Salt and sugar crystals have wonderfully distinctive crystal forms. They might well be good subjects for introducing minerals, crystals and some of the more complex geometric solids.
Cube shaped salt crystals under 40x magnification.
The salt crystals are clearly cubic, even though some of the grains seem to be made up of overlapping cubes.
The atoms that make up salt's atomic lattice are arranged in a cubic shape, which results in the shape of the salt crystals. The smaller grey atoms are sodium (Na), and the larger green ones are chlorine (Cl).
Salt is an ionic compound, made of sodium and chloride atoms (NaCl). When a number of these molecules get together to form a crystal, they tend to arrange themselves in a cubic pattern. As a result, the salt crystals are also cubic. In fact, if you break a salt crystal, it will tend to break along the planes that are at the surfaces of the planes of the atomic lattice to create a nice, shiny crystal faces. Gem cutters use this fact to great effect when they shape diamonds and other precious stones.
Of course different crystals have different atomic arrangements. The difference is clear when you compare salt to sugar.
A single sugar crystal looks a bit like a fallen column.
Sugar crystals look a bit like hexagonal pillars that have fallen over. According to the Beet-sugar handbook (Asadi, 2007), sugar crystals actually have a monoclinic form, which could end up as asymmetric hexagonal pillars. Salt crystals, on the other hand, have the habit of forming cubes.
Proper respect for other living things requires us to minimize the waste we produce, and learn from the creatures we eat.
First off, three cheers for Viet Hoa, the Vietnamese food market on Cleveland Ave in Memphis. I’ve been searching for a source of fresh, uneviscerated, marine fish in this mid-continental city for quite a while, and I’ve finally found them. The market was the source of the subjects of an excellent anatomy lesson, and a delicious dinner.
I’d grabbed three fish, and a few goodies, and packed them on ice on the day before our trip. The large red snapper was a little pricey because it was fairly big, but I knew it would be quite tasty and I was hoping the internal organs would be big and clearly visible. The milk fish was an unknown, but it was big and cheap so worth experimenting on. The last fish was the smallest, and I’m not quite sure what kind it is, except that it’s marine. I’d tried one at home the previous week and found that while it had an excellent taste, the internal bits were on the small side.
Red Snapper
On the first night of the immersion I started with the biggest fish, the red snapper, with everyone around the table. I’m happy to say that all my students were there for the lesson, facing the table, even the more vegetarian minded. I’ve always believed that there is a certain, necessary, ethic to knowing where your food comes from, and what went into preparing it for you. If you’re going to eat meat, you should be able to spare a moment to think about the animal.
Small intestines are very long (and stretchy).
The digestive system was the easiest to identify and trace. The mouth and anus are pretty obvious on the outside. After cutting through the skin of the belly, you can follow the intestines from the anus all the way to the stomach. The intestines are quite long.
Shrimp-like stomach contents.
We found two partially digested, shrimp-like creatures in the stomach of the red snapper.
From the other end of the digestive system, once you get all the contents out of the body cavity, you can stick a probe through the mouth (watch out for sharp teeth) down through the esophagus to the stomach.
Pulling back the gills, you can see all the way through to the mouth. One student noticed how bright red the gills were, so we talked about oxygenation of blood and compared the fish’s gills to the human respiratory system.
Finally, I laid the fish on a bed of thinly sliced onions, surrounded it with wedges of tomato (seeded), covered it with lemon slices, dribbled a tablespoon of olive oil on top, and forgot to add the cup of white wine (which we did not seem to have on hand for some reason) and the bay leaf. It was a big fish so we ended up baking it for about 40 minutes at 400 degrees Fahrenheit.
Then we ate it. I say we, but it really was just a couple of students and myself who did most of the eating, although I believe I convinced everyone to at least try it. Of the more serious students of anatomy, the eyeballs were highly prized; with only three fish we did not have enough to go around.
Dinner is served.
By the time we were done with dinner the skeletal system was very nicely exposed.
The Other Fish
Opening the body cavity of the Milk fish.
A couple of my students did the honors of cleaning the other two fish. With its large organs, the milk fish was an excellent subject for dissection, but it was not particularly palatable. We did however find the gall bladder.
