So, Tell Me Again… What Killed the Dinosaurs?
The Chicxulub crater at the time of impact. So, what really killed the dinosaurs? Two main camps exist in paleontology today, each having a different view of what killed the dinosaurs and other organisms at the time of the Cretaceous-Tertiary (KT) boundary: A large asteroid impact in the Yucatan Peninsula or volcanic eruptions worldwide, but predominantly in the Deccan Traps of India. Controversy has surrounded the topic for the last four decades and it has become difficult for the general public (and the scientific community at large) to understand the issue due to the tangled assemblage of data which seems to point in many different directions. Luckily, the controversy has not harmed the study of mass extinction causation, but rather has made it a more dynamic and interesting area of study. There has been no settlement to the issue so far, and no clear one is foreseeable. In general, it seems that many paleontologists lean towards the volcanic eruptions side, while many astronomers and physicists favor the asteroid impact side. Geologists are probably evenly split between the two. But recent evidence suggests that the answer may be a combination of the two theories, with the ultimate killer being global climate change triggered by the two events in tandem. It looks like the asteroid that killed off the dinosaurs probably rang the Earth like a bell, triggering super-volcanic eruptions around the globe that may have contributed to the devastation – A one-two punch that ultimately killed-off 75 percent of life on the planet. (Content Credit: University of California at Berkeley) (Image Credit: NASA)
So, Tell Me Again… What Killed the Dinosaurs?
The demise of the dinosaurs is the world's ultimate who-dunit. Was it an asteroid impact in the Gulf of Mexico? Volcanic eruptions in the Deccan Traps of India? Climate change? Too many pesky mammals running around eating dino eggs? All of the above? None of the above?
A new study led by The University of Texas at Austin has confirmed that an asteroid was definitely involved. Whether it was the sole cause is still up for debate, but the evidence clearly shows that the trigger for the worldwide Cretaceous-Tertiary (KT) extinction that wiped out the dinosaurs was caused by the asteroid. When the asteroid slammed into the planet, the impact set wildfires, triggered tsunamis, and blasted so much sulfur into the atmosphere that it blocked the Sun, which caused global cooling that ultimately doomed the dinos. This has been confirmed through hard evidence uncovered in the hundreds of feet of rocks that filled the impact crater within the first 24 hours after impact. But it looks like the asteroid that killed off the dinosaurs probably rang the Earth like a bell, triggering super-volcanic eruptions around the globe that may have contributed to the devastation – A one-two punch that killed-off 75 percent of life on the planet.
The evidence for a massive asteroid strike includes bits of charcoal, jumbles of rock brought in by the tsunami’s backflow, and conspicuously absent sulfur. They are all part of a rock record that offers the most detailed look yet into the aftermath of the catastrophe that ended the Age of Dinosaurs, said Sean Gulick, a research professor at the University of Texas Institute for Geophysics (UTIG) at the Jackson School of Geosciences.
“It’s an expanded record of events that we were able to recover from within ground zero,” said Gulick, who led the study and co-led the 2016 International Ocean Discovery Program scientific drilling mission that retrieved the rocks from the impact site offshore of the Yucatan Peninsula. “It tells us about impact processes from an eyewitness location.”
The research builds on earlier work that described how the crater formed and how life quickly recovered at the impact site. An international team of more than two dozen scientists contributed to this study.
Most of the material that filled the crater within hours of impact was produced at the impact site or was swept in by seawater pouring back into the crater from the surrounding Gulf of Mexico. Just one day deposited about 425 feet of material -- a rate that’s among the highest ever encountered in the geologic record. This breakneck rate of accumulation means that the rocks record what was happening in the environment within and around the crater in the minutes and hours after impact and give clues about the longer-lasting effects of the impact that wiped out 75 percent of life on the planet.
Gulick described it as a short-lived inferno at the regional level, followed by a long period of global cooling. “We fried them and then we froze them,” Gulick said. “Not all the dinosaurs died that day, but many dinosaurs did.”
