains how this could cause an ice age.

You're extrapolating madly, to the point of confabulation. Ms. Smith provides little more than hand-waving. Here's the key passage:

The Earth's atmosphere would absorb the energy, which would separate nitrogen and oxygen molecules in the atmosphere, creating nitrogen oxides, including nitrogen dioxide, which plays a major role in the atmospheric reactions that produce ground-level ozone or smog.

The scientists' research has led them to believe the long-term effects of gamma-ray bursts would deplete the ozone and cause global cooling and acid rain. It would also increase the amount of direct ultraviolet rays from the sun, which only reach a depth of 10 meters in water. This explains why only shallow marine species were involved in the extinction.

It is quite unclear what exactly produces the "global cooling." For instance, does the ozone depletion mentioned right in front of it figure in the chain of causation or is it just another effect? Even the wording is ambiguous. What exactly causes ambient temperatures to fall worldwide? Runaway albedo effect? Decreased greenhouse gasses? What?

[gcruse]

wow

[Ichneumon]

It is quite unclear what exactly produces the "global cooling." For instance, does the ozone depletion mentioned right in front of it figure in the chain of causation or is it just another effect? Even the wording is ambiguous. What exactly causes ambient temperatures to fall worldwide? Runaway albedo effect? Decreased greenhouse gasses? What?

Relevant to the point made in post #17, concerning how "science reporting" often garbles the original works, I'd like to remind folks that abstracts of almost every scientific paper published in the past decade or two are available online, and the full text of a substantial fraction of the papers are available as well.

It took me all of three minutes with Google to track down the paper described in the article which started this thread, and it turns out that the whole paper is available online:

"Did a gamma-ray burst initiate the late Ordovician mass extinction?", A.L. Melott, B.S. Lieberman, C.M. Laird, L.D. Martin, M.V. Medvedev, B.C. Thomas, J.K. Cannizzo, N. Gehrels, & C.H. Jackman

Abstract: At least five times in the history of life, the Earth experienced mass extinctions that eliminated a large percentage of the biota. Many possible causes have been documented, and gamma-ray bursts (GRB) may also have contributed. GRB (Mészáros, 2001) produce a flux of radiation detectable across the observable Universe. A GRB within our own galaxy could do considerable damage to the Earth's biosphere (Thorsett, 1995; Scalo & Wheeler, 2002; Dar & DeRújula, 2002). Rate estimates (Thorsett, 1995) suggest that a number of such GRB may lie within the fossil record. The late Ordovician mass extinction shows a water-depth dependent extinction pattern that is a natural result of the attenuation of the strong ultraviolet radiation expected to result from a nearby GRB. In addition, a GRB would trigger global cooling which is associated with this mass extinction.

When in doubt, consult the original source.

(The paper is in PDF format ["Portable Document Format"], as are most scientific papers and many other documents online. If you don't already have it, you'll need to install the free Adobe Acrobat Reader.)

The key passage which describes the mechanism producing global cooling is:

The resulting highly reactive products of N₂ dissociation form various oxides of nitrogen. Nitric acid greatly exceeding anthropogenic levels is a probable product (Thorsett, 1995). Global cooling is expected (Reid, 1978) from the absorption of visible light by NO₂.

The paper cited in support of global cooling is:

Reid, G.C., McAfee, J.R., Crutzen, P.J. (1978) Effects of intense stratospheric ionization events. Nature, 275. 489-492.

I can't find that full paper online (if anyone's curious they can always go look up the back issue of Nature in any well-stocked library), but I found a couple of synopses:

A supernova remnant shell (SNR) is used to explain the mass extinctions of the past. Shows how a SNR would increase cosmic ray levels reaching the earth, (100-1,000 times present level for several hundred years), increase atmospheric nitrogen levels, and deplete the ozone. Believes the Cretaceous-Tertiary (K-T) extinctions were caused by this phenomenon

And:

Speculates that the Earth must have passed through the remnant shell of ancient supernovae which would have resulted in periods of harsh environmental conditions. Specifically increased UV radiation, a cooler, drier climate, and reduced photosynthetic activity.

