Como desapareceram os dinossauros?
- Iniciador de tópicos Nthor
- Data de início
ja não devemos ca tar para ver isso, mas acredito que um dia isto vai tudo acabar, basta ver que sem o meteorito ja temos grandes variaçoes de temperaturas
zerorpm
New member
Extinction theories
Main article: Cretaceous-Tertiary extinction event
The sudden mass extinction of non-avian dinosaurs, an event that occurred approximately 65 million years ago, is one of the most intriguing mysteries in paleontology. Many other groups of animals also became extinct at this time, including ammonites (nautilus-like mollusks), mosasaurs, plesiosaurs, pterosaurs, herbivorous turtles and crocodiles, most birds, and many groups of mammals.[54] The nature of the event that caused this mass extinction has been extensively studied since the 1970s; at present, several related theories are supported by paleontologists. Though the general consensus is that an impact event was the primary cause of dinosaur extinction, some scientists cite other possible causes, or support the idea that a confluence of several factors was responsible for the sudden disappearance of dinosaurs from the fossil record.
Asteroid collision
The Chicxulub Crater at the tip of the Yucatán Peninsula, the impact of which may have caused the dinosaur extinction.
The asteroid collision theory, which was first proposed by Walter Alvarez in the late 1970s, links the extinction event at the end of the Cretaceous period to a bolide impact approximately 65.5 million years ago. Alvarez proposed that a sudden increase in iridium levels, recorded around the world in the period's rock stratum, was direct evidence of the impact. The bulk of the evidence now suggests that a 5–15 km wide bolide hit in the vicinity of the Yucatán Peninsula, creating the 170 km-wide Chicxulub Crater and triggering the mass extinction. Scientists are not certain whether dinosaurs were thriving or declining before the impact event. Some scientists propose that the meteorite caused a long and unnatural drop in Earth's atmospheric temperature, while others claim that it would have instead created an unusual heat wave.
Although the speed of extinction cannot be deduced from the fossil record alone, various models suggest that the extinction was extremely rapid. The consensus among scientists who support this theory is that the impact caused extinctions both directly (by heat from the meteorite impact) and also indirectly (via a worldwide cooling brought about when matter ejected from the impact crater reflected thermal radiation from the sun).
Multiple collisions—the Oort cloud
While similar to Alvarez's impact theory (which involved a single asteroid or comet), this theory proposes that a stream of comets was dislodged from the Oort cloud due to the gravitational disruption caused by a passing star. One or more of these objects then collided with the Earth at approximately the same time, causing the worldwide extinction. As with the impact of a single asteroid, the end result of this comet bombardment would have been a sudden drop in global temperatures, followed by a protracted cool period.[55]
Environment changes
At the peak of the dinosaur era, there were no polar ice caps, and sea levels are estimated to have been from 100 to 250 metres (330 to 820 feet) higher than they are today. The planet's temperature was also much more uniform, with only 25 degrees Celsius separating average polar temperatures from those at the equator. On average, atmospheric temperatures were also much warmer; the poles, for example, were 50 °C warmer than today.[56][57]
The atmosphere's composition during the dinosaur era was vastly different as well. Carbon dioxide levels were up to 12 times higher than today's levels, and oxygen formed 32 to 35% of the atmosphere, as compared to 21% today. However, by the late Cretaceous, the environment was changing dramatically. Volcanic activity was decreasing, which led to a cooling trend as levels of atmospheric carbon dioxide dropped. Oxygen levels in the atmosphere also started to fluctuate and would ultimately fall considerably. Some scientists hypothesize that climate change, combined with lower oxygen levels, might have led directly to the demise of many species. If the dinosaurs had respiratory systems similar to those commonly found in modern birds, it may have been particularly difficult for them to cope with reduced respiratory efficiency, given the enormous oxygen demands of their very large bodies.[54]
Main article: Cretaceous-Tertiary extinction event
The sudden mass extinction of non-avian dinosaurs, an event that occurred approximately 65 million years ago, is one of the most intriguing mysteries in paleontology. Many other groups of animals also became extinct at this time, including ammonites (nautilus-like mollusks), mosasaurs, plesiosaurs, pterosaurs, herbivorous turtles and crocodiles, most birds, and many groups of mammals.[54] The nature of the event that caused this mass extinction has been extensively studied since the 1970s; at present, several related theories are supported by paleontologists. Though the general consensus is that an impact event was the primary cause of dinosaur extinction, some scientists cite other possible causes, or support the idea that a confluence of several factors was responsible for the sudden disappearance of dinosaurs from the fossil record.