Researchers estimate the asteroid hit with the equivalent power of 10 billion atomic bombs of the size used in World War II. The blast ignited trees and plants that were thousands of miles away and triggered a massive tsunami that reached as far inland as Illinois. Inside the crater, researchers found charcoal and a chemical biomarker associated with soil fungi within or just above layers of sand that shows signs of being deposited by resurging waters. This suggests that the charred landscape was pulled into the crater with the receding waters of the tsunami.
Jay Melosh, a Purdue University professor and expert on impact cratering, said that finding evidence for wildfire helps scientists know that their understanding of the asteroid impact is on the right track.
“It was a momentous day in the history of life, and this is a very clear documentation of what happened at ground zero,” said Melosh, who was not involved with this study.
However, one of the most important takeaways from the research is what was missing from the core samples. The area surrounding the impact crater is full of sulfur-rich rocks. But there was no sulfur in the core.
That finding supports a theory that the asteroid impact vaporized the sulfur-bearing minerals present at the impact site and released the sulfur into the atmosphere, where it wreaked havoc on the Earth’s climate, reflecting sunlight away from the planet and causing global cooling. Researchers estimate that at least 325 billion metric tons would have been released by the impact. To put that in perspective, that’s about four orders of magnitude (that is, 10,000 times) greater than the sulfur that was spewed during the 1883 eruption of Krakatoa, which cooled the Earth’s climate by an average of 2.2 degrees Fahrenheit for five years.
Although the asteroid impact created mass destruction at the regional level, it was this global climate change that caused a mass extinction, killing off the dinosaurs along with most other life on the planet at the time.
“The real killer has got to be atmospheric,” Gulick said. “The only way you get a global mass extinction like this is an atmospheric effect.”
This latest research was funded by a number of international and national support organizations, including the National Science Foundation.
Determining a Precise Date for the Cretaceous-Tertiary Extinction
In 2013, scientists at the Berkeley Geochronology Center, the University of California at Berkeley, and universities in the Netherlands and the United Kingdom determined the most precise dates yet for the dinosaur extinction 66 million years ago and for the well-known impact that occurred around the same time.
The dates are so close, the researchers said, that they believe the asteroid, if not wholly responsible for the global extinction, at least dealt the dinosaurs their death blow.
"The impact was clearly the final straw that pushed Earth past the tipping point," said Paul Renne, UC Berkeley Professor of Earth and Planetary Science. "We have shown that these events are synchronous to within a gnat's eyebrow, and therefore the impact clearly played a major role in extinctions, but it probably wasn't just the impact."
The revised dates clear up lingering confusion over whether the impact actually occurred before or after the extinction, which was characterized by the almost overnight disappearance from the fossil record of land-based dinosaurs and many ocean creatures. The new date for the impact, 66,038,000 years ago, is the same within error limits as the date of the extinction, said Renne, making the events simultaneous.
The extinction of the dinosaurs was first linked to a comet or asteroid impact in 1980 by the late UC Berkeley Nobel Laureate Luis Alvarez and his son, Walter, who is a UC Berkeley Professor Emeritus of Earth and Planetary science. A 110-mile-wide crater in the Caribbean off the Yucatan coast of Mexico is thought to be the result of that impact. Called Chicxulub (cheek-she-loob), the crater is thought to have been excavated by an object six miles across that threw into the atmosphere debris that can still be found around the globe as glassy spheres or tektites, shocked quartz, and a layer of iridium-enriched dust.
Renne's quest for a more accurate dating of the extinction began in 2010 when he noticed that the existing date conflicted with other estimates of the timing of the extinction and that the existing dates for the impact and the extinction did not line up within error margins.
Renne and his colleagues first went to work recalibrating and improving the existing dating method, known as the argon-argon technique. They then collected volcanic ash from the Hell Creek area in Montana and analyzed it with the recalibrated argon-argon technique to determine the date of the extinction. The formation below the extinction horizon is the source of many dinosaur fossils and one of the best sites to study the change in fossils from before and after the extinction.
