It's the Earth's "birthday!" Today, October 23, is the anniversary of the 4004, BCE creation of the cosmos, according to Archbishop James Ussher, Primate of All Ireland and Archbishop of Armagh. Ussher is famous for having made a pre-geology attempt to date our planet using a literal interpretation of Biblical scripture and a carefull tallying of "begats." Though a scholarly and noble attempt given the intellectual context of his day, Ussher's ideas were soon supplanted with the discovery of deep time by geological studies, starting ~100 years later with another James, James Hutton. The accepted age of the Earth was pushed back further and further by subsequent geological work, and our currently accepted age for the planet (and the Solar System) is approximately 4.6 billion years. Despite these insights, there are a substantial number of "Young Earth" creationists who stick to Ussher's number, or a similarly itty-bitty age derived from a Holy Book of their choosing. This bizarre contention puts them in the awkward position of having to deny the fossil record, the decay of radioactive isotopes, the expansion of the universe, and (of course!) the evolution of species by mechanisms other than Special Creation by a diety. Because Ussher was a scholar and a thinker as well as a religious man, my suspicion is that if he were alive today, he would reject the close-minded anti-science that so many creationists voice.

I love the fact that Ussher's title was "Primate," considering that the main issue creationists have with evolution is that they don't want to be descended from non-humans. The word primate comes from the Latin for "first" (as in "primary") and reflects Ussher's position at the top of the Church of Ireland, and Linnaeus' view that the primates were "first" among the mammals, an anthropocentric bias that persists in uncountable ways today. The truth of the matter is that humans are primates, and so are baboons, lemurs, gorillas, and yes, even chimpanzees.

Ussher was indeed a primate -- just like the rest of us. Happy birthday!

Labels: geologic time, history, words

Somehow, I've gotten a lot of reading done over the past six months. A lot of this reading consisted of books on climate change -- more on that in another post. But I wanted to share my thoughts on a few other books:

Sand - Michael Welland [blog]

Awesome. The perfect little book for those interested in geology. Looking at the world through a grain of sand. Very diverse, chock full of fascinating stuff that appeals to the intellect on many levels. Smart, erudite, funny. Recommended.

Stories In Stone - David Williams [blog]

A good read; like reading a compliation of feature stories in EARTH magazine; however, unlike Sand, no single unifying theme ties them all together. The overall idea is that the rocks we make our buildings out of have interesting backstories. The book is organized into a dozen or so chapters, each about a different building stone. Some are common (Indiana limestone), some are rare (petrified wood). All have got interesting stuff going on in terms of their geological history, human tie-ins, and architectural tweaks. If you live or work in a building, it's worth reading.

Your Inner Fish - Neil Shubin

Superb. Learned a ton about evolution's lingering fingerprints on our bodily blueprint. Did you know that the nerve which controls our larynx runs from the brain to the larynx via the heart? This unintelligent design is a vestige of the way our body develops from an embryo -- and can be traced directly to fish. There wasn't as much about Tiktaalik in here as I expected, but just enough to make the point.

Bones, Rocks, and Stars - Chris Turney [blog]

Really interesting, though the chapter on King Arthur didn't do much for me. But the rest of it is a great introduction to the various ways we figure out how old things are (Subtitle: "The Science of When Things Happened"). Great chapters on the orbital forcing of ice ages, carbon dating of Homo florensis (which Turney did), and Pleistocene megafauna extinctions. Recommended.

Glacial Lake Missoula - David Alt

Not so great as a book. Really more of a field guide, but not even all that great on that level. It essentially traces the geologic evidence of GLM "and its humongous floods" from Missoula north, west, south, and west again -- the path of the big Channeled Scablands-forming megafloods. A good resource for specific outcrops that illustrate parts of our understanding of this huge event, but not especially enjoyable to read.

Bretz's Flood - John Soennichsen

Much better -- a lovely biography of J. Harlan Bretz, the geologist from the University of Chicago who first documented the Channeled Scablands and deduced that they must have been carved by an enormous flood. A perfect little portrait of an academic's career. Bretz appears to have been quite a character! I really enjoyed the perspective this gave me on the whole "megaflood" idea.

