Stories tagged dinosaur extinction

Dec
06
2013

Victim of mass extinction: Will current species suffer a similar fate due to current environmental trends?
Victim of mass extinction: Will current species suffer a similar fate due to current environmental trends?Courtesy Mark Ryan
A new and troubling paper from the Committee on Understanding and Monitoring Abrupt Climate Change and its Impacts predicts possible and somewhat grim outcomes for some of Earth's natural systems from climate change that could rival the extinction event of the non-avian dinosaurs at the end of the Cretaceous Period 65 million years ago.

The abrupt impact could be coming faster than previously expected and would negatively affect human and physical climate systems as well. The document warns that the abruptness of the changes could be unanticipated and could find us unprepared to deal with them

Records of past climate preserved in tree rings, ice cores, and ocean sediments show that the atmosphere contains higher levels of carbon dioxide than it has in a very long time. Carbon emissions from human activity continue to add to this rising concentration. Other activities including deforestation and resource extraction place additional environmental pressures on our climate and other natural systems.

At the end of the Cretaceous, all species of non-avian dinosaurs, along with the megafauna of flying and swimming reptiles were wiped off the face of the Earth. Many dinosaur species showed signs of decline even before the Chicxlub asteroid delivered the final kibosh on their existence.

Dr. James W.C. White, a professor of Geological Sciences and of Environmental Studies at the University of Colorado at Boulder chaired the committee which included more than a dozen earth scientists and ocean researchers from universities in both Canada and the United States, and from the National Academy of Science.

A prepublication copy of the entire 201-page paper is available to read without charge on the National Academies Press page. You can also download it for free although it was a little tricky getting it to my computer.

SOURCE
MinnPost story

Mar
06
2010

What sent the dinosaurs packing?: The number one suspect, a gigantic asteroid, has finally been convicted of the crime.
What sent the dinosaurs packing?: The number one suspect, a gigantic asteroid, has finally been convicted of the crime.Courtesy Mark Ryan
After studying all available evidence and listening to alternative theories (and despite no eyewitnesses), a panel of 45 international scientists has decided it was a huge asteroid that killed all the non-avian dinosaurs some 65 million years ago.

The asteroid, described as a 7 mile-in-diameter chunk of space rock, has been the prime suspect in the ruling reptile’s demise ever since scientists Luis Alvarez and his son Walter first identified a one-inch layer of iridium in Late Cretaceous-age rock exposures throughout the world. The layer was located exactly at the point in the rock record where the Cretaceous period ended, and the Tertiary period began (K-T boundary). Smoking gun for dinosaurs' demise: K-T Boundary with 1-inch iridium layer (arrow) exposed 10 miles west of Trinidad, Colorado. The element iridium is very rare on Earth but concentrated in meteors and comets. The same iridium layer is found in several exposures around the world, and corresponds in age with the Chicxulub meteor crater in Mexico's Yucatan Peninsula. The layer marks the end of the Cretaceous era, and no non-avian dinosaur remains have ever been found above the boundary. The coal layers above and below the iridium suggests a swampy environment when the layer was laid down in this area of Colorado.
Smoking gun for dinosaurs' demise: K-T Boundary with 1-inch iridium layer (arrow) exposed 10 miles west of Trinidad, Colorado. The element iridium is very rare on Earth but concentrated in meteors and comets. The same iridium layer is found in several exposures around the world, and corresponds in age with the Chicxulub meteor crater in Mexico's Yucatan Peninsula. The layer marks the end of the Cretaceous era, and no non-avian dinosaur remains have ever been found above the boundary. The coal layers above and below the iridium suggests a swampy environment when the layer was laid down in this area of Colorado.Courtesy Mark Ryan
They predicted a meteor impact crater of the same age would be found as the source of the iridium since the element is rare on Earth but common in outer space. Then in 1990 their predictions were verified when the Chicxulub impact crater was discovered in Mexico.

Although the impact site was mostly submerged off the north coast of the Yucatan Peninsula, samples taken from it dated to the end of the Cretaceous period. This and other corroborating evidence helped bolster the killer asteroid hypothesis as the primary theory for the extinction event that wiped out 70-75 percent of life on Earth including non-avian dinosaurs, and other large reptiles. The asteroid is estimated to have slammed into Earth traveling 10 times faster than a rifle bullet, and released the energy of a billion atomic bombs. The impact instantly vaporized a large area of terrain, and sent an explosion of dust and rocky debris up into space, much of which fell back into the atmosphere in a fiery rain. It left a crater 110 miles across, and a cloud of dust circling the planet for weeks. The diminished sunlight would have disrupted the environment severely, including the food chain. Mammals and other smaller creatures were able to survive across the boundary and flourish in later periods.

But not everyone was convinced by the evidence. Other causes for the mass extinction, such as extreme volcanism in India, falling sea levels, disease epidemics, and even fungal infection were all tossed around as possible culprits.

