(I should note that I caught wind of the story via a friend on Facebook – JurassicMatt on Twitter – in confirmation of the valauble role social networking can play in dissemninating information; as if revolting Egyptians on Twitter wasn’t enough.)

Pretty wild, eh? You can be forgiven if you are skeptical. Contrary to popular reports, Tyche is not confirmed, but should be visible in the data from the Wide-field Infrared Survey Explorer (WISE). The excellent Bad Astronomy blog offers a more in-depth analysis on this theme.

What interests me in this story is the resurgence of the idea that a 26 million-year mass extinction cycle on Earth is evidence for Tyche’s existence. Following the discovery by Raup and Sepkoski (1984) (pdf) of a ~26 million-year periodicity, Whitmire and Jackson (1984) (abstract) along with Davis et al. (1984) (abstract) proposed an extraterrestrial origin for these extinction events. This came to be known as the Nemesis hypothesis: a black-dwarf companion star to the Sun that periodically disrupted comets and caused Earth-crossing orbits, resulting in impacts and mass extinctions. The problem, however, is that the original idea is unsupported by the evidence in the geological record, and applying the reasoning to Tyche is misguided at best.

First, Matese and Whitmire (2011) do not invoke the extinction periodicity as evidence for Tyche. They argue on the basis of an anomalous concentration of comets in the outer Oort cloud, which they attribute the gravitational effects of a planetary body over the weak stellar impulse.  From my limited understanding of physics, I speculate that the mechanism of the described phenomenon is related to the Roche-limit segregation of debris orbiting Saturn into its characteristic rings. Speculation aside, the point remains clear: if one of the original authors of the Nemesis hypothesis is not referencing his previous work, then what justifcation do bystanders have for doing so?

Second, the reported 26 million-year periodicity in mass extinctions only covers the past 250 million years. Fossil evidence of macroscopic animal life extends back to ~580 Ma, so what about the previous 330 million years? I haven’t checked if updated research has extended the periodicity back prior to the Permian-Triassic boundary (ca. 250 Ma), but neither have the Tyche-extinction proponents. Additionally, the vast majority of extinction events depicted in the figure below barely register as “elevated” after Keller (2008) (abstract), and some, such as the events in the Tertiary, plot near/within “background” levels. Only the end-Permian and end-Cretaceous events rate as “major” mass extinctions, so any argument of a clear extinction periodicity is hardly convincing.

Adapted from Raup and Sepkoski (1984)

Third, the current state of research is skeptical about the role of bolide impacts on known mass extinctions. Apart from the K-T event that knocked out the dinosaurs (which is still controversial), major mass extinctions are linked to other causes such as flood basalt volcanism, ocean anoxia, and climate change.

To date, characteristic evidence for high-velocity impactors (regardless of composition) such as spherule layers, crater structures, turbidites, carbon mats, microdiamonds, and Ni/Cr anomalies is conspicuously absent in the record. Furthermore, ideas of antipodal or depressurized impact-volcanism relationships are soundly refuted. Indeed, the lack of evidence is not evidence itself, but just as the lack of evidence for you being a serial killer is not reason to believe you are, pursuing the impact-extinction idea without research to back it up is a logically-bankrupt position.

So with three strikes on the Tyche-extinction speculation, is there any reason to persist with the notion? I like the idea of comets and asteroids destroying all life as much as the next Hollywood fanatic, but let’s be honest here – the research is not favourable to the idea and there is no good reason to perpetuate it at this time.

Further reading available from various links:

Bailer-Jones (2009) – The evidence for and against astronomical impacts on climate change and mass extinctions: A review 

Arens and West (2008) – Press-pulse: a general theory of mass extinction?

White and Saunders (2005) – Volcanism, impact and mass extinctions: incredible or credible coincidences?

Keller (2005) – Impacts, volcanism and mass extinction: random coincidence or cause and effect?

Wignall (2001) – Large igneous provinces and mass extinctions

Fig. 1. Deuterium/hydrogen ratios of the proto-Sun (peach), Earth (blue), Moon (red), carbonaceous chondrites (black), and comets (green). The D/H ratio is multiplied by 10^6 reflecting parts-per-million quanities of deuterium with respect to hydrogen. Adapted from Robert (2011).

