The useful links section of the sidebar now contains links to the GeoReM database and a pdf of K, L, and M X-ray emission lines.
blogroll and bad links have also been culled or updated.
The useful links section is mostly designed as a link hotline for numbers or formulae I can't remember but want to look up in a hurry. It is designed mostly for mineral chemists. If there is anything that ought to be there but isn't, let me know.
Friday, April 30, 2010
The useful links section of the sidebar now contains links to the GeoReM database and a pdf of K, L, and M X-ray emission lines.
Monday, April 26, 2010
The blogosphere is abuzz with the news that an Iranian cleric has recently hypothesized that immodest dress causes earthquakes. One aspect of this proclamation has been ignored by the commentariat, however. As a scientific hypothesis, this prediction is very well formulated. More so, in fact, than many of the statements made by professional scientists.
The reason that it is well formulkated is simple: As stated, the hypothesis is easily tested. Furthermore, it can be tested via a variety of independent methods, thus reducing the possibility that selection or methodological bias is clouding the results. Professor Jefferson over at Highly Allochthonous has already described one experimental method of verifying the cleric’s statements, the results of which will hopefully be revealed later this week. But because of the sweeping nature of the statement, historical data should also be able to be mined to determine its accuracy.
The USGS maps the earthquake density for the entire world.
Using this map, we should be able to predict the relative modesty of various parts of the planet. One would expect more quakes in immodest places. A close look at the Mediterranean region shows that the Eastern Mediterranean (from Italy East) has a higher earthquake density than the Western Mediterranean; similarly, the north coast has more quakes than the south. Thus, we would expect the attire in somewhere like Lebanon to be less modest than, say, Morrocco. Thanks to the wonders of the internet, we can instantly acquire completely unbiased and accurate data relating to this subject simply by doing a Google image seach of “X beach” where X is either Lebanon or Morocco. And here are the results:
A Lebanon beach:
A Moroccan beach:
These results are broadly in line with the cleric’s prediction; the dress on the Moroccan beach is substantially more modest than that found in Lebanon. So the Iranians might be right about this.
However, a central tenet of science is that results should be repeatable; repeating this test for other regions should yield similar results most of the time. So let us try again.
Looking at the world map outside of the Mediterranean region, one of the largest earthquake-free continental areas is Brazil, in eastern South America. Therefore, we would expect Brazilians to have the planet’s most modest clothing. If we contrast their attire to that worn in an earthquake-prone region, such as the cleric’s native Iran, we should be able to confirm his beliefs.
Brazilian beachware generally looks like this:
And already, you can see that we have a problem. In theory, this should be less revealing than both Morocco and Lebanon, but that’s not what I’m picking up here. Still, if the swimwear of Iran is very, very revealing, then there may be a point to be had.
So let’s have a look.
Pardon the frequent carriage returns.
If this next picture is as...
Immodest as the clerics predict,
It is probably a good idea to keep the reader’s hand on their computer controls, if you know what I mean.
So without further delay,
The infallible Google image seach informs us that
An Iranian beach looks like this:
I see only two possible explanations. The first is that the clerics are wrong, and immodesty has nothing to do with earthquakes. However, there is another possibility.
If God is from New Zealand, then the Iranian picture is far more risqué than the Brazilian one (by traditional New Zealand standards), and the hypothesis is still intact.
I don’t believe the cyber commentariat has considered this possibility. Thus further analysis is required, and I encourage all of you to search for location-specific images of scanty attire. After all, this is why the internet was invented. If anyone asks why you have twenty browser windows full of bikinis, tell them it's for science.
Friday, April 23, 2010
A recent radio news segment I heard was fearmongering on a laser technology that, if deployed, could potentially destroy us all in the coming nuclear apocalypse. I found a writeup here.
The idea is this: a few decades back, Some Australian researchers developed a technology to perform isotopic separation on uranium using lasers. Uranium has 2 main isotopes, 235U and 238U. 235U has a short (706 million years) half-life, while the half-life of 238U is about the age of the Earth. As a result, the Earth still has ½ of its original 238U supply, while about 63 64ths of the initial 235U has decayed. As a result, modern U has a very high 238U/235U ratio: 138:1.
It is the less abundant isotope- 235U- that undergoes neutron-induced fission in nuclear power plants, research reactors, and atom bombs. And the 238U gets in the way. So before uranium can be induced to fission, some of the 238U has to be removed. The remaining uranium after most of the 238U is removed is ENRICHED uranium. The level of enrichment depends on the purpose for which the uranium is to be used, and can result in a 238U/235U ratio of anything from 50 (low enrichment) to 0.1 (weapons grade).
The 2238U-rich uranium removed from the process is known as DEPLETED uranium, and generally has a 238U/235U ratio of about 400-500, depending on the particular source (I have a funny story about measuring this by accident- maybe some later post).