But in the end it seems the evidence implicating the asteroid in the K-T* extinction event was just too strong, and after much deliberation, the impact has been determined as the official cause of death. The panel published its decision in the latest issue of Science.

*“K-T” stands for Cretaceous-Tertiary, however, use of the term Tertiary is being discouraged now, and the time span it occupied has been replaced with the Paleogene and Neogene periods. So a more proper, up-to-date term would be Cretaceous-Paleogene or K-Pg extinction event.

LINKS AND SOURCES
More about dinosaur extinction
BBC story
Impact theory counterview

Dec
19
2007

Extreme volcanism may have put the kibosh on the Mesozoic: Unaware of their impending doom, dinosaur contemporaries frolic in the Late Cretaceous sea.
Extreme volcanism may have put the kibosh on the Mesozoic: Unaware of their impending doom, dinosaur contemporaries frolic in the Late Cretaceous sea.Courtesy Mark Ryan
The mass-extinction that signaled the end of the Cretaceous period, as well as the Age of Dinosaurs has long been blamed on an Earth-shaking collision with an asteroid that struck 65 million years ago near Chicxulub on Mexico’s Yucatan peninsula. Some scientists however have long argued that extreme episodes of volcanism around the same time played a significant if not major role in the event.

Now, a Princeton University paleontologist claims that evidence in the fossil record adds weight to the latter argument saying the volcanic activity that poured out massive amounts of toxic gases and the expansive flood basalts in India’s Deccan Traps may have been the real villain in the Mesozoic era’s demise.

In a recent presentation at the Geological Society of America, Gerta Keller explained that microfossils known as foraminifera show steep decline nearly half a million years before the Chicxulub asteroid event happened, and just when the Deccan event was beginning.

The volcanoes poured huge amounts of toxic gasses into the atmosphere, and flooded something like 600,000 square miles of south-central India with lava flows. To give you an idea of the magnitude of the outpouring, when Mount St. Helens erupted in 1980, the volcano unleashed a cubic kilometer of volcanic material. And the eruption of Mount Vesuvius that buried the city of Pompeii nineteen hundred years earlier had poured out something like 8 cubic kilometers. But the Deccan event is estimated to have produced 512,000 cubic kilometers!! Yikes!

Just prior to the end of the Cretaceous period, the Deccan eruptions would have released massive plumes of carbon dioxide and sulfur dioxide into the atmosphere – possibly ten times more toxic gases than generated by a meteor impact, according to one volcanologist. At any rate, it set off extreme global warming and acid rain, and significantly weakened the biosphere. When the asteroid arrived a half-million years later, the environment would have been ripe for collapse. Nearly thirty years ago, physicist Luis Alvarez and his geologist son, Walter, discovered the crater at Chicxulub, and claimed that asteroid that created it could be the one responsible for the dinosaurs’ demise. But Keller thinks it may have been a case of being in the wrong place at the wrong time.

"The Chicxulub impact could not have caused the mass extinction," she said, "because this impact predates the mass extinction and apparently didn't cause any extinctions."

Keller studied the sediments directly above and below the Chicxulub impact layer, in Mexico, Texas, and India, expecting to find evidence of a new bloom of plankton to fill the void left by a mass extinction. Instead, she found no significant change in the micro-marine environment.

"We cannot attribute any specific extinctions to this impact,” she said. But where she did find evidence of a new bloom was in strata that had been laid down 300,000 years after Chicxulub and just about the time when the output of the Deccan volcanoes would have been at its greatest.

In India, near the Bay of Bengal, about 1000 kilometers from the Deccan lava fields, Keller discovered two lava “traps” each with four lava layers. The telltale bloom of microfossils was found in nine meters of marine sediment located just above the lower trap, which marks the Deccan event’s climax.
"We've shown convincingly the mass extinction came about 300,000 years after the asteroid impact,” she said.

But what about the famous iridium layer found in the K-T boundary? If the Chicxulub impact didn’t produce it, then where did it come from?

Keller thinks a second asteroid impact – not the Chicxulub one- may have been responsible for laying down the worldwide iridium layer that divides the Cretaceous and Tertiary rock layers. Direct evidence of this later impact (such as a crater) has not yet been found.

But to add fuel to the fire –pun definitely intended- it may be that the iridium source isn’t even extraterrestrial at all. Volcanism could be another possible source of increased iridium in the rock layer. The Deccan eruptions were peaking right at the time of the dinosaurs’ demise and maybe that’s all that was needed to send them on their way into extinction.

At any rate, the case against the dinosaurs’ killer or killers is certainly not closed.

LINKS
Story at ScienceDaily
The Chicxulub debate on Gerta Keller's site
More on the Deccan Traps
More on the Deccan Traps Extinction Theory
The Cretaceous Extinction Event