The Milky Way Galaxy's Spiral Arms and Ice-Age Epochs and the Cosmic Ray Connection

1. Ice Age Epochs and Milky Way Spiral Arm Passages:

Figure 1 - The cosmic ray link between solar activity and the terrestrial climate. The changing solar activity is responsible for a varying solar wind strength. A stronger wind will reduce the flux of cosmic ray reaching Earth, since a larger amount of energy is lost as they propagate up the solar wind. The cosmic rays themselves come from outside the solar system. Since cosmic rays dominate the troposphere ionization, an increased solar activity will translate into a reduced ionization, and empirically, also to a reduced low altitude cloud cover. Since low altitude clouds have a net cooling effect (their "whiteness" is more important than their "blanket" effect), increased solar activity implies a warmer climate. Intrinsic cosmic ray flux variations will have a similar effect, one however, which is unrelated to solar activity variations.
Different empirical evidence convincingly support the existence of a link between solar activity and the terrestrial climate. In particular, various climate indices appear to correlate with solar activity proxies on time scales ranging from years to many millennia. For example, small but statistically significant temperature variations (of about 0.1°C) exist in the global temperature, following the 11 year solar cycle. On longer time scales, the climate system has enough time to adjust, and larger temperature variations arise from the secular variations in the solar activity.

One mechanism which can give rise to a notable solar/climate link was suggested by the late Edward Ney of the U. of Minnesota, in 1959. He suggested that any climatic sensitivity to the density of tropospheric ions would immediately link solar activity to climate. This is because the solar wind modulates the flux of high-energy particles coming from outside the solar system. These particles, the cosmic rays, are the dominant source of ionization in the troposphere. Thus, a more active sun which accelerates a stronger solar wind, would imply that as cosmic rays diffuse from the outskirts of the solar system to its center, they lose more energy. Consequently, a lower tropospheric ionization rate results. Over the 11-yr solar cycle and the long term variations in solar activity, these variations amount to typically a 10% change in this ionization rate. Moreover, it now appears that there is a climatic variable sensitive to the amount of tropospheric ionization - clouds. Thus, the emerging picture is as described in figure 1.

Figure 2 - An artist rendition of the spiral structure of the Milky Way's spiral structure. Illustration Credit: R. Hurt (SSC), JPL-Caltech, NASA.
If this is true, then one should expect climatic variations while we roam the galaxy. This is because the density of cosmic ray sources in the galaxy is not uniform. In fact, it is concentrated in the galactic spiral arms (it arises from supernovae, which in our galaxy are predominantly the end product of massive stars, which in turn form and die primarily in spiral arms). Thus, each time we cross a galactic arm, we should expect a colder climate. Current data for the spiral arm passages gives a crossing once every 135 ± 25 Million years. (See fig. 2 on the left. Note also that the spiral arms are density waves which propagate at a different speed than the stars, that is, nothing moves at their rotation speed).

A record of the long term variations of the galactic cosmic ray flux can be extracted from Iron meteorites. It was found in the present work that the cosmic ray flux varied periodically (with flux variations greater than a factor of 2.5) with an average period of 143 ± 10 Million years. This is consistent with the expected spiral arm crossing period and with the picture that the cosmic ray flux should be variable. The agreement is also with the correct phase. But this is not all.

Figure 3 - An Iron meteorite, a large sample of which can be used to reconstruct the past cosmic ray flux variations. The reconstructed signal reveals a 145 Myr periodicity shown below. This particular one is part of the Sikhote Alin meteorite that fell over Siberia in the middle of the 20th century, it broke off its parent body about 300 Million years ago.
The main result of this research, is that the variations of the flux, as predicted from the galactic model and as observed from the Iron meteorites is in sync with the occurrence of ice-age epochs on Earth. The agreement is both in period and in phase: (1) The observed period of the occurrence of ice-age epochs on Earth is 145 ± 7 Myr (compared with 143 ± 10 Myrs for the Cosmic ray flux variations), (2) The mid point of the ice-age epochs is predicted to lag by 31 ± 8 Myr and observed to lag by 33 ± 20 Myr. This can be seen in the first figure.

