Sunday, March 31, 2013

The Eye of Africa

Deep in the western Sahara Desert, in the country of Mauritania, is a spectacular circular structure that can be seen from space called the "Eye of Africa" or the Richat Structure (Guelb er Richat).

This structure is about 50 km (30 mi) across and was only discovered in the mid-1960s when Project Gemini spacecraft observed it from orbit.

The Richat Structure in Google Earth (21°07'30" N, 011°24'00" W)

Oblique view from Google Earth

It's pretty impressive.  Check it out in Google Maps and you'll see it's visible as you zoom out to orbital distances.

So what the hell is this structure? "Theories" on the Internet abound. Here are a couple of comments I saw on one web site:

I have a suggestion. It looks like a hole that could have been opened up when God flooded the Earth. “In the six hundredth year of Noah’s life, in the second month, the seventeenth day of the month, the same day were all the fountains of the great deep broken up, and the windows of heaven were opened.” -Genesis 7:11 Later God plugged the holes: “The fountains also of the deep and the windows of heaven were stopped, and the rain from heaven was restrained” – Genesis 8:2
There can be no question that it is a standing shock wave. It is well known that it is not a result of direct impact. I have a theory that I have not seen posted elsewhere. I think it is a shockwave as a result of a large object impact at the antipode of this location. The current antipode to the Richat Structure is East of the Coral Sea. Tectonic plate movements may have shifted the actual impact. This makes the most sense to me. The structure is simply too symmetrical and undulating to be anything BUT a shockwave. If this is correct, it would have formed very rapidly and would have been incredible to witness. 
What about it being a wortex generated by dominating winds in the area?
Looks like a crash landing site. From what exactly? That’s an interesting thought. 
Its Earth asshole!
(OK, maybe the last comment wasn't serious!)

This is why you have to be careful about what you read on the Internet, boys and girls. Lots of people have crazy ideas based on nothing but ignorant, wild-ass speculation.

If you have a lot of money you don't know what to do with, it is possible to do a Land Rover 4x4 tour of this area. The problem, however, is that the Richat Structure is so big that you can't really see it from the ground.   That's why it wasn't even recognized until the Space Age.  Here are
a couple of images from the ground showing not much more than rocks and hills.

Geological circular features like  the Richat Structure are generally caused by one of three things - a meteorite impact, volcanic activity, or a domical uplift from an igneous intrusion.

When this structure was first noticed, it was thought to be a meteor crater. Once geologists got out there, however, it was determined that this structure had none of the characteristics that would have been expected from an astrobleme (impact crater).

The sedimentary strata surrounding this structure is upwarped, but not heavily broken up or overturned as is common in an impact crater. The multi-ringed structure of sedimentary rock without a depressed center is also not typical of craters. Large impacts also alter the crystalline structure of quartz grains in the surrounding rocks (called shock metamorphism) and there's no sign of that here.

[Dietz, R.S., et al. 1969. Richat and Semsiyat Domes (Mauritania): Not Astroblemes. Geological Society of America Bulletin 80: 1367–1372]
Geological fieldwork also showed that this structure is not a simple volcanic caldera (a large volcanic crater).  There is, however, evidence of past igneous and volcanic activity here (movement of molten rock - magma - in the subsurface).

Geologically, the structure is composed of three nested rings dipping outwards from the center.  They are composed of a sequence of  sedimentary rocks dating from the Upper Proterozoic Period (about 650 million years ago) to the Ordovician Period (about 450 million years ago).  The center of the structure is a limestone shelf with a lens of breccia (rock created from angular fragments of rock cemented together).  The whole structure is intruded by various types of volcanic rocks.

So what caused this?  A proposed mechanism (G. Matton, 2008) for the formation of the Richat Structure is as follows:

In Stage 1, prior to 100 million years ago, there was an intrusion of magma from the lithospheric mantle below the continental crust.  This intrusion domed up the overlying sedimentary rocks and formed radial and ring dike fractures above the intrusion.

In Stage 2, around 100 million years ago, there's reactivation of the magma chamber and the intrusion of different composition magma.  Groundwater circulating through the fractured, overlying rocks gets heated by the hot igneous intrusion and acidic leading to the dissolution of the overlying limestone.  The limestone collapses into sinkholes and gets cemented into a breccia.

In Stage 3, more igneous activity as magmas rise and interact with either shallow groundwater or surface water lakes in the center of the structure and explosive activity leads to collapse of the central part of the structure, much like a piston in a cylinder.

In Stage 4, erosion creates the circular, tilted layers (cuestas) of resistant quartz sandstone and exposes the central part of the structure where the limestone breccia and volcanic rocks occur.  Earlier radial and ring dikes are exposed in places.