Separating isotopes requires a lot of energy- so much that it is a significant source of inefficiency in nuclear power, and one of the main technological hurdles involved in making a nuclear weapon. All the concern about Iran at the moment is related to their uranium enrichment process, for example, because election stealing, mistreatment of women, and generally thuggery are comparatively minor offences.
The big deal with laser-excitation isotope separation is that it is more efficient than previous methods. So if you have a clandestine nuclear weapons program, you can use much smaller factories, which are harder to detect. Or, if you are trying to stop global warming, you can make nuclear power generation more efficient. So the consequences of the technology depend greatly on the motives of the people deploying it.
Because of the potential negative consequences, the technology was transferred from the Australian university lab where it was developed to the US government back in the 90’s. And they classified it, so I can’t tell you the details of how it works. Especially not the details of attaching the lasers to the sharks.
The reason it has come up now is that a laser separation plant has been proposed for North Carolina. As far as I know, there are no plans for a tarheel bomb. While NC did fight the United States during the civil war, there is little evidence that the state wants to resume the conflict. They’re even considering ignoring that part of history. Unlike South Carolina, they know the war is over, and even voted for the black liberal guy in the last presidential election. So unless you’re a fanatical kosher evangelist who finds the world’s best BBQ pork to be an international outrage, North Carolina is not a rogue state.
In fact, the critics of this planned laser separation technique don’t even explain how they expect proliferation to happen. It is just a vague sentiment that if this particular nuclear technology works, it will somehow spread to the hands of the bad guys.
I don’t buy this, for the following reason. The technology has already been discovered- it is 12 years old. So rogue operators have had all that time to figure it out. Stopping a peaceful application will not prevent the bad guys from building their own systems using the theory. Building a peaceful system is only a risk if the technology from that system is then sold to the bad guys. And I don’t really see GE putting their surplus lasers on craiglist Tehran. GE makes entire reactors, and if they were in the proliferation business, they already have plenty of other ways of giving out nuclear technology.
In short, there is nothing specific about this laser system that makes it particularly likely to proliferate, so the arguments against it are general anti-nuclear efficiency arguments. So this is hardly the nightmare scenario that it was hyped up to be.
In a way, this is disappointing. I can think of some bona-fide nightmare isotope separation proliferation scenarios, and this is nowhere near what I would call worrying.
For example, geochemists often measure natural changes in isotopic ratios because these changes can tell us about various geologic or biologic processes. In generally heavy elements like U naturally separate less than light isotopes like H. But under ideal conditions, heavy isotopes can fractionate (“fractionate” is the word for natural separation). And one of the most powerful natural fractionation methods is biological activity. Photosynthesis causes most of the biosphere’s carbon isotopic fractionation, for example, and biologic fractionation has been documented in elements as heavy as Hg. So a real, bona-fine nightmare separation technology would involve not lasers, but microbes. A uranium-fractionating bacterium or yeast would be far, far more threatening than laser technology or any other technologically sophisticated system.
Unlike lasers, microbes breed. And they don’t use electricity, they just eat. So instead of needing a factory to separate isotopes, you could use a bottle. Every tub of yoghurt, every vat of beer would be a potential weapons lab. Tzatziki and chaca would become proliferation risks. And fermentation extracts such as vegemite would be proscribed as the planet’s most terrifying "V-bomb" precursors.
In short, learning that yeast had been weaponized, or that landfill methanogens were accumulating a critical mass under Fresh Kills or Woodlawn would be a nightmare scenario. This laser stuff? Bush league material for Bond Villain wannabes.
Monday, April 19, 2010
Erik at Eruptions has been providing amazing blog coverage of this eruption. His updates are timely, thorough, and well presented. I have nothing to add, except a general reminder that plane-killing ash (which is basically pulverised glass) is not the same as planet-cooling sulphate aerosol. So check out his blog for the latest on the eruption.
Thursday, April 15, 2010
Looking for a way to make your tax return more bearable? Need to make room in the beer section of the fridge? Trying to take your anger of the injustices of the tax system? Want an incentive to get to the end of the next section? Then the Income Tax Drinking Game is for you.
Get your pen and calculator, a glass of your favorite poison, and get stuck in.
SIP: Every time you fill a space on the return with a zero.
SIP: Whenever you don’t understand a set of instructions.
DRAIN THE GLASS: Every time you tear out or download a new form, schedule, or attachment.
SIP: Each time they ask for a form that isn’t provided by employers in your country.
CHUG: Every time you work through a worksheet to determine that it does not apply.
SIP: Every time you need to pick through your bank statements one transaction at a time to determine a value.
CHUG: Every time you find you need a document that is physically impossible to get by April 15.
DRINK YOURSELF TO SLEEP: When you realize that your 2009 salary is less than half of your 2008 salary thanks to the economic damage done by a bunch of greedy bankers halfway around the world.