A second agreement is in the long term activity: On one hand there were no ice-age epochs observed on Earth between 1 and 2 billion years ago. On the other hand, it appears that the star formation rate in the Milky way was about 1/2 of its average between 1 billion and 2 billion year ago, while it was higher in the past 1 billion years, and between 2 to 3 billion years ago.

Another point worth mentioning is that, unlike some articles which misquote me (or copy from a misquoting article), I don't think we wont have an ice age coming in the coming few tens of millions of years. If this galactic-climate picture is correct (and you should judge yourself from the evidence, in particular by the paper in New Astronomy), it implies that we are at the end of a several 10 million year long "icehouse" epoch during which we have ice-ages come and go, and gradually over the next few millions of years, the severity of ice-ages should diminish, until they will disappear altogether. I wouldn't buy real estate in Northern Canada just yet.
Figure 4 - The top panel describes our passages through galactic spiral arms. The second panel describes the predicted cosmic ray flux and the predicted occurrence of ice-age epochs. The third panel describes the actual occurrence of ice-age epochs. The fourth panel indirectly describes the variable cosmic ray flux. Due to the fact that the cosmic ray flux is the "clock" used to exposure date meteorites, the meteoritic ages are predicted to cluster around periods when the "clock" ticks slower, which is when the cosmic ray flux was lowest, as is seen in the data.

2. Cosmic Rays vs. CO2 as a climate driver over geological time scales:

By comparing cosmic ray flux variations to a quantitative record of climate history, more conclusions can be drawn. This was done together with Jan Veizer, whose group reconstructed the temperature on Earth over the past 550 million years by looking at 18O to 16O isotope ratios in fossils formed in tropical oceans. The following astonishing results were found once the reconstructed temperature was compared with the reconstructed cosmic ray flux variations:
Figure 5: Comparison between the reconstructed cosmic ray flux and the quantitative temperature reconstruction over the Phanerozoic: The top panel describes the reconstructed Cosmic Ray Flux variations over the past 500 Million years using the exposure ages Iron Meteorites. The bottom panel depicts in black, the reconstructed tropical ocean temperature variations using isotope data from fossils. The red line is the fit to the temperature using the cosmic ray flux variations. The notable fit implies that most of the temperature variations can be explained using the cosmic ray flux, and not a lot is left to be explained by other climate factors, including CO2. This implies that cosmic rays are the dominant (tropical) climate driver over the many million year time scale.
  1. Cosmic Ray Flux variations explain more than 2/3's of the variance in the reconstructed temperature. Namely, Cosmic Ray Flux variability is the most dominant climate driver over geological time scales.
  2. An upper limit can be placed on the relative role of CO2 as a climate driver.
  3. Using point #2, an upper limit can be place on the global "radiative forcing" sensitivity - the ratio between changes to the radiation budget and ensuing temperature increase. The upper limit obtained is lower than often stated value. This implies that a large fraction of the global warming witnessed over the past century is not due to CO2. Instead, it should be attributable to the increased solar activity which diminished the cosmic ray flux reaching Earth (It has nothing to do with spiral arms as some people misquote me!).

Note however:
  • Some of the global warming is still because of us humans (probably about 1/3 to 1/2 of the warming)
  • There are many good reasons why we should strive towards using less fossil fuels and more clean alternatives, even though global warming is not the main reason.
  • A more recent analysis, which includes: (a) Corrections to the temperature reconstruction due to ocean pH variations, and (b) more empirical comparisons between actual temperature variations and changes in the radiative budget further constrain the global sensitivity to about 1-1.5°C change for CO2 doubling (as compared with the 1.5-4.5°C with the "commonly accepted range" of the IPCC, obtained from global circulation models).


