The Research Staff of the North Carolina Museum of Natural Sciences includes experts in a wide variety of scientific disciplines who conduct exciting research investigations, maintain and expand the Museum’s natural science Research Collections, and participate in the Museum’s public education and outreach mission. Check this blog often to learn about all of the great science happening at the Museum!
One of the most common canards I hear about North Carolina geologic is, “The Appalachians are the oldest mountains in the world.” I hear the same about the Uwharries, which are not even in the contest. The age of the Appalachians is tied to the question of “When were they built?” The answer is that there was no single time in which they were built or finished. The story of the Appalachians was built through observation of crosscutting relationships, then augmented with isotopic dates: See Part 1 of this blog series. The map at the top of this article is from Jim Hibbard of NCSU and his co-authors (2006, Lithotectonic map of Appalachian Orogen from the Geological Survey of Canada) which can be downloaded here. That map gives you a quick understanding of the complexity of the Appalachians.
Mountain ranges are built in events called orogenies, which go in fits and starts. The first event in the Appalachians was the Grenville Orogeny, about 1 billion years ago. Grenville age rocks are found from Canada to Alabama, so you know that whatever produced them is a continent-scale event. This orogeny was the result of collision between proto-North America and what is now the west coast of South America. A map from Dr. Chris Scotese’s PaleoMap Project is available here. Grenville-age rocks are found beneath the Amazon. In North Carolina, Grenville-age rocks are exposed in the Blowing Rock gneiss, the Cranberry gneiss, the older rocks beneath Pilot Mountain and Hanging rock, and the Toxaway gneiss.
So which is older, North American Grenville or South American Grenville? It’s a tie. This is a recurring theme in plate tectonics: a tectonic event, like an orogeny or rifting, usually has a mirror on the other continent involved. Even though these areas are now widely separated, they used to be much closer.
Other events in the Appalachians include the Taconic Orogeny and the Acadian Orogeny, with other orogenies recognized locally. By locally, I mean in northern, central or southern Appalachians. We’ll skip over them, because they get very complicated, and go straight from the start of collisions to the end of the collisions. There’s one view of it here, with nice pictures, although geologists in the Southern Appalachians might take issue with the details. The point is, we have several episodes of mountain building, usually re-cycling parts of earlier episodes.
The final event in the Appalachians was the Alleghanian Orogeny, widely accepted to be coincident with the collision of North America with Gondwana, a conjoined Africa and South America. Another good map is here, or here. When did it start and end? This brings up a common problem in tectonics: diachronous events. Isotopic dating shows that the Alleghanian in the Northern Appalachians is a bit older than in the Southern Appalachians. Evidently the Iapetus ocean closed like a zipper instead of like an elevator door. So you can’t put a single date on the Alleghanian Orogeny for the whole mountain chain.
Collisions like thus produce scars in the form of faults, and produce granites. Alleghanian thrust faulting further built the Appalachians, and the Alleghanian Orogeny recycled parts of the earlier Grenville and Taconic and Acadian Orogenies. The collision also produced granites around 300 million years in age, now found as Mount Airy, Rolesville, Churchland, Castalia, Sims, and Lilesville granites. We can say that active collision, in North Carolina, was completely done by the end of the Permian Period, about 245 million years ago. Take a look at the granites, just chock full o’ zircon and dated with relative ease. Granites that have been deformed by squeezing, and granites that have not, straddle the age of 245 million years ago.
Then collision stopped. About 200 million years ago, North America and Africa rifted apart, creating Triassic basins and the Atlantic Ocean. Now, the East Coast is a passive margin, quietly piling up sediments, and the Appalachians are no longer undergoing active thrust faulting.
You may be asking, “Are we done yet?” Well, the Appalachians aren’t done yet. Recent sedimentary studies suggest that there has been Cenozoic uplift in the Southern Appalachians over the past 65 million years. If you look at the topography in southwestern North Carolina, you can see that it is much more rugged than what surrounds it. (If you drive Highway 64 up the Nantahala Gorge, you’ll see what I mean.) This all suggests that the mountains are bobbing up a bit, trying to reach some equilibrium between crust and mantle. This was underscored by a recent article from NCSU scientists, Sean Gallen, Karl Wegmann, and Del Bohnenstiehl, published by the Geological Society of America in GSA Today. The article is here.
As an added treat, you can hear Dr. Wegmann talk about his research, on Thursday, April 10, 2014, starting at 7 p.m. at the Daily Planet cafe. He also works on landslides, so this is a good chance to ask questions about the recent events in Oso, Washington.
