GSA meeting, Day 3


After my late night on Monday, I got a bit of a late start this morning but still made it to the poster session with plenty of time to look around. Jared Karr and Matthew Clapham looked at the preservation of fossil insects over time, to look for trends in whether the insects tend to be whole articulated specimens or isolated fragments. They found that lacustrine (lake) environments tend to have better preservation, such as those found at the Solite Quarry (above). But since articulation becomes more common after the Jurassic regardless of environment, they also suggest that the development of diatom mats after that time may contribute to the increase in articulated specimens. It appeared from their poster that the Solite deposits may have been underrepresented in their sample (much of it has not been published), so I don’t know how that might affect their results.

I especially wanted to see Laura Vietti’s second poster (with Beverly Flood and Jake Bailey) on the effect of microbial mats on bones from whale deadfalls. Bone collagen is generally quite resistant to microbes unless acids break down the apatite in the bones, but their work suggests that bacteria on deadfalls are both capable of breaking down collagen, and of making the local environment more acidic.

Sofie Gouwy and others examined Ordovician conodonts from Wisconsin to look for evidence of climatic changes. Specifically, they looked at specimens above and below several large volcanic ash deposits. Temperatures should drop after these eruptions, and a drop in temperature should result in a change in the ratio of Oxygen 16 to Oxygen 18 in sea water, which could be reflected in the ratio of the same elements in the conodonts remains. They didn’t see any change in the conodont isotope ratios, which suggests that any drop in temperature was of such short duration that it doesn’t show up in this level of resolution.

After lunch, just for fun, I spent some time in the Planetary Geology 30th anniversary theme session. As a child I closely followed reports from Voyager and Viking, but things have come a long way since then.

Steven Squyres reviewed the history of Martian exploration, which goes all the way back to the late 1960s with the Mariner spacecraft, and has included six landers.

Viking engineering mockup, National Air and Space Museum

Jeff Moore and Alan Stern discussed the Pluto system, which now includes at least three satellites with a possible fourth. The New Horizons spacecraft is en route to Pluto, but data collected from the Hubble Space Telescope and other sources already indicate that Pluto may be as geologically interesting as small bodies closer to the sun.

Jeff Moore and others also discussed the other small bodies in the outer solar system that have already been visited, the moons of Uranus and Neptune, which were visited by Voyager 2 in the 1980s. The various moons of Uranus are geologically diverse, but seem to exhibit processes similar to those observed on Saturn’s similar-sized moons. Triton seems to be a captured dwarf planet, which has a retrograde orbit, cryo-volcanism, and nitrogen geysers. It is thought that Pluto may be similar.

Voyager engineering mockup, National Air and Space Museum

Saturn’s largest moon, Titan, is one of the most fascinating objects in the solar system. Its surface temperature and pressure (it has a dense atmosphere) are near the triple point of methane. As described by Jason Barnes, Titan has methane clouds that develop into thunderstorms and drop methane rain across the landscape. There are river channels apparently carved by flowing methane, and methane lakes near the north pole that are so smooth that apparently there are no waves larger than just a few millimeters in height. And if that’s not enough, there is a vast dune field surrounding the entire moon at the equator.

Paul Schenk covered Saturn’s other large, icy moons, which show lots of evidence of tidal heating that tends to smooth out their surfaces over time. But there are still a lot of unusual features that haven’t been fully explained. Two of the most unusual are the equatorial ridge on Iapetus and the “string of pearls” feature along the equator of Rhea. Both these raised features almost exactly parallel their respective equators, and may be debris from rings that landed on the surfaces of these moons.

Equatorial ridge on Iapetus, from NASA/JPL/Space Science Institute

William McKinnon examined similar issues with Jupiter’s three large icy moons, Callisto, Ganymede, and Europa. These moons are compositionally similar, and their difference seem to largely be a result of different amounts of tidal heating. Europa, the innermost of the three, almost certainly has a subsurface water ocean.

In the last talk I attended today, Callan Bentley reported on the perceptions his students have about his blog, “Mountain Beltway“, to see if the net effect on his students was positive or negative. The results were almost universally positive, so keep blogging, bloggers!

Tim and I start driving back to Virginia tomorrow, so I don’t know if I’ll make it to any more talks. But it has been a very productive meeting.

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