Tuesday, February 19, 2013

An Account Of Natural Selection By A Victorian Gentleman

Who wrote this...Darwin or Wallace?

There is a law universal in nature, tending to render every reproductive being the best possible suited to its condition that its kind, or organized matter, is susceptible of, which appears intended to model the physical and mental or instinctive powers to their highest perfection and to continue them so. This law sustains the lion in his strength, the hare in her swiftness, and the fox in his wiles. As nature, in all her modifications of life, has a power of increase far beyond what is needed to supply the place of what falls by Time's decay, those individuals who possess not the requisite strength, swiftness, hardihood, or cunning, fall prematurely without reproducing—either a prey to their natural devourers, or sinking under disease, generally induced by want of nourishment, their place being occupied by the more perfect of their own kind, who are pressing on the means of subsistence . . .

There is more beauty and unity of design in this continual balancing of life to circumstance, and greater conformity to those dispositions of nature which are manifest to us, than in total destruction and new creation . . . [The] progeny of the same parents, under great differences of circumstance, might, in several generations, even become distinct species, incapable of co-reproduction.

The answer is neither.

Friday, February 15, 2013

Mexican Silver And Japanese Samurai

 My Book Shelf # 24

A post by Metageologist on tracking the source of silver in English coins from Medieval to early modern times caught my eye.

Silver formed by different geological processes may have distinct isotopic signatures. Metageologist points to a study which recognized English silver coins being sourced initially from silver taken from European mines and then later from the mid 1500's from Mexico via the Atlantic trade route. The silver from rich deposits in Peru primarily took the Pacific route and went to satisfy Chinese demand.

People too moved across continents along with silver. I came across this fascinating passage from 1493- Uncovering The New World Columbus Created by Charles Mann on the outsourcing of security for silver shipments-

Known collectively as chinos, Asian migrants spread slowly along the silver highway from Acapulco to Mexico City, Puebla, and Veracruz. Indeed, the road was patrolled by them- Japanese samurai perhaps in particular. Katana-swinging Japanese helped supress Chinese rebellions in Manila in 1603 and 1609. When Japan closed its borders to foreigners in the 1630's Japanese expatriates were stranded wherever they were. Scores, perhaps hundreds migrated to Mexico. Initially the viceroy had forbidden mestizos, mullatos, negros, zambaigos, and chinos to carry weapons. The Spaniards made an exception for samurai, allowing them to wield their katanas and tantos to protect the silver shipments against the escaped-slaves-turned-highwaymen in the hills.

Charles Mann is right when he calls the Mexico of this period a "crazy soup".

Tuesday, February 12, 2013

Gorgeous Paper On Carbonate Diagenesis In Journal Sedimentary Research

The January 2013 issue of the Journal of Sedimentary Research is open access. There is a long and beautifully illustrated study on the diagenesis of Permian carbonates from the Guadalupe mountains of New Mexico U.S.A. by David A.Budd and colleagues.

These carbonates were fractured very early during their depositional history, in fact the fractures are syndepositional i.e. they formed as the sediments were accumulating. Sometimes calcium carbonate sediments undergo cementation and hardening by sea water just a few centimeters to meters below the sediment water interface and they then are rigid enough to fracture. Budd and co-workers painstakingly analysed the materials filling these fractures using a variety of sedimentary petrology and geochemical techniques and found out that these fractures acted as conduits for the movements of fluids not just early on but through the entire geologic history of these rocks. So the geometry of fluid flow networks may be established very early in the rock history with implications for the distribution of porosity and localization of economic deposits.

I love such detailed petrologic studies. I was consumed by this kind of research during my PhD days, thinking about marine and meteoric cements and porosity formation and the movement of fluids and its interaction with rock from its deposition to deep burial. It was a real pleasure to read this long and exhaustive work.

I said beautifully illustrated so let me post below an example from the paper. The image shows the cementation and interpreted geologic history of a fracture using plain light and cathodoluminescent microscopy.

Explanation from the paper:

A) Paired plane light and B) cathodoluminescent photomosaics through fracture fill B. The wall of the large fracture is lined with bladed dolomite cement (black arrows). Overlying the dolomite is a first generation of luminescently zoned (non to dull to bright orange) calcite cement (CC1). With subsequent refracturing, those first generation cements were mechanically rotated, brecciated, and lightly etched (white box), and then the combined fracture opening was encased in a bright orange luminescent calcite (CC2).

Just to show off, let me put up a similar kind of image from my PhD work in the Upper Ordovician strata of the southern Appalachians U.S.A.  Again a pore space illuminated by cathodoluminescence shows different cement generations.

Long live Sedimentary Geology!

Sunday, February 10, 2013

Geologist Robert Young On Rebuilding After Superstorm Sandy

The complicated decision on whether to and how much to rebuilt coastlines after destruction from a major storm lies at the intersection of geology, climate change, sea level rise, preserving communities and livelihoods, and the economics of insurance risk and the real estate market.

Geologist Robert Young, director of the Program for the Study of Developed Shorelines and professor of coastal geology at Western Carolina University speaks passionately and authoritatively about these issues in a talk hosted by Tom Ashbrook on OnPointRadio.

As he says; The map of the coastal U.S. 50 years on will look very different from now and we need a national plan to get from here to there. Its good to hear a geologist at the center of this discussion.

Listen: After Big Storms: Rebuild Or No?