Labels: books, evolution, floods, geologic time, sediment

One of the highlights of this past summer's Northern Rockies field course was an afternoon set aside as a "choose your own adventure" hike in Teton National Park. Some students opted for Cascade Canyon; others climbed Blacktail Butte. Four of us wanted something really challenging, so we chose Hanging Canyon at the recommendation of my friend Amy Manhart, who lives in Jackson and knows the Tetons like the back of her hand.

We took a ferry across Jenny Lake along with the Cascade Canyon Crew, and then started climbing up. A thunderstorm rolled up Jackson Hole, with much ominous booming and lightning, but we didn't get hit with the storm directly. The climb was very steep, but we entertained ourselves along the way with a geological conundrum: We discussed how best to interpret a hypothetical piece of float that is half granite and half diorite: Is it more parsimonious to guess that the granite represents an intrusion or an inclusion? The implications for the relative dates of the two units are huge: if the diorite is an intrusion, it's younger than the granite. If the diorite is a xenolith (an inclusion) within the granite, then it's older than the granite. Consider the possibilities:



Ultimately, there's no answer to this question without finding an outcrop of the rock in situ, which is why it's entertaining to consider when you're slogging up a 2000 foot hillside. My co-instructor Pete Berquist and I upped the ante by each doggedly defending one of the two indefensible interpretations and sticking to it for the sake of argument. Pete was the xenolith man, whereas I came down fully on the side of the dikes. Our students Joel and Ken were "fortunate" enough to listen to Pete and I bicker about the relative merits of our favored interpretations. Rest breaks came whenever either Pete or I found a boulder along the hillside that showed evidence to support our position. We would stop to consider it, catch our breath, and the resume the uphill climb and the argument. The bad weather passed and the day was beautiful. We were unencumbered by the need to reach a conclusion or acknowledge the obvious: the best interpretation is that such half-&-half clasts "cannot be interpreted."

Here's Pete posing with an obvious dike (I forced him! Ha!):


Here's me posing with an obvious xenolith (Oh well, fair's fair...):


We had a similar ongoing "argument" on the trip about the merits of "Tertiary" versus "Paleogene." I think it keeps students amused to see their professors going back and forth over geologic ideas -- surely if these fellows spend this much energy and thought discussing some geologic question, it must be valid and important... ...right?

More on the Hanging Canyon hike tomorrow...

Labels: archean, geologic time, igneous, national parks, nova, structure, travel, wyoming, xenoliths

Another in the photo/sketch series...

This is an outcrop I saw in the Teton range (Wyoming) this summer. It's a nice example of relative dating, I think...

Labels: art, geologic time, structure, wyoming

The June edition of the geoblog carnival The Accretionary Wedge is now live and ready for you to read. Where would geologist bloggers go if they had a time machine? Find out here!

Labels: blogs, geologic time, geology, websites

As a high school student in Arlington County, Virginia, I used to take regular hikes down a path called Windy Run, and then walk along the south shore of the Potomac River, upstream. It was in the days before I knew anything about rocks, and I was mainly appreciating other aspects of nature, like the plant life, the birds, the bugs, the salamanders, and occasionally something really cool like a raccoon. But I was aware that the scene I observed and enjoyed was not the same scene that had always persisted.

I heard rumors from my uncle about patches of woods inside the DC Beltway that preserved virgin forest -- giant trees that gave a hint of the former majesty of this eastern hardwood forest. I read about an eastern herd of bison that would migrate north and south through the Piedmont and Coastal Plain, crossing the Potomac near Alexandria (before we killed them all). I noticed a gazillion deer, and had it explained to me that the lack of predators like cougars and wolves resulted in the herbivores' population explosion. We used to have elk here, but European colonists had extirpated them. The last of the bison were killed off by 1800, and the final elk met a bullet around 1850. This used to be a pretty wild place!

I observed trash nearly constantly, often mixed obscenely with natural debris, sheathed in mud, or woven into birds' nests. Every few minutes, a jet airplane on its approach to National Airport would thunder overhead. Those of us who lived in the flight path would learn to automatically put conversations on "pause" during the 30 seconds it took for the planes to pass. Visitors didn't know what to do about the noise; it was too pervasive to be ignored. But live here long enough, and you learned to ignore it. You adapted, like the birds adapted by putting aluminum foil and plastic bags into their nests.

