Why dinosaurs died out

The challenge of explaining this huge loss of biological diversity has been the province of geologists and palaeontologists. Their expertise in dating rocks and in reconstructing the characteristics of these long-gone life forms, from fossil bone and tooth fragments, is a remarkable achievement of scientific observation and analysis. Nevertheless, there has not been unanimous agreement in interpretations amongst these expert investigators.

Because, from the vantage point of the present, the extinction of such a vast range of species seemed to have suddenly occurred, the concept has been proposed that some catastrophic environmental change is a unifying hypothesis to explain their disappearance.

Some investigators, on the other hand, suggest that the time frame of the process of extinction from a biological viewpoint was very long and that the various species had declined in number over many generations. The conflict between catastrophism and gradualism to describe the process of extinction has been debated extensively during the second half of the 20th century.

The case for a catastrophic cause of mass extinction was strengthened by the discovery of a worldwide enrichment of the rare element iridium in a narrow band of geological strata formed 66 Mya , 1. The source of that iridium was proposed to be from a huge asteroid or comet that collided with the Earth, coinciding with the time of the mass extinctions , 2 — 4. The discovery of the Chicxulub impact crater in the Yucatan Peninsula on the Gulf of Mexico confirmed, from its size and structure, that a large celestial object had collided with the Earth at the time that the mass extinctions had occurred , 5.

The consequences of that impact would indeed have been catastrophic, not just in the geographic region around the impact site, but worldwide because of environmental changes from an atmospheric dust and aerosol cloud that would have remained for years in the stratosphere , 2. Those who favour a gradual decline towards extinction of all species of the dinosaur family, except the ancestors of modern birds, have some plausible arguments.

The dating of fossils of all known dinosaur species is incomplete and is only well established for a range of dinosaurs in North America. It has been argued that long-term environmental changes had diminished the number of species over millions of years before the asteroid or comet impact, particularly the large-bodied Saurischian and Ornithischian dinosaurs , 6. Careful review of fossil records of both classes of dinosaurs has indicated that the number of species was in decline over millions of years.

Thus the family Dinosauria would have been susceptible to extinction by a range of environmental changes to which they could not adapt , 7. Nevertheless, others have concluded that there is little evidence for a gradual decline worldwide in the diversity of dinosaur species, in contrast to that in North America, over the long term before the fossil record indicated that all non-avian dinosaurs had become extinct , 8. Although the debate between the gradualists and the catastrophists appears to be still unresolved, both groups of palaeontologists do agree that the dating of dinosaur fossils ended in the era of the Chicxulub impact event.

Even if the diversity of dinosaur species had been in decline, the gradualists do acknowledge that the worldwide environmental changes caused by that impact could have led to their final extinction. Clearly the effect of the asteroid or comet collision would have been devastating to all life forms in a wide geographical region around the impact site.

The proposed environmental changes that would have occurred worldwide include a period of dim sunlight because of solar radiation absorption by ejected particles and aerosols in the atmosphere and stratosphere.

Consequently, there would have been a short-term temperature drop , 9 , which, together with diminished sunlight, would have inhibited or killed photosynthetic plants. However, perhaps a more significant effect, as far as the dinosaurs were concerned, was a consequence of the geological site of impact.

A result of the asteroid impact would have been the ejection into the stratosphere of particulate carbon soot, CO 2 and sulfate aerosols , This would have had a marked cooling effect on the climate from the absorption of much solar radiation. Because such geological sites that are rich in sulfur and carbon deposits are not plentiful, it has been suggested that if the asteroid impact had occurred in most other regions of the world, the probability of mass extinctions would have been much less , Conclusions about the biological effects of the Chicxulub impact have focused on the undoubted environmental changes of temperature, light intensity, sea temperatures, sea levels and climate disruption in the months and probably years following the impact.

The implications of these changes are that a consequent restricted food supply for many life forms that disappeared would have contributed to their extinction. One result of the asteroid collision with Earth, that has not been considered from a biological perspective, is a particular effect from the ejection into the stratosphere of the sulfur aerosols.

