Archive for August, 2011

Thomas Jefferson, the reluctant seismologist

24 August 2011

Photo by Trevor.Huxman used under Creative Commons 2.0

Depite his distinction as the first American paleontologist (sorta), Thomas Jefferson was something of geophobe.  In a letter written in 1805, Jefferson confessed:

I have not much indulged myself in geological inquiries, from a belief that the skin-deep scratches which we can make or find on the surface of the earth, do not repay our time with as certain and useful deductions as our pursuits in some other branches.

Five years later, fresh out of the Presidency, Jefferson ducked an inquiry from Thomas Cooper regarding the geology of Virginia on similar grounds, “Our researches into the texture of our globe could be but so superficial, compared with its vast interior construction, that I saw no safety of conclusion from the one, as to the other.”

Despite his avowed geo-agnosticism, Jefferson was both well-versed in the geological thinking of his day and an attentive observer of the geologic forces that shaped the landscape around him. In Notes on the State of Virginia Jefferson provides a detailed discussion of the Deluge theory that dominated geological thinking in the 18th Century, but voices considerable skepticism that the distribution of rocks and fossils on the Earth could be easily explained by events recorded in Genesis. Jefferson recognized that tilted strata and seashells lodged in the sides of mountains suggested some significant geological “convulsions” in the past. But he was never comfortable that studies of rocks could ever truly clarify the ancient history of the Earth, concluding, “Ignorance is preferable to error; and he is less remote from truth who believes nothing, than he who believes what is wrong.”

Nevertheless, later in that same work Jefferson wrote thoughtfully about the geomorphic landscape of western Virginia, in prose so vivid that it puts John McPhee to shame. Here he even reveals some nascent appreciation for the geologic forces that shaped that terrain.

The passage of the Patowmac through the Blue ridge is perhaps one of the most stupendous scenes in nature. You stand on a very high point of land. On your right comes up the Shenandoah, having ranged along the foot of the mountain an hundred miles to seek a vent. On your left approaches the Patowmac, in quest of a passage also. In the moment of their junction they rush together against the mountain, rend it asunder, and pass off to the sea. The first glance of this scene hurries our senses into the opinion, that this earth has been created in time, that the mountains were formed first, that the rivers began to flow afterwards, that in this place particularly they have been dammed up by the Blue ridge of mountains, and have formed an ocean which filled the whole valley; that continuing to rise they have at length broken over at this spot, and have torn the mountain down from its summit to its base. The piles of rock on each hand, but particularly on the Shenandoah, the evident marks of their disrupture and avulsion from their beds by the most powerful agents of nature, corroborate the impression. But the distant finishing which nature has given to the picture is of a very different character. It is a true contrast to the fore-ground. It is as placid and delightful, as that is wild and tremendous. For the mountain being cloven asunder, she presents to your eye, through the cleft, a small catch of smooth blue horizon, at an infinite distance in the plain country, inviting you, as it were, from the riot and tumult roaring around, to pass through the breach and participate of the calm below. Here the eye ultimately composes itself; and that way too the road happens actually to lead. You cross the Patowmac above the junction, pass along its side through the base of the mountain for three miles, its terrible precipices hanging in fragments over you, and within about 20 miles reach Frederictown and the fine country round that. This scene is worth a voyage across the Atlantic. Yet here, as in the neighbourhood of the natural bridge, are people who have passed their lives within half a dozen miles, and have never been to survey these monuments of a war between rivers and mountains, which must have shaken the earth itself to its center. – Thomas Jefferson, Notes on the State of Virginia 1781-1783.

But sometimes the mountain comes to Monticello. Jefferson himself recorded a convulsion that shook the state of Virginia in 1774,

“Feb. 21, at 2:11 P. M. felt a shock of an earthquake at Monticello. it shook the houses so sensibly everybody ran out of doors.” – Excerpt from Thomas Jefferson’s Garden Book, edited by Edwin Morris Betts (1999).

Despite this rather cool account, the 1774 quake may have played a role in a family calamity, the death of Jefferson’s sister Elizabeth, whose body was found floating in the Rivanna river three days after the quake. Elizabeth, “rather deficient in intellect” may have been attempting to flee from the earthquake and subsequent aftershocks when she was caught up in the flooding river. Maybe.

Geologic instability in central Virginia also shook up Jefferson’s granddaughter, when a quake hit in 1833.

