Single massive asteroid wiped out dinosaurs: study

[one...two...tree 2,762]

By Will Dunham, Reuters

A single, gigantic asteroid slammed into Earth 65 million years ago, dooming the dinosaurs and many other species, scientists said on Thursday in a new study rebutting theories that multiple impacts did the deed.

An examination of rock sediments drilled from five sites at the bottom of the Atlantic Ocean strongly supports the notion that one massive hunk of space rock caused the mass extinction, a research team led by University of Missouri-Columbia geology professor Ken MacLeod found.

"It's a completely straightforward, single-impact scenario," MacLeod, whose findings appear in the Geological Society of America Bulletin, said in an interview. "It was a haymaker that nobody saw coming. One shot, and that's all you need to explain it."

Scientists believe that an asteroid about 6 miles wide hurtled to Earth 65.5 million years ago at the end of the Cretaceous Period, plunging into what is now Mexico's Yucatan Peninsula to carve out the Chicxulub (pronounced CHIK-shu-loob) crater measuring about 110 miles across.

To put it mildly, it was a bad day to live on Earth.

The impact triggered a worldwide environmental catastrophe, many scientists believe, expelling vast quantities of rock and dust into the sky, unleashing giant tsunamis, sparking global wildfires and leaving Earth shrouded in darkness for years.

The dinosaurs, which had ruled for 160 million years, were wiped out. So were large marine reptiles like the mosasaurs and the plesiosaurs, the flying reptiles known as pterosaurs, the tentacled ammonites that populated the seas and many species of marine plankton. The birds suffered losses but survived.

The mammals made it through as well, allowing these warm-blooded, furry little creatures to eventually dominate the land and ultimately setting the stage for the rise of human beings.

EVIDENCE IN THE ROCK

Evidence of the single-asteroid calamity, in the form of debris from the impact scattered worldwide, is contained in rocks dating back to 65 million years ago.

Scientists 26 years ago found a band of iridium -- a metal rare on Earth but common in meteorites -- dating to the end of the Cretaceous Period that suggested a big space rock had smashed into the Earth and blasted its remains around the globe. The subsequent discovery of the Chicxulub crater, dating to the same time, was hailed by many as the smoking gun.

But a group of researchers led by Princeton University's Gerta Keller has advanced a competing theory that the impact that created the Chicxulub crater actually predated the end of the dinosaurs by 300,000 years and did not cause the mass extinction.

They propose that one or more additional big hunks of space rock later hit the Earth and finished the job, but the impact craters they would have left behind have not yet been found.

MacLeod's team examined sediment drilled far below the sea surface about 2,800 miles from the Yucatan impact site, a location they believed to be ideal. Any rock samples taken too close to the crater may be altered by events that occurred immediately after the impact, like waves, earthquakes and landslides. Samples taken too far away may contain too little debris evidence from the impact.

The samples they examined boasted a telltale layer of impact-related material, but there was none on top or below -- indicating, they argued, there were no other impacts.

Keller said MacLeod's research does not settle the matter.

"Unfortunately, these claims are rather hyper-inflated and do not withstand close examination," Keller said by e-mail.

[GaryC 7]

That has always seemed logical to me. I just can't figure out why only the dinosaurs died out and not the more fragile species didn't. How is it the frogs lived through it but now they are saying that global warming (a much less severe event) is killing them off? Why did alligators live through it and the aquatic dinosaurs died out? We are still missing something.

[one...two...tree 2,762]

That has always seemed logical to me. I just can't figure out why only the dinosaurs died out and not the more fragile species didn't. How is it the frogs lived through it but now they are saying that global warming (a much less severe event) is killing them off? Why did alligators live through it and the aquatic dinosaurs died out? We are still missing something.

Frogs are disappearing not because of Global Warming directly but because of habitat depletion and toxic pollutants.

Dr Stuart said it was now widely believed that chytridiomycosis played a pivotal role in the devastation, which took place in a dry period.

The disease is less of a problem in most parts of the world, including Europe, Asia and Africa, where habitat destruction, air and water pollution and consumer demand are causing the decline.

Bruce Young, a zoologist with the international conservation group NatureServe, said: "We need greater protection of natural areas and accelerated research on amphibian diseases to stem the extinction tide."

Scientists began noticing the disappearance of amphibians in the late 1980s and early 1990s, but before this study they had never conducted a worldwide assessment of the frogs, toads, salamanders and legless caecilians, also called rubber eels.

"We've never documented anything like this for any other species. When species become rare and begin disappearing we nearly always know why," Dr Stuart said. "This has taken the scientific world completely by surprise."

http://www.smh.com.au/articles/2004/10/15/1097784050839.html

[GaryC 7]

That has always seemed logical to me. I just can't figure out why only the dinosaurs died out and not the more fragile species didn't. How is it the frogs lived through it but now they are saying that global warming (a much less severe event) is killing them off? Why did alligators live through it and the aquatic dinosaurs died out? We are still missing something.

