27 February 2017
As mentioned over the weekend, last Friday was my first field day of the season. I visited a spot called “Indian Spring” in the central Fort Valley. The spot is on private property, but the landowner (Will G.) invited me and Tom Biggs (University of Virginia) to check it out. Tom’s mapping the Rileyville quadrangle, so it allowed him to put another spot on his map.
Here’s Will orienting us to the site:
Can you spot bedding and cleavage in these images?
Here, I’ll help tease it out for you:
The bedding is Devonian, when this part of Virginia was a deep marine basin, with fine silt and clay slowly sifting in, making the massive mud rock called the Mahantango Formation.
The cleavage is a tectonic “overprint” imposed on these rocks more recently, when Africa rammed into eastern North America in a profound event called the Alleghanian Orogeny. That was in the late Paleozoic, Pennsylvanian and Permian.
The bedding was laid down sometime around 392 to 385 million years ago. The cleavage developed as these rocks were squeezed almost 100 million years later, around 300-250 million years ago. You can’t deform something unless it already exists.
Bedding can be identified in these relatively unstratified mud rocks by horizons of shelly material, like this:
Most of the fossils are brachiopods, including prominent Devonian index fossil Mucrospirifer, here seen as an internal mold:
The brach-rich beds are studded with these chunky shells. Here’s a view looking up at the bottom of a bed:
Here’s the trace of another bed:
And a sample that broke out in a slab-like shape defined by the cleavage, with just a nubbin of bedding left on the bottom. It shows distorted spiriferid brachiopods, with their shape changed due to Alleghanian squeezing, the same circumstance that caused the cleavage to develop:
Here’s a wall that shows both bedding (inclined moderately to the left) and cleavage (inclined steeply to the right):
Same wall, but with sun shining on it:
Here’s a look down on a fossil-free bedding plane, and you can see anastomosing traces of cleavage overprinting it:
We were able to measure the orientation of both bedding and cleavage here, and add that data to the map. Both strike NNE, but as seen above, the two planar features have opposite dips. The bedding dips WNW, while the cleavage dips ESE. The cleavage is a tectonic “scar” that reflects the injurious birth of the supercontinent Pangaea. Rock splits into flakes today because Africa squeezed it 300 million years ago… Intense.
25 February 2017
Yesterday was a gorgeous late spring day* in the Fort Valley, and I was delighted to engage in my first day of field work of 2017. Skies were clear, the temperature soared to a decadent 80°F, and I thrilled to be out geologizing!
I went out in the central Fort Valley with University of Virginia geologist Tom Biggs, who is mapping the Rileyville quadrangle. We stopped to examine some enormous concretions along the bedding plane in shale/siltstone of the Devonian Millboro Formation.
Here’s a double concretion, with a dump truck looming in the background:
These suckers are BIG. Here’s a single oblate** ellipsoid concretion, with a lens cap (upper right-center) for scale:
Concretions like these are typical of the Millboro. These behemoths are the largest I’ve seen, though.
I made a 3D model of this one:
24 February 2017
For your Friday fold this week, I present to you a 3D model of a sample of kinked schist from Beavertail State Park, Rhode Island.
Spin it right round, baby:
22 February 2017
I just finished Richard Dawkins’ book for younger readers and/or a general audience, The Magic of Reality. It’s a general-interest science education book, written in Dawkins-speak – very conversational and emphatic about key points. It consists of a series of chapters about different topics, with each chapter guided by a big question, like “What is a rainbow?” or “What are things made of?” or “Who was the first person?” Dawkins opens the chapter with the recounting of myths from various cultures that attempt to answer those questions. These are delightful in the context of comparative anthropology, and I was delighted to see that the myths of the Hebrew tribes of the Middle East are mixed in with the stories of the Dogon of West Africa, Australian Aborigines, Scandinavian Vikings, and the Ainu of Japan. No special priority is given to any particular strain of non-scientific thinking. But don’t take that to mean that Dawkins is delivering his often scalding critique of religion in this book as he did in The God Delusion. This is toned down significantly from the approach he’s employed elsewhere. Anyhow, once the myths have been enjoyably recounted and no insight has been gained, Dawkins re-asks the question — “But what is a rainbow really?” and “Who was the first person really?” and then attempts to answer it as best he can. Some of these explanations are more compelling than others, based on what I assume is Dawkins’ familiarity with the source science. He’s spent a lot of time thinking about evolution, and as a result the answer to the “first person” question is elegant and excellent. He puts forth a terrific thought experiment wherein readers are asked to imagine building up a pile of portraits: your own on the bottom, with your father’s on top, and his father’s on top of that. One parent at a time, going back 185 million generations. Guess where you end up? …At a fish! Dawkins makes the point that each of these photos shows an organism that is the same species as the one before it and the one after it – no child is a different species than his or her father, no parent is a different species than his/her child. And yet, in a sequence like this, a thick enough stack of portraits in between two individuals would indeed render them different species. Evolution is (for the most part) a gradual process, and this thought experiment is an elegant way of demonstrating that concept. The book isn’t quite as strong when it comes to discussing the spectrum of light and earthquakes and atoms, but that’s like saying that Dickens isn’t Shakespeare: It’s still quite good, even if in some cases I had a quibble with the level of simplification chosen. Overall, The Magic of Reality would be an ideal book to give to an early teenager with a general interest in science.