Not much detail there, but related Googling turned up this more detailed article on the same recent paper:

Water would protect marine organisms from the heat of a GRB, but not from its other effects, argues Melott's team. Its gamma-rays would convert some nitrogen and oxygen in the atmosphere into nitrogen dioxide, the brownish gas present in urban smog.

Nitrogen dioxide would filter out sunlight, turning the skies dark. The cooling effect could trigger an ice age - there is evidence of widespread glaciation 440 million years ago. Nitrogen oxides also cause acid rain and destroy the ozone layer, exposing Earth to more of the Sun's harmful ultraviolet rays.

That helps clarify the short line in the paper under discussion, "Global cooling is expected [cite] from the absorption of visible light by NO2."

So there you go. The upper atmosphere would block and absorb a lot of the Sun's energy, preventing it from heating the surface where life resides. And much of the absorbed upper-atmosphere heat would be reradiated back out into space, or directly lost as more higher-energy molecules "leaked" off into space.

Sounds reasonable to me as a mechanism, but of course the remaining question is how much NO₂ would have been produced, and how hefty would the Sun-blocking effect have been?

From this good article on the same paper, we get:

Melott estimates that a burst would produce enough of the gas to darken the sky, blotting out half the visible sunlight reaching the Earth.

Yeah, that'd ruin your whole millennium...

It also included this handy graphic:

I ran across references to a few other cheery papers on the same topic:

Terry, K. D. & Tucker, W. H. 1968. Biological effects of supernovae. Science 159:421-423. (Estimate that the Earth is exposed to a radiation dose of 500 r [Roentgens -- Ich.] once every 50 m.y. and a dose of 1500 r once every 300 m.y. as a result of supernovae. It goes on to note that most lab animals die after exposures between 200-700 r).

Ruderman, M. A. 1974. Possible consequences of nearby supernova explosions for atmospheric ozone and terrestrial life. Science 184:1079-1081. (Suggests that more than 90% of the Earth's ozone may have been destroyed by supernovae radiation at least a few times during the Phanerozoic).

Clark, D. H., McCrea, W. H. and Stephenson. F. R. 1977. Frequency of nearby supernovae and climatic and biological catastrophes. Nature 265:318-319. (argues that the Earth should (on average) pass close to (within 3262 light years) a supernovae once for each galactic revolution. This pass would alter the ozone layer, reduce greenhouse warming and possibly initiate an ice-age).

The Ordovician extinction being studied in the paper which started this thread was a huge one: 60% of all marine invertebrate genera and 25% of all families went extinct. This also implies that far more than 60% of marine species went extinct, and *way* more than 60% of individual organisms died off (like 90+% of species and 98+% of organisms). Whatever caused that extinction, it was *enormous*, and nothing like a minor climactic change or continental shifts or period of increased volcano activity would qualify. Something like the cosmic gamma ray blast described in the paper is one of the few things big enough to bodyslam the Earth's biosphere like that. (List of mass extinctions)

Meanwhile, I tripped over this article which describes a paper (full text) which may have identified a "smoking gun" tying a specific cluster of recent supernovae (20 supernova explosions over the past 20 million years) to a specific (different) mass extinction in Earth's history. The Scorpius-Centaurus OB cluster made its nearest approach (130 light-years) to Earth during the period 1.5-3.5 million years ago. And the Pliocene-Pleistocene marine extinction occurred 1.8 million years ago. Further confirming the connection is a layer of the rare isotope of iron, ⁶⁰Fe in the Pliocene-Pleistocene boundary, which is a) clearly of "recent" origin since 60Fe has a half-life of 1.56 million years and none would be left from Earth's origins, and b) 60Fe is formed in supernova explosions, and c) the amount found on Earth is consistent with a supernova explosion around 100 light years away around 2 million years ago... Finally, the amount and type of marine extinctions at the PP boundary are what one would expect from the amount of Ozone-layer destruction such a supernova would cause. So supernova involvement in Earthly extinctions seems like it might be more common than previously thought. Fascinating.