The breached gall bladder is on the lower right of the picture.
Even the smallest fish proved a worthwhile subject for the more patient student.
Up to the knuckles in fish.
Instead of eating the rather unappetizing, baked milk fish I combined it in a soup with some clams I’d picked up from Viet Hoa. I’d grabbed the clams so we compare modern bivalve shells to the cretaceous ones we’d find at Coon Creek. A bit of boiling with a few herbs, made for an excellent broth the following night.
In Summary
Cleaning fish for an anatomy lesson worked very well. As we excavated each internal organ, we could talk about what it did, why the fish needed it, and what was its analogue in humans. And, in the end, they made for a couple excellent meals.
P.S. – From the Gulf Coast Research Lab’s Marine Education Center, here’s a reference image for a perch dissection.
We’re studying biomes and I don’t know a better way to consider how they’re distributed around the world than by talking about the global atmospheric circulation system. After all, the primary determinants of a biome are the precipitation and temperature of an area.
Diagram showing global atmospheric circulation patterns.
It’s a fairly complicated diagram, but it’s fairly easy to reproduce if you remember a few fairly simple rules: hot air rises; the equator is hotter than the poles; and the Earth rotates out from under the atmosphere.
Hot air rises
Light from the Sun hits the equator directly but hits the poles at a glancing angle, so the equator is warmer than the poles. Warm air at the equator rises while cold air at the poles sinks.
The equator receives more direct radiation from the Sun. A ray of light from the Sun hits the ground at an angle near the poles so it’s spread out more. More radiation at the equator means the ground (or ocean) is warmer, so it warms up the air, which rises.
The warm air can’t rise forever, gravity puts a stop to that. If we did not have gravity the atmosphere would float off into space (and the universe would be a fundamentally different place). Instead, when the air reaches the upper atmosphere at the equator it diverges, heading either north or south toward the poles.
From all around the hemisphere the air converges on the poles. The air is cooling as it moves away from the equator, and when it gets to the pole it sinks to ground level and then makes the journey back to the equator. It’s a cycle, aka a circulation cell.
Hot air rising near the equator and sinking near the poles creates a cycle, a circulation cell, in each hemisphere. In this picture, the winds at ground level (dashed blue lines) would always be blowing from the poles toward the equator. This is what the world might be like without the coriolis effect.
Standing on the ground, the wind would always be blowing towards the equator from the poles. If you were in the northern hemisphere, in say Memphis, you would always be getting northerly winds.
The ITCZ and the Polar High
At the equator the rising air also takes with it water vapor that was evaporated from the oceans or from the land (evaporation and transpiration, which are together called evapotranspiration). The warm air cools as it moves up in the atmosphere and the water vapor forms clouds.
You get a lot of clouds and rainfall anywhere there is a lot of rising air.
Because air is coming together, converging, from north and south at the equator, and the equator is in the middle of the tropics, the zone where you get all this rising air is called the Inter-Tropical Convergence Zone or ITCZ for short (that’s an acronym by the way). The ITCZ is pretty easy to identify from space.
The line of clouds near the equator shows where air is converging at ground level and rising to create clouds. It's called the ITCZ. (Image via NOAA, which also hosts real-time images of the Tropical Atlantic that show the ITCZ very well).
All the rain from the ITCZ, and the warmth of the equator means that when you go looking for tropical rain forests, like the Amazon and the Congo, you’ll find them near the equator.
Locations of rainforests (more or less). Notice that in addition to the Congo and Amazon, Indonesia is pretty well forested too. All because of the ITCZ.
Now at the pole, the air is sinking downward from the upper atmosphere. Sinking air tends to be very dry, and places with sinking air also tend to be dry (it’s not a coincidence). So although the poles are covered with ice, they actually tend to get very little snowfall. What little snow they get tends to accumulate over tens, hundreds and thousands of years but the poles are deserts, arctic deserts, but deserts all the same.
The region of sinking air near the poles is called the polar high because of the high pressure generated by all that descending air.
We’ll complicate the picture of atmospheric circulation now, but the ITCZ and the polar high don’t change.