All resulting in this.

NASA Landsat 7 image of the Richat Structure

Really cool!

Thursday, March 28, 2013

Obama Care & Adjuncts

Just about every college and university relies on both full-time and adjunct instructors to teach classes. Adjunct instructors are part-time faculty who are basically hired on a semester-to-semester contractual basis to teach specific classes. It truly is an exploitive system for a number of reasons.

The amount of pay adjuncts receive is low (at our institution it currently ranges from around $2,200-$2,500 for a three-credit course before taxes - the higher value for adjuncts who have taught at least 24 three-credit courses!). Try to put together a living wage this way. Just to get above the $11,175 (2012) poverty line, you would have to teach a minimum of 5 classes a year - even if you were at the high end of the pay scale. To get above $20,000 a year (before taxes), you'd have to teach 8 three-credit classes. Guess what, you can't teach 8 three-credit classes a year at most colleges due to contractual restrictions that keep adjuncts below 12 credits per semester (7 three-credit classes would be the limit).

Let's even look at this even closer. The so-called Carnegie model assumes, for both faculty and students, that a three-credit class involves nine hours of work - two hours outside of class for every hour in the classroom. For students, those two hours are for studying, reading, homework, etc. That's why 12-15 credits a semester is considered full-time for a student. For faculty, those extra hours are for lecture preparation, grading, discussions with students outside of class, etc. So an adjunct faculty member teaching a three-credit course making $2,500 (highest end of pay scale) is paid for working 9 hours per week for a 15 week semester. That's $2,500 for 135 hours or $18.50/hour.

Doesn't sound too bad, right?

Keep in mind, however, that this is not full-time work so it doesn't add up to much. Adjuncts need to teach at multiple colleges (due to restrictions on how much they can teach at any one college) to make enough money to survive so spend lots on gas and wear-and-tear on their cars (especially in rural areas like mine). Each semester they have to struggle to fit together class schedules at different colleges. Needless to say, they get no benefits (health or otherwise). They also have no job protection and may have classes canceled at the last minute.

As mentioned above, adjuncts are also contractually restricted to generally teaching less than 12 credits a semester (4 three-credit classes). This varies from college to college. Why the restriction? If it didn't exist, some colleges would staff the entire campus with adjuncts and never pay anyone benefits or a living wage. Even with this restriction, the college where I teach has 1/3 of the faculty as full-time and 2/3 as adjuncts. This is not good for students (see my previous post on this) but an economic reality of higher education today given the public and politicians do not support public higher education in this country (not how it counts, with adequate public funding).

We have adjuncts at our community college who have PhD degrees in their field of study and sometimes tens of thousands of dollars in student loan debt! Working for essentially minimum wage. Most of them do it because full-time faculty jobs are very hard to get. Many of them hope to get a full-time position at some point. Most of them won't. It's a terrible system.

This terrible system will get even worse in January of 2014. The reason is that Obama's new Affordable Care Act regulations will require companies to provide benefits to those employees working 30 or more hours a week. Because of the Carnegie model mentioned above, adjuncts teaching 10 credits or more now fall under this restriction. Guess how companies will deal with this new law?

Brain-dead politician: "Uninsured working people who can't afford private insurance is a problem. Hey, let's solve it by passing a law saying you have to give health insurance to part-timers working 30 hours or more a week."

Chief financial officer at a company: "Part-timers are not allowed to work 30 hours or more a week anymore."

Result: Poor working people without insurance become even poorer!


Our college, along with many if not most others, will cut adjunct hours beginning in January 2014 and restrict them from a maximum of 11 credits/semester to a maximum of 9 credits/semester (a difference of up to five grand in their pay!).  It's even worse since many math and English adjunct instructors at our school also work at the college's math tutoring and writing centers.  These hours now count toward that 30 hour limit.
Adjunct faculty will now be screwed over yet again.  Is it too much to ask politicians to think through the consequences of their half-assed laws?

Wednesday, March 27, 2013

Ancient chemistry, etymology, & beauty

The word "kohl" comes from Arabic (كحلkuḥl) and refers to a black powder used to enhance the area surrounding both men's and women's eyes.  Kohl has been used as a cosmetic for over 5,000 years, first used (as far as we know), around 3,000 BC by the ancient Egyptians.

