Telling a dinosaur footprint from a hole in the ground

Posted on October 21, 2008 by Chris Rowan

ResearchBlogging.orgIf they weren’t being mentioned all over the place, these things would make a fine geopuzzle; I certainly wouldn’t guess that these things were dinosaur tracks. They look much more like potholes to me, and if If I came across this in the field, that would probably be what I’d call them. Which shows how much I know.

dinoprints.jpg

A more interesting question is, how do Winston Seiler and Marjorie Chan justify this interpretation? In their paper, they provide a number of reasons. The first one is that they “are of the proper size range”, which is a bit weak. Fortunately, they also provide more compelling reasons. For a start, about one sixth of the impressions that they studied in detail actually look like footprints.

dinoprint.jpg

Furthermore, there seems to be a morphological continuum from the clearer examples like this into various grades of “if you squint…”. In other words, if you look carefully, you can clearly see the obvious footprints are clearly just better-preserved versions of the less obvious ones. If they were weathering features, you’d probably expect a lot more randomly shaped, clearly unrelated impressions.
Another good indicator is that the floors of the “prints” are not flat, but slope in a fairly consistent direction. The shape and the consistency are both important. As the weight on your foot shifts when you push forward off a soft surface, the toe will push further down into the ground than the heel. If you have a track, the slope of every print should point in the direction of travel.
Finally, the way the rims have slumped and deformed suggest that these impressions formed early, before the mud became rock.
Thus, as if by magic, an ancient trampling ground for dinosaurs is revealed. It’s not magic at all of course, but a lot of careful study. To conclude that these things were footprints required the position, shape, and distribution of almost 500 of them to be carefully recorded. Without that sort of attention to detail, claiming dinosaur tracks would have had just as much support as calling them holes in the ground.
W. M. Seiler, M. A. Chan (2008). A Wet Interdune Dinosaur Trampled Surface in the Jurassic Navajo Sandstone, Coyote Buttes, Arizona: Rare Preservation of Multiple Track Types and Tail Traces PALAIOS, 23 (10), 700-710 DOI: 10.2110/palo.2007.p07-082r

Categories: fossils, geology, paper reviews

A more geological Googling experience

Posted on October 14, 2008 by Chris Rowan

Kim is a little concerned that her geology-themed Googling keeps on bringing up stuff that she herself has written. This might have something to do with her blog being a top-notch source of geological insight, of course (someone is clearly going to have to work on her raging egomaniac chops, or the internet is going to eat her up). Still, it did remind me of an idea that I toyed with when I first heard of Google’s funky custom search function, which basically allows you to tune a search so that it only looks through, or prioritises, pages from what you deem to be the worth corners of the internet. Therefore, I present the Geology Search Engine:

Thus far, I’ve only added a handful of sites, like the USGS and NASA’s Earth observatory. To be useful, it really needs more, so if you think this might be a good idea feel free to suggest some, or lots. If it works out, it’s another thing to try and squeeze into the sidebar, of course…

Categories: geology

The comprehension gap

Posted on October 12, 2008 by Chris Rowan

I’ve always been rather suspicious of economics. All of the technical vocabulary and the pretty graphs often appear to be nothing more than a smokescreen, a method of obscuring the fact that economics is fundamentally about people – people who are rarely the ‘rational actors’ that many economic models try to pretend that they are. Self delusion and groupthink are, I think, a little tricky to parameterise.

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Categories: ranting

Geological analogies of the tectonic kind

Posted on October 9, 2008 by Chris Rowan

Callan asks:

What are some of your favorite analogies for explaining geological concepts to other people?

Teaching through analogy – explaining new concepts to people by referring to things that they know or understand already – can be a powerful tool, and since geology is at its core very much a descriptive science, it’s no surprise that useful analogies abound.

putty.jpg

My favorite one is used to combat my least favorite geological misconception: the mantle isn’t molten, it’s made of Silly Putty. Silly Putty responds to short, sharp forces, such as being bounced against a wall, as if it is solid and elastic; but it will change shape and flow if you apply a sustained force over time, even if that force is just the pull of gravity. In a similar way, rocks deep in the mantle are much closer to their melting point than rocks at the surface, but they remain rigid enough in the short term to allow the passage of shear waves generated by earthquakes; however, over geological timescales thermal and compositional bouyancy forces will cause them to flow in giant convection currents.

biscuits.jpg

Here’s another: in one attempt to describe one of the aims of my PhD research in New Zealand, I have likened the Earth’s crust to a biscuit. Of course, there are many different types of biscuit: ginger nuts, for example, in addition to being very tasty, are quite hard to break, and when they do they will snap into a couple of large pieces. HobNobs, on the other hand, whilst being equally delicious, crumble easily into lots of smaller fragments. If you look at how continental crust deforms, sometimes it behaves like it’s a ginger nut, with a small number of large-ish fragments separated by big faults, and sometimes it behaves like a HobNob, with lots of much smaller fragments all jostling against each other. Determining whether the crust in a particular region is more ginger nut-like or more HobNob-like is the key to properly describing the tectonics, and assessing things like the seismic hazard (for what it’s worth, my research suggested that New Zealand is more like a ginger nut, although I’m still arguing with the Hob-Nob faction over that one).
So there’s two for Callan; it’ll be interesting to see what everyone else comes up with. Other responses so far: Tuff Cookie, Hypocentre, Callan himself, Lockwood.

Categories: geology, public science, tectonics

Some calls to arms

Posted on October 9, 2008 by Chris Rowan

Just a couple of things for fellow geoblogospherians to consider, if you haven’t already. Firstly, Maria is participating in the Donors Choose funding drive. The projects that she’s trying to get funded are all aimed at bringing geological goodness to those in educational need. Plus, now she’s even offering bribes prizes to those who donate. If you haven’t already, think about sticking a few dollars in the pot.
Secondly, I’ve just registered myself for the ScienceOnline09 Blogging conference, being held next January in North Carolina. It would be cool if we could get a posse of geobloggers in the same place for once. We could even have our own session… in a manner of speaking. Anyone interested?

Categories: bloggery, public science