The most widely accepted theory is that a meteorite/asteroid plummeted through the atmosphere and caused such a large explosion (which rivals that of a nuclear explosion) that the shock wave was too toxic/hot that it killed pretty much all living creatures on the planet. The dinosaurs had evolved so well for their environment that the huge change caused too much variance for them to survive. Only those that were slightly evolved but not entirely (mammals for example) could handle with the variance.

People killed them. Check out this video by Dr. Kent Hovind. I suggest downloading Google Video player and downloading the video to your PC. Better quality. Remember this is just a theory. OH! and be patient, he doesn't get right into his dino speech right away.

Here are five theories: Probably the most popular theory right now is the Asteroid Theory. According to this theory a large asteroid or comet collided with Earth about 65 million years ago. Scientists think that such a large collision would throw so much dust into the air that sunlight would not be able to shine and plants and animals would die. The dramatic changes in climate that resulted from this huge collision were too much for the dinosaurs. They were not able to survive. Another theory that could explain how the dinosaurs became extinct is volcanic activity. A huge increase in volcanic activity at around 65 millions years ago could have pumped so much ash into the air that it blocked out the sun killing the dinosaurs. Some scientists believe that there was a severe ice age. Throughout Earth's history there have been many ice ages. The last one ended about 10,000 years ago. A very severe ice age could have changed temperatures and frozen a lot of Earth's water. The dinosaurs would not be able live under such conditions and that is how the dinosaurs became extinct. It has also been suggested that desease killed off the dinosaurs. A very deadly and contagious desease may have circulated among the dinosaurs forcing them to become extinct. Still yet another theory is that the Earth just gradually changed in climate over a long time period and the dinosaurs were not able to adapt to the cooler, dryer climate.

AH, now this is not based on evidence or anything like that, but I have my own crackpot theory. Tiny midgets ate the dinosaurs. It's a shame, but meh

The owners rounded them up and took them away to be placed somewhere close by. The fossils are just dead dinosaurs living life. The live one are gone.

they just witherd away and died. they ate something that didn't agree with them and it killed them.

My theorie is that there was a worldwide flood came and killed all animals and mankind but those that were on the Ark. I know many of you may not agree with this, but I am a Christian and this is what I believe.

I think Gary Larson was right They became extinct by smoking unfiltered cigarrettes. Its possible that the unballanced crust of the Earth may have spun a time or two on its molten core and I have absolutely no evidence to support either theory!

Do you mean why did the dinosaurs disappear? If so they didn't, they evolved. The meteor theory holds no water as many species had died out beforehand (they were on the decline for 10 million years before the K/T boundary). They either died out through natural selection or evolved into something else. Birds in all likelihood. :)