3. Cosmic Rays and the Faint Sun Paradox:

The sun, like other stars of its type, is slowly increasing its energy output as it converts its Hydrogen into Helium. 4.5 Billion years ago, the sun was 30% fainter than it is today and Earth should have been frozen solid, but it wasn't. This problem was coined as the "Faint Sun Paradox" by Carl Sagan.

If the Cosmic Ray Flux climate link is real, it significantly extenuates this discrepancy. This is because the young sun, which was rotating much faster, necessarily had a much stronger solar wind. This implies that less cosmic rays from the galaxy could have reached Earth because cosmic rays lose energy in the solar wind as they propagate from the interstellar medium to Earth. Since less cosmic rays implies a higher temperature, this effect will tend to compensate for the fainter sun.

Plugging in the numbers reveals that about 2/3's of the temperature increase required to warm the young Earth to above today's temperature, can be explained with this effect. The remaining 1/3 or so, can be explained with moderate amounts of greenhouse gases, such as 0.01 bar of CO2 (amounts which are consistent with geological constraints), or some NH3 or CH4.

Detailed Bibliography
Figure 6 - Cover of GSA Today - A geology magazine with a spiral galaxy on it!

A) Details Scientific Papers:

For detailed papers on this work, see the following:
  1. The first paper describing the link between the Milky Way spiral arms was - published in Physical Review Letters (4 Journal Pages, Abstract, PDF)
  2. An extremely detailed analysis of the link between Milky Way spiral arm passages and Ice-Age epochs. It includes a reconstruction of the past cosmic ray flux variations from Iron meteorites. Published in New Astronomy (29 Journal Pages, Abstract, PDF)
  3. Shaviv & Veizer article in GSA Today. A quantitative comparison between the reconstructed cosmic ray flux and the reconstructed global temperature. (7 Journal pages, External PDF, local PDF or HTML)
  4. Towards resolving the Faint Sun Paradox - How the Cosmic Ray flux / Climate link helps resolve the faint sun paradox by explaining 2/3s of it. (Appeared in JGR, PDF or PS)
  5. On Climate Response to Changes in the Cosmic Ray Flux and Radiative Budget (Appeared in JGR-Space, Abstract, PDF).
B) More online material:

C) Various articles in general press:

D) And some non english articles:

And a movie made on the topic.

ContentType:

Comments

How do stars move in the galaxy as opposed to spiral arms? If our solar system is located in one spiral arm, how can it move through another? Are there any video links that could clarify this for me? Thanks.

Dear J. Dark,

Spiral arms are not material arms. Namely, nothing moves at the speed of the arms. Instead, they are a pattern which propagates at another speed.

A traffic jam is a good example. Suppose you have a slow moving truck. It will cause a traffic jam which propagates at the speed of the truck. The cars composing the traffic jam will all the time be time different. If you look at a particular car, it will approach the moving traffic jam at some speed, then, in the jam it will slow down, pass through it, and then accelerate back.

Stars rotating around the milky way do exactly the same. They rotate at some rotational velocity (which depends on the galactic radius). As they approach the spiral arms, they slow down and cause a "stellar traffic jam". They then pass through it, and accelerate on the other side. I hope it clarifies the point.

shaviv, i'm just a lowly engineer... :)... but i don't understand what would cause the "acceleration" in the scenario you describe...

i would have assumed that if the arms of a galaxy are higher densities of stars [which make them the "arms" in the first place], if anything, our solar system would be attracted to the "next arm" and would accelerate towards it, then decelerate after it left, due to the larger mass now "behind it."

help? what am i missing here? what can cause that acceleration?

Nir
Your graph showing a correlation of the earth's temperature and the cosmic ray flux is very interesting. However, the time scale, being millions of years' is a bit beyond my period of interest. What I am wondering is if your theory can be used to predict the earth's temperature in the nearer term say perhaps the next 100 years. Do you have a graph showing that prediction?

Secondly, it seems to me that the world faces quite a dilemma. If the CO2 induced warming theory is correct then we should be worried about warming and presumably doing something to mitigate it. On the other hand if your theory is correct then the earth's temperature is largely unaffected by man. Then it will likely do what is has every time following an interglacial warming period for the past 1/2 million years; cool off and plunge into another ice age.

