Paleonews

Il blog dedicato ai Paleontologi !!!!

2009-04-27 – Nuova teoria riguardo l`estinzione dei Dinosauri e l`impatto dell`asteroide (Dinosaur extinction and Asteroid impact: a new theory)

New Blow for Dinosaur-Killing Asteroid Theory

Impact didn’t lead to mass extinction 65 million years ago, geologists find

chicxulub-crater
This artist’s rendering shows the Chicxulub crater at the time of the meteorite’s impact.
Credit and Larger Version

April 27, 2009

The enduringly popular theory that the Chicxulub crater holds the clue to the demise of the dinosaurs, along with some 65 percent of all species 65 million years ago, is challenged in a paper to be published in the Journal of the Geological Society on April 27, 2009.

The crater, discovered in 1978 in northern Yucutan and measuring about 180 kilometers (112 miles) in diameter, records a massive extra-terrestrial impact.

When spherules from the impact were found just below the Cretaceous-Tertiary (K-T) boundary, it was quickly identified as the “smoking gun” responsible for the mass extinction event that took place 65 million years ago.

It was this event which saw the demise of dinosaurs, along with countless other plant and animal species.

However, a number of scientists have since disagreed with this interpretation.

The newest research, led by Gerta Keller of Princeton University in New Jersey, and Thierry Adatte of the University of Lausanne, Switzerland, uses evidence from Mexico to suggest that the Chicxulub impact predates the K-T boundary by as much as 300,000 years.

“Keller and colleagues continue to amass detailed stratigraphic information supporting new thinking about the Chicxulub impact, and the mass extinction at the end of the Cretaceous,” says H. Richard Lane, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research. “The two may not be linked after all.”

From El Penon and other localities in Mexico, says Keller, “we know that between four and nine meters of sediments were deposited at about two to three centimeters per thousand years after the impact. The mass extinction level can be seen in the sediments above this interval.”

Advocates of the Chicxulub impact theory suggest that the impact crater and the mass extinction event only appear far apart in the sedimentary record because of earthquake or tsunami disturbance that resulted from the impact of the asteroid.

“The problem with the tsunami interpretation,” says Keller, “is that this sandstone complex was not deposited over hours or days by a tsunami. Deposition occurred over a very long time period.”

The study found that the sediments separating the two events were characteristic of normal sedimentation, with burrows formed by creatures colonizing the ocean floor, erosion and transportation of sediments, and no evidence of structural disturbance.

The scientists also found evidence that the Chicxulub impact didn’t have the dramatic impact on species diversity that has been suggested.

At one site at El Penon, the researchers found 52 species present in sediments below the impact spherule layer, and counted all 52 still present in layers above the spherules.

We found that not a single species went extinct as a result of the Chicxulub impact,” says Keller.

This conclusion should not come as too great a surprise, she says. None of the other great mass extinctions are associated with an impact, and no other large craters are known to have caused a significant extinction event.

Keller suggests that the massive volcanic eruptions at the Deccan Traps in India may be responsible for the extinction, releasing huge amounts of dust and gases that could have blocked out sunlight and brought about a significant greenhouse effect.

-NSF-

Media Contacts
Cheryl Dybas, NSF (703) 292-7734 cdybas@nsf.gov

source: http://www.nsf.gov/news/news_summ.jsp?cntn_id=114648&org=NSF&from=news

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Dinosaur Demise Came 300000 Years After Crater, Scientists Say

Bloomberg – ‎9 ore fa‎
By Chantal Britt April 27 (Bloomberg) — The demise of the dinosaurs probably occurred 300000 years after a giant meteor struck what is now Mexico,
New Blow For Dinosaur-killing Asteroid Theory Science Daily (press release)
Annunci

aprile 27, 2009 Posted by | - R. Dinosauri, 1 Cretaceo, An. Vertebrates, Articolo sc. di riferimento, Mesozoic, P - Extinctions, Paleontology / Paleontologia | , , , , , , , , , , | Lascia un commento

2009-01-21 – Un estinzione rapida per i Dinosauri (Dinosaur speedy extinction ?)