The Earth Rotates
The complication is the coriolis effect. You see, as the Earth rotates it kind-of drags the atmosphere with it. After all, the atmosphere isn’t nailed down. It’s got it’s own motion and intertia, and doesn’t necessarily want to rotate with the Earth.
Deflection of the wind, represented by a ball, because of the movement of the Earth beneath it. The ball here moves in a straight line but it appears to curve because the Earth is rotating out from under it. Click the image for a bigger, better version.
So a wind blowing from the North pole to the equator gets deflected to it’s right; the northerly wind becomes an easterly.
I could write an entire post about coriolis (and I will) but for now it shall suffice to say that the low-level wind from the pole gets deflected so much that it never reaches the equator. The high-level wind from the equator never reaches the pole, either. Instead of the one, single, circulation cell in each hemisphere, three develop, and you end up with the picture at the top of this post.
In this diagram, the convention is that it shows the circulation cells along the side of the globe, in profile, while the arrows within the circle of the globe show the wind directions on surface.
Note also that the winds in the region just north of the equator (where the label says “Tropical Air”, come from the northeast. These are the northeast trade winds that were vital to the transatlantic trade in the days of sailing ships. Know about them help a lot in the Triangular Trade game.
The Sub-Tropical High and the Sub-Polar Low
With three circulation cells you add the sub-tropical high, and the sub-polar low to the ITCZ and polar high as major features that affect the biomes.
Remember, rising air equals lots of rain, while descending air is dry.
So the sub-tropical high, with its descending air, makes for deserts. Since it’s in the sub-tropics these are hot deserts, the type you typically think about with sand-dunes, camels and dingos.
Sub-tropical deserts from around the world. They're located in the zones 30 degrees north and south of the equator at the sub-tropical high. Base map by Vzb83 via Wikimedia Commons.
The USGS also has a great map that names the major deserts.
Biomes
So if we now look at the map of biomes and climates from around the world we can see the pattern: tropical rainforests near the equator, deserts at 30 degrees north and south, temperate rainforests between 40 and 50 degrees latitude, and arctic deserts at the poles.
Map of biomes from around the world. The different biomes are closely related to the general atmospheric circulation model. (Image adapted from Sten Porse via Wikipedia)
Like addicts racing to get their overdue fix, my students raced to the computers this afternoon after having had to survive all day without power and without the internet. I’ll confess that I felt the same urge, but was able to restrain it. Until now.
We usually don’t have internet access during our immersions, but then it’s expected and students are not inside needing to refer to the study guides to figure out their assignments. At the beginning of the year I gave everyone paper copies of the study guides, but now there are just a core few who request them.
Fortunately, we had a couple of smart-phones so one student would look up the reading assignment and post the page numbers on the whiteboard. Fortunately, the reading assignments were out of the book.
We weren’t quite surviving without technology, but it was close, and students were getting innovative.
We’ve had storms every few days for the last couple of weeks, which is typical for Memphis at this time of year. Over the last few days a frontal system has just been pushing back and forth over us. When it pushes south we get a cold front with thunderstorms and rain, but clear skies afterward. When the front pushes north it gets warm and humid, and the sky goes overcast for most of the day.
Weather map for Wednesday, April 20th. The blue and red line passing through the southeastern U.S. show the mixed warm and cold fronts that have been oscillating past Memphis for days. Image from the National Weather Service.
This line of fronts marks the general location of the sub-polar low, which is moving north with the spring. But more on that tomorrow.
The Coastal Plain, one of the three major geologic provinces of the southeastern United States. From the Teacher-Friendly Guide to the Geology of the United States (Picconi, 2003).
J.E. Picconi, from the Paleontogical Research Institution, has a nice website that describes the geology of the different regions of the U.S..
This image shows the low-energy, offshore environment of the grey shales like that of Coon Creek. From Picconi (2003).
The site has a nice clean design, and is readable to anyone with a basic grasp of geology and geologic time.
I’ve looked at the the section on the southeastern U.S., which even a section on the different, official state fossils.
I particularly like the icons they use to show the environments in which the different fossilized organisms once lived.
These maps show the difference between last winter's average temperatures and the long term average (from 1951-1980). Notice that the scale goes up to 11. Image from Hansen and Sato, 2011.