21 February 2017
Remember I have a Google Form to allow anyone to submit questions anonymously. Silly questions are fine, like last week’s one about walking on the Sun. Even if it’s a goofy notion, I might be able to make an interesting response. My goal is to answer a couple of questions per week. This week, I only got to one. But it’s a meaty one! Sink your teeth in:
5. A possible new continent was discovered. Article in Nature here (Caution, scary science). It sounds like this discovery hinges on determining the ages of rocks. I know about Carbon Dating (and other isotopes), but that relies on an organism taking up exogenous carbon until it dies. How do you date rocks, particularly when you can’t trust that they’re “static” in the crust?
First off: I appreciate the detail in this question, and the citation of sources!
This is a neat finding that changes the way we view a particular spot. It’s an example of a small thing — literal atoms in a literal grain of sand — that implies a big thing — “a continent!” Much of geology advances this way – but studying small details, and then reflecting on what those tiny bits imply about the very biggest picture.
So let’s start with the big picture: if you were an extraterrestrial coming to planet Earth for the first time, you’d likely be struck by two observations: (1) the presence of life, and (2) a stark dichotomy in the appearance of the crust. About 2/3 of the planet is covered by a relatively thin, dark, dense kind of crust (basalt and gabbro are the main rock types), while the other third is a thick, buoyant, light-colored kind of crust (granodiorite and gneiss are the main rock types). When you look at an image of our planet with the ocean stripped away and all the land cover color variation zeroed out, it’s really stark at how bifurcated our crust is. Put on your alien googles and take a look:
This image, by Lim and Varner (based on data in Muller, et al., 2008) shows it in a different way: gray is continental crust, rainbow colors show oceanic crust (with red = young, and blue/purple = old):
Note that continental crust doesn’t correspond one-for-one with the continental landmasses as we know them. Parts of the continents are submerged below sea level: southeast of Argentina, for instance, or Canada’s Hudson Bay, or the Arafrura Sea between Australia and New Guinea. Also, there are islands like Madagascar, Greenland, and Cuba that are made of continental crust, but are not “continents” in their own right. And just because it’s an island, that doesn’t make it continental crust: Hawaii, Iceland, and the Kerguelen Plateau are all examples of thick piles of basalt.
Not only is there this stark difference in the shape of the outermost rocky layer of the Earth, but there’s a stark age difference, too. Oceanic crust is constantly being generated and then recycled. It forms at oceanic ridges, and is destroyed at subduction zones. Oceanic crust is ephemeral, on the geologic timescale. It’s temporary. The oldest oceanic crust on the planet is only 200 million years old. In contrast, the buoyant rafts of continental crust resist being subducted, and when “matched” against oceanic crust, will override it, “winning” (surviving) every time. It persists. The oldest continental crust is over 4000 million years old. Its average age is younger, but there’s still an incredible discrepancy between their ages: the continental crust is on average an order of magnitude older than the oceanic crust.
Now that we’ve established that big picture, let’s consider the small picture: the zircon crystals that are key to this study. Zircon is a mineral that is made from three elements: oxygen and silicon (O and Si, which is what most of the crust is made of), plus this less common atom called zirconium (Zr). The chemical formula is ZrSiO4.
Here’s how those atoms get put together to make a zircon crystal in an interactive JSmol 3D model: Blue is zirconium, tan is silicon, and red is oxygen. Grab it and give it a wiggle:
Zircons are really, really useful in a range of different kinds of studies. The reasons for this are:
1) They are hard. On the Mohs scale, they rank a 7.5, which is harder than quartz.
