Dinosaur extinction

Yet it is not impossible to gather enough clues to find out what happened long ago. Just as paleobiologists—scientists who study ancient life—have theorized about a comet or asteroid impact causing the dinosaur extinction, archaeological chemists have studied artifacts to learn something about the life and death of Otzi, as well as the rise and fall of Roman civilization. 

The last globally catastrophic collision between Earth and an asteroid probably took place 65 million years ago at the end of the Cretaceous period. It now seems reasonably likely that the extinction of many species, including the great dinosaur extinction which occurred at the Cretaceous-Tertiary boundary, was caused by the impact of an asteroid approximately 6.2 mi (10 km) in diameter. The submerged remnants of the giant impact crater produced in this terminal Cretaceous collision were recently discovered on the coast of the Yucatan peninsula in Mexico. The crater, Chixulub (pronounced CHIKS-a-lub), is approximately 112 mi (180 km) in diameter and has long been buried under coastal sediments. 

Iridium may be a key element in the puzzle of dinosaur extinction. Scientists search for iridium in the soil to track the impact that a giant meteor had on Earth 65 million years ago. 

Iridium s Link to Dinosaur Extinction Iridium occurrences may hold the key to solving the mystery of why the dinosaurs went extinct. The question of what happened to the dinosaurs has long been one of the most interesting and puzzling issues in science. What happened to make these huge reptiles disappear in such a short period of geologic time ... 

How does the study of dinosaur extinction illustrate the scientific method ... 

In your opinion, is it justifiable to refer to the asteroid explanation as the theory of dinosaur extinction ... 

The Natural Reactor. Some two biUion years ago, uranium had a much higher (ca 3%) fraction of U than that of modem times (0.7%). There is a difference in half-hves of the two principal uranium isotopes, U having a half-life of 7.08 x 10 yr and U 4.43 x 10 yr. A natural reactor existed, long before the dinosaurs were extinct and before humans appeared on the earth, in the African state of Gabon, near Oklo. Conditions were favorable for a neutron chain reaction involving only uranium and water. Evidence that this process continued intermittently over thousands of years is provided by concentration measurements of fission products and plutonium isotopes. Usehil information about retention or migration of radioactive wastes can be gleaned from studies of this natural reactor and its products (12). 

Mesozoic Triassic 245 Myr Continents begin to drift apart. Early dinosaurs first mammals gymnosperms become dominant diversification of marine invertebrates. Moss extinction at end of period (ca. 75% of all species disappear)... 

Some have left behind them traces of elements rare on Earth, such as iridium. The detection of traces of iridium from a large meteorite has led to a proposal that major extinction of species on Earth, namely the dinosaurs, could be due to the meteorite impact, causing chemical, light and temperature fluctuations, i.e. global climate changes, though this proposal is not universally accepted. 

Figure 1.6 Impact frustration (a) the Chicxulub crater, seen as a three-dimensional gravity map, thought to be responsible for the extinction of the dinosaurs (b) the cratered surface of the Moon. (Reproduced from photos by courtesy of NASA)...

Impact frustration A process typified by the extinction of the dinosaurs where the Earth s surface may have been sterilised of all life forms by the impact of a large meteorite or comet... 

Impact frustration The collision of a large meteorite with a planet that results in the extinction of some or all species on the planet, causing the sterilisation of life. An example would be the extinction of the dinosaurs. 

We were not able to determine exactly the length of time associated with the deposition of the clay layer. Instead the laboratory studies on the chemical and physical nature of the Cretaceous-Tertiary boundary led to the theory that an asteroid collision with the earth was responsible for the extinction of many forms of life including the dinosaurs. 

The extinction of the dinosaurs had one enduring consequence for us mammals we took over as important players among the living organisms on Earth. While the dinosaurs reigned, the mammals were bit players on the stage of life. If dinosaurs had survived, mammals might have continued to be of minor importance on Earth. 

An interesting story as to how most of the iridium appeared on Earth was explained recently by scientists who discovered a thin layer of iridium in the sediments that were laid down in the Earth s crust at the end of the Cretaceous period. This was a period about 65 million years ago when meteors and asteroids crashed into the Earth. These extraterrestrial bodies contained a high percentage of iridium. Dust from the impact spread around the Earth and blocked the sun for months, resulting in the extinction of many plants and animals, including the dinosaurs. This extensive dust cloud also deposited a thin coat of the element iridium that was contained in the fiery bolides. 

The novel, and subsequent film, offered an exciting story, but one that is unlikely to ever become a reality. DNA degrades, even DNA deposited in locations with little chemical activity. For instance, although parts of Otzi s body were preserved for more than 5,000 years, researchers could not recover any nuclear DNA and foimd only bits and pieces of mitochondrial DNA. Since the dinosaurs became extinct about 65 million years ago, any hope of recovering enough dinosaur DNA to duplicate or reproduce these animals is imreaUstic. 

The end-Cretaceous mass mortality took place at a time, 65 My ago, that all major oceans were already in place, while India was still an island of the Indian Ocean. Perhaps caused by a great meteoric impact, this phenomenon brought extinction to the dinosaurs, leaving Earth fiiUy open to the expansion and diversification of mammals. 

Other large animals, such as the elephant and rhinoceros, have similar metabolic characteristics, as do diving mammals such as whales and seals. Dinosaurs and other huge, now-extinct animals probably had to depend on lactic acid fermentation to supply energy for muscular activity, followed by very long recovery periods during which they were vulnerable to attack by smaller predators better able to use oxygen and thus better adapted to continuous, sustained muscular activity. 

Ir anomalies. Currently, scientists are attempting to establish the order ol mass extinctions. Present opinions seem to suggest that the extinction of terrestrial lanna. including the dinosaurs, teas an csent that followed rather than occurring concurrently with the catastrophe met by many murine species. Sec also Chemical Elements, and Platinum and Platinum Group. 

Cenozoic Era A geologic time span that ranges from the extinction of the dinosaurs about 65 million years ago to the present. 

Iridium is a lesser-known transition metal, but it has become a famous clue in the mystery of how and why the dinosaurs became extinct 65 million years ago. There is an unusually large amount of iridium in rock layers all over the world that date to the time of the dinosaur die-off. In 1980, a team of scientists suggested that the iridium came from a huge meteorite that struck the Earth 65 million years ago, creating firestorms and throwing up a huge dust cloud all around the planet. Many other plants and animals disappeared at the same time as the dinosaurs, and so far the massive meteorite strike is one of the most convincing explanations for all these extinctions. 

About 250 million years ago, 90% of life on earth was destroyed in some sort of cataclysmic event. This event, which ended the Permian period and began the Triassic (the P-T boundary), is the most devastating mass extinction in the earth s history— far surpassing the catastrophe 65 million years ago that wiped out the dinosaurs (the K-T boundary). 

Yes. Of course this sort of calculations and the models which are applied here by Sagan and Toon were firstly developed for the dust storms on Mars. Low temperatures were discovered as soon as the dust started blowing. That was one point but they later applied it also for the extinction of dinosaurs. 

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