For much of the U.S., last winter was pretty cold. If you look at the maps above, you can see that the eastern United States was up to 4 °C colder than normal in December. However, if you look a little further north into Canada, you’ll see a broad, pink region, where the temperatures were up to 11 °C warmer than normal.
The rate at which the world has been warming has been accelerating. It’s been interesting watching the predictions of the relatively crude computer models of the 1980’s coming true.
The red line show that the actual warming has been awfully close to the middle scenario predicted by climate modelers. The figure was slightly adapted from Hansen and Sato (2011).
Although, it’s really the broadest, more general predictions that tend to be more reliable. One of those predictions, that’s been consistent for a long time and with a lot of different models, is that the poles would warm significantly faster than the rest of the planet.
What’s also been interesting, if somewhat depressing, is seeing the political consensus lag behind the scientific consensus. Twenty years ago there was a real debate in the scientific community about if global temperatures were rising. Now scientists argue mainly about what to do: reduce greenhouse gas pollution, adapt to the inevitable, or some mix of the two. Yet two weeks ago the House Science Committee heard testimony from a professor of marketing, advocating for an end to all government funding of climate research. Perhaps the belief is that if we don’t look it won’t happen.
At the same time, Kate (on climatesafety.org) observes that NASA’s James Hansen has had to add a new color (pink on the graphs at the top of the page) to his climate anomaly maps because of the unexpectedly large warming over last winter.
Looking at the smear slides of Coon Creek Sediment Matrix got me thinking about just how important these little, microscopic shells have been for what we know about the Earth’s past climate. In fact, they provide the background knowledge that we have about the changes in climate that we’re seeing today.
Deep sea drilling vessel, JOIDES Resolution. Image via the National Science Foundation.
Back in the 1970’s the Deep Sea Drilling Project collected a lot of sediment cores from all around the world. The deeper you drill under the sea bed the older the sediments are, so micropaleontologists could look at how the organisms that lived in a certain area changed over time. Certain forams that could only live in warm oceans were found living far to the north. By combining all the information from all the sediment cores, they could construct paleo-geographic maps showing what the climate was like in the far past. It’s one of the reasons we know that the Jurassic climate was a lot warmer than today’s climate.
Then they invented mass spectrometers.
Mass specs can find the mass of individual atoms. Calcium carbonate has the chemical formula CaCO3. Water, as we should know by now, is H2O. They both have oxygen atoms, but not all oxygen atoms are equal; some are more equal. Actually, the mass of any atom is made up of the mass of the protons plus the mass of the neutrons in its nucleus. Now, by definition, any atom with eight protons is oxygen; however, while oxygen usually has eight neutrons, it sometimes has nine or even ten.
Your standard oxygen, with eight protons and eight neutrons has an atomic mass of sixteen, and is written as 16O or oxygen-16. Well, oxygen with ten neutrons is going to have a mass of eighteen (8p + 10n) and be called oxygen-18 (18O). These different versions of the same element are called isotopes.
Oxygen-18 has two more neutrons than the much more common oxygen-16. Note that both atoms have eight electrons, but their masses don't count because electrons are really small compared to the protons and neutrons which have about the same mass.Water molecule with a molecular mass of 20.
What does this have to do with climate? Well a water molecule with two hydrogen atoms, each weighing one atomic mass unit, and one oxygen-16 atom will have a molecular mass of 18, while a water molecule with an oxygen-18 atom will have a mass of 20. When water evaporates from the oceans, the water with the lighter isotope will have an easier time going from liquid to a gas in the atmosphere.
So, during an ice-age for instance, lots of water evaporates from the oceans, falls on land as snow, and then gets trapped in the enormous glaciers that cover entire continents. Since the lighter water molecules evaporate easier from the oceans, they’re the ones that will end up falling as snow and being compressed into glacial ice. The water molecules left behind in the ocean will tend to have the heavier oxygen-18 isotopes. Since the forams use the ocean water as part of the process of creating their calcium carbonate shells, the oxygen from the water ends up in the carbonate (CO3) of the shells. Since the ocean water has extra oxygen-18s during an ice-age, then the shells will have extra oxygen-18 isotopes during an ice-age.