2) They are stable (at chemical equilibrium) over a wide range of conditions. This means they don’t melt too easily, they don’t recrystallize too easily, and they don’t “rot” too easily. So a zircon can form in a magma that is cooling to make an igneous rock, then be uplifted to the surface unchanged, then be weathered out of that rock and tumble down a stream into a river and be dumped on a beach, and it’s still the same old mineral. This might not sound particularly shocking to the average person, but it’s a big deal. Many other minerals will rot away or change their shape if they get squeezed, or start vibrating their atomic bonds if they get hot, letting impurities out that don’t mesh with their crystal structure. (Now, why should that last bit matter? Read on!)
3) Very important: they are a little bit impure. One key impurity is uranium. In zircon’s crystal structure, atoms of the element uranium can substitute for the element zirconium. As the crystal is forming (growing atom by atom in a magma, surrounding by as-yet-unbonded atoms), it will add oxygens and silicons and zirconiums in their appropriate place as it grows, but if a uranium shows up, the growing crystal structure can cope with sticking that uranium atom where a zirconium “ought” to be. At the same time, other random atoms that show up are ‘rejected,’ because chemically they don’t fit in the growing zircon crystal. Lithium? Neon? Gold? The growing zircon crystal sneers: Take a hike. Aluminum? Lead? Carbon? Get lost. But if uranium shows up, knocking on the molecular door? Well, come on in! So a critical handful of zirconiums give up their places, substituted for by uranium:
Modified from screenshot of a Mindat.org model
The result of this strong selection is that the final zircon crystal carries a load of uranium ‘special guests’ who are now deep inside its lattice. But the uraniums don’t last. Uranium is radioactive, meaning that over time, some of those atoms will fall apart, spontaneously. The forces that hold the atom’s nucleus together can’t cope with all those neutrons and protons, and so eventually, it goes ka-pow. The uranium splits into a couple of pieces, releasing energy. It’s not uranium any more. Now the bigger piece of the leftovers is a new element. Eventually, you end up with a growing accumulation of atoms of a non-radioactive element that is produced by the radioactive decay of uranium. That’s lead (Pb). The lead is not “happy” inside the zircon crystal lattice where it suddenly finds itself. Remember, lead was actively rejected by the young, growing crystal. Chemically, the lead doesn’t belong – it’s more like a stowaway than a special guest. Geologists can compare a zircon crystal’s proportion of ‘special guest’ uranium atoms to its load of ‘stowaway’ lead atoms, and that ratio, compared to the time it takes for uranium to fall apart and yield lead (its half-life) makes it possible to figure out when the crystal first formed. Here’s a video I made (4 minutes) explaining the process: Radioactive decay and isotopic dating of rocks and minerals. The astonishing thing about this is we are talking about a trace impurity within a mineral crystal that is the size of a grain of sand. It is often literally a grain of sand! And it can tell us something really profound: the numerical age of that grain, its “birthday” in an ancient magma chamber.
So the general answer to the question is that: you must have (1) a mineral which takes in a radioactive parent isotope, but (2) actively excludes the daughter isotope as it is forming. Then (3) any daughter isotope produced through the radioactive breakdown of its parent needs to then be “imprisoned” in the mineral crystal. Zircons pull this trick with uranium (parent) and lead (daughter). Other minerals like monazite can do the same thing. But the vast, vast majority of rock forming-minerals are worthless for isotopic dating, either because (1) they don’t have a spot in their crystal lattice for the radioactive parent isotope, or (2) they let plenty of daughter isotope into the crystal as its forming, so you can’t trust the measurement of daughter isotope to reflect the time since the mineral formed – who knows how much of it is part of the original load? or (3) maybe the mineral crystal cannot hang on to daughter product that is produced through radioactive decay. Minerals that “leak” their daughter isotope load will be worthless as isotopic ‘clocks.’ Any one of those conditions would rule out the use of that [mineral + isotope] system as a tool for geologic dating.