Kohl-enhanced eyes of an ancient Egyptian
Egyptian kohl cosmetic tube
Here's a more "modern" example...
Keith Richards of the Rolling Stones in case you didn't recognize the mug.
It's an unfair world when you realize how many beautiful women
this ugly, but talented, bastard has slept with in his drug-addled life.
Speaking of good-old Keith, the word kohl, referring to the eyeliner, has a shared etymology with the word alcohol.  It's a bit convoluted, but the word was originally applied to a fine powder produced by the sublimation of a mineral called stibnite (more about this below).  Sublimation produces a vapor from the mineral which then deposits as a powder.  This powder was thought to represent the "essence" or "spirit" of the mineral.
The Arabic phrase (الكحل al-kuḥl) for "the kohl" (al is a definitive article in Arabic translated simply as "the") became the word alcohol as it made its way to European alchemists and was used to refer to any fine powder produced by the sublimation of a substance.  By the 16th century, the term came to be applied to fluids obtained by distillation including "alcohol of wine" or ethanol - eventually becoming the word alcohol we're familiar with today.

Kohl has been made from a variety of materials - one of which is the mineral stibnite.  Stibnite (Sb2S3) is a mineral with the chemical composition of antimony sulfide (the element antimony is abbreviated Sb because the ancient Greeks called the mineral containing it stibi (στἰβι) meaning "mark" (because it was used to make kohl, of course).  Stibnite often occurs, sometime spectacularly, as radiating clusters of dull gray metallic crystals. It forms in hydrothermal deposits (hot groundwater typically in volcanic areas) and the American Museum of Natural History has a 1,000 pound specimen on display.  Here's one particularly pretty example:

Stibnite (Sb2S3) with barite (BaSO4)  

The name antimony comes from the Greek ἀντί + μόνος (anti monos) meaning "not alone" since it was believed never to exist in pure form.  Greek naturalist Pliny the Elder called it platyophthalmos (πλατυόφθαλμος) meaning "wide-eye" due to its cosmetic use (kohl again).  Antimony sits below arsenic on the periodic table and shares many of its properties including its toxicity.  As with many toxins, it was frequently used for medicines throughout the ages (toxic materials often have antibacterial properties).

Some have speculated that Mozart accidentally killed himself by dosing with antimony-based medications (here's an interesting blog post about antimony).  Kohl, by the way, has also been made from galena, a lead sulfide mineral, but that's a post for another time.

Original uses of kohl may have been practical - the antibacterial properties of antimony may have protected from eye infections, the oils usually mixed with the powdered kohl moistened the skin in this dry arid climate, and black around the eyes afforded some protection from the fierce sunlight (the same reason football players smudge under their eyes).

I'll close with a more attractive use of kohl than the Keith Richards example above - the classic, exotic, and mysterious Arabian woman's eyes.

It's easy to see why the use of kohl has remained popular for thousands of years.

Monday, March 25, 2013

Ancient Ice Ages

Recently, in my historical geology class (historical geology is the history of the Earth, by the way, not the history of geology) I discussed a famous rock unit known as the Gowganda Formation.  The Gowganda Formation consists primarily of conglomerates (diamictites, really, but most people aren't familiar with that term) and laminated mudstones.  Here's a picture of one of the conglomerates I picked up once on a field trip in Michigan (it's been glacially polished and rounded by transport during the last ice age).
This picture really doesn't do it justice - it's a beautiful rock.  The conglomerate is not just any conglomerate either, it represents special type of rock called a tillite.  When large ice sheets from glaciers move across the landscape they erode the bedrock and pick up material of all sizes from microscopic clays to large boulders.  When the climate warms, and glaciers melt, they drop all of this unsorted geologic material into deposits known as glacial till or simply till.  Till, over periods of geologic time, can be lithified into a sedimentary rock known as tillite.  Tillites are therefore representatives of past ice ages.
Here's a nice picture of the Gowganda tillite in the field.
The other major rock unit in the Gowganda Formation are laminated, or varved, mudstones.  These also form in environments characterized by glaciation.  As glaciers are melting, large ice margin lakes form which may be open in the summer and frozen in the winter.  This results in differences in winter (finer clays) and summer (coarser silts and sands) sedimentation on the lake bottom leading to yearly couplets of lighter and darker laminations called varves.  Counting the varves allows one to determine how long the ice-margin lake existed.
The outcrop above, in a quarry just north of Lake Huron and east of Sault Ste Marie (46.413° N, 83.325° W) in Ontario, shows at least 750 years of varve couplets in a mudstone (also called an argillite by geologists).  Also shown, with the black arrow in the image, is a granite dropstone - the same granite seen in the tillite above).  Here's a better picture of a dropstone in the Gowganda varved mudstone sequence.
Dropstones form when chunks of ice break off from the glacier, float into the large ice-margin lake, and melt.  When they melt, they'll drop anything their carrying including, at times, sizable rocks which become dropstones in the lakebed sediments as seen above.
The two lithologies (rock types) of tillites and argillites, along with the varves and dropstones in the argillite, clearly indicate glaciation at the time these rocks were forming.  Some locales even show multiple advances of ice (tillites separated by thick argillite sequences).  So when did this glacial event occur?
The age of the Gowganda Formation is difficult to pin down.  It's too old to contain fossils (the most advanced form of life on Earth at the time was single-celled and mostly bacterial) and sedimentary rock can't be radiometrically dated.  The formation does lie on metamorphic basement rocks which have been dated to 2.6 billion years old and it's intruded by igneous rocks that are 2.1 billion years old so all we can say for certain is that it's between 2.1 - 2.6 billion in age (a big spread of half a billion years!).