They also gathered previously dated tektites from Haiti and analyzed them using the same technique to determine how long ago the impact had occurred. The new extinction and impact dates are precise to within 11,000 years, the researchers said.
"When I got started in the field, the error bars on these events were plus or minus a million years," said paleontologist William Clemens, a UC Berkeley Professor Emeritus of Integrative Biology who has led research in the Hell Creek area for more than 30 years, but was not directly involved in the Renne study. "It's an exciting time right now, a lot of which we can attribute to the work that Paul and his colleagues are doing in refining the precision of the time scale with which we work. This allows us to integrate what we see from the fossil record with data on climate change and changes in flora and fauna that we see around us today."
Dinosaurs at the Tipping Point
Despite the synchronous impact and extinction, Renne cautions that this doesn't mean that the impact was the sole cause. Dramatic climate variation over the previous million years, including long cold snaps amidst a general Cretaceous hothouse environment, probably brought many creatures to the brink of extinction, and the impact kicked them over the edge.
"These precursory phenomena made the global ecosystem much more sensitive to even relatively small triggers, so that what otherwise might have been a fairly minor effect shifted the ecosystem into a new state," he said. "The impact was the coup de grace."
One cause of the climate variability could have been a sustained series of volcanic eruptions in India that produced the extensive Deccan Traps. Renne plans to re-date those volcanic rocks to get a more precise measure of their duration and onset relative to the dinosaur extinction.
"This study shows the power of high precision geochronology," said Darren F. Mark of the Scottish Universities Environmental Research Center, who conducted independent argon-argon analyses on samples provided by Renne. "Many people think precision is just about adding another decimal place to a number. But it's far more exciting than that. It's more like getting a sharper lens on a camera. It allows us to dissect the geological record at greater resolution and piece together the sequence of Earth history."
Renne’s work was supported by the Ann and Gordon Getty Foundation, UC Berkeley's Esper S. Larsen Jr. Fund, and the National Science Foundation.
Sean Gulick’s Earlier Work at the Chicxulub Crater
In 2008, Sean Gulick completed the most detailed three-dimensional seismic images of the Chicxulub crater to date and helped modify the theory explaining the extinction event. The Chicxulub crater was formed when an asteroid struck on the coast of the Yucatan Peninsula. Most scientists agree the impact played a major role in the “KT Extinction Event” that caused the extinction of most life on Earth, including the dinosaurs.
According to Gulick, the new images revealed that the asteroid landed in deeper water than previously assumed and therefore released about 6.5 times more water vapor into the atmosphere.
The impact site also contained sulfur-rich sediments called evaporites, which would have reacted with water vapor to produce sulfate aerosols. According to Gulick, an increase in the atmospheric concentration of the compounds could have made the impact deadlier in two ways: by altering climate (sulfate aerosols in the upper atmosphere can have a cooling effect) and by generating acid rain (water vapor can help to flush the lower atmosphere of sulfate aerosols, causing acid rain). Earlier studies had suggested both effects might result from the impact, but to a lesser degree.
“The greater amount of water vapor and consequent potential increase in sulfate aerosols needs to be taken into account for models of extinction mechanisms,” says Gulick.
Mechanisms that have been proposed to link the asteroid impact to extinctions include: a few hours of intense heat immediately following the impact caused by ejected material falling back through the atmosphere, aerosol clouds blocking out sunlight and killing off plants followed by a domino effect of plant eaters and eaters of plant eaters, global firestorms, unprecedented earthquakes, and mega-tsunami waves hundreds of meters tall.
An increase in acid rain might help explain why reef and surface dwelling ocean creatures were affected along with large vertebrates on land and in the sea. As it fell on the water, acid rain could have turned the oceans more acidic. There is some evidence that marine organisms more resistant to a range of pH survived while those more sensitive did not.
Gulick says the mass extinction event was probably not caused by just one mechanism, but rather a combination of environmental changes acting on different time scales, in different locations. For example, many large land animals might have been baked to death within hours or days of the impact as ejected material fell from the sky, heating the atmosphere and setting off firestorms. More gradual changes in climate and acidity might have had a larger impact in the oceans.