Not only that, but zircons are often zoned: meaning that you can see their history of growth preserved inside them, like the rings in a tree stump. Take a look at these two images for examples. They are produced using a special kind of microscopy called cathodoluminescence that makes the zoning really clear:
Courtesy of Karl Lang
Courtesy of Karl Lang
The neat things about this is that this is a kind of microscopic stratigraphy – the oldest parts of the crystal are in the middle, and the younger “layers” are outboard of that. We actually have instruments precise enough to date different parts of a single zircon crystal, and to be able to say (for instance) “the core of this zircon grew 1.2 billion years ago, then it added some layers around 360 million years ago.” When you weave in insights that can be gained from the study of the textures and structures in the crystal, you can make more profound statements still, stuff like “the core of this zircon grew 1.2 billion years ago in a magma chamber, then it was uplifted to the surface and tumbled down a river to a beach, then it was partially melted, then it was metamorphosed around 360 million years ago.” All that – from a grain of sand!
So where does that leave us with the paper the questioner asked about by the questioner, the new one from Lewis Ashwal and colleagues (Ashwal, et al., 2017)? It details dating work on zircons from the island of Mauritius (former home of the extinct giant flightless pigeon called the dodo) in the Indian Ocean, east of Madagascar.
Here’s Figure 1 from the paper:
I’ll decode that for you, at least insofar as it’s relevant to this discussion. Southwestern India and eastern Madagascar share similar geology, and are interpreted to have once been adjacent. As they broke up, some chunks of continental crust slipped into the gap between them, swathed in basalt from the seafloor spreading that generated new oceanic crust between the two separating ‘continents.’ Imagine tearing a loaf of rye bread in half, and pouring brownie batter into the gap between the halves. Some bread crumbs and rye seeds may fall into the gap, and be draped in chocolate. The island of Mauritius, marked on the map with a circled “M,” is interpreted to be atop one of these crumbs. The rye seeds are its zircons, which don’t match up with the volcanic “brownie” that surrounds them.
This study looked at 13 zircon crystals extracted from a sample of trachyte (which is a quartz-poor volcanic rock) from Mauritius. Ten of them had young ages (~5 million years old), which is the sort of thing you would expect for a volcanic island in the middle of oceanic crust. But three of them had much older ages, from 2500 to 3000 million years old (depending on what part of the crystal you analyzed). Take a look at two of the grains, one example from each group, each shot full of holes from the ion beam that was used to measure the uranium and lead isotopes to get the ages, annotated by me from Figures 2 and 4 in the Ashwal, et al. (2017) paper.
[decoding a few things in that figure: Ma stands for “mega-annum,” the Latin for “millions of years ago”; μm means micrometer, or micron, a unit of distance that is one-billionth of a meter. Qtz and Ksp are abbreviations for small chunks of non-zircon minerals, quartz and potassium feldspar, that are included within the zircon crystal.]
The age discrepancy is unexpected if Mauritius were 100% oceanic crust. The three old grains are 600 times older than the rock of Mauritius generally is. Those astonishingly old dates fall in the Archean eon of geologic time, and specifically within the last part of that eon, the Neoarchean era. Note the position of Mauritius on the map above, and notice the adjacent bands of light blue in both Madagascar and Indian: these blue zones are Neoarchean rocks, with similar ages. So that all lines up really nicely. It suggests those continental crust rocks were the source of the zircons that somehow can incorporated into the much, much, much younger rocks from Mauritius’ ~5 million year old volcanic trachyte.
So there is strong evidence for some continental crust under Mauritius, in the form of these three sand-sized grains of zircon, extracted from a single sample of trachyte rock. The fact that, though tiny, these crystals exist, is a signal that there is more going on beneath Mauritius than the usual oceanic crust ± mantle plume. But is this enough evidence to posit “Mauritia” as its own “continent”? I’m not convinced that claim is warranted. The world is a messy place, and while these grains demonstrate that there must be some Archean crustal material being “tapped into” beneath the volcanoes of this island, I can think of ways of doing that without invoking a whole new “continent.” That said, the proportion of Neoarchean zircons in the study (three out of 13, or ~23% of the grains dated) suggests that the proportion of continental crustal material might be pretty significant. What would a second sample of rock tell us? How would the story change when we hear the testimony of another dozen zircons? In summary: This study documents a tantalizing finding, and if I were in the business of dating zircons, it would motivate me to scour Mauritius and neighboring islands and neighboring seafloor for evidence that might corroborate this interpretation (or negate it entirely).
Here’s something apropos: As I was preparing this blog post, another study was announced, with much the same “hidden continent” implications: this time it’s in the Pacific Ocean, and the “continent” is dubbed Zealandia. ‘Tis the season for discovering lost continents, it would seem!