They could not adapt to the changing life conditions on earth. There are several webpages devoted to this subject. I quote from one (http://web.ukonline.co.uk/a.buckley/dino.htm): "The two main 'serious' theories are the asteroid and volcano theories, both of which make some use of the analysis of the rocks in and around the K-T boundary (the Cretaceous - Tertiary boundary). The use of K comes from the Greek word for chalk (Kreta) which is found in great quantities in the rocks of the Cretaceous. (...) In the late 1970's Luis and Walter Alvarez (father and son) along with a team of scientists from the University of California were making a study of the rocks around the K-T boundary in Gubbio, Italy. In particular they were looking at an unusual layer of clay at the boundary point which contained an unusual spike in the amounts of the rare element iridium. This spike revealed that the levels of iridium contained in the clay were roughly 30 times the normal levels. (...) From these figures it can be seen that iridium is an extremely rare element, so it's discovery in 'large' amounts indicates that something serious happened. There are 2 sources of iridium, the main source comes from outer space in the form of cosmic dust which is constantly showering the planet. A second source is the Earth's core when there are eruptions of certain types of volcano. It is believed that the iridium, plus many other rare elements, were carried down and concentrated in to the Earth's core while the Earth was still largely molten. During this time certain types of primitive chondritic meteorites were formed where no concentration could have taken place due to rapid cooling. This means that it is possible that within the primitive chondritic meteorites there could be reasonable levels of iridium. From this information it can be seen that there are only two possible theories to explain the increased presence of iridium in the clay layer either an asteroid strike or a massive volcanic eruption. (...) Of the two more serious theories perhaps the most well supported theory is concerned with the impact of a large asteroid type body. It is a well-known fact that throughout the history of the planet there have been many thousands of impacts some large and some small. The results of these impacts can have a wide variation. Two recent (in geological time) events show these differences in results very well. (...) The first people to suggest the asteroid theory were the team lead by Luis and Walter Alvarez. It has been calculated that a chondritic asteroid approximately 10km in diameter would contain enough iridium to account for the iridium spike contained in the clay layer. Since the original discovery of the iridium spike other evidence has come to light to support the asteroid theory. Analysis of the clay layer has revealed the presence of soot within the layer. It is thought that the presence of the soot comes from the very large global fires that would have been the result of the large temperatures caused by an impact. Something else that was found within the clay were quartz crystals that had been physically altered. This alteration only occurs under conditions of extreme temperature and pressure and quartz of this type is known as shocked quartz. Despite all of this evidence many geologists did not believe in this theory and many were saying 'show us the crater'. (...) In 1990 a scientist called Alan Hildebrand was looking over some old geophysical data that had been recorded by a group of geophysicists searching for oil in the Yucatan region of Mexico. Within the data he found evidence of what could have been an impact site. What he 'found' was a ring structure 180km in diameter which was called Chicxulub. The location of this structure was just off the northwest tip of the Yucatan Peninsula. The crater has been dated (using the 40Ar/39Ar method) as being 65 million years old. The size of the crater is comparable to that which would have been caused by an impacting body with a diameter of roughly 10km.So we now have some of the proof of the asteroid theory. We know that a chondritic meteorite with a diameter of 10km contains enough iridium to cause a spike. We also know that about 65 million years ago there was an impact of a large object. The big question is what were the results, and how did they effect the dinosaurs. If a 10km diameter object impacted at the point at which it struck it would have a velocity of roughly 100,000 km/h. At this velocity there would have been an initial blast (with an estimated force of many millions of tons of TNT) which would have destroyed everything within a radius of between 400 and 500km, including the object. At the same time large fires would have been started by the intense shock wave which would have traveled long distances. Trillions of tons of debris (dust, gases and water vapour) would have been thrown into the atmosphere when the object vaporized. Many enormous tidal waves would be started causing even more damage, the evidence of such waves has been found all the way round the Gulf of Mexico. Along with the tidal waves the blast would also start a chain reaction of earthquakes and volcanic activity there would have also been very high winds caused by the blast. In the days and weeks following the impact the cloud of debris would have been carried over large distances by the post blast high winds. This will have caused months of darkness and a decrease in global temperatures. After this there would have been an increase in temperatures caused by the large amounts of CO2 released by what would have been global fires. Eventually this would cause chemical reactions that would result in the formation of acid rains. (...) On the land the effects of the impact on the flora and fauna would have been devastating, especially on the large animals which would need large food supplies and on the dinosaurs which would need sun light to keep warm. The global fires would have destroyed considerable amounts of vegetation (by the analysis of the soot in the K-T boundary it is estimated that 25% of the vegetation cover was destroyed), the immediate effect of this would have resulted in the death of the large herbivores. A knock on effect of this would have killed off the large carnivores. Only the small active scavengers, like birds and mammals with the ability to find food from a wide range of sources would have survived. Analysis of the K-T boundary fossils shows that there was a short term takeover of the land by the hardy ferns, which moved into the areas were there had been fires. In the sea the effects would have been just as dramatic. There would have been a decrease in the oxygen levels in the seawater as low oxygen deep seawater would have been brought up by massive under water currents. This would have resulted in a massive disturbance of the marine food chain through the death of much of the plankton. This would have resulted in the eventual death of the marine reptiles which would have relied on the food chain. There would also have been a massive death rate amongst the shelled sea animals like the ammonites. There could also have been a serious increase in the acidity of the seas caused by the acid rains. This may have also killed off some of the sea species. The period of recovery would have seen the surviving species moving into the ecological niches left vacant by the dead species. After a short period of time some of the plants that had been burnt down would have regrown from buried seeds or rootstock. As is common with all mass extinctions there would have a sudden evolutionary burst as new species developed. The age of the mammals was beginning."