Changing Trajectory
To compile the seismic image, the team placed 28 ocean bottom seismometers in the Gulf of Mexico and 87 land based seismometers on the Yucatan Peninsula. They then used the National Science Foundation Research Vessel Maurice Ewing to tow an airgun array and a hydrophone streamer along 1800 kilometers of transects crossing over the crater. When the airguns fired, sound traveled into the subsurface and reflected and refracted back up to the seismometers and hydrophones. These data were combined to produce the most detailed three-dimensional image of the crater yet.
Earlier images of the crater’s structure in the subsurface were based on gravity measurements and less extensive seismic surveys. Based on those images, scientists had speculated that the asteroid came in from the southwest or southeast (depending on varying interpretations) at either a low or high angle (again depending on the interpretation). They also estimated that before impact, the site was flat and sitting in less than 100 meters of water.
Gulick and his collaborators originally set out to learn more about the trajectory of the asteroid. Instead, they discovered that the target site was quite different from original assumptions. According to the new interpretation, the impact site on the continental shelf had originally sloped from about 100 meters depth to over 1200 meters. That also meant that it was under much more water.
“We discovered that the shallow structure of the crater was determined much more by what the impact site was like before impact than by the trajectory of the impactor,” says Gulick.
If scientists can determine the trajectory, it will tell them where to look for the biggest environmental consequences of impact, because most of the hazardous, shock-heated and fast moving material would have been thrown out of the crater downrange from the impact.
Researchers at Imperial College in London are already using computer models to search for possible signatures in impact craters that could indicate trajectory regardless of the initial surface conditions at the impact site.
“As someone who simulates impact events using computers, this work provides valuable new constraints on both the pre-impact target structure and the final geometry of the cratered crust at Chicxulub,” says Gareth Collins, a research fellow at Imperial College.
Gulick and his collaborators have proposed a project to drill into the crater to help answer questions about the asteroid’s trajectory, the energy released by the impact, and how local life forms changed just before and after impact. Gulick says one theory is that the impact would have created hydrothermal vent systems that could support exotic forms of life. He’s eager to find out if there is evidence of such vents at the site. He also hopes this work will help scientists better understand impacts on bodies throughout the solar system.
According to an International Scientific Panel: An Asteroid Killed Off the Dinosaurs – Case Closed
The Cretaceous-Tertiary mass extinction, which wiped out the dinosaurs and more than half of species on Earth, was caused by an asteroid colliding with Earth and not massive volcanic activity, according to a comprehensive review in 2010 of all the available evidence according to a panel of 41 international experts, including UK researchers from Imperial College London, the University of Cambridge, University College London, and the Open University.
The scientists reviewed 20 years' worth of research to determine the cause of the Cretaceous-Tertiary (KT) extinction, which happened around 66 million years ago. The extinction wiped out more than half of all species on the planet, including the dinosaurs and large marine reptiles, clearing the way for mammals to become the dominant species on Earth.
The evidence shows that the extinction was caused by a massive asteroid slamming into Earth at Chicxulub in Mexico. The asteroid, which was around six miles wide, is believed to have hit Earth with a force of 10 billion atomic bombs of the size used in World War II. It would have blasted material at high velocity into the atmosphere, triggering a chain of events that caused a global winter, wiping out much of life on Earth.
But some scientists have argued that the extinction was caused by the asteroid or by volcanic activity in the Deccan Traps in India, where a series of super volcanic eruptions lasted approximately 1.5 million years. These eruptions spewed 1,100,000 cubic km of basalt lava across the Deccan Traps, which would have been enough to fill the Black Sea twice, and were thought to have caused a cooling of the atmosphere and acid rain on a global scale.
In the new study, scientists analyzed the work of paleontologists, geochemists, climate modelers, geophysicists, and sedimentologists who have been collecting evidence about the KT extinction over the last 20 years. Geological records show that the event that triggered the extinction destroyed marine and land ecosystems rapidly, according to the researchers, who conclude that the Chicxulub asteroid impact is the only plausible explanation for this.