Here’s figure 2, the map, from that paper (Mortimer, et al., 2017):
In arguing for Zealandia as a continent, Nick Mortimer and his colleagues have more to work with than three grains of zircon. Their case is built on the thick crust surrounding New Zealand and New Caledonia, as well as geology: bands of rocks like granite, rhyolite, graywacke, schist, and gneiss, arranged in what they interpret to be orogenic belts and rocks like limestone, quartzite, marking out what they interpret as sedimentary basins puddled on top of the continental crust “basement.” Orogenic belts are basically mountain belts (places where plates have collided and built mountains) where the topographic peaks of the mountains have been ground down by erosion and “leveled off.” To my mind, that’s a pretty compelling case for there being a big piece of continental crust in “Zealandia” as opposed to “Mauritia.”
Ashwal, Lewis D., Wiedenbeck, Michael, and Torsvik, Trond H. 2017. Archaean zircons in Miocene oceanic hotspot rocks establish ancient continental crust beneath Mauritius. Nature Communications 8, article #14086. doi: http://dx.doi.org/10.1038/ncomms14086
Nick Mortimer, Hamish J. Campbell, Andy J. Tulloch, Peter R. King, Vaughan M. Stagpoole, Ray A. Wood, Mark S. Rattenbury, Rupert Sutherland, Chris J. Adams, Julien Collot, and Maria Seton, 2017. Zealandia: Earth’s Hidden Continent. GSA Today, March/April 2017. doi: 10.1130/GSATG321A.1
Müller, R.D., M. Sdrolias, C. Gaina, and W.R. Roest, 2008. Age, spreading rates and spreading symmetry of the world’s ocean crust, Geochem. Geophys. Geosyst., 9, Q04006, doi:10.1029/2007GC001743.
Trond H. Torsvik, Hans Amundsen, Ebbe H. Hartz, Fernando Corfu, Nick Kusznir, Carmen Gaina, Pavel V. Doubrovine, Bernhard Steinberger, Lewis D. Ashwal, and Bjørn Jamtveit, 2013. A Precambrian microcontinent in the Indian Ocean. Nature Geoscience 6, p. 223–227. doi:10.1038/ngeo1736
20 February 2017
I recently discovered a terrific series of videos on YouTube called “Kate Tectonics.” Watch episode 2, “The History of Geology,” here, to get a taste of the series’ excellent production values and its hip, humorous style:
I asked one of the creators, namesake Katelyn Salem, to share a bit of information about the series:
- Who’s involved in the series? The credits seem lengthy! Can you give a bit of the “backstory” for key personnel?
Our director is Michael Aranda. He’s worked on some great YouTube shows like Crash Course, SciShow, and The Brain Scoop. Both our animator, Marcus Schlueter, and our cinematographer/editor, Sarah Meismer also work for SciShow. Marcus has his own weekly web comic, Consistent Tangerine, which is just a joy to see every week. Our writer is Khyan Mansley, an amazingly talented and funny man who’s acted and written for several short films. He also has his own YouTube channel which he writes comedic skits for. Todd Williams and Michael Morgan are our producers and money guys. They try to hold everything together. I am the Kate of Kate Tectonics. Along with hosting I write up the basic outlined script of science we want to teach in each episode.
- Where did the inspiration for the “Kate Tectonics” video series come from? What’s your background in geoscience?
Michael and I came up with the idea together. He was already very involved with online video and I had just gotten my degree in geoscience from the local university, The University of Montana. He was looking to start his own production company and we noticed that there wasn’t a lot of highly produced geology content on the internet. I had the degree and we lived in this beautiful state of Montana surrounded by the Rockies, so we went for it!
courtesy of Kate Tectonics
- How would you describe your “approach” to the material?
We try to go into each episode thinking about different ways to present typical, not always very interesting, topics in a bold and new way. We wanted to make each episode “more than just a talking head” as Michael would say. So, with the help of Khyan we try to throw in some comedy and interesting visuals for each episode.
- What role do you see for fun, informal videos like this in the greater “scene” of science education? Are they a supplement to traditional classroom science education? …a replacement? How do videos like yours relate to other media like science blogs or TV series such as Planet Earth or Cosmos? I see you’re offering “merch” for sale as part of what I presume is a larger branding strategy. Can you comment more on the “big picture” of the “Kate Tectonics” initiative?