Asteroid collision
The Chicxulub Crater at the tip of the Yucatán Peninsula, the impact of which may have caused the dinosaur extinction.
The asteroid collision theory, which was first proposed by Walter Alvarez in the late 1970s, links the extinction event at the end of the Cretaceous period to a bolide impact approximately 65.5 million years ago. Alvarez proposed that a sudden increase in iridium levels, recorded around the world in the period's rock stratum, was direct evidence of the impact. The bulk of the evidence now suggests that a 5–15 km wide bolide hit in the vicinity of the Yucatán Peninsula, creating the 170 km-wide Chicxulub Crater and triggering the mass extinction. Scientists are not certain whether dinosaurs were thriving or declining before the impact event. Some scientists propose that the meteorite caused a long and unnatural drop in Earth's atmospheric temperature, while others claim that it would have instead created an unusual heat wave.
Although the speed of extinction cannot be deduced from the fossil record alone, various models suggest that the extinction was extremely rapid. The consensus among scientists who support this theory is that the impact caused extinctions both directly (by heat from the meteorite impact) and also indirectly (via a worldwide cooling brought about when matter ejected from the impact crater reflected thermal radiation from the sun).
Multiple collisions—the Oort cloud
While similar to Alvarez's impact theory (which involved a single asteroid or comet), this theory proposes that a stream of comets was dislodged from the Oort cloud due to the gravitational disruption caused by a passing star. One or more of these objects then collided with the Earth at approximately the same time, causing the worldwide extinction. As with the impact of a single asteroid, the end result of this comet bombardment would have been a sudden drop in global temperatures, followed by a protracted cool period.[55]
Environment changes
At the peak of the dinosaur era, there were no polar ice caps, and sea levels are estimated to have been from 100 to 250 metres (330 to 820 feet) higher than they are today. The planet's temperature was also much more uniform, with only 25 degrees Celsius separating average polar temperatures from those at the equator. On average, atmospheric temperatures were also much warmer; the poles, for example, were 50 °C warmer than today.[56][57]
The atmosphere's composition during the dinosaur era was vastly different as well. Carbon dioxide levels were up to 12 times higher than today's levels, and oxygen formed 32 to 35% of the atmosphere, as compared to 21% today. However, by the late Cretaceous, the environment was changing dramatically. Volcanic activity was decreasing, which led to a cooling trend as levels of atmospheric carbon dioxide dropped. Oxygen levels in the atmosphere also started to fluctuate and would ultimately fall considerably. Some scientists hypothesize that climate change, combined with lower oxygen levels, might have led directly to the demise of many species. If the dinosaurs had respiratory systems similar to those commonly found in modern birds, it may have been particularly difficult for them to cope with reduced respiratory efficiency, given the enormous oxygen demands of their very large bodies.[54]
RPalma
New member
Caro Nthor, com as ferramentas que este novo formato do fórum nos oferece não há necessidade de fechar tópicos por este motivo.
Os posts foram apagados mas os nomes dos membros cuja "veia humorística" sobressaiu continuam lá.
Agradeço a esses membros que usem a sua "veia humorística" nos tópicos próprios, evitando "estragar" tópicos que até podem ter algum interesse para ou outros users deste forum.
Cumps,
RP
Os posts foram apagados mas os nomes dos membros cuja "veia humorística" sobressaiu continuam lá.
Agradeço a esses membros que usem a sua "veia humorística" nos tópicos próprios, evitando "estragar" tópicos que até podem ter algum interesse para ou outros users deste forum.
