Asteroid found guilty of killing dinosaurs!!
in Earth and Space Science, Life Science, and Biological Populations Change Over Time
What sent the dinosaurs packing?: The number one suspect, a gigantic asteroid, has finally been convicted of the crime.
Courtesy Mark RyanAfter 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.
Courtesy Mark RyanThey 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
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Georges Cuvier
Courtesy Public domain via Wikipedia Commons
Born August 23, 1769, naturalist Georges Cuvier was one of the most influential scientists of the late 18th and early 19th centuries, and helped establish the fields of comparative anatomy and vertebrate paleontology. One of his most important contributions to science was establishing that species extinction was a fact. You can read more about him here. Cuvier died in 1832.
Extinction could be a family affair
in Life Science, Diversity of Organisms, and Biological Populations Change Over Time
Extinction: It may run in the family.
Courtesy Mark RyanExtinction is a fact of life. Species rise up, consume energy, reproduce, radiate to fill their range, and die off. It happens all the time. In fact, nearly 99% of all creatures that have ever lived on Earth have gone extinct. That’s just the way it is. Sometimes the cause for extinction is minor – a subtle change in the environment such as increased competition for a food source or the introduction of a harmful contaminate or virus. Other times it can be more heavy-handed, like when a giant asteroid hurls in from outer space and slams into the planet sending the biosphere into a tizzy, and wiping out entire faunas. Either way it sucks big time.
But now there may be a third, more insidious reason. Extinction could be built into the genes of some unfortunate creatures, and according to the new study, it may be get passed on as an ancestral species branches out into new ones. Meaning extinction is a family affair.
The research team, composed of Kaustuv Roy of the University of California, Gene Hunt from the Smithsonian Institute, and David Jablonski of the University of Chicago, studied a whole gamut of extinction patterns in shelled marine animals such as clams, mussels and scallops. Their paper, which appeared recently in the journal Science, suggests that propensity for extinctions could be passed on through the whole groups of species that share common ancestors.
"Biologists have long suspected that the evolutionary history of species and lineages play a big role in determining their vulnerability to extinction, with some branches of the tree of life being more extinction-prone than others," said Roy, a biology professor at UC San Diego.
"Background extinctions" are the normal extinction rates that occur between major extinction events (e. g. killer asteroids), and usually don’t include those caused by human activity. (I don’t see why not – are we not part of Nature?) Anyway, when the team analyzed ‘background rates” from the Jurassic to the present they were struck by how some of the marine species with the highest rate of extinction during those “normal” times were also the most vulnerable (along with their close relatives) during major extinction events.
"Big extinctions have a filtering effect. They tend to preferentially cull the more vulnerable lineages, leaving the resistant ones to proliferate afterwards," Hunt said.
This means extinction isn't as random as we’d like to think, and actually tends to affect entire genera not just species within them. These clustered extinctions chop off larger branches from the family tree and cut deeper into the lineage history.
"Now we know that such differential loss is not restricted to extinctions driven by us but is a general feature of the extinction process itself," Roy said.
The study, according to evolutionary biologist Charles Marshall of Harvard University, shows how fossils are an important record of evolution’s workings.
"Only by analyzing the past do we get a direct sense of the rules by which evolution has worked and will continue to work,” he said.
LINKS
Dinosaur-killing asteroid may be off the hook
Killer asteroid?: Artist conception of impact event
Courtesy NASAThe old “What really killed the dinosaurs” controversy is back in the news. And once again, it’s Princeton geophysicist Gerta Keller stirring up the pot.
Death from above?: Perhaps not.
Courtesy Mark RyanKeller and her colleague Thierry Adatte of the University of Lausanne in Switzerland have published yet another paper challenging the prevailing theory that an asteroid was the major cause of the extinction of the dinosaurs at the end of the Cretaceous Period 65 million years ago. The extinction affected over 60 percent of animal species including all of the non-avian dinosaurs.
Actually a number of events were occurring around the end of the Cretaceous including long-term volcanic activity, rapid marine regression, and the infamous asteroid impact. There’s also evidence that some of the dinosaur population was already in decline 10 million years prior to the events. But the scenario is usually played out with the meteor coming late in the sequence and delivering the deathblow to an already weakened eco-system, and paving the way for mammals to take over the ecological gap.
K-T boundary layer: The Cretaceous-Tertiary boundary layer located near Trinidad, Colorado. The pale-gray 1-inch iridium layer (arrow) is sandwiched between coal layers and contains shocked quartz and other evidence of a large asteroid impact. The scale bar is 6 inches in length.