Despite evidence for relatively active volcanism in Deccan Traps at the time, marine and land ecosystems showed only minor changes within the 500,000 years before the time of the KT extinction. Furthermore, computer models and observational data suggest that the release of gases such as sulphur into the atmosphere after each volcanic eruption in the Deccan Traps would have had a short lived effect on the planet. These would not cause enough damage to create a rapid mass extinction of land and marine species.
Dr Joanna Morgan, of the Department of Earth Science and Engineering at Imperial College London, said: "We now have great confidence that an asteroid was the cause of the KT extinction. This triggered large-scale fires, earthquakes measuring more than 10 on the Richter scale, and continental landslides, which created tsunamis. However, the final nail in the coffin for the dinosaurs happened when blasted material was ejected at high velocity into the atmosphere. This shrouded the planet in darkness and caused a global winter, killing off many species that couldn't adapt to this hellish environment."
Dr Gareth Collins, also from the Department of Earth Science and Engineering at Imperial College London, added: "The asteroid was about the size of the Isle of Wight and hit Earth 20 times faster than a speeding bullet. The explosion of hot rock and gas would have looked like a huge ball of fire on the horizon, grilling any living creature in the immediate vicinity that couldn't find shelter. Ironically, while this hellish day signaled the end of the 160 million year reign of the dinosaurs, it turned out to be a great day for mammals, which had lived in the shadow of the dinosaurs prior to this event. The KT extinction was a pivotal moment in Earth's history, which ultimately paved the way for humans to become the dominant species on Earth."
In the review, the panel sifted through past studies to analyze the evidence that linked the asteroid impact and volcanic activity with the KT extinction. One key piece of evidence was the abundance of iridium in geological samples around the world from the time of the extinction.
Iridium is very rare in Earth's crust and very common in asteroids. Immediately after the iridium layer, there is a dramatic decline in fossil abundance and species, indicating that the KT extinction followed very soon after the asteroid hit.
Another direct link between the asteroid impact and the extinction is evidence of "shocked" quartz in geological records. Quartz is shocked when hit very quickly by a massive force and these minerals are only found at nuclear explosion sites and at meteorite impacts sites. The team stated that an abundance of shocked quartz in rock layers all around the world at the KT boundary lends further weight to their conclusions that a massive meteorite impact happened at the time of the mass extinction.
Not So Fast – Don’t Dismiss the Importance of the Volcanic Eruptions at the Deccan Traps
Clearly, the crater discovered in 1978 in northern Yucatan measuring about 180km in diameter, records a massive extra-terrestrial impact. And when spherules from the impact were found just below the Cretaceous-Tertiary (KT) boundary, it was quickly identified as the ‘smoking gun’ responsible for the mass extinction event that took place approximately 66 million years ago. It was this event which saw the demise of dinosaurs, along with countless other plant and animal species.
However, a number of scientists have since disagreed with this interpretation. In 2009, a study led by Dr. Gerta Keller of Princeton University and Thierry Adatte, University of Lausanne, Switzerland, used evidence from Mexico to suggest that the Chicxulub impact predates the KT boundary by as many as 300,000 years.
Dr. Gerta Keller believes that a series of monumental Super Volcanic eruptions in India may have killed the dinosaurs 66 million years ago, not a meteor impact in the Gulf of Mexico. The eruptions, which created the gigantic Deccan Traps lava beds of India, are now the prime suspect in the most famous and persistent paleontological murder mystery, say scientists who have conducted a slew of new investigations honing down eruption timing.
"It's the first time we can directly link the main phase of the Deccan Traps to the mass extinction," said Princeton University paleontologist Gerta Keller. The main phase of the Deccan eruptions spewed 80 percent of the lava which spread out for hundreds of miles. It is calculated to have released ten times more climate altering gases into the atmosphere than the nearly concurrent Chicxulub meteor impact, according to volcanologist Vincent Courtillot from the Physique du Globe de Paris.