 Un ritrovamento di una ricca fauna a dinosauri nel cretaceo terminale della Russia (Area sub-artica) sembra sconfessare il modello di estinzione lenta dei dinosauri.

——————————————————————————————————————————————-Published online 19 January 2009 | Nature | doi:10.1038/news.2009.40

News

Dinosaur fossils suggest speedy extinction

Arctic find challenges the idea that the massive reptiles declined slowly.

Fossils uncovered recently in the Arctic support the idea that dinosaurs died off rapidly — perhaps as the result of a massive meteor hitting Earth. The finding contravenes the idea that dinosaurs were already declining by this time.

Geological evidence indicates that an impact occurred near the Yucatán Peninsula at the end of the Cretaceous 66 million years ago. But whether the event created an all-out apocalypse that wiped out the dinosaurs is still a matter of debate. Despite many species dying out, many others survived, including mammals and the small feathered dinosaurs that were the ancestors of today’s birds.

Some palaeontologists suggest that non-avian dinosaurs were in decline before the impact — perhaps as a result of major volcanic events or global cooling.

Now, reporting in Naturwissenschaften1, Pascal Godefroit at the Royal Belgian Institute of Natural Sciences and his colleagues describe fossils found in northeastern Russia that suggest dinosaurs were not in decline at all. Although dinosaur fossils have already been found in the Arctic, the new find is unique because of its age: Godefroit and his team have dated the beds at between 68 million and 65 million years old — just before the time of the extinction.

“We found that there is no indication that the biodiversity of dinosaurs decreased just before the [extinction] event,” says Godefroit. The team found that herbivorous, duck-billed hadrosaurs and velociraptor-like bipedal theropods seem to be as common as they were in other parts of the planet at the time. Along with this discovery is the presence of the first dinosaur eggshells found in polar regions, hinting that the dinosaurs were residents rather than migrants.

Bang or whimper?

That such healthy polar populations existed just before the extinction would seem to strike a blow against the theory that the animals were already declining. But palaeontologists are cautious.

“The presence of these dinosaurs is certainly concordant with the idea of a sudden extinction, but not incontrovertible evidence for it,” says Tom Rich of Museum Victoria in Melbourne, Australia.

Robert Spicer of the Open University’s Earth sciences department in Milton Keynes, UK, suggests that when the dinosaurs died out, the site may have lain along the edge of the Arctic Circle rather than deep within it.

“The weak link here is the palaeoposition of the site,” he says. “With that said, such diversity even at this latitude suggests that dinosaurs were far more robust than we give them credit for. It makes me ask very serious questions about what could make animals that were resilient enough to live under these conditions suddenly go extinct.”

Attributing the extinction to any one cause is risky, adds Bill Clemens of the University of California, Berkeley. Work by David Wake, also at the University of California, Berkeley, and Vance Vredenburg of San Francisco State University2, suggests that the decline of modern amphibians involved a variety of factors ranging from the introduction of predators to disease and habitat loss, Clemens says.

“Ask what is endangering modern amphibians, the answer varies according to species,” he adds. “I think the same was probably true with the dinosaurs.”

  • References

    1. Godefroit P. et al. Naturwissenschaften advance online publication doi:10.1007/s00114-008-0499-0 (2009).
    2. Wake D. B.[/author] & [author]Vredenburg, V. T. Proc. Natl. Acad. Sci. USA 105, 11466-11473 (2008).