And the river itself? It's gross. In the modern day, it's constantly muddy and silty, with a foul-smelling sewage/sediment biofilm all over the rocks and logs in the water. There's scummy flotsam and rumors that you'll get a rash if you swim in it. There's people fishing down by Teddy Roosevelt Island, and you have to wonder why... They're not going to eat the fish they catch out of this polluted stream, are they?

The theme of this month's Accretionary Wedge is "time warp." The Wedge is a geoblog 'carnival,' though it's been inactive for a while, this month sees its return to 'accreting.' For those of you who are new readers to NOVA Geoblog, it's probably a great opportunity to check out some of the dozens of other interesting geoblogs out there. So what does this have to do with my reflections on the local woods, and the Potomac River? This month's Wedge host is Lockwood from Outside the Interzone. He asked geobloggers, "Where and when would you most like to visit to witness and analyze an event in Earth's history?"

I'm going to use my time travel experience to go back in time right here, in Washington, DC. I want to go back to 1491*. I want to see what my home looked like before European settlers showed up and brought their particular brand of industrialization / civilization / land use changes / ecological perturbations to the Potomac River valley. It may surprise readers to learn that I'd opt for this -- a simple experience of pre-colonization North American nature -- over something tectonic and structural, but that's what calls to me on a deep, emotional level. I want to see a vibrant ecosystem with big trees. I want to see the water of the Potomac River look like water; I want to go swimming in it. I want to see what bird migration looked like before it dropped off so precipitously. I want to see a passenger pigeon, a carolina parakeet. I want to see for myself what a healthy amphibian population looks like. And bison fording the Potomac in Alexandria... perhaps emerging from the clear water with the autumn colors ablaze on the far side of the river? That would just be... awesome.

* Note that there's a good book by this same name, on this same theme, 1491. The book makes the case that there was already a lot of landscape/ecological modification playing out before Europeans arrived: that native Americans played a significant role in messing with natural systems and we shouldn't imagine an ecological paradise, just less of an ecological disaster.

Of course, going back to 1491 may have some negative aspects to it: there would be malaria endemic to DC at that time, and the native tribes might not take kindly to a time traveler popping in to ogle their forested homes. But I'll take those risks (they exist today in other places I've visited), since the pay-off would be such a profound deepening of perspective.

If I had the ability to go back in time, I'd use it to gain experience with pre-colonial North America. I'd check out the same river banks I would walk 500+ years later, and see what we've lost.

...And, once I've seen that former world, I can't guarantee that I'd come back.

Labels: amphibians, birdies, blogs, dc, environmental, geologic time, mammals, piedmont, rivers, virginia

A couple of days ago, I asked for someone to tell me the geologic history of this boulder, in correct chronological order. To make it easier, I labeled the relevant rock units with letters. I promised that the first person to post the correct sequence of events in the comments would win a GEOLOGY ROCKS bumper sticker.



From first to last, the correct sequence of events is X, D, R, M, F.

Thomas Donlon got it right! Congratulations, Thomas -- I'll mail you a bumper sticker.

So let's delve into more detail: what actually happened with this rock?

First, a mafic source rock was weathered, generating chunks of rock "X." Then those clasts were mixed in with a bunch of sand and mud to generate the graywacke that makes up most of the boulder. This was later metamorphosed (not shown with a letter) to generate rock "D." Later, rock "D" with inclusions of "X" was split open, and granitic magma intruded into that fracture to make the dike labeled as "R." Later still, another cross-cutting event took place, cutting across everything that had come so far, to generate the vein of milky (hydrothermal) quartz labeled as "M." Finally, these rocks were uplifted and exposed, and various fractures, including "F," liberated this boulder from its source area. Now it is free, adrift on the Chain Bridge Flats, and posing for geologists. The final event was me discovering and gracing it with a quarter before snapping its portrait.

Labels: contest, dc, geologic time, piedmont

Inspired to give those Californians a run for their money with their cool examples of relative dating exercises, I took this photo last week down at Chain Bridge Flats, the westernmost corner of Washington, DC:



Your assignment, should you choose to accept it: tell me the geologic history of this boulder, in correct chronological order. To make it easier for you, I've labeled the relevant rock units with letters here. (The letters were chosen randomly, and do not by their alphabetic nature imply any sort of order. Note that "F" is the fracture surface defining the planar outer edge of the boulder.) First person to post the correct sequence of events in the comments area below wins a GEOLOGY ROCKS bumper sticker.