I looked to see if there was a related cooling of the Earth around 2 million years ago, but since it occurred in the middle of the existing Pleistocene ice-age, it's hard to say. It might have made the existing ice age deeper or more prolonged, but that wouldn't be as obvious as the start of a temperature dip in the middle of an otherwise non-ice age period.

Yet another related find: Supernova poised to go off near Earth .

[gcruse]

Thank you for that. It gets so frustrating being unable to refute the creeps who see something they don't understand so they slam the authors and walk away.

[Ichneumon]

[Havoc:] Our tax dollars at work. Millions upon billions in grants for a bunch of degreed nutballs to theorize - a fancy word to make guessing sound more palletable.

...and then test those "guesses" to determine which ones are correct, so as to build upon the technological knowledge of the human race which has brought us so far from our hunter-gatherer beginnings. Did you "forget" to mention that part?

[polemikos:] There are more theories than there are scientists. What's up with that?

Exaggerating the number of hypotheses doesn't help your case. As far as "what's up with that", science works by having people propose as many possible explanations as they can think of, and then testing them to see which ones best explain the evidence and correctly predict the results of additional experiments and/or the nature of further evidence. If none are entirely satisfactory then it's time for more "guessing" in search of the full answer.

[Erik Latranyi:] The above article conclusively proves that science know absolutely nothing about what causes anything. Once again.

If you think that "science know [sic] absolutely nothing" about things, perhaps it has something to do with how unclear you are about straightforward notions such as what constitutes "conclusively proving" something.

Read my prior post, it shows how there's a lot more knowledge regarding and support for the ideas in the paper under discussion than you apparently grasp.

Looking at the actual contents of the paper, we see a number of things that certain folks might find educational.

First, it very clearly labels its model as hypothesis. It specifically calls it a "hypothesis" four separate times. This is the technical word for "guess", basically, so this should forestall any accusations that the authors were trying to overstate their case, or were recklessly mistaking their "guesses" for established facts.

Second, this "guess" (proposed explanation for available evidence) wasn't just something they came up with at some late-night beer-fueled bull session at the local student union because it sounded "far out, man". Instead, they base it on a great deal of prior foundation in several fields (biology, paleontology, nuclear physics, astrophysics, geology, etc.) Perhaps you missed the two and a half pages of references.

In fact, the model itself (GRBs initiating mass extinctions), as they freely admit (by citing earlier works) is not new. It has already been established as a workable theory ("theory: a coherent group of general propositions used as principles of explanation for a class of phenomena") by prior research and verifications. Their own contribution in this paper is simply to apply that theory to a particular case (the Ordovician mass extinction) and see whether the GRB model well explains the features of that particular mass extinction, or not. They state their hypothesis explicitly: "We suggest that the late Ordovician extinction may have been initiated by a GRB."

Third, this is what's known as testing a model. That's how science separates the correct models from the incorrect ones. That's how it progresses beyond "knowing absolutely nothing" on a subject to knowing a great deal about it and increasing human knowledge. That's what makes it worth "Millions upon billions in grants" to pay scientists to engage in a complex undertaking which begins (but hardly ends) with making "guesses". Not that this particular one cost much money, they appear to have mostly spent their time digging up relevant prior papers and bringing together the relevant results to check out the details.

Fourth, the authors of this paper did a lot more than just go, "we're calling a press conference to say that gosh, who knows, maybe GRBs made the Earth cold or something and had something to do with an extinction or two". (In fact, no press conference was involved, they just published their paper and several outlets picked up on it.) They spent their time checking to see how well predictions of the GRB model lined up with known findings about the Ordovician extinction. First they worked out the expected theoretical results of a GRB:

1. "A strong burst of cosmic rays at the Earth would be expected only for isotropic GRB emission with a very hard spectrum. Thus, the instantaneous biotic effects of GRB will be moderate and confined to the facing side of the Earth."

