Tuesday, November 29, 2011

US science tour schedule

I'll be in the SW USA for the next week and a half giving talks about SHRIMP and attending AGU. The talks are:

Arizona State University

Thursday 1 Dec time: TBA, Chemistry dept (probably) Title TBA (this one is pretty informal, if you haven't guessed)

University of Texas at Austin

Friday Dec. 2

Understanding the SIMS U/Pb calibration

Jackson School of Geosciences
JGB 3.222 at 11 AM.

American Geophysical Union Fall meeting, Moscone Center, San Francisco

SHRIMP geochronology using an 18O primary beam

Session Title: V33G. Innovations in Isotope Mass Spectrometry and Isotope Metrology II
Session Type: Oral
Date: 07-Dec-2011
Start Time: 03:10 PM
End Time: 03:25 PM
Location: Room 3022 (Moscone West)

Texas abstract:
In preparation for the production of the new SHRIMP IV, a number of experiments were run to characterize the behavior of the U/Pb calibration under various analytical conditions. Repetition of early SHRIMP One work showed that the calibration appears to primarily reflect the dependence of Pb ionization on oxygen activity. In order to constrain the effects of oxygen, further experiments were performed using an 18O primary beam, so that the relative contributions of oxygen from the beam (18O) and the natural samples (16O) could be discerned.

The use of the 18O primary has shown that the ratio of sample oxygen to primary oxygen in the secondary ions varies based on the target mineral and the primary beam impact energy. For baddeleyite, there is also an orientation effect. In some circumstances, the 18O/16O ratio can be used to correct for scatter along the calibration line, allowing sub-percent level accuracy for Paleozoic U/Pb dating of zircon.

The cause of calibration-related uncertainty is still not precisely known, but can probably be related to a number of factors. This work, combined with recent demonstration of SHRIMP geochronology of chemically abraded zircon, suggests several potential ways of improving calibration accuracy. In addition to the standard approaches of high quality sample preparation and wide energy windows, new approaches include the use of 18O to correct for source fluctuations, active change neutralization using a medium energy electron gun, and chemical abrasion. These techniques have not yet been used simultaneously on unknown zircons.

AGU abstract:
The key constraint of uranium-lead geochronology is the variation in ionization efficiency of uranium and lead. As the ionization efficiency of Pb is dependent on oxygen availability, a calibration relating the UO/U or UO2/U ratio to the Pb/U ionization efficiency is commonly used. However, these calibrations have historically been limited to errors of about 1%.
We have identified the origin of the oxygen in the UO and UO2 species by feeding the primary column duoplasmatron source with 18O gas. This creates labeled UO and UO2 isotopologues at nominal masses of 254, 256, 270, 272, and 274, where the 18O isotopologues contain 18O from the isotopically labeled primary beam, and the 16O isotopologues contain oxygen from the natural silicate, phosphate, or oxide geochronology target mineral. The ratio of U18O to U16O depends on the target mineral, and primary ion species (atomic vs. molecular oxygen). In zircon, the variation in U18O vs. U16O can be used to correct for calibration scatter, allowing for more precise and accurate geochronology. This correction only applies to SIMS instruments such as SHRIMP, which can perform uranium-lead geochronology without the use of a third source of oxygen, such as oxygen flooding.

Monday, November 28, 2011

Billions of years of conference badges

ASI was lucky enough to be the lanyard sponsor at the recent Biennial Geochemical SIMS workshop, held in Hawaii at the beginning of this month. The meeting was fantastic. But rather than do the usual slog of simply plastering our logo on the lanyard, we decided to give it a geological timescale. The scale is one year per angstrom. Various important events are designated by the isotopic system used to define them and/or cartoons. Being very long and skinny, it is hard to display in a blog, but here’s a photo of one curled up (click to enlarge).

We have some extras, so if anyone wants me to bring some to AGU for you guys to wear, let me know and I'll pack some.

Tuesday, November 22, 2011

Migrating dinosaurs and oxygen isotopes

ResearchBlogging.orgA recent paper made a claim that dinosaurs must migrate, based on the oxygen isotopes in dinosaur teeth. This paper is both awesome and flawed.