As you can see, there are a couple of interesting isotopic associations. The Earth overlaps strongly with carbonaceous chondrites, while the Moon spans a range of D/H values, potentially indicating a significant affinity with comets.

Why might this disparity between the Earth and Moon exist? The prevailing hypothesis for the formation of the Moon is the impact of Theia with Earth, so within this framework, it stands to reason that water on Earth appeared after the formation of the Moon via significant contributions of water from carbonate chondrites.

By comparison, Greenwood et al. (2011) discovered that abundant lunar water exists bound up within the hydrous mineral apatite, which represents a mafic phase within the mare basalts and anorthositic highlands. The interesting thing about the Moon, however, is that a number of sources are identified including solar protons, the lunar mantle, and comets (D/H ratios increasing respectively, with the solar fraction as the lightest). These different sources potentially explain the wide range of D/H ratios observed in lunar rocks.

This appears to be a tidy hypothesis, but as Robson (2011) hints, how do you explain the prominent influence of comets on lunar water, and its apparent absence in terrestrial water? The Earth and Moon are next-door neighbours in the context of the solar system, and Greenwood et al. (2011) predict a likewise cometary bombardment of the Earth at this time.

So where is the terrestrial D/H isotopic signature reflecting this cometary bombardment interval? Or is it there, but just obscured by the lighter, carbonaceous chondrite fraction? That may be the case following the research of Kulikov et al. (2006) which indicates that the relatively high D/H ratio on Venus arises from the equivalent loss of a terrestrial ocean; something which most certainly did not occur on Earth.

References

Greenwood, J.P., Itoh, S., Sakamoto, N., Warren, P., Taylor, L., and Yurimoto, H., 2011: Hydrogen isotope ratios in lunar rocks indicate delivery of cometary water to the Moon. Nature Geoscience, vol. 4, p. 87-92.

Robert, F., 2011: Planetary science: A distinct source for lunar water? Nature Geoscience, vol. 4, p. 74-75.

Good reading:

• Not Exactly Rocket Science: Mono Lake bacteria build their DNA using arsenic (and no, this isn’t about aliens)
• Discoblog: NASA Found Aliens! Or Not. The Worst Coverage of Arsenic-Loving Bacteria
• We, Beasties: Arsenate-based DNA: a big idea with big holes
• RRResearch: Arsenic-associated bacteria (NASA’s claims)

As implied, my own reaction is one of amused fascination. The science I see when doing a term paper or collecting information for my undergrad thesis is so far removed from the public discourse that it’s actually quite enjoyable to see people grinding it out in a public arena.

Of course, there are the obvious questions: Does this event represent the sensationalizing of research findings, and if so, do events like this cheapen science as a whole? Do scientists and scientific instititions run the risk of alienating an already overly-cynical, non-specialist population if the research is shown to be false or invalid? Does specialist criticism in blog-form circumvent or negatively impact the peer review process? Do scientists have a responsibility to disseminate their findings to the general public, or conversely, preserve the rigid strictures of specialist debate?

My gut reaction to these questions on all counts is, “no” “maybe”; but I readily admit I am unable to evaulate that position in any meaningful way. What I can relate, however, is my own disappointment with the story overall as a function of the media structure that brought it to my attention in the first place. It reminds me of the recent skepticism surrounding Gliese 581 g, following the initial media frenzy about having a habitable planet in the near galactic neighbourhood (~20 light years away). You get stoked only to realize your excitement was premature (and whose fault is that?).

Are we developing a trend of rushing out big headlines before the actual research is ready? It’s one thing for scientists to bicker about controversial claims, as they understand the process and realize that uncertainty is a good thing, but it’s quite another for the general public. Yes, we in the western world follow the democratic process, but it’s also worth pointing out that the process doesn’t mitigate stupidity. I’d argue that this kind of messy, scientific discourse in the mainstream media creates the opportunity for it to be maligned and exploited by any manner of creationists, conspiracy theorists, or assorted kooks with money and political pull.

I don’t think it’s a good way to conduct the debate, and I don’t think it helps; especially when so many news outlets run stories of pure fiction about NASA finding extraterrestrial life.

Case-in-point, “Expanding Earth Theory” (EET):

(Apart from the fact that YouTube hardly passes muster as a peer-reviewed source, what qualifies a comic book artist to comment on anything science-related?)

