Friday, January 25, 2008

Musca si dinozaurii

Most lead­ing the­o­ries on how di­no­saurs died out fo­cus on as­ter­oid im­pacts or mas­sive vol­can­ism. But a new book blames a much less thun­der­ous force: in­sects.
The rise and evo­lu­tion of these bugs—the bit­ing dis­ease-carriers, in par­ti­cu­lar—co­in­cided fate­fully with the mighty rep­tiles’ lat­er days, write George Po­inar Jr. of Or­e­gon State Un­ivers­ity and his wife Ro­ber­ta in the book, “What Bugged the Di­no­saurs? In­sects, Dis­ease and Death in the Cre­ta­ceous."

The Poinars say the ev­i­dence is pre­served in life­like detail, in the form of var­ied in­sects trapped in an­cient am­ber.
“There are se­ri­ous prob­lems with the sudden-im­pact the­o­ries of di­no­saur ex­tinc­tion, not the least of which is that di­no­saurs de­clined and dis­ap­peared over a pe­ri­od of hun­dreds of thou­sands, or even mil­lions of years,” said George Poi­nar.
He didn’t deny that there is ev­i­dence for cat­a­stroph­ic events such as an as­ter­oid strike or la­va flows around that time. These “cer­tain­ly played a role” in the die­off, but don’t ac­count for its slow­ness, said Poi­nar, an en­to­mo­log­ist.


On the oth­er hand, he added, “com­pe­ti­tion with in­sects, emerg­ing new dis­eases and the spread of flow­er­ing plants over very long pe­ri­ods of time is per­fectly com­pat­ible with ever­ything we know about di­no­saur ex­tinc­tion.” Pests and ill­ness may have sub­jected T. rex and its scaly kin to a slow­er tor­ment, but pos­sibly the fa­tal one ul­tim­ate­ly, ac­cord­ing to the au­thors.
The grad­u­al down­fall of the di­no­saurs came around a pe­ri­od known as the K-T Bound­a­ry, be­tween the so-called Cre­ta­ceous and Ter­tiary pe­ri­ods some 65 mil­lion years ago. But some di­no­saurs sur­vived for thou­sands of years there­af­ter, Poi­nar not­ed; a num­ber of lin­eages lived even long­er and evolved in­to modern-day birds.




Poinar and his spouse have spent much of their ca­reers stu­dy­ing plants and an­i­mals found pre­served in am­ber, us­ing them to re-cre­ate en­vi­ron­ments of yore. A semi-precious gem that orig­i­nates as sap ooz­ing from a tree, am­ber has a un­ique abil­ity to trap ti­ny crea­tures or oth­er ma­te­ri­als and pre­serves them al­most per­fectly in nat­u­ral dis­play cases for mil­lions of years. The phe­nom­e­non has been in­val­u­a­ble in re­search; it al­so formed the prem­ise for the film Ju­ras­sic Park, in which fiction­al sci­en­tists ex­tracted di­no­saur DNA from am­ber-trapped mosquitoes.


In­sects are be­lieved to have orig­i­nat­ed more than 400 mil­lion years ago from worms, but un­der­went a ma­jor flour­ish­ing in the Cre­ta­ceous era, when the lat­er di­no­saurs lived. The spread of new in­sect lin­eages went hand-in-hand with that of flow­ers, which had mu­tu­ally de­pend­ent rela­t­ion­ships with many in­sects.
This rise of flow­ering plants was itself bad news for di­no­saurs, which tra­di­tion­ally fed on oth­er types of greens, said Poi­nar. Mean­while, in­sects came to com­pete for some foods with the great rep­tiles.
But things got worse, Poinar went on. By the late Cre­ta­ceous “the as­socia­t­ions be­tween in­sects, mi­crobes and dis­ease trans­mis­sion were just emerg­ing,” he said. “We found in the gut of one bit­ing in­sect, pre­served in am­ber from that era, the path­o­gen that causes leish­ma­ni­a—a se­ri­ous dis­ease still to­day, one that can in­fect both rep­tiles and hu­mans. In anoth­er bit­ing in­sect, we disco­vered or­gan­isms that cause ma­lar­ia, a type that in­fects birds and lizards to­day.