My interest for the show has always been to first, try and get the general public interested in geology and the Earth since it’s not a very popular science and second, to try and make good, cinematic content for the people who are already interested in the science.
With any science and especially with a science like geology, some of the topics can get very “heavy” and difficult to learn either without visuals or with the fact that the topic may just be boring to someone. In this case, I think it’s great if teachers have videos like these that are a break from the typical coursework and are entertaining but are also just as likely to teach students about a topic as the teacher teaching it from a book would be.
The great thing about YouTube is that you can make the videos as short or as long and complex as you’d like and you can do it in any format that you think will work best for your audience and what you’re trying to do. You aren’t stuck with only trying to teach things verbally and with pictures like in books or a blog, and you aren’t restricted to certain topics or certain formats like you would be in a TV series. You can literally make a video about any topic in any way you see fit.
Our long term plan for Kate Tectonics is to make it a go-to place for geology and earth science videos and provide videos with a style and personality that people can enjoy to watch even without the desire to learn. We would love to see a community of viewers form and to continue making videos as long as we’re able to.
- How many episodes are planned in “Kate Tectonics”? What’s the time line for the series? What else is in the works?
Thanks to the Big Sky Film Grant from the Montana Film Office, we’re able to produce 10 videos for the series for the first half of this year. If the videos are successful and we are able to financially produce more, we have ideas for 50 possible episodes in the future solely based off of a basic geology course curriculum. The actual amount of topics for videos we’d love to cover is nearly endless. Our next video will take Dwayne, my pet rock, and me to space to learn about the creation of the elements!
- Describe your workflow from conceiving a video, to planning, to filming and postproduction. When do you employ props, and when do you opt for digital effects?
Our process starts with an outline of the basic science topics to cover in an episode from me, then gets handed off to our writer to come up with a script. After a few meetings between, myself, the writer, and the director to decide on the direction of the episode, the whole production crew meets for a pre-production meeting to talk about props we need to find or make and animations that need to be started. The director and cinematographer then decide on how they want to shoot each scene and the producer makes any calls for permissions if we need to visit a certain location. Once everything is planned and gathered together, we set aside a weekend or two days to shoot the episode on our set. The footage goes through a rough cut, we double check for scenes that maybe need to be changed or audio that needs to get re-done. A finished edit then goes to our animator to add in our animations, then any final coloring, editing, and sound design are done to the video.
Our second episode went with puppets instead of digital animations. We did this because we knew almost the entirety of the episode would be much more entertaining if the scenes were changing constantly instead of having myself talk in front of the camera about the history of geology for most of the time. We didn’t want a “talking head”, so we opted for a video of just animation, and practical animation instead of digital to keep the video as unique, practical, and interesting as possible. There aren’t a lot of videos out there that use paper puppets, that I’ve seen.
“Dwayne” the pet rock (in his space helmet), courtesy of Kate Tectonics
- How has feedback been so far?
The feedback for what we’re doing has been so overwhelmingly positive! More so than any of us expected. Only a couple out of hundreds of comments have been anything but supportive and excited about the videos. We’re excited other’s excitement for it and hope that the positivity continues to grow as we grow the channel.
- What else would you like Mountain Beltway readers to know?
We’re producing these videos because we love film, we love science, and we love a smarter general public. We encourage people who enjoy the videos to share them and help make people smarter and more knowledgeable about the Earth. I also think that people don’t quite realize how much a single share helps small channels like our’s when we’re starting out. More eyes means more attention, more attention means more attention from communities like Mountain Beltway that can really help us spread this information to more and more people. Once our grant from the state for the first 10 episodes is done, we will need support from people like our amazing patrons on Patreon. Anyone who is able and would like to support financially as well is able to at our page patreon.com/katetectonics if they’d like to help us be able to make more videos.
17 February 2017
Garnetiferous beds from the aureole of the Leinster Granite east of Baltinglass, County Wicklow, Ireland (Declan De Paor’s senior thesis mapping area, 1973). Manganese-rich metasediments. The prominent ‘elasticas’ or fan folds (folds with a negative inter-limb angle) are superimposed on isoclinal folds: so the brownish layer at top and bottom are the same, though that is not obvious from the image. This is a sample from the structural geology collection of Declan De Paor and Carol Simpson.