So should we buy land in Alaska or Florida? I don't mean to make light of it, but most of the world's countries have embarked on ambitious programs to reduce CO2 emissions. The US may soon join them. The plan recently proposed by Al Gore would have a serious impact on our way of life. It would be nice to know if we are doing it for a valid reason. And if the reason is not valid then we should not do it. My question here is; what is the likelihood that your work will be peer reviewed and will alter the conventional wisdom on global warming?

Climate drivers are different on different time scales. Over the geological one, it is most likely (well, for sure if you ask me) spiral arm passages. This has totally nothing to do with centennial and millennial-scale variations. These arise from changes in the solar activity which modulates the cosmic ray flux (as opposed to variations in the CRF in the solar neighborhood). Thus, to predict climate change over the next 100 years, due to solar activity (affecting cosmic rays), one should try to predict the expected solar activity variations. Unfortunately, I don't think this can be reliably done.

As to your second point, yes, but this may happen in a few thousand years. Of course, anthropogenic warming, may offset it a little, but I am not sure it will be able to save us from another ice-age.

As to your third point, my work was published in peer reviewed journals (e.g., physical review letters). However, in this highly politicized issue, pure science (whether reviewed or not) is not the main driver of anything... As for conventional wisdom changing, it will take time. Many climate scientists have so much vested interest in anthropogenic global warming, that it is only with quite a few years of no warming (e.g., a decade) that this issue will really reverse.

Cheers,
Nir

Nir
Please accept this as the musings of an over-the-hill retired engineer with perhaps too much time on his hands. But is there a chance that solar activity is affected by tidal forces exerted on the sun by Jupiter and the other planets? The 11 year sunspot cycle roughly corresponds with Jupiter's orbital period. And it would also seem reasonable that the gravitational pull of the planets would slightly reshape the surface of the sun in the same way that the sun and the moon cause tides. Whether that effect would "stoke the fire" of the sun I don't know.

Respectfully
David

David. your jupiter theory - assumes the sun has a 'free surface' on which waves can propagate -why not. How about this one : earth's core is molten iron - magnetic north can move around and invert according to the fossil record - the earths magnetism gives us the magnetosphere in the same way the sun's magnetism gives us the heliosphere - if the sun's electromagnet had a 11 year periodicity - some kind of resonance - then its magnetic strength could wax and wane - even better - it could be connected to Jupiter's magnetic field properties. How about that?

Nir
Figure 5 shows temperature in black and cosmic ray flux in red. If I'm reading it right the peaks and valleys of the temperature plot occur before the those in the cosmic ray plot. What would account for that?
Respectfully
David

David,
I don't think this lag is statistically significant. We don't know the {\em exact} periodicity of the cosmic rays (due to the finite measurement error), so any such small lags or leads are within the error and most likely meaningless.
Best,
Nir

Nir
I hope you don't mind me bothering you with another question. I've been thinking about the two theories of what could be causing global warming; 1, the greenhouse effect and 2 your theory that cloud cover has been reduced by the effect of the solar wind on the gama ray flux.The greenhouse effect proposes that greenhouse gases act like insulation and reduce the heat radiated back into space.The cloud cover theory assumes that reduced cloud cover allows more sunlight to reach the earth thus causing warming during the day. These are very different mechanisms. If we think of the earth as a control volume in steady state then the portion of the sun's energy which is absorbed by earth must be equal to the heat energy radiated back into space. The greenhouse theory does not assume additional energy coming in from the sun so there can be no additional heat radiated out. The heat radiated out today should be the same as it was 20 or 50 or 100 years ago. But under the cloud theory the additional solar energy being absorbed by the earth must be balanced by additional heat energy radiated out. So the heat energy radiated by the earth today must be greater than it was in the past.