Cumps,
RP
PauloOliveira
New member
Tenho a ideia que todos concordam que se terá tratado de um extinction-level event (ELE).
E não ouve só um... mas 5 documentados.
(quick search no google)
http://en.wikipedia.org/wiki/Extinction_event
E não ouve só um... mas 5 documentados.
(quick search no google)
http://en.wikipedia.org/wiki/Extinction_event
Nthor
Banido
Os meus agradecimentos ao moderador pelo restabelecimento da ordem no tópico e as minhas desculpas por um julgamento tão precipitado da minha parte sobre o trabalho da moderação.
.
Nthor
Banido
Não obrigado [
].A intenção é mesmo "trazer a baila" este assunto e estimular o espírito critico, pela partilha de conhecimentos de quem mais sabe, para quem, como eu, só tem uma luzes sobre este tema.
CarlosPinto
Banido
Karma
New member
Há pessoal que leva isto demasiado a sério. [
] Respondendo ao tópico:
Aquilo que eu sei sobre o tema está no google.
http://www.google.com/search?hl=en&q=dinosaurs+extinction+theories&btnG=Search
Obtuso
Well-known member
Há pessoal que leva isto demasiado a sério. [
Respondendo ao tópico:
Aquilo que eu sei sobre o tema está no google.
http://www.google.com/search?hl=en&q=dinosaurs+extinction+theories&btnG=Search
De facto.[
] Quanto ao assunto do tópico não há certezas de nada. Existem sim provas circunstânciais que apontam para os efeitos do impacto do tal meteorito.
Para qualquer acontecimento são formuladas várias teorias assentes em vários factos. O que acontece é que uma teoria que seja mais coerente e válida, leva a um maior número de apoiantes (cientistas, investigadores, comunidade académica, etc) sendo a "oficialmente" aceite.
manucas
New member
Alguns dizem que foi a alteração da temperatura do globo terrestre, outros dizem que foi de uma era glaciar, outros, das alterações da alimentação. Que eles desapareceram é um facto. Tb sei que a PJ já está no terreno e já andou a vasculhar as casas vizinhas ao local desaparecimento e inclusive estar a usar cães pisteiros...
Obtuso
Well-known member
Deve ter sido um moderador da altura...[
] Agora a minha contribuição para o tópico:
Os dinossauros não foram extintos. Foram é dizimados maioritariamente, sobrevivendo poucos ou quase nenhuns.
Um exemplo disso é a actual galinha, que pela análise da sua evolução terá tido como antecessor um dinossauro.
PauloFVF
New member
Deve ter sido um moderador da altura...[
Agora a minha contribuição para o tópico:
Os dinossauros não foram extintos. Foram é dizimados maioritariamente, sobrevivendo poucos ou quase nenhuns.
Um exemplo disso é a actual galinha, que pela análise da sua evolução terá tido como antecessor um dinossauro.
[
] excesso de zelo......
sendo assim, o topico da primavera, e os posteriores do mesmo cariz deveriam ser extintos também.....
já agora todos nós non-sense idem![
] epá.....isto hoje em dia é a caça á multa, ao bolso, ao post, ao grelo....tamos lixados
(joking foi bem feito)
segundo as palavras de um ..........seborreias gramatical
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A extinção K-T ou evento K-T foi uma extinção em massa, ocorrida há mais ou menos 65,5 milhões de anos, que marca o fim doperiodo cretaceo, e o início do períodoTerciário(T). Este evento teve um enorme impacto na biodiversidad da Terra e vitimou boa parte dosseres vivos da época, incluindo os dinaussauros e outros repteis gigantes. O registro estratigráfico mostra que o desaparecimento abrupto das espécies que foram extintas coincide com um nivel estatigráfico , denominado nível K-T, rico em ridiio, umum elemento quimico pouco abundante na Terra[1] e geralmente associado a corpos extraterrestres. Diversas teorias tentam explicar a extinção K-T, sendo que a mais aceita atualmente é a que justifica a catástrofe como sendo resultado da colisão de um asteroidecom a Terra.
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