I take a perverse pleasure in perusing the comments sections of paleontology/geology news articles around the web, mostly because they often remind me of how important it is to be a sane human being. This particular post is inspired by many of the comments to the CBC article, “Mammals got 1,000 times bigger after dinosaurs” (which is not exactly new information, but still an interesting article). Often the commenters are just clueless creationists used to reading Kent Hovind and Ken Ham, but I’m also noticing an abundance of users who appear to make a concerted effort to seek out and side with pseudo-scientific tangets that stand in opposition to accepted, mainstream scientific theories that are actually backed by evidence.

All of this starts to resemble a phenomenon to which I was recently introduced, which I think is itself relatively new on the scene: denialism. Best explained by denialism blog, the term is thus defined:

“Denialism is the employment of rhetorical tactics to give the appearance of argument or legitimate debate, when in actuality there is none. These false arguments are used when one has few or no facts to support one’s viewpoint against a scientific consensus or against overwhelming evidence to the contrary. They are effective in distracting from actual useful debate using emotionally appealing, but ultimately empty and illogical assertions.”

The illusion of debate especially stands out in my mind. For instance, consider the discussion page on Wikipedia for EET where a proponent links to approximately 40 refereed (or so we assume) articles in an attempt to argue that EET is a valid theory and a serious contender to plate tectonics. 40 references? Sounds pretty impressive, right? Well, no:

1. Approximately 1/4 of the references date prior to mainstream acceptance of plate tectonic theory. This does not mean they are wrong, but it means the articles were published in an entirely different context than today – one in which EET may have been examined as a possible contender.

2. The remaining 3/4 of the references are historical reviews, or published in either backwater journals no one’s ever heard of (e.g. Annali di Geofisica), journals solely created to give voice to “alternative” theories that cannot get published in reigning journals (e.g. New Concepts In Global Tectonics), or journals which are simply pseudo-scientific in scope such as Journal of Scientific Exploration which features articles on cold fusion, reincarnation, sasquatch sightings, and alien contact.

(It’s worth pointing out that “peer review” does not mean getting someone who’s as insane as you are to rubber-stamp your bullshit.)

3. A couple of the references are actually heated criticisms of EET, such as Briggs (2003) and Briggs (2006), the latter in which the author outlines seven broad problems for EET:

“(1) the Precambrian to Palaeozoic fossil record of marine life indicating extensive oceans, (2) the absence of cracks across the planet caused by expansion, (3) the absence of a drastic fall in sea level that would have been caused by the expansion, (4) the abundant evidence of largescale subduction that absorbed the older sea floor, (5) the lack of evidence for the generation of the internal energy necessary for expansion, and (6) no evidence of the rapid reduction in the Earth’s rotation that would have been caused by such expansion. In addition, his theory fails to pass a rigorous palaeomagnetic test.”

(This is not a debate; this is a wholesale slaughter)

4. A topic search of “tectonics” on Web of Science yields 20,000+ results. This does not include the additional geoscientific articles a GeoRef search would yield, or the thousands of peer-reviewed articles and government survey reports founded upon the plate tectonic paradigm that do not use the overly general “tectonics” keyword in favour of something more specific, and, oh, actually useful.

So is there a debate as the user mentioned above tried to argue? None whatsoever - it would appear that EET is a strong contender for a denialist designation, at least in terms of the above definition.

denialism blog goes on to delineate several more denialist criteria, including conspiracy theories, cranks, cherry picking, fake experts, impossible expectations, and logical fallacies. Since this post is getting long I’ll cut it short for now, but I plan to revisit some of these themes in more detail later (eventually along with other crank geological claims such as a 6,000 year-old Earth, abiogenic oil, etc.). In the meantime, I urge you to take a look yourself.

The first task? Take my structural measurements – foliations, lineations, joints, and veining – and plunk them into a stereonet. For my joints I’d already done this by hand a few weeks ago (mainly to see how they looked), but for ease of use I opted for GEOrient – stereonet software which is free for academic use. Using software is a treat because you simply export a spreadsheet of your structural measurements into a tab delimited .TXT file from Excel or Open Office, and import it in GEOrient, which itself is an easy task.