Of course that's based on steady state conditions. And if the earth is warming then steady state does not exist. So how would that affect the above conclusions? For non-steady state conditions; Energy in = Energy out + Energy stored. (Energy stored is that due to the warming of the earth.) Under greenhouse theory "Energy in" does not change so if the "Energy stored" is increasing then the "Energy out" must diminish until equilibrium is restored. Radiant heat increases with the 4th power of the temperature. Under the greenhouse theory the temperature of the earth must rise until the additional energy emitted balances the blocking effect of greenhouse gases. So while the earth is warming the amount of heat energy radiated into space must decrease relative to past times.
Under the cloud theory additional energy is absorbed from the sun, so "Energy in" increases. Some of that energy will go into warming the earth and will go to "Energy stored". But as soon as the Earth begins to warm then the radiated energy will rise and Energy out will increase as well.

Overall the conclusion I reach is that under the greenhouse theory heat energy leaving the earth must either be remaining constant or decreasing. Whereas under the cloud theory the amount of heat energy leaving the earth must be increasing relative to past times.

I'm looking for ways to put both theories to the test, but before I do I wonder if you would be good enough to comment on what I've said so far. Does it make sense or am I cuckoo?

Respectfully
David S

PS If you're too busy to comment I fully understand.

For one, you think instead of allowing yourself to be fed media digested propaganda.

In principle you are totally correct that there should be differences between global warming caused by GHG and global warming caused by solar activity through the cosmic ray link, or through other links.

You are also correct that if it were just a change in the amount of greenhouse gases, the amount of radiation reemitted back to space in the IR should have been the same. There are however two problems.

First, it is hard to reconstruct the IR measurements over long time scales, since there are measurements only from the time of the satellite era.

Second, and this is the crucial point, any warming, caused by GHGs or solar activity would cause additional changes in the climate system which could change the albedo and thus also the IR emission, changing it in the GHG warming scenario.

Irrespectively, there are different fingerprints which could be used to distinguish between the two mechanisms (or others). For example, GHG warming predicts a warming all over the troposphere. solar activity / cosmic rays probably affects primarily the lower troposphere since the effect is seen in low altitude clouds. The observations, of course, point to most of the warming taking place close to the ground...

Cheers,
Nir

Nir
Have you seen Professor Lindzen's paper "Deconstructing Global Warming"? http://wattsupwiththat.files.wordpress.com/2009/10/cooler_heads_lindzen-talk-pdf.pdf
Apparently the ERBE and CERES satellites have been measuring both reflected sunlight and emitted long wave radiation for the past 16 years. Page 38 of that paper shows that long wave radiation has been increasing over the duration of that 16 years until about 2003 at which time it goes flat or slightly downward. It also shows reflected sunlight decreasing over the same period and also going flat at 2003.

As I read it, less reflected sunlight means more sunlight is getting through to earth and causing the warming evident in the temperature records. As the earth's temperature increases it emits more LW to balance the energy equation.
Also the magnitude of the reduction in reflected sunlight is about the same as the increase in emitted LW, about 4 or 5 watts per m^2.
This is what I was suggesting in my earlier post although I didn't have the satellite data at the time. What do you think?

Also by correlating the radiant energy data to the SST Lindzen is able to show that the overall feedback is negative rather than positive as the models predict. If that's correct it pretty much throws cold water on the AGW theory. :-) Any temperature increases will be far less than the IPCC predicts. What's your opinion?

Dave

I was wondering if you would like to comment on Mikhail V. Medvedev and Adrian L. Melottpropose's recent paper linking the solar system's path in and out of the disk of of the galaxy as a cause for periodic (64 My) redutions in species diversity. As far as I know they have not tried to relate this mechanism to climate change but, if it results in a change in overall cosmic ray flux I would think it could. They calculate that CRF can vary by a factor of 4.6 when the solar system is at the northern most peak of its cycle, due to the greater intensity of intergalactic cosmic rays in the direction of the Virgo cluster. Have you included this factor in your theory?