There are various calculations of the amount of sulfur, as sulfate or SO 2 , based on estimates of the size of the impacting asteroid and the density of sulfur deposits at the impact site. One estimate is that — gigatonnes of SO 2 were distributed globally in the stratosphere , Another, in broad agreement, put the quantity of stratospheric SO 2 in the range of — gigatonnes , The effect of such quantities of SO 2 on global climate can be deduced from observations on the changes from sulfur ejected into the upper atmosphere from volcanic eruptions , Yet in the following 12 months, this relatively small amount, compared with that from the Chicxulub impact, had a noticeable cooling effect on the world climate , An alternative environmental catastrophe postulated as the cause of dinosaur extinctions is a series of vast volcanic eruptions in India which created the Deccan basalt larval floods, known as the Deccan Traps.

It has been argued that the timing of this volcanism is more likely to have been associated with the demise of the dinosaurs than the Chicxulub impact event , Nevertheless, geological evidence puts the timing of the Deccan volcanism and the asteroid collision so close together that it has been suggested that the Chicxulub impact actually triggered the largest of the volcanic eruptions which gave rise to the Deccan Traps , Although volcanic activity in general has not been considered to produce stratospheric sulfate aerosols in the quantities anywhere near that of the Chicxulub impact, the Deccan volcanism may have been an exception.

Denisovans are an extinct species of hominid and a close relative to modern humans. Denisovans may have ranged from Siberia to Southeast Asia during The Neolithic Revolution, also called the Agricultural Revolution, marked the transition in human history from small, nomadic bands of hunter-gatherers to larger, agricultural settlements and early civilization. The Neolithic Revolution started around 10, B.

Researchers believe that if the 9-mile wide asteroid had made impact less than a minute before or after it did, it likely would have crashed into the much deeper Atlantic or Pacific oceans, and not in the Gulf of Mexico, where shallower waters resulted in a massive, dense cloud The Stone Age marks a period of prehistory in which humans used primitive stone tools.

Lasting roughly 2. During the Stone Live TV. This Day In History. History Vault. Many Theories, No Proof Dinosaurs roamed the earth for million years until their sudden demise some Recommended for you. Why Did the Dinosaurs Die Out? Unearthing Dinosaurs. Dinosaurs The prehistoric reptiles known as dinosaurs arose during the Middle to Late Triassic Period of the Mesozoic Era, some million years ago.

Neanderthals Neanderthals are an extinct species of hominids that were the closest relatives to modern human beings. Ice Age An ice age is a period of colder global temperatures and recurring glacial expansion capable of lasting hundreds of millions of years. In , Nobel Prize-winning physicist Luis Walter Alvarez and his geologist son Walter published a theory that a historic layer of iridium-rich clay was caused by a large asteroid colliding with Earth.

The instantaneous devastation in the immediate vicinity and the widespread secondary effects of an asteroid impact were considered to be why the dinosaurs died out so suddenly. Luis Walter Alvarez left and his son Walter right are known for their theory that an asteroid collided with our planet 66 million years ago and caused all non-bird dinosaurs and many other animals to die out.

Asteroids are large, rocky bodies that orbit the Sun. They range from a few to hundreds of metres in diameter. Any fragment of an asteroid that survives landing on Earth becomes known as a meteorite.

The Alvarez hypothesis was initially controversial, but it is now the most widely accepted theory for the mass extinction at the end of the Mesozoic Era. Paul says, 'An asteroid impact is supported by really good evidence because we've identified the crater. It's now largely buried on the seafloor off the coast of Mexico. It is exactly the same age as the extinction of the non-bird dinosaurs, which can be tracked in the rock record all around the world.

The asteroid is thought to have been between 10 and 15 kilometres wide, but the velocity of its collision caused the creation of a much larger crater, kilometres in diameter - the second-largest crater on the planet. Iridium is one of the rarest metals found on Earth. It is usually associated with extraterrestrial impacts, as the element occurs more abundantly in meteorites. The dinosaur-killing crash threw huge amounts of debris into the air and caused massive tidal waves to wash over parts of the American continents.