Unfortunately, while GEOrient does a nice job of plotting your points on the stereonet, it’s not very robust when it comes to the visual display of pole contours. Consider this plot, for example:

It does an excellent preliminary plot, but I notice two things: 1) visually it needs to be retouched A LOT, and 2) there’s a potential problem of the 8% contour continuity across the great circle. The first is no real problem, and no real criticism of the software itself – it aims to plot data, not to be a state-of-the-art graphics package. Things can easily be touched up with other graphics programs such as Illustrator, as exemplified by the final version:

The second, however, is a potential problem, and I’m definitely going to talk to my advisor. In the original, the contour interval crosses the great circle on the NE quadrant, but does not in the SW quad. In the final version I’ve gone ahead and manually traced it. Additionally, the retraced contours were smoothed in Illustrator to provide a better presentation.

However, this potentially raises another issue: I’ve essentially tampered with the data. By extending and smoothing contours, I’ve taken a representation of the plotted data and altered in a manner that looks better and “makes sense”. That said, I’ve only “tampered” with the data if the original GEOrient plots were correct in the first place. Pole positions are certainly correct - it’s quantitative strike/dip data - but the automated contouring is where the trickiness comes in. Although the final stereonet looks pretty slick from a design standpoint, I have to wonder if the contouring can be accepted with a degree of confidence. I’m not sure it can – I’ll have to give it some thought. I think I’ll also try other software packages, as well as hand plots, to compare results between the two.

Ultimately, from a practical standpoint, a stereonet plot can overcome these minor issues with ease. From my final contours I can confidently assert a general, preferred orientation of my foliations. Yes, there is some scatter, and yes, there are some odd things going on, but this is geology after all – and just a first treatment of the data. I’m thinking the next step will be to break down foliations between lithologies in the trench to see if there are distinct generations, as well as potentially identify different structural sub-domains throughout the linear extent of the outcrop.

After working 15 weeks total over the past four-and-a-half months, it appears I am finally back in my house for more than just a few days at a time! The feeling of settled-ness is pretty nice, but it won’t be long before I’m itching to get in a car, plane, and/or helicopter and wander the great Canadian wilderness again.

Attn: Summer ’11 – please get here ASAP!

School’s been on now for a week, and while my courseload is relatively light here in my last year, I’ve been expending a lot of energy trying to find a suitable thesis project to cap off my undergraduate career. With the huge help of my advisor, I think I may have finally stumbled across the ideal opportunity: a structural analysis of an historic Archean lode-gold showing. Fingers crossed!

In other news, now that I’m back, I’m hoping to continue to write on all things geological. A brief scan of the interweb highlights my competition with the proliferation of geology blogs, but no matter. Even though the majority are of a much higher quality than mine,  I will continue to feature posts on my interests and experiences. I am less interested in competition than I am in writing about, and enjoying the great field of the Earth sciences!

What can I say about northwestern Ontario, apart from the fact that it’s where I’ll be spending the majority of my summer? It’s a beautiful place, but it’s also very desolate and lonely. Every morning our helicopter pilot flies me and my co-worker over miles of boreal forest, hopping from lake to lake in search of the next big find.

It can be a very interesting life, but also a life that makes you question a lot of your priorities. I can only be vague because at this point in the game I’m not sure exactly what I’m trying to say… except maybe that what I’m really looking for is very, very far away?

Yeah, that.

The Milankovitch hypothesis proposes that the 100,000 year periodicity of glacial and interglacial intervals present in the geological record is a function of orbital forcing. Changes in the Earth’s axial tilt (obliquity), rotational wobble (precession), and distance from the Sun (eccentricity) combine to affect the latitudinal distribution of incoming solar radiation across the Northern and Southern Hemispheres (i.e. boreal and austral), which is responsible for long-term climatic variation. Axial tilt and precession are the primary controls on insolation (41,000- and 25,700-year periodicity, respectively), but are amplified and modulated by longer-scale changes in orbital eccentricity (100,000 years and, to a lesser degree, 413,000 years). With this in mind, it’s clear that the discrepancies between pre- and post-MBE interglacial intervals need to be explained.

To answer the question, Yin and Berger chose standard insolation values for each successive interglacial peak across the past 800,000 years. Phase congruency between precession and tilt created the insolation standard, and interglacial peaks (i.e. the warmest part of the 100,000 year cycle) were chosen based on the marine δ18O record, otherwise named the ” δ18O minima”. Recall that the marine record exhibits lower δ18O during warm periods while glacial ice records higher δ18O due to evaporation fractionation.

