Category Archives: Geology

Geologic time

One of the hardest concepts to get across to people is the immensity of geologic time. Geologists casually toss around numbers in the millions of years, even billions of years, but how do you really get your mind around such huge periods of time?

For most people the idea of 100 years is a long time back. For example, World War I was fought almost 100 years ago. The Civil War ended almost 150 years ago. The Great Pyramid of Giza was constructed about 4,600 years ago, and that is ancient history. But to even get to the first 1 million years, you have to go back 217 times further.

One scheme for putting this into perspective is the use of the “geologic year.” If we compress all of geologic time into a single year, beginning on January 1, and the present day is midnight on New Year’s Eve, we can place geologic events on the calendar.

The first live appears on the Earth about Feb 25^th, and for most of the year single-celled life dominates. The Cambrian Period, when hard-shelled life and most of the modern invertebrate marine groups appear, happens in the crisp fall of Nov 15^th. The year is almost over, and we have not seen a single vertebrate.

Geologic time represented in a spiral. Note, it is not to scale.

The famed dinosaurs first arrive on the scene about Dec 9^th, and hang around for an incredible long time, until Christmas on Dec 25^th when they go extinct. The dinosaurs and the other reptiles that lived alongside them dominated the large vertebrates for over two weeks, and the next period, the Age of Mammals has lasted less than the last week of the year.

On this scale it takes 2 hours to tick away a million years. Modern humans (Homo sapiens) arrive at 11:37 pm on New Year’s Eve and all of recorded human history (last 5,000 years) takes place in the last 35 seconds before the ball drops.

So, next time you gaze at an outcrop or play with your kid’s dinosaur toys (it’s OK, we all do it), really try to imagine how far back in time you are peering. It is mind-boggling.

Note: To calculate your own dates for the geologic calendar, here are some numbers for you. One day = 12,328,767 years; one hour = 513,699 years; one minute = 8,561.6 years; one second = 142.69 years. Have fun.

What’s the difference between igneous, metamorphic, and sedimentary rocks?

There is something basic in our desire to classify things. Early humans no doubt looked around them at the natural world and instinctively began to group, and subgroup, things. Maybe they grouped things that flew, things that swam, things with leaves, or whatever. And, we have been doing it ever since, trying to create a taxonomy of the natural world that helps us to make sense of it.

Trouble is, our taxonomies are always a best guess, or an approximation, of nature, and this is very evident in the three major groups of rocks. Introductory geology students are usually taught about igneous, metamorphic, and sedimentary rocks, but this really is an oversimplification of nature.

Igneous rocks are those that form from a full melt, where the mineral material is completely turned to a liquid state. From a hot, liquid state, the mix is cooled at various rates and under various conditions to create a variety of igneous rocks. If the mixture cools underground, we call the liquid rock magma, and the rock that forms from it is called an intrusive igneous rock. If the liquid comes to the surface and cools faster, we call it lava, and the rock is an extrusive igneous rock.

Sedimentary rocks generally start with any of the already-formed rock types, and through weathering, transport, and re-deposition, lay down new rock combinations. For example, weathering of a rock may form sand-sized grains that get transported to a beach where it is later solidified into a rock called sandstone. There are other common sedimentary rocks like shale, siltstone, and limestone.

Metamorphic rocks are the hardest to understand in concept, I think. This process is similar to igneous in that it involves heat to cook the rock, but for metamorphic rocks the process does not progress to a full melt of liquid rock. Instead, the heat, and often high pressures of geologic processes, transforms the mineral and rock structure. This is common in mountain-building processes, where the intense pressure of tectonic plates colliding squeezes the rock with immense pressures.

Geologists name the layers of rock that we map to help unravel geologic history. There is a whole code for the naming of rock formations.