Regards,
Doug

Although I haven't checked it, my suspicion with the idea of Medvedev and Melott is that it will not be consistent with the Be isotope ratio age of the cosmic rays. The reason is that if Cosmic rays primarily come from outside the galaxy, and roam the intergalactic space for very long durations (much longer than the typical 20 Million year Be-10 age observed for the cosmic rays), then there will be a discrepancy. Of course, you could solve it by adding local sources injecting "fresh" cosmic rays.

Another point is that there is no notable climate variations on the 60 Million year time scales (as opposed to the various claimed variations on half the period, at around 30 million years, including extinctions, etc.).

Anyway, Medvedev is my friend, we overlapped as post-docs at CITA. Since he is sharp and original, I wouldn't discard his ideas without thoroughly checking them.

Can you explain how the sun intensity can drop and yet the earth continue to warm significantly during the same period if your theory holds any water?

Secondly what is the effect on your theory that cloud margins of dust and water vapour are large and allow sunlight through meaning they are likely to be warming influence?

Thirdly can you explain why despite there being an abundance of CNN in the pacific (DSMs say),meaning the cosmic ray proposed mechanism can't work?

Fourthly can you also expalin why the earth's reflective index hasn't changed much or has actually increased slighty (meaning cooling) in the periods when it should have falling if your theory is correct?

Laslty can you explain why there is actually no correlation of temp tpo cosmic ray variance outside the 1950-80 period?

Just wandering?

Hello Nir

It is nice to see that you and Svensmark dear challenge the political climate debate with an interesting theory.

I was just wondering if somebody has used the theory to forecast the weather for the next hundred years. It is my impression that astronomers have very accurate mapping of the sky. So, it should be possible to predict the future amount of cosmic rays.

perhaps you should take the time to remove this post as it has been Disproven by Realclimate. ;)

http://www.realclimate.org/index.php/archives/2008/03/a-galactic-glitch/#more-534

aaron

It seems that there have been very few sun spots for the last couple of months. In fact right now there are currently zero. Cycle number 24 is apparently vey late in coming. Is that a sign of cooler weather to come?

J. Steiner in 1973 proposed ice age periodicity related to earth's or our sun's galactic orbit (Possible Galactic Causes for Periodic and Episodic Glaciations). It is interesting how your and other studies relate to this. I suppose if ice ages are related to the galactic orbit and the milky way's spiral arms, so too should intervening periods of global warming:-)

There are other related cycles to the ~145 million year cycle described here. In the book "Megacycles" which is the proceedings of a geological cycles conference edited by G Williams, it is reported that there are a series of cycles related by 1:2 ratios of period. These include ~600, 300, 150, 74, 37 million year cycles. Even a 1200 MY cycle is suggested as possible.

In his book "Nanocycles Method" (English translation of Russian title) Geology Prof S Afanasiev of Moscow University explains gow to make very accurate dating of geological deposits (it is based on the changing lunar nodal period). He gives the longer of these cycles period as 586.24 million years. Based on this and a ratio of 2 assumption, the other periods would be: 586.24, 293.12, 146.56, 73.28, 36.64 million years.

The 586 million year cycle also shows as a 586 million light year wave structure of galactic walls in space. It is only recently that this has been verified by more accurate values of the Hubble constant.

I would also recommend the paper "The Case for Cycles" by Edward R Dewey - http://www.cyclesresearchinstitute.org/dewey/case_for_cycles.pdf
This discusses the patterns of cycles with ratios 1:2 and 1:3 observed in a wide range of phenomena.

Finally, I have proposed a theory based on non-linear dynamics which predicts a highly structured series of cycles in the Universe, and explains the distance periodicities of structures at all scales in the Universe from the Hubble scale to particles.
See my web site http://ray.tomes.biz/maths.html

Do the spiral arms of our galaxy move at different velocities? E.g do we at some point come closer to stars as we do with Mars at certain times, orbits?

http://arxiv.org/ftp/arxiv/papers/0906/0906.2777.pdf

"Testing the link between terrestrial climate change and Galactic spiral arm transit"

Their argument is updated models of the history of the milky way dramatically change the picture of when spiral arms existed and that the correlation with climate data disappears. Have you read the paper? Have any comments?