What does this mean? The following figure provides a quick idea of what’s going on:

Fig.1. Obliquity, precession, and δ18O modeled over the past two interglacials from 135,000 to present day. The δ18O black bar represents the peak warming of each interglacial (δ18O minima), while the precession black bar represents when the Earth was closest to the Sun in the Northern Hemisphere summer (perihelion) and the obliquity black bar indicates the maximum tilt of the Earth (~24.5 degrees). Full article text shows 800,000-year record. Adapted from Yin and Berger (2010).

As indicated, the in-phase obliquity and precession curves indicate peak insolation, and pre-date the warmest part of the interglacial interval by about 5,000 years, which is more or less consistent with what is expected. Deglaciation is a long and protracted process with many starts, stops, and feedbacks, so it is typical for there to be a lag between maximum insolation and peak warmth. In a general sense, the Milankovitch hypothesis would only be in trouble if maximum insolation post-dated the warmest part of interglaciation.

In a snapshot discussion, Yin and Berger reveal that complications arise for specific interglacial intervals. And would we expect anything less from Mother Nature? However, averaging the pre- and post-MBE interglacials, the authors identified a clear interglacial warming after 430,000 years ago.

It appears the primary culprit is increased atmospheric CO2 post-MBE present in the geological record, in conjunction with increased winter insolation in the Northern Hemisphere. The authors cite a 60%-30% split (final 10%??), and conclude that a) boreal winters are generally warmer during interglacials after 430,000 years ago than they were pre-MBE, and that b) increased winter warming exerts a stronger control on climate than increased summer warming.

All told, the paper is a good look into some interesting aspects of the late Quaternary icehouse climate. If you have access to Nature Geoscience, check it out.

References

Yin, Q.Z., and Berger, A., 2010. Insolation and CO2 contribution to the interglacial climate before and after the Mid-Brunhes Event. Nature Geoscience, vol. 3, pg. 243-246.

What is the faint young Sun paradox?

Temperature-wise, liquid water exists on the surface of the Earth within very narrow window, but geological evidence indicates the presence of liquid water spanning 4 billion years. Given that the Sun was 25-30% less luminous 3-4 billion years ago, the Earth would have been frozen over with ice during the Archean under present-day conditions.

The long-standing solution to this paradox is to assume that conditions in the Archean were much different than they are today, and given what we know about the Precambrian world, it’s a reasonable assumption to make. Within this context of a changing Earth, the idea is that higher concentrations of greenhouse gases (i.e. CO2, CH4, and NH4) allowed liquid water to persist during this period of lower insolation.

Problems with the GHG solution

Creating a scenario where increased tectonic activity on the early Earth raised atmospheric CO2 levels and led to warmer temperatures is easy to accept. The problem, however, is that evidence such as Archean paleosols, weathering rinds on fluvial clasts, and evaporites point to lower atmospheric CO2 than is required to keep the early Earth ice-free.

Additionally, the presence of iron minerals like magnetite and siderite within Precambrian banded iron formations places a constraint on atmospheric CO2 to an upper limit of three times the present-day level (i.e. ~900 ppm). Minimally, this assumes a coupling (if not equilibrium) between the atmosphere and ocean in which banded iron formations were deposited. As a consequence, Rosing et al. suggest that greenhouse gas concentrations in the Archean atmosphere were too low to keep liquid water stable at that time. Increased methane as a forcing mechanism is also discounted along similar lines of reasoning.

Planetary albedo as a solution?

The authors assert that in the present day, vegetation and cloud cover limit the albedo difference between land and ocean with respect to the land/ocean difference on the early Earth. We understand that land plants did not appear until Ordovician-Silurian time (approximately 460-440 Ma), so the Precambrian is certainly different when it comes to the influence of vegetation on reducing albedo.

In terms of cloud cover, it is argued that in the present day, increased biotic input from plants and eukaryotic algae creates more cloud condensation nuclei and leads to smaller water droplets in clouds (~12 um). Smaller droplets means more scattering of incoming solar radiation, and thus, higher albedo. During the Precambrian when this biotic influence was absent, the authors suggest that cloud droplets were larger (~20-30 um) on account of fewer nucleation sites, leading to lower albedo. As we understand it, planetary albedo is inversely proportional to the average surface temperature of the Earth.