Source: http://www.nature.com/news/2009/090119/full/news.2009.40.html

gennaio 21, 2009 Posted by | - R. Dinosauri, 1 Cretaceo, Articolo sc. di riferimento, Europa, Italiano (riassunto), Mesozoic, P - Extinctions, P - Ritrovamenti fossili, Paleontology / Paleontologia, X - Riviste e Multimedia | , , , , , | Lascia un commento

2008-12-17 Contrasti sull’estinzione dei dinosauri (dinosaur extinction)

 

Paleontologia: USA; nuova tesi e nuovi scontri su dinosauri

 

20:50 16.12.2008

Il dibattito sulle cause dell’estinzione dei dinosauri torna ad animare la comunità scientifica, con una nuova tesi che fa discutere gli addetti ai lavori riuniti in California. Una team di ricerca guidato dalla paleontologa Gerta Keller dell’università di Princeton sostiene che la scomparsa dei giganteschi animali che dominavano la Terra è stata causata da una serie di eruzioni vulcaniche in India, circa 65,7 milioni di anni fa.

Secondo quanto riporta il San Francisco Chronicle, la teoria – presentata di fronte a 14.000 scienziati radunati al Moscone Center West di San Francisco -, avrebbe generato una querelle con quella che domina da una trentina d’anni, secondo la quale un meteorite precipitato in Messico avrebbe liberato dal suolo sostanze radioattive che avrebbero generato un “inverno nucleare” fatale per i dinosauri.

Keller sostiene che il cratere messicano (noto come cratere di Chicxulub) risalirebbe a 300.000 anni prima della scomparsa dei dinosauri e la caduta del meteorite sarebbe dunque indipendente dall’estinzione delle antiche specie. Una serie di quattro eruzioni sarebbero invece all’origine dell’evento epocale che ha portato i mammiferi ad affermarsi sulla Terra e Keller sostiene di avere prove convincenti a suo favore.

Il gruppo di ricerca (di cui fa parte anche un ricercatore francese e uno indiano) ha annunciato che nel corso della settimana inizierà ad illustrare le prove nel dettaglio.

Walter Alvarez, ricercatore dell’università di Berkeley e padre della teoria del meteorite, ha detto che l’argomento del vulcanismo è stato “esaminato e rifiutato da molti altri scienziati”. Alvarez non esclude che l’attività vulcanica possa avere “contribuito” all’estinzione dei dinosauri, ma non ha dubbi: “L’impatto di Chicxulub è stato il fattore scatenante dell’estinzione”.

(ats)

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Another dinosaur extinction theory offered

PRINCETON, N.J., Dec. 15 (UPI) — A U.S. geosciences professor says dinosaurs died gradually from climate change caused by volcanic eruptions in India and not because of a meteor strike.

 Gerta Keller of Princeton University admits her theory contradicts the long-held hypothesis that dinosaurs died due to climate change after a giant meteor hit the Yucatan region of Mexico.

Keller bases her theory on her National Science Foundation-funded field work in India and Mexico that uncovered geologic evidence that the mass extinction and the meteor impact occurred at different times.

“The Chicxulub impact hit the Yucatan about 300,000 years before the mass extinction that included the dinosaurs and, therefore, could not have caused it,” Keller said.

Keller and her team instead found the mass extinction coincided with the end of the main phase of India’s Deccan eruptions, suggesting volcanism killed the dinosaurs.

Keller and her colleagues will present their findings during the December 2009 American Geophysical Union meeting in San Francisco. The work will also be included in an upcoming History Channel feature “What Really Killed the Dinosaurs.”

Published: Dec. 15, 2008 at 2:17 PM

source: http://www.upi.com/Science_News/2008/12/15/Another_dinosaur_extinction_theory_offered/UPI-54221229368635/

dicembre 16, 2008 Posted by | - R. Dinosauri, P - Extinctions, Paleontology / Paleontologia | , , , | Lascia un commento

2008-12-01 – L’estinzione dell’Orso delle caverne (Ursus spelaeus)

Non gli uomini, ma il clima, il nemico dell’Orso delle caverne.

Spostata indietro di 13.000 anni l’estinzione del gigantesco orso preistorico.

Il sito web ARPAKIDS dell’ARPA Sicilia, pubblica periodicamente notizie inusuali sull’ambiente, la natura, gli animali, corredate da spunti e suggerimenti didattici: divulghiamo oggi la notizia e lo spunto di ricerca della settimana.