Therefore, by measuring the amount of heavy oxygen-18 isotopes that are in a single shell, we can tell how large the glaciers were at the time that shell formed, and tell what the global climate was like.
Of course there are some interesting complexities to the story, but that’s the general idea of how the microscopic shells of long-dead plankton can tell us about the history of the Earth’s climate.
Hunting for microscopic fossils at the dinner table. Inside the circle is 100x magnification; outside the circle the magnification is 1.
My students will tell you that I’m never happier than when I have my cup of tea. On the night after our visit to Coon Creek, I put a tiny sample, about the size of a matchstick’s head, of sediment matrix on a microscope slide, and added a drop of water to disperse the grains. Then I sat there, while the chaos of dinner-making swirled around me, and searched for tiny, microscopic fossils of creatures that died long ago. With my cup of hot tea beside me, it was like sitting in the eye of a storm, flaming hamburgers be damned, a modicum of sanity in the asylum.
Quartz grains from Coon Creek Formation sediment seen under the microscope at 100x magnification. Quartz is easy to identify because of the way it breaks with curved fractures.
The first thing I noticed though were the quartz grains. They’re very small, silt-sized, but are the largest grains in the sediment. They’re pretty easy to identify because they break like glass, with curved, conchoidal fractures. They’re also pretty little things under the microscope; little, sharp-peaked, transparent mountains.
Other minerals are visible in the sediments. Though they're relatively large they're still dwarfed by the quartz (100x magnification).
Other minerals are visible in the slides, but they’re dwarfed in size and quantity by the quartz. Yet there is enough of the dark green, glauconite clay to bind the quartz grains together and protect the shells embedded in the sediment from dissolution by the universal solvent, water.
It’s interesting to observe these other minerals, because they take the more classic crystalline shapes and forms. The sharp edges are parallel to one another because of the alignment of the atoms in the mineral crystal.
Snail like shape of what's probably a planktonic (lives in the water) foram. (100x magnification).
Finding the micro-fossils took a little patience. The entire slide had only four obvious specimens. Since they’re so small that meant a lot of going back and forth under the small field of view of the 100 magnification objective lens. They look like foraminfera to me, but it’s been a while since I’ve encountered them. Foraminfera, or forams for short, are tiny organisms that secrete beautiful calcium carbonate shells. They can be found in, or in the sediments beneath, most of the world’s oceans, particularly in the warmer areas.
Finding forams in the Coon Creek Matrix is a nice little exercise. One of my students, seeing what I was doing, wanted to try it too, so she made her own slide and searched until she found her own specimen. It was somewhat inspiring, so I’ve put together a more detailed post about finding microfossils.
We also found a neat little shell that looks like the overlapping scales on a pine cone. We were disconnected from the internet, so I was only able to look it up when I got back to school.
What looks like a type of bolivina foraminfera. It's benthic, which means that it lives in the sediments not in the water. (100x magnification).
Dr. J Bret Bennington at Hofstra has posted a nice PowerPoint of his introduction to marine microfossils lecture. As a basic introduction, it’s quite comprehensible to middle-school students, or people like myself who did not pay as much attention as they should have during that part of Paleontology. Anyway, based on these notes, the pine-cone-shaped thing is probably a variety of bolivina, a benthic foraminfera. The Foraminifera.eu-Project, is a wonderful, volunteer-produced resource for pictures and identifying forams.
Bolivina are benthic, which means they spend most, if not all of their time in the mud. Planktonic micro-organisms, on the other hand, spend their lives floating around in the water.
Foraminfera have calcium carbonate shells, as do clams and oysters. In the shallow oceans there is a slow rain of them that cover the sea-bed over the millenia. You can end up with thick layers. In fact, the white cliffs of Dover are white because of all the microscopic calcium carbonate shells. In the deeper reaches of the oceans there are much fewer of these shells because they dissolve under high pressure. As a result, down there you tend to find microfossils of diatoms and radiolarians, things with silica shells. Silica is that same material from which glass is made, and is the same material in quartz.
Finding microfossils has actually been quite important for understanding the history of the Earth’s oceans and climate. But that’s another story.