Tuesday, April 13, 2010
Tuesday, April 06, 2010
A few weeks back Chris posted a lovely writeup of his work on the Oman cryogenian diamictites, and the snowball earth hypothesis. A recent paper on some Chinese diamictite ages has a nice summary of the chronology of this time period, so I thought I would throw it up here.
First, a short introduction. Between about 750 and 580 million years ago, a number of glacial sediments appear in the sedimentary record. Some of these appear to have been deposited fairly close to what was the equator at the time, and it was hypothesized that this may have been evidence for the planet having completely frozen over- a scenario known as the “Snowball Earth”. Subsequent stratigraphy identified three or four potential episodes of worldwide glaciation.
One of the ways of testing this theory is to see if all of the glacial strata assigned to a particular episode were actually deposited at the same time. Because there were no widespread diagnostic fossils this early in Earth’s history, biostratigraphy is not an option. One method used is to look at isotopic excursion in the sediments, on the assumption that they reflect a global signal, and not a local phenomenon. Another approach is to use radiometric dating to constrain the ages.
The problem with a radiometric approach is that there are relatively few sedimentary minerals that can be dated directly. So one generally looks for volcanic ash beds, crosscutting dykes, or other igneous rocks with an unambiguous relationship to the sediment in question. If these exist, then you can bracket the sediment in question with older-than / younger-than relationships.
There are several methods used to determine radiometric ages of neoproterozoic rocks. The most widespread is SHRIMP U/Pb geochronology. This method directly analyses the mineral zircon from igneous rocks of interest. Its advantage is that it is an in-situ method that only analyses a small portion of the grain, so it can be used on a wide variety of zircon crystals. The disadvantage is that achieving accuracy of better than 1% is difficult.
Another increasingly common method is CA-TIMS. In this method, zircon minerals are leached to remove damaged parts of the crystal, thin dissolved in acid and run on a traditional thermal ionization mass spectrometer. The advantage of this method is that it is much more accurate. The disadvantage is that it requires higher-quality zircons; inclusions and multiple growth episodes are more problematic.
A new method starting to be used is black shale Rhenium-Osmium dating, which directly dates the sedimentation of disseminated molybdenite in anoxic shales. This method should have similar accuracy to SHRIMP, but it is new enough that there could be unforeseen issues with its widespread application.
Neoproterozoic rocks have generally been metamorphosed since deposition, so K/Ar dating is usually not applicable.
In this paper, Xu et al. determine the age of three ash layers within a diamictite sequence using SHRIMP U-Pb geochronology. They then compare their results to those taken from allegedly correlated units from around the world, and those comparison charts (their figure 4) are shown below.
The following figures are laid out sideways, with older to the right. The lines represent the uncertainty in the measurement; the yellow arrow represents the relative age of the dated rock to the glacial event: younger, older, or synchronous.
As can be seen from the Gaskiers results, literature values do not contradict the existence of a short-lived, synchronous glaciation in the 580-590 Ma range. This study does not further refine this constraint, but the measurement is consistent with Xu et al’s uppermost unit being a Gaskiers correlate.
The Elatina/ Nantuo event is more commonly referred to as the Marinoan glaciation. However, the Marinoan rocks, in South Australia, have very poor age constrains, while the Nantuo is very well constrained.
So when testing for synchronicity, the Nantuo is a more sensible reference (in fact, it may be the golden spike). Once again, the Xu data does not shed much light on this event, but previous data does not contradict a single event in the 643-635 age range.
Finally, we get to the Sturtian. As is shown in this figure, ages for the glacial rocks below the Marinoan glaciation are all over the place.
Xu’s data is no exception; His data indicate a prolonged period of glaciation that precedes most Sturtian-aged rocks from other locales. As an examination of previous Sturtian work shows, a single world-wide Sturtian event is only allowed under the following conditions:
1. It is very long- with a minimum length of 40 million years.
2. It gradually thaws, with some areas deglaciating and precipitating carbonate caps tens of millions of years before other areas.
An open-access copy of the full paper can be found here.
XU, B., XIAO, S., ZOU, H., CHEN, Y., LI, Z., SONG, B., LIU, D., ZHOU, C., & YUAN, X. (2009). SHRIMP zircon U–Pb age constraints on Neoproterozoic Quruqtagh diamictites in NW China Precambrian Research, 168 (3-4), 247-258 DOI: 10.1016/j.precamres.2008.10.008
Monday, April 05, 2010
The USGS is reporting a m6.9 Earthquake just south of the US border, in Northern Baja. The location is consistent with movement on the San Andreas system, but the first motion tensor is not up yet. Strong to moderate shaking has been reported from Yuma AZ and southern California. Much less information from the Mexican side of the border, which is a little bit worrying.