Nuove ricerche condotte dal Dipartimento di Paleontologia dell’Università di Vienna sembrerebbero finalmente assolvere gli uomini preistorici dall’accusa di aver causato l’estinzione del più grande orso mai vissuto sul Pianeta: l’Orso delle caverne (Ursus spelaeus). Il colpevole sarebbe stato invece il clima dell’Ultimo Massimo Glaciale, il periodo in cui, durante l’ultima glaciazione (glaciazione Würm, iniziata circa 120.000 anni fa e terminata da circa 12.000) si ebbe la massima espansione dei ghiacciai, con l’occupazione di tutta l’Europa settentrionale. Inoltre, vaste estensioni di territorio intorno ai ghiacciai erano permafrost, ovvero, terreno in cui la temperatura media è inferiore a 0°C per almeno due anni consecutivi. Le condizioni climatiche estreme del Massimo Glaciale durarono circa 2.000 anni e, tra ghiacciai e permafrost, la vegetazione, che costituiva la principale risorsa alimentare di molte specie, scomparve quasi del tutto. Nonostante quanto si possa credere, l’Orso delle caverne, un bestione che ritto sulle sue zampe poteva essere alto più di tre metri, e pesante almeno una tonnellata (il peso medio del Kodiak, il più grande orso contemporaneo, che vive in Alaska, è di circa 600 Kg.) era principalmente erbivoro e sarebbe stata questa sua abitudine alimentare a causarne l’estinzione. Fino ad oggi, si pensava che l’orso (qui ne vediamo una ricostruzione di fantasia e la foto di uno scheletro) fosse entrato in qualche modo in competizione con gli uomini preistorici: non solo perché occupavano anch’essi le caverne, ma perché si pensava che lo cacciassero e che questo, insieme ad altri fattori, avesse contribuito alla sua estinzione. A quanto pare, non sarebbe così. Secondo dati riportati da Boreas, la rivista internazionale di ricerche sul Quaternario, non esiste alcuna prova convincente della “colpevolezza” degli umani. Al contrario, esistono quelle della scomparsa delle fonti alimentari, la stessa causa che avrebbe causato l’estinzione del mammuth, dei cervi giganti, del rinoceronte lanoso e del leone delle caverne. Sempre stando alle ricerche paleontologiche, condotte con l’ausilio del carbonio radioattivo, l’Orso delle caverne avrebbe lasciato per sempre la Terra circa 28.000 anni fa, quasi tredicimila anni prima di quanto non si pensasse e proprio quando l’espansione di ghiacciai e di permafrost raggiunse il massimo. L’estinzione delle altre specie che abbiamo citato sarebbe avvenuta invece più tardi, iniziando intorno a 15.000 anni fa. In Italia, la presenza dell’Orso delle caverne era una cosa abbastanza comune. Sono numerose le grotte in cui sono stati ritrovati resti fossili, le più famose sono nell’Italia settentrionale (grotte di Toirano in Liguria e di Monte Fenera in Piemonte) e la più spettacolare è forse il Buco del piombo, vicino Erba, in Lombardia, un vero e proprio museo all’aperto che conserva le “storie” avvenute in migliaia di anni in quella regione.

Dunque, è ancora una volta il clima l’elemento con cui si debbono fare i conti finali. Certo, gli esseri umani non possono influenzare o impedire le glaciazioni che sicuramente verranno, ma poiché è ormai accertato che i cambiamenti causati dal riscaldamento globale costituiscono una minaccia per il futuro dell’umanità, dobbiamo cercare di impedire o almeno di rallentare il processo, fino a che non si trovino soluzioni per abbattere l’emissione dei cosiddetti “gas serra”.

fonte: http://www.parks.it/news/dettaglio.php?id=4454

dicembre 2, 2008 Posted by | - Mammiferi, 1 Olocene, An. Vertebrates, Cenozoic, Lang. - Italiano, Paleontology / Paleontologia | , , , | Lascia un commento

2008-10-22 – Vetlesen Prize al Prof. Walter Alvarez

Il celebre prof. Walter Alvarez (ora alla Univ. di Berkeley) è stato premiato con il Vetlesen Prize per le Scienze della Terra (una sorta di premio Nobel) con tanto di medaglia d’oro e assegno da 250 mila dollari.

