Friday Rock-Blogging: a (chemistry) teaching moment

I haven’t rock-blogged in a while, and while putting together a lecture on stratigraphy I came across this photo from a field trip to the southwest last summer.

This was taken at the beginning of a hike along the Frying Pan trail (well-named if you walk it in late June) in Capitol Reef National Park and shows the contact between the Chinle formation and the Wingate Sandstone (above). The photo scale is Rachel, a former student who came along on the trip as a volunteer/TA. The Owl Rock member of the Chinle in this region consists mostly of slope-forming siltstones and shales representing an inland delta.

Utah, especially in the southern deserts, is known for the bright red colors of certain formations, a result of deposition in highly oxidizing terrestrial environments. The upper member of the Chinle here is no exception, and I had spent part of the previous evening explaining to several students about the oxidation states of iron. Imagine my surprise and delight when we climbed up to this contact and found these green veins extending several feet into the mudstone.

These veins represent mudcracks that formed as the shales and mudstones dried. As they opened up they were filled with organic debris that, as it decayed, created a highly localized reducing environment and turned the red clays green. Some of the cracks also contain veins of gypsum.

The image below is a view of mudcracks in the same (or a similar) surface from above. It's not as pretty or instructive as the image at the top, but it is clearly the same effect, and a student spotted it first. It's always a nice feeling when a student notices and points out the geologic features to me...

Women For President Meme

To begin with, I'm a supporter of John Edwards for president. Barack Obama is my second choice. That said, I don't believe that there are serious objections to Hillary's candidacy based on sexism. I actually haven't heard anyone claim that this is true.

Those on the left of the party don't support her because she is the most conservative Democrat still in the race. I've no idea why the right dislikes her so vehemently. Ultimately her husband's greatest successes in office came from co-opting Republican ideas.

That said, I'm kind of amazed at the willingness of various commentators, male or female, to make blatantly sexist comments about Hillary. A female McCain supporter felt free to call her a Bitch on camera, and Mike Allen of the Politico commented "What voter in general hasn't thought that?" Chris Matthews has referred to her as "Nurse Ratched" and to her male supporters as eunuchs and castratos.

I don't expect that the folks in New Hampshire following her around with "Iron My Shirt" signs were supporters of any of the major Democratic candidates. Try to imagine signs with a roughly equivalent insult directed at Obama or Bill Richardson, and then imagine photos of the incident showing up on the front page of national newspapers, or TV commentators giggling and joking over a videotape of the incident.

OK, I got that off my chest. Women I would support for president if they were running:

1. Barbara Boxer
2. Christine Gregoire
3. Janet Napolitano
4. Hillary (as I said, not my first choice among present candidates but at least she hasn't suggested staying in Iraq for hundreds or thousands of years).

Energy and environment in the new millenium

One of our newer geobloggers, Callan Bentley, posted recently about his new Toyota Prius. Energy use is a pretty hot topic in all of my classes, as it relates to discussions of fossil fuels and peak oil and to climate change. For what its worth, here’s my first 18 months worth of Prius ownership (I picked it up on the June solstice in 2006):

I used about 250 fewer gallons of gasoline in my first year of ownership, compared to the mileage I got in my Nissan pick-up (my average mpg over the last four years for the pick-up was 20.5). That said, on my Death Valley field trip last October we used more gas (34 students, two instructors, four Ford vans) in 3 days than my Prius used for the first year. Of course a geology field trip is infinitely more justifiable than my daily commute…

I’m personally convinced that the kind of changes we need to be making as a culture are going to require some fundamental changes in our attitudes about the energy we use. While we are encouraged to switch to more energy efficient light bulbs we are paying a couple dollars/liter to drink tap water that has been forced, at huge energy expense, through a reverse osmosis system before being recharged with the calcium and magnesium removed by the RO and then packed into PET (Polyethylene terephthalate) bottles that, per kilogram of plastic, consume about 6.5 kg of oil and release 4 kg of greenhouse gases. Or, if you prefer bottled spring water you can (usually) skip the RO process and spend the energy shipping the water from France or Fiji…

One of my resolutions this year is to start commuting by bus a couple of days a week (I’ll keep you updated on how this works out…). It’s 45 minutes to an hour of additional inconvenience per day, but a partial acknowledgment that the use of the automobile for regular commuting is one of the conveniences we need to give up.

But I’ve never believed that the solutions to our problems lie in individual choices. The environment is the commons, after all. The more people use public transportation, or buy cars that get high mileage, the better. But decisions to expand public transportation, or to require that passenger cars get better gas mileage, are made collectively. The free market doesn’t respond to consumer needs, it attempts to manufacture consumer desires (see water, bottled).

