Saturday, May 30, 2009

The Trilobite Eye


Holochroal eye: found in nearly all Orders few to very many lenses (to >15,000!) lenses typically small, numerous one corneal layer covers all lenses lenses in direct contact with others no sclera between lenses corneal membrane covers surface only.



Schizochroal eye: found in some Phacopida only typically fewer lenses (to ca 700)
lenses much larger, fewer each lens bears an individual cornea lenses separated from each other sclera between lenses very deep corneal membrane extends into sclera.



Abathochroal eye: found in Cambrian Eodiscina only few lenses (to ca 70) lens size small, not numerous each lens bears an individual cornea lenses separated from each other interlensar sclera not deeper than lenses corneal membrane ends at lens margin.


All early trilobites (Cambrian), had holochroal eyes and it would seem hard to evolve the distinctive phacopid schizochroal eye from this form. The answer is thought to lie in ontogenetic (developmental) processes on an evolutionary time scale. Paedomorphosis is the retention of ancestral juvenile characteristics into adulthood in the descendent. Paedomorphosis can occur three ways: Progenesis (early sexual maturation in an otherwise juvenile body), Neoteny (reduced rate of morphological development), and Post-displacement (delayed growth of certain structures relative to others). The development of schizochroal eyes in phacopid trilobites is a good example of post-displacement paedomorphosis. The eyes of immature holochroal Cambrian trilobites were basically miniature schizochroal eyes. In Phacopida, these were retained, via delayed growth of these immature structures (post-displacement), into the adult form.

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Electrum



Formula:
(Au, Ag)
Lustre: Metallic
Name: From the Greek ήλεκτρου for "amber," in allusion to its colour.
A variety of Gold

Gold-Silver Series. A variety of gold containing silver, usually with >20% of silver. from

The Pactolus River beside the slopes of Mount Tmolus in the kingdom of Lydia was one of the most important sources of electrum in the ancient world. According to Greek mythology, the river acquired its electrum when King Midas of nearby Phrygia bathed in it to wash away his golden touch, which had turned even his food into gold, a telling parable about the destructiveness of wealth. In actuality, The Paktolos River acquired its electrum from electrum-laden quartz deposits near Mount Tmolos (called Mount Bozdag today). from

Friday, May 29, 2009

Little, Big

"One by one the bulbs burned out, like long lives come to their expected ends. Then there was a dark house once made of time, made now of weather, and harder to find; impossible to find and not even as easy to dream of as when it was alight. Stories last longer: but only by becoming stories. It was anyway all a long time ago; the world, we know now, is as it is and not different; if there was ever a time when there were passages, doors, the borders open and many crossing, that time is now now. The world is older than it was. Even the weather isn't as we remember it clearly once being; never lately does there come a summery day such as we remember, never clouds as white as that, never grass as odorous or shade as deep and full of promise as we remember they can be, as once upon a time they were."

from Little, Big by John Crowley

May 29, 2009 - Theorists Reveal Path to True Muonium


Menlo Park, Calif.—True muonium, a long-theorized but never-seen atom, might be observed in future experiments, thanks to recent theoretical work by researchers at the Department of Energy's SLAC National Accelerator Laboratory and Arizona State University. True muonium was first theorized more than 50 years ago, but until now no one had uncovered an unambiguous method by which it could be created and observed.

Thursday, May 28, 2009

gallery: sergio cittolin


A drawing of the innermost part of the CMS detector, bristling with silicon tiles, took inspiration from the nine circles of hell in Dante Alighieri’s Divine Comedy.

Monday, May 25, 2009

Hallucigenia, Corrected




Most people realise that reconstructions of animals from their fossilised remains is a risky business, and that when there are only a few fossil specimens, opportunities for misinterpretation are many. Add to this an investigator who declares `I have a natural temptation to emphasise the unusual', then the probability of error is greatly increased. All these ingredients are present in the case of an organism named Hallucigenia, first described in 1977 by Conway Morris in the journal Palaeontology.

However, new evidence has come to light which suggests that Hallucigenia exists only in our imagination. Lars Ramiskold of the Swedish Museum of Natural History and Hou Xianguang from the Nanjing Institute of Geology and Palaeontology have been studying worm-like fossils from Southern China. They consider that the fossils have a body plan similar to the velvet worms of modern rain forests, but that they were armoured - bearing protective spines. After comparing the characteristics of the Hallucigeniafossils with those of their own, they were able to conclude that the reconstruction was wrong, that Hallucigenia was actually an armoured velvet worm, and that it belongs to the phylum Onychophora.

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Sunday, May 24, 2009

Hallucigenia



Hallucigenia is an extinct genus of animal found as fossils in the Middle Cambrian-aged Burgess Shale formation of British Columbia, Canada. It was named by Simon Conway Morris when he re-examined Charles Walcott's Burgess Shale genus Canadia in 1979. Conway Morris found that what Walcott had called one genus in fact included several quite different animals. One of them was so unusual that nothing about it made much sense. Since the species clearly was not a polychaete worm, Conway Morris had to provide a new generic name to replace Canadia. Conway Morris named the species Hallucigenia sparsa because of its "bizarre and dream-like quality" (like a hallucination).

When originally discovered and prepared, fossils of the animal Hallucigenia appeared to have preserved two rows of spines on one side of the animal and one row of tentacles on the other. Identifying its head was a problem - the fossil showed only a rounded, dark stain at one end and a narrower, dark stain at the other.
Hallucigenia

Based on the appearance of those initial fossil preparations, the first restoration made in 1977 presented us with an animal walking along the bottom of the seafloor on spiny stilts, waving seven dorsal tentacles from its back. The "tentacles" seemed to have a mouth at each tip. These were believed to be feeding aids. You can easily see why Hallucigenia got its curious name.

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