Recently (24 April, 2012), Nigel Calder released information to the press about Henrik Svensmark's latest research. As he puts it: "Today the Royal Astronomical Society in London publishes (online) Henrik Svensmark’s latest paper entitled “Evidence of nearby supernovae affecting life on Earth”. After years of effort Svensmark shows how the variable frequency of stellar explosions not far from our planet has ruled over the changing fortunes of living things throughout the past half billion years. Appearing in Monthly Notices of the Royal Astronomical Society, It’s a giant of a paper, with 22 figures, 30 equations and about 15,000 words. See the RAS press release athttp://www.ras.org.uk/news-and-press/219-news-2012/2117-did-exploding-stars-help-life-on-earth-to-thrive

Well, Dr. Shaviv, having read your treatise on cosmic ray's influence on global climate based on our solar system's position in the galactic spiral arms, posted on your blog in 2006, I am wondering why you didn't get any credit for Svensmark's research. I recall at the time that Svensmark was conducting research on our own sun's influence on cosmic rays modulated by the solar wind, but you had the big cosmos picture in mind even then. Why no credit since credit seems due?

In principle, we expect future variations of the sun to affect the climate (as it modulates the cosmic ray flux). Unfortunately, this cannot be reliably predicted since it depends on the chaotic behavior of the convection layer of the sun...). All that can be said is that since the sun in now in its highest state of activity, we can expect on the time scale of several decades for it to calm down, and with it have a lower global temperature (which will sort of compensate a large fraction of the anthropogenic contribution towards the warming).
-- Nir

Nir--

Great stuff.

I was looking at the blue and green lines in Fig. 1 of Shaviv and Veiser 2003 and wonder why you don't comment
much on the strong oscillations every ~33 Ma. "Periods" of this length are often ascribed to galactic plane crossings:

Bahcall & Bahcall

My sense is based on your meteorite data that you don't believe in these shorter period epicycles, but perhaps the meteorite data is just too sparse to show anything on that short a period. Maybe the sun does cross regularly, but the longer-period crossings you emphasize are "particularly perilous" because of their magnitude or other factors.

Also a quick and dirty overlay of extinction rates suggests some correllation of extinction to either peaks or troughs of the finer-binned O isotope data. This might suggest that biodiversity suffers when long term cooling or warming trends reverse. It would be interesting to plot the second derivative of the O isotope curve vs. the best available species extinction rate, and also look at it on a fine scale around some extinctions.

-Andy

Dear Nir Shaviv,
I would be glad to receive your comment about the recent paper from Andrew C. Overholt et al 2009 ApJ 705 L101-L103 doi: 10.1088/0004-637X/705/2/L101 TESTING THE LINK BETWEEN TERRESTRIAL CLIMATE CHANGE AND GALA
Does it mean
- the spiral arm mechanism you suggest doesnt fit
- can some other mechanism explain your measurements and hypothesis
- does this have an impact on the cosmic ray climate theory or not
If we talk about the paradox of the faint young sun, imho its still an issue that any mechanism solving the problem of the major ice ages occuring each 140 million years in the last billion, doesnt work for the first 3 billion years. Except so far your connection. I would be glad to have an answer on this topic from you.
Best regards Polentario

PS.: Same applies for the Paper of Coryn A.L. Bailer-Jones, The evidence for and against astronomical impacts on
climate change and mass extinctions: A review. Here mostly the critisim of jahnke and Rahmstorf is repeated. However this (as well with regard) to the Stockholm meeting massed amount of rebuttals respective attempts to do so deserves an answer.

Their is one major fault in that paper. The authors say that they use one pattern speed (which is correct), but in their calculation they actually use another pattern speed, a wrong one! Their mistake it that they have used $ \Omega_p $ instead of $ \Omega_\odot - \Omega_p $