Answer in a couple of days. Good luck!

Labels: contest, dc, geologic time, piedmont

Elizabeth Kolbert writes about topics I'm interested in reading. I dig her.

The latest is a piece she wrote in last week's New Yorker entitled "The Sixth Extinction?"

It's about the decline in biodiversity around the world, using frogs succumbing to a deadly fungus and white-nose syndrome in bats as case studies in extinction. It has a decent (though not perfect) geologic perspective -- worth reading. The online version is hidden behind a paywall, but maybe you can access it at your local library.

Labels: amphibians, evolution, geologic time, mammals

Two of my bestest students got me this card for my birthday last week:

Labels: art, geologic time, humor, teaching

Yesterday, there was an excellent post on Stratigraphy.net about what we are calling the various time-slices of the Cenozoic. As has already been noted, "Tertiary" and "Quaternary" mean "third" and "fourth," definitions which rankle those of us who think that there was a lot more time before them than two (or three) periods. So the International Commission on Stratigraphy (ICS) officially dropped Tertiary and is in the process of sorting out how best to drop Quaternary too.

Anyhow, trace the evolution of the nomenclature, as defined by the ICS.

Labels: blogs, geologic time, stratigraphy

Labels: art, geologic time, oceans, plate tectonics

Tuesday, I asked for my fellow geo-bloggers' favorite analogies, with a promise that I would share mine in 48 hours. The time of revelation is nigh... Here are a few of my favorite "geo-nalogies":

The continental crust is high-proof liquor
I see partial melting as a kind of distillation. Just as "sour mash" can be distilled to concentrate the alcohol it contains (separating it from the water it's dispersed in), so too can partial melting act as a "distillation" of the silicate earth. The minerals with the lowest melting temperatures will melt, leaving behind a solid residue enriched in Fe, Mg, Mn, and Ca, and yielding a magma that is enriched in Si, K, Na, and O. With its~granitic composition, the continental crust is 80-proof Jack Daniels. Where did it come from? It's distilled from the sour mash we call "the mantle":

Rocks are cookies
I love a good chunky cookie. Save your Oreos and Lorna Doones for yourself. What I really like is one of those cookies with chocolate chips, oatmeal flakes, raisins, macadamia nuts, and those sinfully good butterscotch chips. What I like about these cookies is not so much how they taste, but how I can tell the difference between the individual ingredients and the cookie they comprise. I use this analogy early on in Physical Geology to illuminate the difference between minerals and the rocks that the minerals comprise:

Continents are old sofas
Like many of us, I had an old sofa in college. The sofa was ripped, had been scratched by a cat, and had coffee spilled on it. It was draped in several layers of blanket in an attempt to cover up the lousy state of the upholstery. Someone added a pillow to the sofa at some point. When I was working for the C&O Canal National Historical Park (translating their geologic history into non-geology-speak), it struck me that the North American continent* was kind of like that old sofa. It had been scratched by glaciers instead of cats, and lava had been spilled on it kind of like that errant French Roast. It had rift valleys, but unlike the sofa's, North America's rifts didn't have springs poking out. New material had been added in the form of exotic terranes, kind of like that pillow got added to the sofa. And the blankets draping parts of the continent were made of sediment instead of fabric... but essentially the two were alike:

*Yes, I know that's the outline of the contiguous 48 United States, not North America the continent. So shoot me.

Tectonic plates are UFOs
In cross-section, a tectonic plate could be seen to have a profile kind of like a flying saucer. The thick part in the middle is the continental crust, but then it has a thin fringe encircling it (the oceanic crust). You can hardly blame a visiting Martian for feeling kind of attracted to it:

The Washington Monument shows geologic time
I didn't come up with this one... But read it somewhere (McPhee, maybe?) that I have since forgotten. Anyhow, the basic idea is that the Washington Monument's obelisk here in Washington, DC can show the difference between the Precambrian portion of geologic time (most of the monument, 88% of Earth history) and the Phanerozoic eon (post-Cambrian, 12% of Earth history). The little pyramid-shaped bit on top is the Phanerozoic. The thickness of a single sheet of paper draped on top of the tippy-top would represent the entire span of human history:

Okay, that's all I've got for today. What have YOU got?

Labels: analogies, geologic time, geology, granite, minerals, teaching

Labels: canada, dc, geologic time, news