But this neat taxonomy of igneous, metamorphic, and sedimentary is not always clear-cut. Many rock types are really a combination of processes; we should not expect that nature falls into our simple categories. Take ash fall deposits for example. Ash is spewed from volcanoes during an eruption (an igneous process) and then blown across the landscape, often forming very thick deposits (a sedimentary process). There are several examples of ash like this across the Central Plains, far from where the ash originated. One prime example is at Ash Fall State Park in central Nebraska where a herd of rhinos was buried by a thick ash deposit.

Travertine is another rock that has a mixed origin. Water is heated at depth by proximity to magma (igneous) and picks up minerals. The water can then travel to the surface where it cools and deposits the minerals layer upon layer (sedimentary), building up travertine. This rock often has interesting texture and colors due to mineral impurities, making it a nice decorative stone used for tiles.

So, we start with basic guidelines as way to understand geologic processes. I have described this as “lying” to intro students, not maliciously, but by giving them principles that are true enough, but oversimplified. If you go on in geology you spend the rest of your education learning the exceptions to the rules.

New evidence on the sizes of pterosaurs

The flying reptiles, pterosaurs, were an amazing successful group of prehistoric animals. They ranged from the Late Triassic through the end of the Cretaceous periods, a span of time of about 156 million years. That is over 2 times longer than the time since dinosaurs became extinct, and mammals have dominated the terrestrial landscape.

Pterosaurs were the first vertebrates to achieve powered flight, followed later by the birds and bats. However, during their hay-day, pterosaurs achieved an incredible range of diversity in form and size, and occupied countless niches within the Mesozoic world.

Interestingly enough, the first pterosaur remains to come from North America were found in Kansas. Flying reptiles had been known from Europe, but during an 1870 collecting trip through the western territories, O. C. Marsh stopped off in Kansas. Near the end of the trip he spotted a long, slender bone weathering out of the chalk formation, and collected what he could before heading back to Yale on the train. He thought the bone looked like the finger bone of the pterodactyls from Europe, but this bone was much larger. He estimated the wing-span to be 20 feet. The next year, he traveled back to collect the rest of the animal in the Kansas formation, and found that in fact his estimate of its giant size was correct. He named this new animal Pteranodon.

Greg dusts the life-sized models of Pteranodon sternbergii in the Sternberg Museum of Natural History

As more and more flying reptiles have been found in the fossil record, as basic question about them has puzzled scientists—how well could they fly? Estimating the body mass is a fundamental part of this inquiry. We can look at modern birds and see the constraints that flight dictates for body mass at least today. How do the pterosaurs compare?

In a recent publication, the question of body mass in pterosaurs is addressed (Henderson 2010). In the most detailed study yet of pterosaur body mass, Henderson set out to explore this question and to compare the results to birds. He created a model of body mass based on modern birds by creating digital, three-dimensional models of their bodies. His model was corrected for differences in density from different areas of the body. For example, the wings will have a different average density than the trunk, where the volume of the lungs greatly impacts its overall density.

Using birds, he refined his model to accurately calculate their masses and centers of gravity. Then, he turned to the pterosaurs. What he found was very interesting. The pterosaurs in his study ranged from less than an ounce for Anurognathus to an astonishing 1,200 pounds in mass for Quetzalcoatlus (more on this in a moment).

The giant pterosaur Hatzegopteryx compared to a modern giraffe. Illustration by Mark Witton.

The giant pterosaur Quetzalcoatlus northropi compared to a modern giraffe. Illustration by Mark Witton.

Excluding the giant Quetzalcoatlus for a moment, the other heaviest pterosaurs were Pteranodon at 41 pounds and Tupuxuara at 50 pounds. The estimates for the ancient fliers are not too far off the masses of the largest modern flying bird the Great Bustard, at 35 pounds. So, we know that it is at least possible for an animal of that weight to get airborne on a regular basis.