I’m going to write more about this in the next few months. If we are indeed successful in lobbying for a presidential science debate this year I can’t imagine energy and environment not being the most important topics.

Pale Blue Dot

Phil Plait reminded me that Carl Sagan died 11 years ago today. I'm too old for this to be true, but Cosmos was what inspired me to a career in science. Better late than never.

In February 1990 the Voyager 1 spacecraft, by then 12.5 years and four billion miles from home, spun around to take a “family portrait” of our Solar System from about 32 degrees above the ecliptic. The image above is of Earth, a few pixels of blue against the blackness of space. The light streak is a ray from the sun, just off the image to the right.

Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there — on a mote of dust suspended in a sunbeam.

The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors, so that, in glory and triumph, they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds.

Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.

The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment the Earth is where we make our stand.

It has been said that astronomy is a humbling and character building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known.

-- Carl Sagan in a commencement address, May 11 1996

The Reason for the Season

It's been a week since Phil Plait posted this link on his Bad Astronomy blog. It made me very angry, that I didn't think of it first. Nonetheless, it will from this year forward be my Christmas card...


Merry Christmas, y'all!

Where On (Google) Earth? #80

Well I managed to win my first northern hemisphere WOGE challenge, though it looks like Ron may have had a better claim had he signed on a few minutes later, after Joe re-posted the image.

It only seems fair to stay with the recent trend and not invoke the Schott Rule this time.

However to add to the challenge this time I won't remind you to look at the north arrow.

Accretionary Wedge #4: My Pet Rock

For show-and-tell today I brought this fulgurite specimen, which I unfortunately did not collect myself.

In 1998 I took a group of intro geology students on a trip to Capitol Reef National Park in southern Utah, and while we watched a storm play out over the Henry Mountains I gave an impromptu lecture on convective thunderstorms and lightning.

Lightning is the sudden release of huge static charges that develop in convective storms due to rapid vertical movement of air. No one really understands the details of the transfer of charge (the primary carrier of charge appears to be small fragments of ice crystals), but typically the cloud becomes a 5-10 km high capacitor with negative charge concentrated near the base. When the stress becomes too high the cloud discharges very rapidly. Globally there are roughly 5000-10000 lightning discharges per minute, mostly in the tropics, of which roughly one third strike the ground (the rest occur between clouds or within the cloud).

A cloud-to-ground strike transfers billions of joules of energy, most of which dissipates in the atmosphere (heating the air to tens of thousands of degrees and creating visible as well as infrared light that ranges down into the radio spectrum). In the end only a tiny amount of the original energy is delivered at the point of impact, but anyone who has observed or experienced the results will testify that it is sufficient.

Since the cloud is looking for the easiest path to the ground, it is most likely to strike objects above the local base level, as trees, houses, and people (especially those holding lightning rods golf clubs) are much better conductors than relatively dry air.

The subject of fulgurites, or fossil lightning, came up and I explained that quartz has a melting point of about 1600 degrees C, a temperature easily achieved in the near surface, though in very wet soils the charge can be dissipated pretty rapidly. The best examples therefore result when lightning strikes the ground directly in an area where the soil is dry and is thus not a good conductor.

Quartz sand works particularly well as it conducts heat as poorly as it conducts electricity. This prevents charge from dissipating rapidly, so the bolt can travel through the ground for several meters, fusing sediment to glass and vaporizing all of the volatile components. Some of the best examples of fulgurites are discovered in dune fields, where dry unconsolidated sands subsequently are eroded by winds, exposing the fused structure. Unfortunately fulgurites are quite fragile and tend to crumble when excavated.

One of the students on that trip was visiting relatives in Temecula later that year when she saw lightning strike the ground a few hundred feet from her back door. She got her husband to help her dig up the yard after the storm had passed, and she brought us a shopping bag full of this broken chunks of this fossilized lightning. The largest piece here is about 25 cm long and 8 cm in diameter and was found less than 40 cm beneath the surface.

The soil was very sandy in this location, and was fused to glass at temperatures exceeding 2000 degrees C. You can see what a poor conductor of heat this material is, as it transitions from glass to barely altered sand in less than a centimeter. There is a general relationship between current and diameter indicating that this sample was created by a fairly powerful lightning strike.

The moisture and organics flashed to vapor, leaving lots of vesicles. The explosive expansion of the volatiles can create hollow tubes down the center of the structure, pushing the molten (or melting) sand outward. There is a common misconception about these hollow tubes that they represent a zone where temps were high enough to vaporize quartz, but this is not true.

The second piece is from about a meter beneath the larger sample and is barely more than a glass tube. You can see the charge branching off from this piece in several directions simultaneously.

I've found that, in addition to being great samples to pass around when I’m talking about thunderstorms in class, fulgurites are great ringers to slip into an igneous rocks practical exam.