Edgehill, Aug. 28, 1833.
… We had the most severe shock from an earthquake yesterday morning that had ever been experienced before by any of us … When it began the noise resembled the rolling of a wheel barrow, or something heavier, under the house, but gradually increasing until the house trembled all over. A dressing box on one of the tables being open, and the top leaning against the wall, was shaken almost off the table. It would have fallen, I suppose, if its fall had not been arrested by Mary Page’s hand, which she put out to save it. The windows rattled violently, and I began to fear the chimney might be shaken off, and made Emily, who was sitting near the fireplace … move away. When it had reached its heighth it gradually diminished until it went off entirely. The children from the nursery ran into my room, and Patsy and Mary followed them. I never saw so many pale faces and blue lips. I think it must have been partly occasioned by the motion: of the house and partly from terror … I have heard of the trembling of a vessel in a storm sometimes, & I think the motion of the house must have resembled it. – From MacCarthy 1958, “A Note on the Virginia Earthquake of 1833”.

Judging from contemporary accounts, that quake was likely centered on the same Central Virginia Seismic Zone that gave rise to yesterday’s tremor. The 1774 earthquake felt by Jefferson might well have had similar origins.

It’s hard not to wonder. Perhaps, if the magnitude of the 1774 Virginia earthquake that shook Monticello had been on par with the August 23, 2011 quake, it might have shaken into Jefferson a greater curiosity about the goings on beneath his feet. But, perhaps it’s for the best he didn’t get distracted, Jefferson had other things to do.

It is now above a fortnight since Congress should have met, and six States only appear. We have some hopes of Rhode Island coming in to-day, but when two more will be added seems as insuceptible of calculation as when the next earthquake will happen – Thomas Jefferson in a letter to James Madison, December 1783.

Postscript: 1000000 bonus points to the enterprising journalist or historian who tracks down Jefferson’s living descendants and records their personal experience of yesterday’s earthquake for posterity.

Icon of evolution knocked from its perch, or, wait…how about “arthropod origins, waters around, muddied?”

10 August 2011

Since its original description six months ago, the fossil lobopod Diania has become one of the most celebrated fossils of all time, inspiring everything from elaborate back tattoos to a trendy sportswear line. This beloved “walking cactus” was championed by scientists as a key player in the origin of the most diverse and successful group of living animals. But startling new research suggests that this icon of evolution, this upstart URthropod, was in fact nothing more than an ordinary lobopod with bad skin.

In a series of brief communications published this week in Nature, two groups present revised analyses of the evolutionary relationships among 520 million year old fossil and its presumed relatives including euarthropods (e.g. insects, arachnids and crustaceans), anomalocarididsvelvet worms, water bears, and a variety of extinct stem-arthropods and lobopods, like the bizarre Hallucigenia. The phylogenetic analysis presented with the original description of Diania by Liu and colleagues found the creature to be closely related to a clade that included living arthropods and the outlaw Bavarian folk hero Schinderhannes, this result, coupled with the armored covered legs of Diania, was taken as an important clue to the origins of the stiff, jointed-appendages that are a hallmark of true arthropods.

However, the new reappraisals find Diania several nodes further removed from arthropod origins, mucking around in a polytomy that includes the tardigrades, onychophorans and extinct lobopodians. If these results are correct, it implies that the armored limbs of Diania are likely irrelevant to the origin of hardened jointed legs among arthropods. In a reply, Liu and company concede the tenuous placement of Diania in the family tree of arthropods and their relatives, but provide some additional support for their original interpretation and argue that further study is required to resolve the debate.

Surely, the question of whether Diania is a close relative of arthropods or not will continue to rock the paleontological community for years to come.

Refs:
Mounce, Ross CP and Matthew A Wills (2011) “Phylogenetic position of Diania challenged” Nature 476:E1 doi:10.1038/nature10266

Legg, David A et al. (2011) “Lobopodian phylogeny reanalysed” Nature 476:E1 doi:10.1038/nature10267

Liu, Jianni et al. (2011) “Reply” Nature 476:E1 doi:10.1038/nature10268

About how I just bathed a little salamander

8 August 2011

coated in hair and lint, who had been curled up by the hamper in the bathroom and whom my wife conferred “belonged to me.”

Not this salamander, obviously.  But a relative. No doubt.

Post-script. I found a photo of the salamander in question. Online.