Courtesy Mark RyanThe asteroid impact hypothesis was first proposed in 1980 by Luis Alvarez of the University of California after he and his son Walter discovered a claystone layer rich in the rare-earth element iridium and peppered with shocked quartz in many locations around the world. Iridium is a rare-earth element not commonly found on the Earth’s surface but abundant in meteorites. Shocked quartz was first noticed in sand grains in craters created by nuclear test bombs and later in meteor impact sites. Alvarez hypothesized that the only other possible source for this naturally deposited strata would be from a large extraterrestrial object hitting the Earth. From studying the amount of iridium found in Cretaceous-Tertiary (K-T) boundary formations, he calculated that a bolide about 6 miles across would have been necessary to create that much iridium around the world. But at the time evidence of such an was unknown. It wasn’t until after Luis Alvarez’s death in 1988 that a crater on the Yucatan Peninsula near Chicxulub Mexico became the chief suspect. The Chicxulub impact crater was the right size and the right age fitting all the criteria of a Cretaceous extinction event.
But Keller claims the asteroid came too early to put the coup de grace on dinosaurs or any species for that matter. Her study of spherules in strata at localities in Mexico has convinced her that the asteroid collided with Earth 300,000 years before any mass extinction.
At El Penon, a location very near the impact crater site, Keller and Adatte studied a 30-ft layer of sandstone above the iridium layer that they calculated had been laid down at a rate of about 1-inch per thousand years. This means it took 300,000 years to pile up the entire section of sediment.
Fossils were analyzed on either side of the iridium layer and the researchers found that of 52 species counted below the iridium layer (meaning before the impact), the same 52 species were found above it, meaning the asteroid hadn’t caused any extinction. But at the top of the 30 feet of sandstone overlaying the iridium claystone things were different.
"The mass extinction level can be seen above this interval," Keller says. "Not a single species went extinct as a result of the Chicxulub impact."
The more likely culprit, according to Keller, is India’s Deccan Traps flood basalts which for several million years poured out tremendous amounts of lava and noxious fumes into the atmosphere that would have had put long and tremendous stress on the existing ecosystem. Keller seems to roll out a paper on the subject every year or so in the last decade. We covered some of her Deccan Traps research 2007 which you can read here.
Whatever the case we do know is that non-avian dinosaurs left the planet after the Cretaceous, as none of their fossils have been found above the K-T Boundary. Well, even that doesn’t appear to be the case anymore. Recent dinosaur fossils found in the San Juan Basin in northwestern New Mexico are suspected to come from a stratum that post-dates the Cretaceous extinction. More research needs to be done on the find, but even this wouldn’t be unexpected. Even after the host declares the party’s over, there are always some stragglers who just don’t want to leave.
Keller's paper was published this week in the Journal of the Geological Society.
MORE LINKS
ScienceDaily story
What Killed the Dinosaurs?
Gerta Keller's Chicxulub Debate
Dinosaur Killer May Have Been Volcanism
We post plenty of stories here on the Buzz telling the sad stories of impending, or completed, animal extinctions. Here's a great story on how over the past 50 years, Minnesota's surplus bear population has helped bring back Arkansas's nearly extinct bear population back from the brink. No word on what, if any, role Bill Clinton played in this effort.
After being hunted nearly to extinction a century ago, the North Atlantic right whale is starting to make a comeback. Though still critically endangered, it's population has tripled in recent years, and this year has already shattered the record for live births.
Man vs. mammoth: Is a face-off like this in our future...again?
Courtesy redskunkScientists are another step closer to making Jurassic Park a reality. Well, not quite Jurassic Park, but certainly Pleistocene Park.
Researchers at Pennsylvania State University have decoded 80 percent of the DNA for the woolly mammoth, an elephant ancestor that went extinct about 10,000 years ago. The results of their study appear in the journal Nature.
The DNA was extracted from actual mammoth hair found preserved in the permafrost of Siberia. Hair encapsulates DNA, providing a purer source of the genetic material than that found in fossil bones that are vulnerable to contamination by bacteria and other creatures involved in decomposition. We covered this in a previous post.
About six million years of evolution separate the wooly mammoth from its modern descendents the Indian and African elephants. And so far they appear genetically to be very similar, although a complete assessment of differences won’t be available until the complete genomes of mammoths and modern elephants are mapped. The data sets for each is comprised of about 4 billion DNA bases.
But even then you don’t have to worry about rogue mammoths running amok on the interstates (have you ever hit a moose? Multiply that experience by about 15). Science is still decades away from cloning an actual specimen – or even a hybrid with a living elephant - from the genetic material. The technology just isn’t there yet. But that’s not the only thing in the way.
"It could be done,” said co-author Stephan Schuster, a biochemistry professor at Penn State. “The question is, just because we might be able to do it one day, should we do it?"