2. "Long-term effects of GRB would spread around the Earth and include ozone layer depletion, global cooling, acid rain, and radionuclide production."

3. "A GRB may have paradoxically produced darkened skies and heightened UV radiation. Modest increases in UV flux, particularly around 300 nm, can be lethal to a variety of organisms (Kiesecker et al., 2001; Hader et al., 2003), including the phytoplankton which are the basis for the marine food chain as well as oxygen production."

Fifth, they then compared the magnitudes and characteristics of those predicted results with the actual features of the Ordovician extinction:

1. Species living in shallow water were more likely to go extinct than those dwelling in deeper water (UV light does not penetrate into deep water).

2. There is a very strong correlation between the amount of time that a trilobite species spent in a planktonic larval stage and its chance of extinction in the Ordovician (UV affects small creatures more than large).

3. The Ordovician extinction is already known as a period of two alternating cooling/warming cycles, and cooling followed by warming would be expected from a GRB event.

4. Supernovae tend to occur in clusters, and the spacing of the two Ordovician cooling cycles is consistent with supernovae "chain" spacing.

5. The Ordovician was not a period where known causes of other cooling cycles or ice ages were in effect.

6. Other kinds of extinction-causing changes would have produced different patterns of extinction.

Sixth, they outline one type of further investigation that could be done to confirm or disprove the hypothesis, so that further knowledge can be gained on this issue:

"This hypothesis suggests that a closer look be taken at the geographical distribution of extinctions in the late Ordovician along the line of what Anstey et al. (2003) have done. A strong initial muon burst might seriously irradiate only one side of the Earth to considerable ocean depth, while the other side would mostly be irradiated by post-burst solar UV due to ozone loss. This suggests an extinction pattern emphasizing depthdependent extinction predominantly in one hemisphere, with more complete extinction in the other hemisphere."

Seventh, by publishing the paper they knowingly initiate the next stage which is always the purpose of scientific publishing: To invite additions from the rest of the scientific community concerning things the authors may have overlooked, possible contrary evidence or competing theories, confirming evidence from others who might have knowledge that seems to make more sense in light of the hypothesis, suggested action on what evidence might be specifically hunted for (or experiments performed) that would have the best chance of proving/disproving the hypothesis, etc.

The work on this hypothesis is not finished, of course, but then in a real sense no scientific model's work is ever done, and the authors clearly know this. Every author just adds the pieces of the scientific puzzle he can, and passes it on to the scientific community to see what else someone may be able to add. Over time the unworkable sections drop out, and the workable sections of the "big picture" get more and more detailed and begin to join each other to form even larger interrelated views of the entire puzzle of how the universe works and what has happened in it in the past.

This is how science is done. I don't think anyone in our technological age can argue with the results.

[polemikos]

Exaggerating the number of hypotheses doesn't help your case. As far as "what's up with that", science works by having people propose as many possible explanations as they can think of

Your first problem is that I stated no "case".

Your second problem is your assumption I was seeking to help my "case".
Since I did not put forward a case, there was nothing I sought to "help".

Lastly, your critique of my remark is disproved by your own words.
If scientists "propose as many possible explanations as they can think of"
and assuming all scientists are reasonably intelligent (a leap, I know),
then every scientist must have put forward at least one theory each.
Since we know there is at least one scientist that has more than one theory,
QED "There are more theories than there are scientists."

[Ichneumon]

Your first problem is that I stated no "case".

It's an expression.

Lastly, your critique of my remark is disproved by your own words.

No it isn't.

If scientists "propose as many possible explanations as they can think of" and assuming all scientists are reasonably intelligent (a leap, I know), then every scientist must have put forward at least one theory each.