Keller's crucial link between the eruption and the mass extinction comes in the form of microscopic marine fossils that are known to have evolved immediately after the mysterious mass extinction event. The same telltale fossilized planktonic foraminifera were found at Rajahmundry near the Bay of Bengal, about 1000 kilometers from the center of the Deccan Traps near Mumbai. At Rajahmundry there are two lava "traps" containing four layers of lava each. Between the traps are about nine meters of marine sediments. Those sediments just above the lower trap, which was the mammoth main phase, contain the incriminating microfossils.
Previous work had first narrowed the Deccan eruption timing to within 800,000 years of the extinction event using paleomagnetic signatures of Earth's changing magnetic field frozen in minerals that crystallized from the cooling lava. Then radiometric dating of argon and potassium isotopes in minerals narrowed the age to within 300,000 years of the 66 million year old Cretaceous-Tertiary boundary, sometimes called the KT boundary.
The microfossils are far more specific, however, because they demonstrate directly that the biggest phase of the eruption ended right when the aftermath of the mass extinction event began. That sort of clear-cut timing has been a lot tougher to pin down with Chicxulub-related sediments, which predate the mass extinction.
"Our results are consistent and mutually supportive with a number of new studies... that reveal a very short time for the main Deccan eruptions at or near the KT boundary and the massive carbon dioxide and sulfur dioxide output of each major eruption that dwarfs the output of Chicxulub," explained Keller. "Our KT age control combined with these results strongly points to Deccan volcanism as the likely leading contender in the KT mass extinction."
"From El Penon and other localities in Mexico we know that between 4 and 9 meters of sediments were deposited at about 2-3 centimeters per thousand years after the impact. The mass extinction level can be seen in the sediments above this interval" says Keller.
Advocates of the Chicxulub impact theory suggest that the impact crater and the mass extinction event only appear far apart in the sedimentary record because of earthquake or tsunami disturbance that resulted from the impact of the asteroid.
“The problem with the tsunami interpretation” says Dr Keller, ‘is that this sandstone complex was not deposited over hours or days by a tsunami. Deposition occurred over a very long time period.”
The study found that the sediments separating the two events were characteristic of normal sedimentation, with burrows formed by creatures colonizing the ocean floor, erosion and transportation of sediments, and no evidence of structural disturbance.
As well as this, they found evidence that the Chicxulub impact had nothing like the dramatic impact on species diversity that has been suggested. At one site at El Peon, the researchers found 52 species present in sediments below the impact spherule layer, and counted all 52 still present in layers above the spherules. In contrast, at a site at La Sierrita which records the KT boundary, 31 out of 44 species disappeared from the fossil record.
"We found that not a single species went extinct as a result of the Chicxulub impact…these are astonishing results that have been confirmed by more studies in Texas" says Keller.
This conclusion should not come as too great a surprise, however. None of the other five great mass extinctions is associated with an impact, and no other large craters are known to have caused a significant extinction event.
In place of Chicxulub, Keller suggests that the massive volcanic eruptions at the Deccan Traps in India may be responsible for the extinction, releasing massive amounts of dust and gases that could have blocked out sunlight and brought about a significant greenhouse effect. The fact that Chicxulub seems to have had no effect on biota, despite its size, indicates that even large asteroid impacts may not inevitably bring death, destruction, and extinction to huge swathes of the biota.
Keller is hopeful that this evidence will lend more weight to a theory she has been arguing for years. Despite an increasingly strong body of evidence against it, the Chicxulub impact theory continues to be adhered to by many.
"The impact-kill theory is beautiful in its simplicity” she admits. In contrast, “the ground truth, the data that supports the impact and at the same time refutes the theory, is messy and complicated by normal geological processes."
If Keller is right, then there could be much more to learn from Chicxulub than what it can tell us about the KT mass extinction, not least the powerful influence of scientific consensus.