Frogs are disappearing not because of Global Warming directly but because of habitat depletion and toxic pollutants.

And the asteroid didn't destroy habitat and pollute their ecosystem? I hardly think that what we are doing is more severe than that.

[one...two...tree 2,762]

That has always seemed logical to me. I just can't figure out why only the dinosaurs died out and not the more fragile species didn't. How is it the frogs lived through it but now they are saying that global warming (a much less severe event) is killing them off? Why did alligators live through it and the aquatic dinosaurs died out? We are still missing something.

Frogs are disappearing not because of Global Warming directly but because of habitat depletion and toxic pollutants.

And the asteroid didn't destroy habitat and pollute their ecosystem? I hardly think that what we are doing is more severe than that.

Do you not believe that humans are capable of bringing a living species to extinction?

[GaryC 7]

That has always seemed logical to me. I just can't figure out why only the dinosaurs died out and not the more fragile species didn't. How is it the frogs lived through it but now they are saying that global warming (a much less severe event) is killing them off? Why did alligators live through it and the aquatic dinosaurs died out? We are still missing something.

Frogs are disappearing not because of Global Warming directly but because of habitat depletion and toxic pollutants.

And the asteroid didn't destroy habitat and pollute their ecosystem? I hardly think that what we are doing is more severe than that.

Do you not believe that humans are capable of bringing a living species to extinction?

Thats not the point. I was only wondering how a fragile animal like a frog survived the asteroid and yet they are (supposedly) going out from our actions. Do you think what humans are doing is worse that the asteroid?

[Mags 112]

I actually thought they had discounted this theory. The last I heard was that the food chains broke down enough so that there simply wasn't enough food to maintain the dinosaurs. The smaller animals survived because they ate different types of food. They are the ones that evolved into what we see today.

Quite simply, the dinosaurs' time passed. Live evolved on in other ways.

I really can't remember where I read this so don't question me about it too much...

[mRx 16]

I actually thought they had discounted this theory. The last I heard was that the food chains broke down enough so that there simply wasn't enough food to maintain the dinosaurs. The smaller animals survived because they ate different types of food. They are the ones that evolved into what we see today.

Quite simply, the dinosaurs' time passed. Live evolved on in other ways.

I really can't remember where I read this so don't question me about it too much...

no no mags, havent you seen Armageddon? Sir Jerry Bruckheimer doesnt lie. It was the asteroids!

[GaryC 7]

I actually thought they had discounted this theory. The last I heard was that the food chains broke down enough so that there simply wasn't enough food to maintain the dinosaurs. The smaller animals survived because they ate different types of food. They are the ones that evolved into what we see today.

Quite simply, the dinosaurs' time passed. Live evolved on in other ways.

I really can't remember where I read this so don't question me about it too much...

Mags I love your kitty pics. Are all those yours?

[one...two...tree 2,762]

That has always seemed logical to me. I just can't figure out why only the dinosaurs died out and not the more fragile species didn't. How is it the frogs lived through it but now they are saying that global warming (a much less severe event) is killing them off? Why did alligators live through it and the aquatic dinosaurs died out? We are still missing something.

Frogs are disappearing not because of Global Warming directly but because of habitat depletion and toxic pollutants.

And the asteroid didn't destroy habitat and pollute their ecosystem? I hardly think that what we are doing is more severe than that.

Do you not believe that humans are capable of bringing a living species to extinction?

Thats not the point. I was only wondering how a fragile animal like a frog survived the asteroid and yet they are (supposedly) going out from our actions. Do you think what humans are doing is worse that the asteroid?

I think that our attitude towards this planet should be of stewardship. That we should always find ways to do the least amount of harm to the environment because life is a complex eco-system and one consequence carries out into multiple consequences that can be devasting to life as we know it.

[Mags 112]

I think that our attitude towards this planet should be of stewardship. That we should always find ways to do the least amount of harm to the environment because life is a complex eco-system and one consequence carries out into multiple consequences that can be devasting to life as we know it.

I agree.

I actually thought they had discounted this theory. The last I heard was that the food chains broke down enough so that there simply wasn't enough food to maintain the dinosaurs. The smaller animals survived because they ate different types of food. They are the ones that evolved into what we see today.

Quite simply, the dinosaurs' time passed. Live evolved on in other ways.

I really can't remember where I read this so don't question me about it too much...

Mags I love your kitty pics. Are all those yours?

Nah, not my kittys. Although my two DO give me many opportunities for silly pics....