Take a look at the whole sample in this GigaPan. If you don’t have Flash enabled on your computer, you’ll have to click through to explore it:
Link 0.58 Gpx GIGAmacro by Callan Bentley
15 February 2017
With the current political climate being what it is, I’m newly motivated to learn the best way to communicate science with the American public. I’ve decided to read several books on the topic that I’ve been aware of for years, but not yet made time for. The first is Randy Olson’s Don’t Be *Such* a Scientist. Olson has a unique perspective to apply to the question: he was a tenured professor of biology before quitting academia and moving to Hollywood to make movies. He knows how academic scientists talk, and he knows how Hollywood tells stories, and the two are really different. More to the point, one works for communicating with the general public, and the other slams the door in their faces.
Key points: Science is a negating profession, and communicating that way comes off as condescending. We scientists are in the business of nurturing fledgling hypotheses, only to slaughter them with facts both blunt and sharp. Karl Popper’s ‘falsifiability’ is the name of the game – we love to find the holes in arguments, the flaws in studies; our prestige is enhanced when we can find new and clever ways of saying “no, that’s not how it works.” This brutal crucible of negation leaves the strongest ideas standing, and we can trust in their robustness relative to weaker notions. But when a scientist takes this inherent negativity into general conversation, it comes off as grouchy or disdainful. I was thinking of this myself the other day when a friend who’s concerned about climate change emailed me a link to an article about the lengthening crack in Antarctica’s Larsen C ice shelf. Olson’s book made me see my response (“I wouldn’t see it as a major scary item by itself though – this is what ice shelves do – ice gets added ‘upstream’ by glaciers, and it “ablates” (breaks off) downstream. People seem to like big dramatic events though, and this is charismatic enough to grab folks’ attention!”) as an example of this negative sort of reaction. I essentially pooh-poohed her engagement with the story of the growing crack in light of my understanding of ice sheet dynamics. In retrospect, I wish I’d engaged differently – it was an opportunity missed for participating in a discussion.
We need to be conscious of where we are pitching out stories. By “where,” I mean where in the human psyche. Olson proposes a “Four Organs” theory of science communication. Metaphorically, we respond to communications with our (1) heads, (2) hearts, (3) guts, and (4) sex organs. Scientists communicate with other scientists head to head, but if you want to reach the general public, it’s more useful to frame your message in terms of an emotional appeal (heart) or humor (guts). Appealing to sex is the most widespread human approach, but it’s so jiggly and disorganized down there in our gonads that it’s difficult to communicate a coherent message. So Olson aims his science stories below the neck but above the belt.
Stories are good. I knew this intuitively, but Olson makes the point well by recounting the construction of his film Flock of Dodos, and how the first several cuts of the movie elicited weak reactions from his screening audiences. He then re-cut the film with an archetypal narrative (“hero saves a damsel from a dragon”) and the audiences found it much more compelling and enjoyable. This is a lesson I pledge to apply going forward. At the very least, I’m going to experiment with it where I can.
A corollary of the ‘make it a story’ edict is that you need not make it a story and have it be a textbook. He examines several films on the same topic (global warming, in this case) and qualitatively compares their information content to their emotion and humor content. While scientists are very interested in information, they value fact-heavy films over fact-light films. But Olson suggests that if there is no “heart” or “gut,” then the fact payload will never be delivered, as a general audience will be bored and change the channel. But a non-scientist audience knows what it likes, and it finds much more of a connection to films that speak from (and to) the hearts and guts of the audience, and the actual amount of information involved really doesn’t matter to them. This is a distinctly non-science conclusion to come from – and it makes me feel astonishingly uneasy to contemplate communicating in that way. That’s why Olson’s book is useful: it forces our community of science communicators to examine ideas that wouldn’t otherwise occur to us, in hopes they might prompt a change in our practice.
If you do science communication, you should read Olson’s book.
13 February 2017
Time for another episode of “you ask the questions”… After posting a Google Form to allow anyone to submit questions anonymously last week, I got some excellent questions/topics submitted. I’ll try to get to a couple per week!
3. Why does the Massanutten Mountain not run the whole length of the Valley?
Some background: the questioner is asking about the mountain ridge system where I live: Massanutten Mountain and the Fort Valley. It is situated in the middle of the much larger Shenandoah Valley, a valley in a mountain in a valley. This is a question about geomorphic expression of the Valley & Ridge province of the Appalachian mountain belt.
So the question is why doesn’t this…
…look like this?…
Google Earth, modified by me!
Basically, it boils down to how “deep” the Massanutten Formation dives into the Earth.