One of those things that “everybody knows” is that the Appalachians are the “oldest in the world.” That conclusion is usually based on the amount that the Appalachians are eroded- young mountains, sharp topography, old mountains, rounded topography. But the age of the Appalachians is a simple question with no simple answer. A good guide can be downloaded from the United States Geological Survey if you click here.
To get at the answer, you need to know something about the way geologists do business. So this is part 1 of a two-part blog.
Geology is often oversimplified as the study of rocks, but if you look closer, it is actually the study of deep time and the sequence of events. You can build a picture of a sequence of events by crosscutting relationships: Younger events cut across older events.
Sediments stack up on top of each other, so it was fairly easy to see what was older and younger. But when they started correlating strata over larger distances, geologists realized quickly that there were missing pieces in the geological record. For instance, some places would have a complete strata from the Cambrian, while others would have the complete section of the Ordovician plus part of the Cambrian. A stratigraphic section is like a piece of music, where the silence and the rests are as important as the notes. The complete Geologic Time Scale was painstakingly pieced together exactly like a geneticist will reassemble a stretch of genetic material from overlapping pieces.
This practice was augmented by the fact that evolution limited certain kinds of fossil to certain ages of sediments. These are called index fossils. The boundaries between geologic periods, epochs and ages are usually marked by extinctions, so it is possible to correlate layers of sediments, and pieces of geology across long distances. It’s a discipline called “stratigraphy”. This is the basic science at work in exploration for petroleum and natural gas: If you find oil in Eocene sediments on the Gulf Coast of the US, then it’s a good idea to look in similar age sediments in the delta sediments of major rivers around the world. Scientists at Exxon Production Research, led by Dr. Peter Vail, produced on of the first comprehensive, worldwide sea level curves to assist in oil exploration. They also published the microfossils that were used to define each time period, unheard of at the time for a petroleum company.
Crosscutting relationships allow you to build up a sequence of events, but only relative ages in the form of “younger than” or “older than.” With the advent of radiometric dating, the “when” of all of these events could be measured. There are a bunch of radioactive decay scheme that are useful for dating different kinds of rocks. The best tool for this is uranium-lead dating of zircon, which is actually the use of two uranium decay systems at one time. By this method, you either get an answer, or you just get noise. Advances in the past twenty years in vacuum technology and electronics have allowed improved analysis of dissolved zircons. Even more so is the ability to fire a stream of atoms at a zircon to blast out a bit of material for analysis. Over the past twenty years, geologists have looked for volcanic sediments near the stratigraphic boundaries, so that absolute dates could be applied to the Geologic Time Scale.
So, the ground rules for Geology:
- Younger events cut across older events, establishing relative ages.
- Certain fossils are limited to certain ages of sediments.
- Isotopic dating can give absolute ages.
And yes, I’ve waited a loooooong time to get in that pun about “ground rules.”
The Digital Smartphone Microscope seemed like a really good idea. The video circulated last year. It looked like fun, which is of course the reason to do anything sciencey. If you clicky here you can watch the original video on YouTube.
I had a couple of middle school volunteers, Andrew and Daniel, working in my laboratory last semester. We took on building three Smartphone Digital Microscopes as a project. In short, it’s a couple of pieces of Plexiglas or Lexan with an adjustable bottom piece for focus. The magnifier/macro lens is cannibalized from a laser pointer. A lot of the parts came from the store where everything was $1.
This was a good project for the middle schoolers for several reasons. First, in a lab you often have to make what you need. You make or fake it because the real deal either doesn’t exist or because it’s too expensive. Second, any project like this teaches that any problem is solved iteratively. Try it, and if it doesn’t work, try something else. Third, it was the culmination of things I had them doing which kind of fell under the heading of Playing With Polarized Light.
Most of my work involves what I call IBS:Itty Bitty…Stuff. The most common tools of my trade are the petrographic microscope, micro-infrared spectroscopy, the electron microprobe, the SEM with EDA, or with Backscatter Electron imaging, and nowadays the Field Emission SEM or microprobe. The idea of a portable petrographic microscope was appealing, so I set Andrew and Daniel to watching the video and getting together some refinements. Then we built it.
Here’s a photomicrograph from my lab scope. An image with crossed polars has a polarizer below, then the thin section, then a polarizer above the section. The above polarizer is rotated 90° from the lower one. The thin section is rotated and the petrographer observes how polarized light interacts with the sample. So how do we build it?