The awesome part:

It is hard to measure oxygen isotopes in teeth. Teeth are a mixture of organic matter and two minerals: calcium carbonate, and hydroxyapatite. The organic matter contains oxygen, the carbonate portion contains oxygen, and the hydroxyapatite contains oxygen in two different parts of the mineral; bound water (the “hydroxyl” part, and phosphate ions.

None of these phases are stable in groundwater, and they generally get replaced by other minerals such as silica during the fossilization process. That is why most of the dinosaur teeth you see in museums are black. Even if the teeth aren’t fossilized, the different components will exchange oxygen with groundwater at different rates. Depending on the groundwater chemistry. So simply finding appropriate samples from the Jurassic- 150 million years ago, is not easy.

Secondly, teeth are hard to analyse for oxygen isotopes in lab, because you need to make sure that the oxygen from the different materials isn’t mixed, especially if some of the oxygen has been compromised. This can also be tricky.

Most oxygen has an atomic mass of 16, from having 8 protons and 8 neutrons. However, about 2 in a thousand oxygen molecules have 2 extra neutrons, giving a mass of 18 amu. This oxygen-18 ( abbreviated 18O) evaporates slightly more difficultly and condenses more easily than normal oxygen-16 (16O), so rainfall is generally depleted in 18O. This gives what scientists refer to as a negative δ18O value, which basically means that the rain water has a lower 18O/16O ratio than seawater. As air cools, more and more 18O rains out, so that snow has a strongly negative δ18O deviation (figure 1).

Figure 1. Tropical lowland rainfall is generally slightly negative in δ18O (left), while mountain snow in generally highly negative (right).

This leads to the flawed part of the paper.

Fricke et al. (2011) state that because their dinosaur teeth have a variation in δ18O, the dinosaurs must have migrated from lowlands to uplands (figure 2).

Figure 2. oxygen isotopic variation in dinosaur teeth in interpreted as arising from migration.

But as the low δ18O snow melts, it forms low δ18O rivers (figure 3). In an environment with seasonal rainfall, local, tropical rain could give a modest δ18O depletion, white water draining from high mountains would have a strong δ18O depletion. This is exactly what Lambs et al. (2005) see in modern day India: The Ganges river, has a δ18O value of -5, while the Bramhaputra, which flows into India from Tibet, has a δ18O value of -11. Despite their different sources, both rivers empty out into the same river delta. So in this case, the water is migrating, by flowing down hill.

Figure 3: Water can move as well.

An animal which drank from locally fed streams and ponds during a wet season, but retreated to a river with a distal source in the dry season, would also have a δ18O anomaly like that of a migrating dinosaur. This would also explain why the dinosaur had more negative δ18O values when it died; the rock which contained the fossils was a river sand.

This is seen by Dettman and Lohmann (2000) in rocky mountain oysters (fossilized bivalves, you pervs). Shellfish fossils have a δ18O value that ranges from -5 to -23, all in the same sedimentary sequence. Nobody interprets this as evidence for oyster migration. Rather, it is thought to be caused by rivers with very different source characteristics feeding the same depositional setting. Just like the modern Ganges delta.

So my opinion is that the analytical work and sample selection were very good, but the interpretation is a bit simplistic.

Fricke, H., Hencecroth, J., & Hoerner, M. (2011). Lowland–upland migration of sauropod dinosaurs during the Late Jurassic epoch Nature DOI: 10.1038/nature10570

1. David L. Dettman and, & 2. Kyger C Lohmann (2000). Oxygen isotope evidence for high-altitude snow in the Laramide Rocky Mountains of North America during the Late Cretaceous and Paleogene Geology, 28 (3), 243-246

Lambs, L., Balakrishna, K., Brunet, F., & Probst, J. (2005). Oxygen and hydrogen isotopic composition of major Indian rivers: a first global assessment Hydrological Processes, 19 (17), 3345-3355 DOI: 10.1002/hyp.5974

Thursday, November 17, 2011

Even bigotry has a silver lining

Professor Anne Jefferson has recently been complaining about a banal sexist article that recently appeared in the prestigious scientific journal Nature. While it is understandable that she has been offended by this insipid and thoughtless piece of writing, there is an obvious lesson here for her and other scientists looking to advance their careers. It is so simple that I can lay it out in outline form:

1. Publishing in Nature is good for your career. There is no doubt about this. For better or worse, Nature has one of the highest profiles of any scientific journal. Some prestigious institutions, when looking for high-impact, earth-shaking original research, tally up only papers published in Nature and Science. So there is no doubt that getting a paper into Nature will be good for your career.
2. Nature will publish tripe. This is obvious from reading the article by Dr. Rybicki which has casued this kerfuffle. “Womanspace” contains no original thoughts, no new insights, and no hint of creativity or intellect.
3. Therefore, anyone looking to advance their career should submit anything and everything to Nature for publication. If you can string 700 words together in an incoherent, vaguely offensive story with jokes as flat as an abyssal plain, then you are at least Dr. Rybicki’s equal. And should you actually put a smidgeon of thought into your writing, well then you’re in like Flynn. So don’t hold back! That inconclusive master’s project? Submit it to Nature. Your high school science fair experiment? Nature. Your 7th grade essay on pea horticulture? Fire away.

Nature has sent a clear message to the scientific community that the standards which once gave their publication its prestige no longer apply. Sure, you could spend years leading a major research effort, like scientists Dea Slade, Jessica Altöldi, or Lisa Welp did. And their research efforts deserve major acclaim. But the publisher of Nature has but their gruelling scientific accomplishments side-by-side with:

“I'd been staying with my friend Russell in Canberra, trying to sort out how we were going to get our book on virus structure together, when Russell's wife Lilia decided that their youngest daughter needed new school knickers. She was too busy making supper…”

Nature has sent a clear message to the scientific community. Nature is no longer interested in keen intellectual arguments or brilliant insight. They now want to publish garbage. Submit it to them, and send the good stuff to Science.

Saturday, November 12, 2011

Some thoughts on the Penn State sex scandal

For anyone who has been living under a rock for the past week, a former Penn State assistant football coach has been charged with sexually assaulting 8 pre-teen boys over a 15 year period. Numerous other administrators have been charged with failure to report the incident, and others, including legendary football head coach Joe Paterno, have been fired.

Needless to say, there has been a bit of internet chatter about this. A lot of it has focused on the football program and the similarities between this incident and those of the Catholic Church. I think this emphasis is mistaken, and potentially damaging.

My take is this. All universities cover up sexual assaults as a matter of course. The key feature of the Penn state case is that this particular incident is simply not containable. The age of the victims means that, unlike most university situations, consent is out of the question. The number of victims means it is not a freak incident, and the multiple third party eyewitnesses preclude it from simply being a he said she said. This is a once in a century campus sex crime.

The problem is that, in the 46 years that Paterno has been coaching Penn State, there have been scores of drunken field trip incidents, hundreds of late night library gropings, and thousands of off-campus drink-spiking rapes. And because those cases have not involved epic falls from grace, state-wide criminal probes, and shocking eyewitness descriptions of underage sex, they have been successfully covered up.

Because the fact of the matter is that universities are very good at sex crime cover-up. They form shadow justice systems designed to give victims whatever they require to stay quiet, they use freshman orientation to scare students into avoiding the cops, and they terrify overseas students by threatening to yank their visas and send them back to their country of origin before they can file charges.

Universities have no divisions of powers, or checks and balances, and they are driven to enhance and protect their institutional reputation at all costs. So their reaction to this case has a direct bearing on the health and safety of students worldwide. If they react by re-enforcing their cover-up mechanisms so that nothing smaller than a Paterno-scale epic will ever see the light of day, then campus life will be degraded. If they react by redirecting all their administrators and councilors and lawyers towards helping their victims instead of covering the institution’s image, then everyone who sets foot on a campus will be better off.

I am not optimistic.

Thursday, November 10, 2011

Energy from the sun

Our house uses a number of different technologies to harness energy from the sun. Three are pictured above. The newest and most expensive of these was just hooked up to the grid today, providing 11.4 kWh for the internet dawlders of Australia. So long as I don't goof around on the computer all night, that should cover our home usage and then some. The Hills Hoist also efficiently utilized solar energy by drying three loads of washing. The seedlings in the pots on the black rack have yet to use sunlight to sequester atmospheric carbon dioxide in the form of tomatoes, but we are hopeful for the future.

Tuesday, November 01, 2011