The Massanutten (Tuscarora equivalent: a big thick package of Silurian quartz sandstone) is a sheet of sedimentary rock. It is a ridge former because it’s dominated by quartz: a hard, chemically-stable mineral. In the Shenandoah Valley, it overlies the Martinsburg Formation, a mix of shale and graywacke sandstone. It is overlain by Devonian limestones and shales. Where the Martinsburg Formation crops out, it weathers away relatively rapidly, making a valley. The same is true for the Devonian limestones and shales. But where the Massanutten Formation crops out, it weathers away more slowly, leaving a ridge.
The strata of the Valley & Ridge are folded, and the base of the Massanutten Formation dives into the Earth at the mountain’s northeastern end and re-emerges at the southwestern end. It’s like the bottom of a canoe:
This is the situation with Massanutten, too:
Massanutten is doubly-plunging synclinorium: an overall canoe-shaped fold that plunges down and inward in the “bow” and in the “stern.”
The one spot where the base of the Massanutten blips up above the land surface is about 2/5 of the way along the range, at New Market Gap, where Route 211 crosses over:
But under the Fort Valley, the bottom of the Massanutten Formation is buried deep in the Earth, and everywhere else (surrounding the mountain east and west, north and south) in the Shenandoah Valley, the bottom of the Massanutten Formation is above the surface of the Earth – or rather, it was, prior to erosion. The “canoe” used to be longer, in other words, and it’s getting whittled away over time. As the differential weathering proceeds on the landscape, the gap at New Market Gap will enlarge, and the Massanutten Mountain system will shrink and shrivel. Eventually, the deepest part (under the central Fort Valley) will be exposed, as a lone ridge, and then it too will succumb to the forces of erosion.
Summary / short answer: Massanutten Mountain isn’t longer because the tough stuff it’s made of has been eroded away everywhere else.
4. When will man walk on the Sun?
This is not going to happen.
There are a couple of issues.
First up: humans cannot walk if they are too hot. The Sun is too hot. The ‘surface’ of the Sun is around ~10,000 °F. That’s about ~9,900 °F hotter than you can take. You’d die before you could take a single step, much less go for a walk. But let’s say you got over the big discrepancy between your comfortable temperature range and what the Sun has to offer. What then?
The Sun is 333,000 times more massive than the planet Earth. So think of how quickly you hit the ground when you trip and fall here on Earth. If you were to stand on the Sun, your mass would be the same, but because the Sun is so much more massive than Earth, the gravity there would be much, much, much much, much, much, much, much, much, much, much, much stronger. In fact, it would not be advisable to attempt to go and see if you could walk on the Sun, because you would pretty much never be able to get away again. So you should know going in, this is the last trip you’re ever going to take. Even if you reconciled yourself to that, your muscles are going to be far too weak to take a single step away from the surface of so massive an object.
And finally, there is the issue wouldn’t be a ‘ground’ equivalent to walk on. The Sun is a big ball of plasma, and I think you’d have a rough time walking on it. It’s not a solid. Now, the average density of the Sun is ~1.4, while Earth is ~5.5, and your body is ~1.0. So your body would be less dense than the Sun’s average, but don’t think that’s a guarantee of ‘floating’ in the uppermost solar plasma. The Sun is roiling with convection, which means that your average non-flammable, impervious, super-strong Joe who steps foot on the Sun is likely to be caught up in one of these convection cells, and quickly pushed toward one of the downwelling zones. Just as convection in a pint of Guinness can drag bubbles (of low density) downward, I wouldn’t count on your relatively low density to save you. Convection is another risk of attempting to walk on the Sun.
So, bottom line: this is not going to happen. Sorry!
Got a question to prompt a bit of discussion here? Use this Google Form to allow anyone to submit questions anonymously.
10 February 2017
Steve Mirsky, an editor at Scientific American (he does their “60 Second Science” podcast), loans us some photographs today for the Friday fold.
Steve took these images in the Grand Canyon, Arizona, on a trip that the National Center for Science Education runs every summer:
Based on where he took them, I think these in the Tapeats Sandstone, base of the Paleozoic sequence that makes up most of the Canyon’s celebrated walls. I wouldn’t expect much folding in that unit, but Garry Hayes has documented some, and it appears to be of a similar character. If anyone knows differently, then please let me know.
Thanks for sharing your fold photos, Steve. Happy Friday, everyone!