The first refinement the guys came up with was to use the third bolt as part of the sample stage. The one in the video was simply too floppy. The second was to leave the lens in the tube in which it came. The video has you take the lens out, which like an invitation for a fumble and a lengthy crawl-around on the floor. In the picture above, I have one of each lens mounted, one in the tube and one removed from the tube.
One of my refinements was to add a rotating stage. Polarizing film (linear polarizing material for you aficianados) goes below the stage and above the lens.
- The focal distance is very short, so specimens have to get very close to the lens. The rotating sample stage actually helps with that. But the sweet spot for getting things in focus is rather small. If you have a thick nut on the bolt holding up the top layer, you might not be able to get close enough to focus.
- Middle school boys are over-rated in terms of their destructive powers in dismantling laser pointers.
- We skipped countersinking the holes for the bolt heads in the bottom of the stand (not my best idea). As a result, if you lean on the stand by accident, you can turn it over.
- Andrew knew more about using my Smartphone camera than I did, which was kind of embarrassing.
- Getting the rotating stage centered under the lens is very difficult.
- A cheap laser pointer lens doesn’t work very well. It distorts around the edge of the lens, called a vignette in photography. Perhaps a more expensive laser pointer would have a better lens, but that kind of defeats the purpose.
- A clip-on gooseneck light from the dollar store works well. The light source is not really needed, and a bright LED light from the dollar store is too strong. This rig actually works better outside.
- This has been rattling around the back of my SUV for a while and still works fine.
- The three-point focus mechanism actually lets you focus with the sample stage slanted, so you can zoom in on side features and not just the top of the specimen.
Getting a photo through the lens takes a lot of fiddling and practice. Not to be too mercenary, but I ran up to the Museum store and bought a couple of pieces of amber with insects to play with ($5 each). Here are some of the results:
You can see here how the lens vignettes around the edges. The brown mineral in the middle is a biotite with a gray apatite crystal in the middle. Dark material is volcanic glass. Black minerals are magnetite. Fish Canyon Tuff, Colorado, crossed polars image.
Many thanks to Andrew and Daniel for their help and for all the fun!
By Roland Kays, director of the Biodiversity Lab at the NC Museum of Natural Sciences.
Originally posted on The Agouti Enterprise:
We all know the feeling – sometimes there just aren’t enough hours in the day to get all our work done. Such is the life of agoutis living in low-quality territories, who have to scrounge around the rainforest floor not only for today’s meal, but also to find seeds they can cache underground for the late rainy season when there will be even less food. To push ourselves as deadlines approach we set the alarm extra early, and have an extra cup of coffee to keep working later. Our latest discovery shows that hungry agoutis also stretch the hours of their day, but face much more dire consequences than a short-night’s sleep.
Our new paper published today in Animal Behavior, led by Lennart Suselbeek from Wageningen University, shows that hungry agoutis that wake up early or stay up late are much more likely to be eaten by ocelots, while…
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By Meg Lowman
Although Americans represent 5% of the world’s population, we use 30% of the world’s resources, and our consumption has doubled in the last 50 years. What happens to finite supplies of fresh water, oil and soil as billions of people in India and China desire to “live just like Americans do?”
Here are a few tips to conserve natural resources, save money, and educate your family about the economics of our environment:
- Become a “locavore”: eat local foods and buy local products. In North Carolina, farmers markets sell fresh local produce. It will lower your energy footprint to buy produce that did not travel far to reach your dinner plate.
- Carpool; Americans spend over 4.5 billion hours per year in commuting alone. William Moomaw, professor at Tufts University and co-author of a recent IPCC (Intergovernmental Panel on Climate Change) Report, calculated that if daily American commuters would carpool for just one day per week, we could significantly reduce America’s carbon emissions by 2050.
- Recycle. Approximately 85% of all American household waste can be recycled. Purchase goods with less packaging, and re-use items such as boxes, paper clips, plastic bags, and packing materials. Wrap gifts in old newspaper or other recycled materials.
- Audit your household electricity. Turn off lights. Buy power strips. Turn off computers when not in use. Buy Energy Star appliances.
- Travel green. When traveling, become energy conscious by staying in energy-efficient hotels. Plan family vacations to eco-tourism destinations that inspire conservation of natural resources.
- Plant trees, especially natives. Trees act as a filter to cleanse the air, produce oxygen, store carbon, and serve as a home to other wildlife. Attractive shade trees invariably raise the value of your real estate.
- Conserve fresh water. An estimated one third of all water in American homes is used to flush toilets. Check toilets and sinks for leaks, and reduce water consumption in your daily habits.