“In di­no­saur fe­ces, we found ne­ma­todes, trema­todes and even pro­to­zoa that could have caused dys­en­tery and oth­er ab­dom­i­nal dis­tur­bances. The in­fective stages of these in­tes­ti­nal par­a­sites are car­ried by filth-visiting in­sects.”
In the Late Cre­ta­ceous, Poinar said, the world was co­vered with warm-tempe­rate to trop­i­cal zones that swarmed with blood-sucking in­sects car­ry­ing leish­ma­nia, ma­lar­ia, in­tes­ti­nal par­a­sites, ar­bo­vi­ruses and oth­er path­o­gens. These caused re­peat­ed epi­demics that slowly but surely wore down di­no­saur popula­t­ions, Poi­nar ar­gued. Ticks, mites, lice and bit­ing flies would have tor­mented and weak­ened them.
“S­maller and sep­a­rat­ed popula­t­ions of di­no­saurs could have been re­peat­edly wiped out, just like when bird ma­lar­ia was in­tro­duced in­to Ha­waii, it killed off many of the hon­ey­creep­ers” Poi­nar said. “After many mil­lions of years of ev­o­lu­tion, mam­mals, birds and rep­tiles have evolved some re­sist­ance to these dis­eases. But back in the Cre­ta­ceous, these dis­eases were new and in­va­sive, and ver­te­brates had lit­tle or no nat­u­ral or ac­quired im­mun­ity.”

A pos­si­ble rea­son why some di­no­saurs lived on to make a come­back as modern-day birds, Poi­nar sug­gested, is that these smaller an­i­mals had a shorter life­span. That might have helped them evolve faster to adapt to the in­sect men­ace, since ev­o­lu­tion oc­curs on a genera­t­ion-to-genera­t­ion ba­sis.
“In­sects have ex­erted a tre­men­dous im­pact on the en­tire ecol­o­gy of the Earth, cer­tainly shap­ing the ev­o­lu­tion and caus­ing the ex­tinc­tion of ter­res­tri­al or­gan­isms,” the au­thors wrote in their book. “The larg­est of the land an­i­mals, the di­no­saurs, would have been locked in a life-or-death strug­gle with them for sur­vival.”

http://www.world-science.net

Detectarea altor universuri


If there are oth­er un­iverses out there—as some sci­en­tists pro­pose—then one or more of them might be de­tect­a­ble, a new study sug­gests.

Such a find­ing, “while cur­rently spec­u­la­tive even in prin­ci­ple, and probably far-off in prac­tice, would surely con­sti­tute an ep­och­al dis­cov­ery,” re­search­ers wrote in a pa­per de­tail­ing their stu­dy. The work ap­pears in the Sep­tem­ber is­sue of the re­search jour­nal Phys­i­cal Re­view D.

Cos­mol­o­gists gen­er­ally hold that even if oth­er un­iverses ex­ist, a con­tro­ver­sial idea it­self, they would­n’t be vis­i­ble, and that test­ing for their ex­istence would be hard at best.

But the new stu­dy, by three sci­en­tists at the Un­ivers­ity of Cal­i­for­nia, San­ta Cruz, pro­poses that neigh­bor­ing un­iverses might leave a vis­i­ble mark on our own—if, per­chance, they have knocked in­to it. For such a scar to be de­tect­a­ble, they add, the col­li­sion might have had to take place when our un­iverse was very young. Just how the bruise might look re­mains to be clar­i­fied, they say.

“The ques­tion of what the af­ter­math of a col­li­sion might be is still quite open,” wrote Mat­thew C. John­son, one of the re­search­ers, in an e­mail. One the­o­ry even holds that a clash be­tween un­iverses could de­stroy the cos­mos we know. But John­son, now at the Cal­i­for­nia In­sti­tute of Tech­nol­o­gy in Pas­a­de­na, Calif., and col­leagues are ex­am­in­ing quite a dif­fer­ent sort of sce­nar­i­o.

Sev­er­al lines of rea­son­ing in mod­ern phys­ics have led to pro­pos­als that there are oth­er un­iverses. It’s a rath­er dodgy con­cept on its face, be­cause strictly speak­ing, “the un­iverse” means ev­ery­thing that ex­ists. But in prac­tice, cos­mol­o­gists of­ten loos­en the def­i­ni­tion and just speak of “a un­iverse” as some sort of self-en­closed whole with its own phys­i­cal laws.

Such a pic­ture, in con­cept, al­lows for oth­er un­iverses with dif­fer­ent laws. These realms are of­ten called “bub­ble un­ivers­es” or “pock­et un­ivers­es”—partly to side­step the awk­ward def­i­ni­tional is­sue, and partly be­cause many the­o­rists do in­deed por­tray them as bub­ble-like.