So, what about the giant Quetzalcoatlus? This animal is known from fragmentary remains from Texas where it was first found in 1971. While mostly known from fragmentary remains it is estimated that it had a wing span of 37 feet or more. Earlier estimates of the weight of this animal vary widely from 141 – 608 pounds. Henderson points out that many of the body mass estimates of the past were influenced by engineering constraints calculated for an animal with this great wing span to be able to fly. The thinking being that an animal evolved from flying animals most likely flew.

But, in an interesting twist, Henderson’s estimate is twice as much as previous estimates, so he turns the issue around and suggests the heresy that maybe giants like Quetzalcoatlus (and I would add Hatzegopteryx by extension) did not fly. Instead, it is perfectly reasonable to assume that a formerly flying species secondarily adapted to a fully terrestrial life style, growing to dramatic size as a protection from predation or for other similar advantage. We certainly can find examples of that in the modern birds too, in the flightless ratites, the emus and ostriches.

No doubt this issue will continue to be explored (for an alternative view see The largest pterosaurs have not been grounded yet) . That is the fun of science—keep probing and answers, and more questions, reveal themselves.

Henderson, D. M. 2010. Pterosaur body mass estimates from three-dimensional mathematical slicing. Journal of Vertebrate Paleontology 30(3):768-785.

My National Geographic moment

“A photographer from National Geographic wants to talk to you.” These words, or words to those effect, met me as I came into the museum office one day back in 2001, and they definitely caught my attention.

It was 2001 and I was Assistant Director of the Sternberg Museum of Natural History. We had just reopened the museum in its new location in Hays, Kansas, a few years before in 1999. The museum had enjoyed some tremendous success at attracting visitors and media attention from across the state. And now someone from National Geographic wanted to talk to us? Wow. I returned Jonathan Blair’s call and began an unusual week of activity.

It turns out that the magazine was going to run a story on pterosaurs, the flying reptiles from the Mesozoic, and they hired Jonathan to get pictures to illustrate it. He had already traveled to some of the great museum collections for pterosaurs in Europe and the United States, but he wanted to visit Sternberg. The Sternberg’s collection of pterosaur material is about the third or fourth largest in the nation, and very significant.

The Sternberg Museum, on the campus of Fort Hays State University, was managed for many years by George F. Sternberg, famed fossil collector. He spent his free time out in the chalk, the Niobrara Formation of western Kansas, collecting the fish and swimming and flying reptiles that left their remains millions of years ago. Sternberg supplemented his salary at the museum by selling specimens to other museums, but if he collected something really nice it went into “his” museum. Over the years, the museum’s collection grew in size and quality.

Besides our amazing collection of fossils, Jonathan had heard about our life-sized pterosaur models we had just installed in our walk-through Cretaceous exhibit. And he had a crazy idea—let’s take a life model of the beast and “fly” it over the very rocks where its remains can be found. He wanted to take one of our life-sized model and photograph it over the chalk beds.

Well, I can bend over backwards for National Geographic, but taking one of our brand new models down from the ceiling, which had not been easy to install in the first place, and which since had walls built up around them, and truck them 70 miles to hang from a crane in the chalk sounded a bit risky to me.

But I did offer to help in any way we could, so I did the next best thing—I found him another pterosaur model.

Over the next several days we made plans and preparations for the big event. We needed to get the model that I was able to find shipped to the museum. It had been kept in storage and was a little beaten up, but the company that supplied it sent a staff member to clean, fix it, and touch up the paint for its big moment. The model, being life-sized, had a twenty foot wing span, flimsy neck with a large head at the end, and feet that stuck out the back, giving the whole thing a cross shape, making it too long in any direction. Not exactly the easiest thing to get into a truck and ship!

We scouted a location for the big photo shoot. I took Jonathan to the Castle Rock area, a well-known outcropping of the chalk that has easy access and grand vistas. We needed to secure special permission as we were going to bring in a crane and another truck to transport the pterosaur model.