There is also evidence of substantial fires from that point in history. But Paul explains, 'The dating of those layers of clay around the world is very accurate - it's estimated to within a couple of thousands of years. So how was it all caused by a rock hurtling into the coast of Central America? Paul explains, 'The asteroid hit at high velocity and effectively vaporised. It made a huge crater, so in the immediate area there was total devastation.

A huge blast wave and heatwave went out and it threw vast amounts of material up into the atmosphere. It didn't completely block out the Sun, but it reduced the amount of light that reached the Earth's surface.

So it had an impact on plant growth. Like dominos, this trailed up the food chain, causing the ecosystem to collapse. The reduction in plant life had a huge impact on herbivores' ability to survive, which in turn meant that carnivores would also have suffered from having less food available. Breeding seasons would have been shorter and conditions harsher.

All living things would have been affected in some way, both on land and in the ocean. He peered at it, his eyes inches from the rock, probing it with the tip of the bayonet. He planned to remove the entire burrow intact, in a block, and run it through a CT scanner back home, to see what it contained. The days of skulduggery in paleontology have not passed; DePalma was deeply concerned that the site would be expropriated by a major museum.

DePalma knew that a screwup with this site would probably end his career, and that his status in the field was so uncertain that he needed to fortify the find against potential criticism. He had already experienced harsh judgment when, in , he published a paper on a new species of dinosaur called a Dakotaraptor , and mistakenly inserted a fossil turtle bone in the reconstruction.

For five years, DePalma continued excavations at the site. He quietly shared his findings with a half-dozen luminaries in the field of KT studies, including Walter Alvarez, and enlisted their help.

DePalma had carved out a space for himself in a corner, just large enough for him to work on one or two jacketed fossils at a time.

When I first visited the lab, in April, , a block of stone three feet long by eighteen inches wide lay on a table under bright lights and a large magnifying lens. The block, DePalma said, contained a sturgeon and a paddlefish, along with dozens of smaller fossils and a single small, perfect crater with a tektite in it. The lower parts of the block consisted of debris, fragments of bone, and loose tektites that had been dislodged and caught up in the turbulence.

The block told the story of the impact in microcosm. One fish was impaled on the other. The mouth of the paddlefish was agape, and jammed into its gill rakers were microtektites—sucked in by the fish as it tried to breathe. Gradually, DePalma was piecing together a potential picture of the disaster. The water arrived not as a curling wave but as a powerful, roiling rise, packed with disoriented fish and plant and animal debris, which, DePalma hypothesized, were laid down as the water slowed and receded.

In the lab, DePalma showed me magnified cross-sections of the sediment. Most of its layers were horizontal, but a few formed curlicues or flamelike patterns called truncated flame structures, which were caused by a combination of weight from above and mini-surges in the incoming water.

DePalma found five sets of these patterns. He turned back to the block on his table and held a magnifying lens up to the tektite. Parallel, streaming lines were visible on its surface—Schlieren lines, formed by two types of molten glass swirling together as the blobs arced through the atmosphere.

Peering through the lens, DePalma picked away at the block with a dental probe. He soon exposed a section of pink, pearlescent shell, which had been pushed up against the sturgeon. Ammonites were marine mollusks that somewhat resemble the present-day nautilus, although they were more closely related to squid and octopi. As DePalma uncovered more of the shell, I watched its vibrant color fade. He stood up. He unwrapped a sixteen-inch fossil feather, and held it in his palms like a piece of Lalique glass.

When I encountered this damn thing, I immediately understood the importance of it. And now look at this. He pointed to a series of regular bumps on the bone. Now watch. Trapped inside were two impact particles—another landmark discovery, because the amber would have preserved their chemical composition. All other tektites found from the impact, exposed to the elements for millions of years, have chemically changed.

The bone was big for a Cretaceous mammal—three inches long—and almost complete, with a tooth. He believes that the jaw belonged to a marsupial that looked like a weasel.