Why is this question in "Infant Sleeping Issues?"

Theories abound, but the most common is that an asteroid struck the earth, causing a huge change in climate and available food.

Wiped out by one big Jurrasic Fart.

Depends who you ask. A popular theory is the asteroid collision but there are big problems with this one. Few dispute an impact (or even a couple) occured but the impact (excuse the pun) of this is very uncertain. There are issues like the famous "frog problem". Another theory is the Deccan traps eruptions causing profound long term climate change. And not all dinosaurs (or other creatures) died out. Some became birds. It was probably a combination of factors. The impact(s) may have been one factor but doesn't explain everything.

Chuck Norris told them to die, so they did.

There are at least 55 different theories have been suggested. These are only a few; • Climate change. • Meteorite. • Volcanic eruption. • Other dinosaurs stilling eggs. • Disease. • A big flood

The size of the dinosaurs, and most prehistoric animals from then were all bigger than anything today, including insects, at the exception of aquatic life. Science shows that things like lizards and insects cannot be this sisely and live in today's environments, because the gravitational pull would crush them. Whereas, the gravity level must have been different back then, if they could survive. So, I think something hit the Earth really bad and knocked it off its axis, unto the one that it finds itself on now. I wonder though, if it was knocked within or without its axis. I can't just base "without" on the fact that it was always hot and humid, therefore logically closer to the sun...because the Earth was young then, and a lot of volcanoes were active. Still, I think this is what killed dinosaurs, and ushered in an ice age due to disrupting the weather so abruptly, which served to wipe everything else out. After adaptation, life started again, but there's where it makes no sense to me anymore, if we believe the evolution of animals, like how feathers were originally scales. I don't get how the evolution could have continued if all life had really been instinct, unless it wasn't everything, except the dinosaurs...I don't know lol. But something along those lines.

I suspect volcanic activity, which blocked out the sun & cooled the earth, which led to an ice age. Then when it warmed up the ice melted and flooded the earth. Anything that managed to survive was in the oceans. What I really want to know is how the dinosaurs were created in the first place (where did they come from?) and why they were so big? At the size they were the earth's resources would have eventually not been able to supprt them ...since they were egg-layers and laid many eggs at once.

"There have been several theories on the cause of the K-T boundary which led to the massive extinction. These theories have centered on either impact events or increased volcanism; some include elements of both. A scenario combining three major postulated causes: volcanism, marine regression, and extraterrestrial impact has been proposed. In this scenario, terrestrial and marine communities were stressed by the changes in and loss of habitats. Dinosaurs, as the largest vertebrates, were the first to be affected by environmental changes, and their diversity declined. At the same time, particulate materials from volcanism cooled and dried areas of the globe. Then, an impact event occurred, causing collapses in photosynthesis-based food chains, both in the already-stressed terrestrial food chains and in the marine food chains. The major difference between this hypothesis and the single-cause hypotheses is that its proponents view the suggested single causes as either not sufficient in strength to cause the extinctions or not likely to produce the taxonomic pattern of the extinction." Source and further information: http://en.wikipedia.org/wiki/Dinosaur_extinction#Causes_of_extinctions (well, not really *my* theories, but they should be right...)

They were just sick and tired of being typecast as stupid maneaters.

They were scared of the Obama administration.

They didnt pay the heating bill.

They evolved into birds we see today.

They wanted to be appreciated more.

It is my theory a cosmic collision tilted the Earth giving it the seasons we now know and expelled debris into the Earth's atmosphere for over a year. Both cooling the Earth to such a degree the earlier plant life became unsustainable.. the basis for not only their food chain but also the very oxygen they needed to breath.

Nicotine addiction....;-D... . . .

So they could let me & you & every human being walk this earth & so the dinosaurs would not stomp us like bugs.

cause they all died out millions of years ago due to a meteor and cold weather. there may have been other factors

What's a dinosuar?

barney caused them to committ suicide

They couldn't fit in Noah's Ark

They evolved prescience.

Because of the Noanic flood. Before 1845, there was no word as dinosaur. In the Bible they are said to be behemoth. There is considerable proof humans and behemoths existed together on the earth.