We needed to arrange for a crane to make the 70 mile one-way trip from Hays to the chalk beds. On this, and on so many other occasions, I marveled at the “can do” spirit of western Kansas people. You want something done just ask a former farm kid. While he might look at you funny, he will get it done.

In between all this activity, I remember some spectacular meals shared with Jonathan, listening to his many adventures from around the world while taking photographs. He also shot pictures around the museum, and he took a couple of photos of me that I have cherished ever since.

Greg dusts the life-sized models of Pteranodon sternbergii at the Sternberg Museum of Natural History. Photograph by Jonathan Blair.

The big day arrived and all was going well. The weather cooperated, the truck was loaded with its ungainly cargo, and the crane made it to the site. We had also brought along a number of crew members to help hold the model. We wanted to lift it into the air for the photograph, but if you know anything about western Kansas, you know it is windy. I was not sure what would happen when you lifted such a thing into the gusty winds, and how hard it might be to control. The only control we had were guy-wires coming down from the wing tips to hold it against unruly behavior.

With trepidation we gave the signal to the crane operator to lift, and the hundred pound model took to the air. And in the end, the wind was no issue—the model, like the animal it represented, was built for the air. It found a comfortable equilibrium and settled into the wind easily. Jonathan snapped his pictures, and just like that we had what he had come after.

Life-sized model of a pterosaur, an ancient flying reptile, soars onces again over western Kansas

Life-sized model of a pterosaur, an ancient flying reptile, soars once again over western Kansas

We took more photos at a few other locations, all of which could have made fantastic desktop images, but he knew he was done. We packed up and came home, and all those days preparation resulted in the lead image for the story. It was all Jonathan’s photo and idea, and I enjoyed the part I played in making it happen—one of the perks for working at a museum.

See the National Geographic story.

Jonathan Blair’s web page

How To Polish Stones By Hand

Ever asked yourself how it was that people two hundred years ago used to get their rocks and gems such as clear quartz to be so clear and perfect when they didn’t have rock tumblers available? It’s not like they could toss a few rocks into the sea and then sit back for a few decades waiting for for the water and sand to do its thing.

No, they did it all by hand. And if you’re interested in giving it a try, you might it to be a rewarding – if somewhat labor-intensive – undertaking.

So how exactly does one go about polishing rocks by hand?

Ideally, you should start with a soft stone – something that registers 3-4 on the Mohs hardness scale. This isn’t an absolute rule – you can work on harder stones, but the time and energy you have to expend is going to rise considerably. Start with something like onyx, or perhaps a calcite or dolomite.

Don some safety goggles, gloves and even an air mask. Rock dust is nothing to sneeze at, if you’ll pardon the pun. Using a small hammer and chisel, remove any chunks from the stone that stand in the way of its ideal form. Once the larger ones are gone, briskly grind the stone against some concrete. This will wear away the smaller protuberances.

When you’re pleased with the general size, get yourself some 50 grain sandpaper and begin to work over the entire stone. Concentrate on consistency – again, what you’re doing here is slowly grinding the stone into a final shape.

Once it’s there, you can start working with a finer grade sandpaper – say 150 grain. Again, simply get comfortable and work away at the stone. You are soothing the marks that were left by the concrete and the 50 grain sandpaper. It’s about this stage that your stone will start to resemble something finer and prettier than you see out in the field.

At this point you can move up to a finer grade of sandpaper – depending on the rock, anywhere from 300 to 600. This is the refinement stage. Any remaining blemishes are going to be smoothed away.

The final stage is working with ultra fine sandpaper – or even better, a soft cloth like denim. Slowly clean and rub the stone. Let it air dry, then apply a commercial stone polish – you can find this at just about any good hobby store that knows a thing or two about rock hounds.

You’ll notice that the final result looks a bit rougher than the stones you get through your tumbler. But take heart – you’ve worked really hard. You might find that a stone polished by hand means a bit more to you now!

Boneblogger: Science and the outdoors

Exploring the natural world