Following the recent theme of science-hubbub in the popular press, a story has been making its rounds for the past couple of weeks concerning a paper by Matese and Whitmire (2011) (pdf on proposing the existence of Tyche: a gas-giant planet 1-4 times the size of Jupiter orbiting around the Sun in the far-off reaches of our Solar System.

(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.

Raup and Sepkoski( 1984)

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

The February issue of Nature Geoscience features a couple of interesting articles on the origin of water in the Earth-Moon system. By way of an introduction, Robert (2011) reviews the known ratios of deuterium (heavy hydrogen; one proton, one neutron) to hydrogen (one proton) of various planetary bodies in the solar system: the proto-Sun, Earth, and Moon, along with carbonaceous chondrite meteorites and comets (Fig. 1).

Robert (2011)

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.


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.

I’m not sure what’s more interesting – that arsenic-based life may potentially exist, or the spectacle of its announcement (and, of course, the eventual fallout). As one who is excited about the prospect of a shadow biosphere on Earth and how it may relate to the possibility of  life elsewhere in our solar system and galaxy, I want the science to stand at the forefront of discussion. But you gotta admit – human reaction to this story is equally worth the mention (and, perhaps unfortunately, is far more relevant with respect to how we progress scientifically as a species. Flying cars, anyone?).

Good reading:

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.

I’ve got a confession to make: I love kooks and crazies – I really do. I don’t know if it’s because their propensity for confrontation and drama makes for some interesting reading, or if it’s because by association I just feel that much smarter. (Here’s a second confession: indeed, their stupidity makes me feel that much smarter.) Good thing for me, there’s a world wide web out there that is rife with all sorts of weirdos and intellectual midgets.

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.

I’ll admit it: I spent more time in the field this fall mapping a trench for my B.Sc. thesis than was actually necessary. Part of the reason was that I wanted to make sure I collected quality field data for the project, but another part of it was that I enjoyed the excuse to get out there into the near wilderness and spend some time alone. However, now that a respectable layer of snow is blanketing southeastern Manitoba, I suppose it’s time to face reality and start treating some of that data.

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:

GEOrient foliation plot

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:

Final version using Illustrator

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.

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