Sounds familiar doesn’t it? The same question was posed by one of the characters in Michael Crichton's book Jurassic Park just before things got really hairy.
SOURCES and LINKS
Penn State's mammoth research page
Live Science story
Previous Buzz story on mammoth cloning
Contrary to previous reports, the Chinese river dolphin may not yet be extinct. A man claims to have videotaped an animal which may be a member of this critically endangered species.
A Permian anteosaurus: He feels vaguely nervous, and oddly sweaty. (image courtesy of Wikipedia Commons)65 million years ago something very sad happened. Well, it was sad for the dinosaurs, because they all died, but great for us mammals. Here – I’ve written a little play about it:
Scene 1
Dinosaur 1: Hey, have you noticed that there seem to be a lot less of us these days?
Dinosaur 2: What? I don’t know. Why?
Dinosaur 1: Probably just my imagination. Forget about it.
Dinosaur 2: …
Dinosaur 1: Hey, what’s that thing up there?
Dinosaur 2: We call it the sun.
Dinosaur 1: No, that thing – it’s getting bigger, I think.
Dinosaur 2: Oh, not to change the subject, but did you watch Entourage last nigh*
Scene 2
(fiery, dusty chaos)
Scene 3
Rodent-like mammal: Yes!
The End
Anyway, the extinction at the end of the Mesozoic (dinosaur times) was a big deal. But, dramatic as it likely was, it was nothing compared to the extinction at the beginning of the Mesozoic.
Before the dinosaurs existed, the world was ruled by a different kind of animal, the therapsids, or “mammal-like reptiles.” These ranged from little rat like guys to huge fanged and clawed lion-like creatures. About 250 million years ago, though, at the end of the Permian period, there was an extinction event way bigger than the one that would eventually kill all the dinosaurs.
The Permian extinction killed off 90% of all the life on the planet, both on land and in the oceans. Life as we know it just squeaked by complete annihilation. The thing is, scientists still aren’t sure exactly what initiated the extinction. Whatever it was, it caused massive amounts of carbon dioxide, and other greenhouse gases to be released into the atmosphere. The earth would have gotten warmer and warmer, the oceans would have become acidic, and by the time things got back to normal, almost every species on the planet had died out.
Jonathan Payne, a paleobiologist at Stanford, is investigating one of the possible causes of the extinction – a massive volcanic eruption occurring at the end of the Permian. This eruption was the larger than any other that has happened in the last 600 million years, and it spread a four-mile thick sheet of basalt the size of the continental US over Asia. Along with the poisonous gases spewed by the volcano itself, it is believed that the spreading magma may have heated the coal-rich strata near the eruption and released vast amounts of carbon dioxide into the atmosphere. Then, you know, the whole horrible global warming and acidic oceans thing.
Fortunately, for all our CO2 production, we aren’t yet in the Permian extinction league of global warming gases. Still, Payne is comparing contemporary signs of global warming to those leading up to the Permian event. For example, under increasing environmental stresses, coral colonies tend to bleach (as algae leaves the reefs). Researchers will be examining fossilized coral colonies from the end of the Permian to see how they reacted to the changing environment. "We hope to reconcile the short-term processes we observe operating in the modern world with the very long time scales seen in the geologic record," says a researcher in Payne’s lab. If the analogy works, we could better understand the processes of past environmental change, as well as the potential future effects of the environmental changes that are occurring today.
My own theory regarding the Permian extinction largely focuses on the refusal of therapsis to carpool, and their insistence on driving larger vehicles than they really needed (cyconodonts were notorious SUV lovers). Unfortunately, this is extremely difficult to verify in the fossil record. I chalk this up to the poor preservation of pre-Triassic GM products, or, possibly, to the fact that therapsids had adapted to finding (and then losing) well concealed parking spots (they were, after all, much more primitive than us).
Enjoy the photograph: photo by Benchilada on flickr.comAfter an “intensive survey of its natural habitat,” the Yangtze River dolphin has been officially declared extinct. So if, as a person, you ever wanted to see one alive, you’re out of luck. And if, as a Yangtze River dolphin, you ever wanted to be alive, also, you’re out of luck.
From a population of thousands in the 1950s, human activity reduced the Yangtze River, or Baiji, dolphin to just a handful of individuals by the turn of the century. Industrialization of the Yangtze River, unsustainable fishing practices, and mass shipping, rather than direct human persecution, placed the Baiji dolphins under extreme pressure, and now they’re all dead, forever. An article in The Guardian states that this is “the fourth time an entire evolutionary line of mammals has vanished from the face of the Earth since the year 1500.” Quite an achievement.
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