La motivazione per la quale ha vinto: La sua teoria è stata importante perchè ha rivoluzionato l’idea che i maggiori cambiamenti nella storia della terra avvenissero lentamente e gradualmente.

La teoria come ben noto è quella secondo la quale l’estinzione K/T (Cretaceo/Terziario) sia stata determinata essenzialmente dalla caduta di un meteorite.

Comm.Pers. – Anche se attualmente si ritiene che la caduta del meteorite possa essere stata al massimo una concausa, come recita la motivazione del premio è innegabile che gli studi di Alvarez siano stati fondamentali nell’abbattere il gradualismo e indicare invece il catastrofismo quale principale causa delle variazioni nella storia della Terra e della vita sulla Terra.

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UC Berkeley Professor Awarded for Research on Dinosaur Extinction

Walter Alvarez

Walter Alvarez




In 1990, the team finally identified the Chicxulub crater in the Yucatan Peninsula as the site of impact. After the discovery, Alvarez said, most scientists accepted his theory as true and recognized the importance of large, dramatic events in Earth’s history.

G. Michael Purdy, the director of the observatory and chair of the award committee, said Alvarez’s theory was important because it revolutionized the idea that major changes on Earth take place slowly and gradually.

“The factor that was key (in the decision) was that his discovery-the Cretaceous-Tertiary boundary, the extermination of the dinosaurs-really changed the way everybody thinks about the evolution of the planet and the evolution of life,” he said.

Purdy said the Vetlesen Prize is as prestigious as the Nobel Prize, which does not have a category for earth sciences.

Instead of dinosaurs being gradually replaced by mammals, Alvarez’s theory states that a dramatic extraterrestrial impact wiped out much of Earth’s life in a short period of time. When he first published his theory in 1980, it was heavily criticized by gradualists.

“There were some people who thought it was a great idea, but there were lots of people that didn’t like it all,” Alvarez said. “Now you could say that geologists recognize that most things in the earth’s past happen gradually, but every now and then, there will be some sort of catastrophic event that changes everything.”

In 1977, Alvarez began working on his theory with a team that included his father, Nobel-winning physicist Luis Alvarez.

They discovered a layer of rock from the time of the extinction containing iridium, an element rare on Earth but common in asteroids and meteors. The team theorized that the iridium came from a massive extraterrestrial impact, but they lacked definitive evidence to support their claim.

“The problem was, if there had been a huge impact, then there also ought to be a huge crater,” Alvarez said. “But there was a period of 10 years where no one could find the crater.”

 

 

 

Alvarez said he now works in “Big Science,” which looks at the history of cosmos, earth, life and humanity.

“If you’re trying to understand all of history, it’s really interesting to know about gradual changes in the history of life and catastrophic ones,” he said. “To me, right now the most interesting thing about the extinction work is trying to tie it into a much broader understanding of all of history.”

Alvarez’s friend and former colleague, integrative biology professor Kevin Padian, said the value of his work also lies in its ability to open new avenues of research.

“(Alvarez) has been tremendously influential in the field. This award recognizes the stimulation of essentially 30 years of research in extraterrestrial influences on Earth’s history,” Padian said. “Research like his really comes along only a few times in a century.”

Tags: GEOLOGY

Rachel Gross covers research and ideas. Contact her at rgross@dailycal.org.

source: http://www.dailycal.org/article/103212/uc_berkeley_professor_awarded_for_research_on_dino

Other links:

http://www.berkeley.edu/news/media/releases/2008/10/20_alvarez.shtml

ottobre 22, 2008 Posted by | G - Prizes / Premi, Geology - Geologia, Italiano (riassunto), P - Extinctions, Paleontology / Paleontologia | , , , , , , , , , , | Lascia un commento