A key thread of rea­son­ing be­hind the idea of bub­ble un­iverses, which are some­times col­lec­tively called a “mul­ti­verse,” is the find­ing that seem­ingly emp­ty space con­tains en­er­gy, known as vac­u­um en­er­gy. Some the­o­rize that un­der cer­tain cir­cum­stances this en­er­gy can be con­vert­ed in­to an ex­plo­sively grow­ing, new un­iverse—the same pro­cess be­lieved to have giv­en rise to ours. The­o­ret­i­cal phys­i­cists in­clud­ing Mi­chio Kaku of ­city Col­lege of New York ar­gue that this might go on con­stant­ly—he has called it a “con­tin­ual gen­e­sis”—cre­at­ing many un­iverses, coex­isting not un­like bub­bles in a foamy bath.

How might one de­tect anoth­er un­iverse? John­son and his col­leagues rea­son that any col­li­sion be­tween bub­bles would, like all col­li­sions, pro­duce af­ter­ef­fects that prop­a­gate in­to both cham­bers. These ef­fects would probably take the form of some ma­te­ri­al ejected in­to both sides, John­son said, al­though just what is un­known. This would in turn af­fect the dis­tri­bu­tion of mat­ter in each pock­et un­iverse.

If such col­li­sions hap­pened re­cent­ly, they might be un­de­tect­a­ble be­cause our un­iverse might be too huge to be markedly af­fected; but not so if the events took place long enough ago, ac­cord­ing to the Un­ivers­ity of Cal­i­for­nia team, whose pa­per is al­so posted on­line. If a knock oc­curred when our ex­pand­ing un­iverse was still very small, they ar­gue, then the af­ter­math might still be vis­i­ble, blown up in size along with ev­er­ything else since then.

When the un­iverse was less than a thou­sandth its pre­s­ent size, it’s thought to have un­der­gone a trans­forma­t­ion. As it ex­pand­ed, it be­came cool enough for atoms to form. It then al­so be­came trans­par­ent. Be­fore that, ev­er­ything had been a thick fog, but with ti­ny varia­t­ions in its dens­ity at dif­fer­ent points; dens­er parts would eventually grow and co­a­lesce in­to ga­lax­ies.

This fog is still vis­i­ble, be­cause many of the light waves it gave off are just now reach­ing us: this is how as­tro­no­mers ex­plain a faint glow that per­me­ates space, called the cos­mic mi­cro­wave back­ground. It repre­s­ents the edge of our vis­i­ble un­iverse and is de­tected in all di­rec­tions of the sky.

A col­li­sion would lead to a re­ar­ranged pat­tern of dens­ity fluctua­t­ions in this back­ground, ac­cord­ing to the Un­ivers­ity of Cal­i­for­nia team. It’s un­clear just how this re­ar­range­ment would look, but it would probably ap­pear as some sort of ar­ea of ir­reg­u­lar­ity cen­tered sym­met­ric­ally on a patch of the sky—s­ince “each col­li­sion will af­fect a disc on our sky,” John­son wrote in an e­mail. An anal­o­gy: if you lived in a beach ball and it bounced off anoth­er beach ball, you’d see a change in a cir­cu­lar ar­ea of your wall.

“Noth­ing like this has pre­s­ently been ob­served, al­though no one has ev­er looked for this par­tic­u­lar sig­nal,” John­son added.

On the oth­er hand, re­search­ers have found at least one strik­ing ir­reg­u­lar­ity in the back­ground glow—a “cold spot,” thought to be re­lat­ed to a vast and anom­a­lous void in the cos­mos. Could that be the mark of a sep­a­rate un­iverse? “I’m go­ing to re­main com­pletely non­com­mit­tal” on that, John­son said. “I can’t even tell you if it would be a hot spot or a cold spot.” Tem­per­a­ture varia­t­ions in the cos­mic mi­cro­wave back­ground are be­lieved to re­flect dens­ity varia­t­ions in the early un­iverse.

John­son and col­leagues stressed that their pro­pos­al may be only the be­gin­ning of a long, pains­tak­ing re­search pro­gram. “Con­nect­ing this pre­dic­tion to real ob­serva­t­ional sig­na­tures will en­tail both dif­fi­cult and com­pre­hen­sive fu­ture work (and probably no small meas­ure of good luck­),” they wrote. But “it ap­pears worth pur­su­ing.”

http://www.world-science.net

Thursday, January 24, 2008

Absence is the essence of desire


Va trebui sa va rog sa-mi scuzati indelungata absenta de pe propriul meu blog. Cum, necum, m-am luat cu treburi personale de tot soiul si timpul ramas n-a putu fi alocat de multa vreme acestui blog... promit insa ca situatia se va remedia cat de curand.


Intre timp, vizitati si blogul meu foto: http://setwhitebalance.blogspot.com