- Go green for the holidays. Can you create special days where no one drives? Candlelight dinners? What about purchasing a live tree, and then planting it after the holidays? Buy gifts with a “green” message. Consider switching traditional outside landscape lights with the new LED ones, significantly minimizing your family’s energy footprint.
Greeting Blogophiles! Are you partial to the Paleozoic? Perhaps you are drawn to the Devonian, or maybe you are more moved by the Mesozoic and are crazy about the Cretaceous. Well, have I got a bridge for you… The third floor bridge between the Main Building and the NRC is now open and it’s about time. Walk with me, would ya?
While we’re walking, let’s do a bit of math shall we? If you were to walk from the Main Building (Nature Exploration Center) to the Nature Research Center via the third floor bridge, how long would it take you to get there (please show your work)? Using the simple equation Time = Distance/Rate or T=D/R, if you know the distance between the two buildings (140 feet) and how fast you are traveling (1 foot per second), you could easily calculate the time it would take (140 seconds or just over two minutes).
Now, let’s say you wanted your trip to take 544 million years, how fast would you need to walk? Let’s see, R = D/T. So 140 feet /544 million years means you would move approximately a quarter of a foot every million years. You’d be long dead and hopefully fossilized, before you even took your first step. Fortunately, thanks to the beautiful artwork tiles by Barbara Page, you can now travel back 544 million years in the time it takes you to cross the bridge, and live to tell the tale.
As a paleontologist, I often think about time and about fossils, but I rarely think of them as art. However, on the third floor bridge, art and science have collided in spectacular fashion, and anytime you want (when the Museum is open and the weather is decent) you can wander to the bridge and plunge into the depths of Earth’s deep time.
The concept behind the tiles is an ingenious one. If one were to turn the layers of the Earth like pages in a book, on each page you’d see something different. But because there is no place on Earth where all of its history is represented, the tiles are a composite of representative fossils found from various geologic time periods around the world. What I find really fascinating about the bridge tiles is that rather than representing what the organisms might have looked like in life, they are images of fossils you might find from rocks of that era. It’s kind of like field work without getting dirty, and everyone is guaranteed to find a fossil.
The other brilliant part of the bridge art is there is math behind it and you don’t have to do it. Barbara Page has done it for you. Each tile represents ≈2 million years, so in effect you can travel through time without worrying about your teleporter inadvertently turning you into a fly. How convenient! Also for those budding ichnology (trace fossil) enthusiasts out there, the tiles at your feet have depictions of some of the tracks or trails you might find. How cool is that?
So next time you’re at the Museum, why not slow down and visit the third floor bridge to do a little field work? It’ll be well worth your time.
To see more of Barbara Page’s artwork please visit her website: http://www.barbarapagestudio.com/index.html
by Meg Lowman
If aviation engineers could apply the wisdom of the chimney swift, several troublesome problems of aeronautics could be solved. Pilots, for example, would never have to worry about the amount of gasoline in their tanks. The chimney swift refuels on the wing, spends almost its entire waking life in the air, and never, except by accident, touches the earth.
Every autumn, many millions of birds migrate from northern breeding grounds to equatorial locations. This annual flight is not only extraordinary in terms of time and energy, but also raises questions about the physiological issue of sleep. Some birds migrate long distances, while others only shift regionally. So how do birds rest during migration, and what are the consequences for migratory sleep deprivation?
In 2011, the Swiss Ornithological Institute affixed electronic sensors to alpine swifts to monitor their movements. This species spends summers breeding in Europe, but winters in Africa, many thousands of miles away. Thanks to electronic tagging, scientists found that these birds were always aloft in the winters, feeding in the air columns. The tags only recorded data every 4 minutes, so these birds could have landed intermittently. But these results indicate that the swifts go long periods without sleep in the conventional sense.
Sleep is incredibly diverse across the animal kingdom, with some animals sleeping two hours, and others sleeping 20. Many factors influence sleep in wild animals, including food, predation, and trophic level (position in a food chain). It is generally thought that every species has a specific sleep “quota,” or an average amount that they sleep every day. However, recent research has shown that there is some flexibility in sleep requirements for some species.
Just prior to migration, white-crowned sparrows reduce their sleep time by two-thirds, yet do not show any of the cognitive impairment generally associated with sleep deprivation. This migratory restlessness has been observed in other bird species, and can be induced in the lab by artificially shortening the length of day. During the very short Alaskan summer, pectoral sandpipers stay awake for almost 2 weeks to maximize breeding opportunities. The males that sleep the least sire the most offspring – a rare case where sleep deprivation is an evolutionary advantage.