Plate tectonics moves continents around over time so another reasonable question would be to ask where this area was during this period of time.  Was it near the poles (in which case glaciation would not necessarily be surprising) or was it at lower latitudes (which would indicate a global ice age during the time)?  Evidence from paleomagnetism (studies of the ancient magnetic field in rocks indicating their magnetic latitude at time of formation) seems to indicate the Gowganda formed at relatively low latitudes.  In other words, at the time of a glacial ice age.

A digression...  Most people know about THE ice age.  That at some point in the past (most people you ask on the street would say millions of years ago but the last great ice sheet melted from the Hudson Valley only about 12,000 years ago), the Earth was covered with massive ice sheets.  What most people don't know, however, is that the Earth has had multiple ice ages in its 4.5 billion-year history.  The one we think of as THE ice age is only the most recent which occurred in a period of time known as the Pleistocene Epoch (beginning only 2 million years ago).

The earliest glacial ice age we know about is the one that formed the sediments of the Gowganda Formation in Ontario, Canada.  Similar age glacial sediments exist in western Austrlia (Hammersley Province) and southern African (Transvaal Basin) and elsewhere indicating a global event (even though those places weren't in the same geographic position they are today because of plate tectonic movements).  This glacial event has been called the Huronian Glaciation (because the Gowganda Formation is found on the north side of Lake Huron).

So why did it take a couple of billion years of Earth history until we had our first glacial ice age?  Recent thinking invokes two probably causes.  The first is the decrease in methane (CH4) in the Earth's atmosphere by increasing oxygenation by photosynthetic cyanobacteria (the earliest Earth had no free oxygen in the atmosphere - it's not until the development of life that the Earth's atmosphere began to significantly change).  The second cause may be due to drawdown of carbon dioxide (CO2) out of the atmosphere by the weathering of silicate minerals  due to increased rifting of continents and extrusion of extensive lava flows (flood basalts) at the time.  Both methane and carbon dioxide are greenhouse gases and reducing their abundance in the atmosphere would have cooled the Earth's climate significantly.

We have abundant geological evidence throughout Earth's history that changing the Earth's atmospheric chemistry will change the Earth's climate - sometimes significantly.  Something to think about as we pump gigatons of CO2 per year into the atmosphere by burning fossil fuels.

Thursday, March 14, 2013

Hey, a new post!

I've really fallen out of the habit of posting on the blog lately.  It's been almost a month since my last post.  My personal and professional life have just been too busy to have the free time necessary to do this.  But, I'll still persist and try to at least get a couple of posts a week in if I can.  I'm working on a geologic post for tomorrow but today I'll just jot down a few random observations...

Happy pi day (pi = 3.14... and today is 3/14 - get it?).  I think I'll celebrate by buying and eating some pie later!

Spring is coming!  I find this time of year maddening since it looks nice out but there's still an icy cold wind at times at the threat of snow still looms (some of the largest Northeastern blizzards have occurred in March).  I've seen some crocuses popping up and flocks of red-winged blackbirds (Agelaius phoeniceus) have been moving though my area this week.  The other day, the trees outside my house were loaded with them trilling their distinctive call.

Haven't heard the spring peepers yet but I have heard a couple of frogs waking up in the wetlands behind my house.  They will be calling soon - the true sign that spring is here.  I can't wait for that first 65 F day when I can go and find a flat rock in a quiet place and lay out absorbing the warm sun.

Still looking for comet C2011/L4 Panstarrs in the western sky just after sunset.  Here in the Mid-Hudson Valley it was cloudy last Tuesday when this picture was taken from elsewhere (from Bad Astronomy).  Can't believe that every night this week in my area has seen clouds in the western sky at sunset - it's very frustrating!

Leaving for a Northeastern Geological Society of America conference this weekend. It's at the beautiful-looking Mount Washington Hotel at Bretton Woods (at the base of, obviously, Mount Washington in New Hampshire).

I'm hoping to get in a little relaxation too since I'll be free of the home-life pressures and teaching duties for a few days.  I'll let you all know if I learn anything interesting (if anyone reading this will be there, send me an email, we'll grab a beer and talk geology).