Given that there is an albedo difference between land and water, continental growth through time clearly exerts a strong control on planetary albedo. As indicated in Figure 1a, continental landmass has increased in time, even if debate over the specifics remains. According to Rosing et al., continent formation was initiated by 4 Ga, experienced rapid growth throughout the Archean and Paleoproterozoic from 3.5 to 1.5 Ga, and leveled off at approximately 1 Ga. In turn, planetary albedo also increased throughout this interval (Fig. 1b.). Figure 1c. accounts for greenhouse gas and cloud influence creating an overall increase in planetary albedo throughout geological time.

Fig. 1. a. Land/ocean ratio through time (i.e. 3.8 Ga to present day) under the assumption of continental growth. b. Estimated surface albedo where increased land leads to an increase in albedo to the present day. c. Average planetary albedo including greenhouse gas and cloud effects, indicating an overall increase. Adapted from Rosing et al. (2010).

All of this comes together in Figure 2, where the authors’ model indicates that albedo forcing at 900 ppm CO2 and CH4 with 20-30 um cloud droplets is effective in ensuring the occurrence of liquid water on the Earth as far back as 3.8 Ga.

Fig. 2. Green: modeled temperature at 900 ppm CO2 and CH4 with droplet size of 20 um (solid) and 30 um (dashed). Blue: temperature at 365 ppm CO2 and CH4 with droplet size 20 um (dashed) and 12 um (present-day; dotted). Adapted from Rosing et al. (2010).

Does the model work?

You decide. It’s clear that significant problems arise when invoking extreme concentrations of greenhouse gases. However, as this paper illustrates, it’s not unreasonable to estimate higher concentrations of greenhouse gases than the present atmospheric level. Because I’m not well-read on the faint young Sun literature, and given that, as Kasting notes, the paradox is almost 40 years old, I wonder how this hypothesis diverges – if at all – from the standing literature. I’m just guessing, but surely this idea has been on the radar before? In any case, as far as I can tell, the authors have provided a pretty elegant response to the faint young Sun paradox.

Is it resolved? I guess we’ll just have to wait and see!

References

Rosing, M.T., Bird, D.K., Sleep, N.H., and Bjerrum, C.J., 2010. No climate paradox under the faint early Sun. Nature, vol. 464, pg. 744-747.

Kasting, J.F., 2010. Faint young Sun redux. Nature, vol. 464, pg. 687-689.

If you’re hazy on what the scandal was about in the first place, the report provides a nice introduction:

“On Friday 20 November 2009 it was reported across the world that hackers had targeted a ‘leading climate research unit’ and that e-mails from the University of East Anglia’s (UEA) Climatic Research Unit (CRU), one of the world’s foremost centres of climate science, had been published in the internet. The story of the substantial file of private e-mails, documents and data that had been leaked helped ignite the global warming debate in the run up to the Copenhagen climate change conference in December 2009. As reported by the press, exchanges on the internet alleged that data had been manipulated or deleted, in order to support evidence on global warming.”

Of course, at no point was there unequivocal evidence that such tampering had occurred, nor did the actions of a scant few have any effect on the science overall, but that was a minor aside in the circus that followed.

The committee’s report comes to three main conclusions:

1. On the issue of access to information, the negative attention paid to the Climate Research Unit and its head, Phil Jones, is misplaced.

2. Unlike what was trumpeted in the media, there was no scientific dishonesty on the part of Jones or the CRU.

3. Because it’s such an important topic, climate science bears a great(er) responsibility to be “irreproachable”.

Even though the first two conclusions will largely be ignored in the coming days, they do clear up the scandal rather handily. What concerns me, however, is the third one. I think the recommendation to be “irreproachable” with published science is a nice ideal, but it’s just that – an ideal. I’m not convinced that science, especially climate science, can ever be irreproachable insofar as I understand the definition of the word. This kind of language is reserved for religionists and ideologues who do not have to contend with, and embrace the underlying uncertainty that characterizes the chaotic systems scientists investigate.

Greater transparency? Sure. Certainty beyond reproach? Fantasy.

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Hat tip: Pharyngula – Watching The Deniers