The rest of the mammal remains in the burrow, to be researched later. At the bottom of the deposit, in a mixture of heavy gravel and tektites, DePalma identified the broken teeth and bones, including hatchling remains, of almost every dinosaur group known from Hell Creek, as well as pterosaur remains, which had previously been found only in layers far below the KT boundary.

He found, intact, an unhatched egg containing an embryo—a fossil of immense research value. The egg and the other remains suggested that dinosaurs and major reptiles were probably not staggering into extinction on that fateful day.

In one fell swoop, DePalma may have solved the three-metre problem and filled in the gap in the fossil record. By the end of the field season, DePalma was convinced that the site had been created by an impact flood, but he lacked conclusive evidence that it was the KT impact.

It was possible that it resulted from another giant asteroid strike that occurred at around the same time. Deposits of Chicxulub tektites are rare; the best source, discovered in , is a small outcrop in Haiti, on a cliff above a road cut.

In late January, , DePalma went there to gather tektites and sent them to an independent lab in Canada, along with tektites from his own site; the samples were analyzed at the same time, with the same equipment. The results indicated a near-perfect geochemical match. The dinosaur feathers are crazy good, but the burrow makes your head reel. Jan Smit, a paleontologist at Vrije University, in Amsterdam, and a world authority on the KT impact, has been helping DePalma analyze his results, and, like Burnham and Walter Alvarez, he is a co-author of a scientific paper that DePalma is publishing about the site.

There are eight other co-authors. And this is the first time we see direct victims. In September of , DePalma gave a brief talk about the discovery at the annual meeting of the Geological Society of America, in Colorado.

He mentioned only that he had found a deposit from a KT flood that had yielded glass droplets, shocked minerals, and fossils. In the real Tanis, archeologists found an inscription in three writing systems, which, like the Rosetta stone, was crucial in translating ancient Egyptian.

DePalma hopes that his Tanis site will help decipher what happened on the first day after the impact. The talk, limited though it was, caused a stir.

Some scientists were wary. He could have stumbled on something amazing, but he has a reputation for making a lot out of a little. Other paleontologists told me that they were leery of going on the record with criticisms of DePalma and his co-authors. All expressed a desire to see the final paper , which will be published next week, in the Proceedings of the National Academy of Sciences , so that they could evaluate the data for themselves.

After the G. The KT tsunami, even moving at more than a hundred miles an hour, would have taken many hours to travel the two thousand miles to the site. The rainfall of glass blobs, however, would have hit the area and stopped within about an hour after the impact. And yet the tektites fell into an active flood. The timing was all wrong. This was not a paleontological question; it was a problem of geophysics and sedimentology.

Smit was a sedimentologist, and another researcher whom DePalma shared his data with, Mark Richards, now of the University of Washington, was a geophysicist. At dinner one evening in Nagpur, India, where they were attending a conference, Smit and Richards talked about the problem, looked up a few papers, and later jotted down some rough calculations.

One of them proposed that the wave might have been created by a curious phenomenon known as a seiche. In large earthquakes, the shaking of the ground sometimes causes water in ponds, swimming pools, and bathtubs to slosh back and forth. Richards recalled that the Japanese earthquake produced bizarre, five-foot seiche waves in an absolutely calm Norwegian fjord thirty minutes after the quake, in a place unreachable by the tsunami. Richards had previously estimated that the worldwide earthquake generated by the KT impact could have been a thousand times stronger than the biggest earthquake ever experienced in human history.

Using that gauge, he calculated that potent seismic waves would have arrived at Tanis six minutes, ten minutes, and thirteen minutes after the impact. Different types of seismic waves travel at different speeds. The brutal shaking would have been enough to trigger a large seiche, and the first blobs of glass would have started to rain down seconds or minutes afterward.

The Tanis site, in short, did not span the first day of the impact: it probably recorded the first hour or so. This fact, if true, renders the site even more fabulous than previously thought. One day sixty-six million years ago, life on Earth almost came to a shattering end.