"Must" they? Unsupported (and obviously false) assertion -- Ten yard penalty.

Nowhere in "my own words" is there any implication that *everyone* is going to put forth a theory. Only that "people" are going to do so. The number of interested "people" on any given topic who are willing and able to put forth a theory is quite small.

You've got a fallacy in there as well. You're presuming that everyone who does put forth one must put forth a different and unique theory. If there are any duplications among them then your reasoning, such as it is, falls to pieces.

Since we know there is at least one scientist that has more than one theory,

On this topic?

QED "There are more theories than there are scientists."

Feel free to support your assertion by naming, say, 500 or so of the theories on the cause of the Ordovician extinction that various scientists must, by your reasoning, have put forth.

[polemikos]

It's an expression

False characterization of opponent's statement.
Ten yard penalty for tackling a Straw Man.

"Must" they? Unsupported (and obviously false) assertion

Of course the "must", otherwise they wouldn't be scientists.
Ten yard pickup and a first down.

Ten yard penalty.

Bad call by the refs. Touchdown is good.

You've got a fallacy in there as well. You're presuming that everyone who does put forth one must put forth a different and unique theory.

Offset by the life-time theory production of each scientist.
Offsetting penalties. Point-After is GOOD!

And the crowd goes wild!!!

[Stultis]

This is how science is done. I don't think anyone in our technological age can argue with the results.

Particularly if they do it by typing the argument into a computer, and promulgating it on a global communications network, all of the above principly powered by petrochemicals located by geologists, etc, etc, etc.

[longshadow]

vaguely similar to "something we've discussed" ping

[Ichneumon]

Offsetting penalties. Point-After is GOOD! And the crowd goes wild!!!

Hitting the champagne a little early for New Year's?

[sixmil]

Interesting theory, but I think the media are just pushing this because of the recent solar blasts.

[Aracelis]

Bump for later read. Sorry, got home late from work and scrambled to fix late-night goodies for the troops. Hope yours was a happy one!

[Political Junkie Too]

my only theory about the ice age is that it was very cold for awhile, then it warmed up a little.

My theory of the ice age is that it was a very harsh existence when I had to keep refilling the trays, but it got much better when I got a fridge with an ice maker.

-PJ

[VadeRetro]

Very, very nice! What you did for a lark, the author of this article was getting paid to do and didn't.

[M Kehoe]

#30

Good post.

5.56mm

[Miss Marple]

Thank you for going to the trouble of tracking down the original paper and explaining its contents. Your work shows how science writing SHOULD be done, instead of the mess we usually see made of it.

[Erik Latranyi]

I stand by my assertion that the article is another example of how so many of our "facts" are nothing more than theories with popularity.

The meteor strike that wiped out the dinosaurs is widely taught and supported by academia.

However, as you point out, there are many, many other theories out there (such as the one in the article) that also show some evidence, but since they simply do not win the popularity contest, they are ignored.

So what does science resort to??? We have solar flares in the news and some scientists predict that the dinosaurs were wiped out by gamma radiation.

The only purpose for this is to utilize fear of the unknown and popular current events (not sound scientific principles) to promote an idea in order to seek funding for their own purposes.

Science today is more in the business of popularity and less in the business of fact.

[bondserv]

Much of the contempt that people have for science on FR is actually just caused by moron non-science writers getting it totally wrong for a general audience, not the scientists themselves.

Science is fun and is more like a convenience store than anything else.

Cell phone, Combustible engine, XM satellite radio or allow my neighbor, who thinks he's a smart ape, to act like an ape for ten more years because of a new medical procedure.

The character of a person is the only thing significant in this life, not the quantity of knowledge one can discuss.

However, science is fun and occasionally helpful. (We were wrong this time, but because science is "pure" we will be right sometime in the future).

The character of a person is the only thing significant in this life. Get to know Jesus Christ so that He can perform a Character transfusion on you as He has been doing for millions of others for 2000 years. Seek and you will find.