As one reviewer wrote in response to an earlier paper by Keller, "I don’t believe it, because how can so many be so wrong for so long?"
But some scientists are coming to the conclusion that extraterrestrial-based theories of great periods of mass extinction on Earth are flawed and that more down to earth factors could have accounted for these devastating events.
Earth history has been punctuated by several mass extinctions rapidly wiping out nearly all life forms on our planet. What causes these catastrophic events? Are they really due to asteroid impacts as is widely believed today? Research suggests that the cause may come from within our own planet, through the eruption of vast amounts of lava and deadly gases from deep inside the Earth that vent into the atmosphere, knocking the Earth’s delicate equilibrium into a tailspin.
In 2006, University of Leicester geologists Professor Andy Saunders and Dr. Marc Reichow took a look at what may actually have wiped out the dinosaurs 66 million years ago and caused other similarly cataclysmic events. At the time, they were keenly aware that they may end up exploding a few popular myths along the way.
The idea that a massive asteroid impact caused a mass extinction has been in vogue over the last 25 years, since Louis Alverez’s research team at the University of California in Berkeley published their work about an extraterrestrial iridium anomaly found in 66 million year old layers at the Cretaceous-Tertiary boundary. This anomaly only could be explained by an extraterrestrial source -- that is a large asteroid hitting the Earth and ultimately wiping out the dinosaurs and many other organisms off the Earth’s surface.
According to Professor Saunders, “Impacts are suitably apocalyptic. They are the stuff of Hollywood. It seems that every kid’s dinosaur book ends with a bang. But are they the real killers and are they solely responsible for every mass extinction on Earth? There is scant evidence of impacts at the time of other major extinctions, for example at the end of the Permian, 250 million years ago, and at the end of the Triassic, 200 million years ago. The evidence that has been found does not seem large enough to have triggered an extinction at these times.”
Flood basalt eruptions are, he says, an alternative planet killing mechanism that should be studied more closely. These do correspond with all main mass extinctions. Furthermore, they may have released enough greenhouse gases (SO2 and CO2) to dramatically change the climate. The largest flood basalts on Earth (known as the Siberian Traps and the Deccan Traps) coincide with the largest extinctions (at the end of the Permian and the end of the Cretaceous periods). “Pure coincidence?” asks Saunders.
While this is unlikely to be pure chance, the Leicester researchers are interested in precisely what the kill mechanism may have been. One possibility is that the gases released by volcanic activity lead to a prolonged volcanic winter induced by sulphur-rich aerosols, followed by a period of CO2 induced warming.
The Siberian Traps are the largest known continental flood basalts. Eruptions about 250 million years ago at high latitude in the northern hemisphere caused these continental flood basalts -- vast outpourings of lava that covered large areas of the Earth's surface. A major debate is now underway concerning their origins and their environmental impact.
Using radiometric dating techniques, the scientists hope to constrain the age and, combined with geochemical analysis, the extent of the Siberian Traps. Measuring how much gas was released during these eruptions 250 million years ago is a considerable challenge. The researchers studied microscopic inclusions trapped in minerals of the Siberian Traps rocks to estimate the original gas contents. Using these data they hope to be able to assess the amount of SO2 and CO2 released into the atmosphere 250 million years ago, and whether or not this caused climatic havoc, wiping out nearly all life on Earth. By studying the composition of sedimentary rocks laid down at the time of the mass extinction, they also hope to detect changes to seawater chemistry that resulted from major changes in climate.
From these data, Professor Saunders and his team hope to link the volcanism to the extinction event. According to Professor Saunders, “If we can show, for example, that the full extent of the Siberian Traps was erupted at the same time, we can be confident that their environmental effects were powerful. Understanding the actual kill mechanism is the next stage.”
In related, but independent research, Dr. Mark Sephton from Imperial College in London said: "The cause of the end Permian extinction has been highly controversial. We show that the terrestrial ecosystem was the first to suffer. The continent-wide nature of the event implies that it was caused by something in the atmosphere. The unique chemical data indicates that something fast and catastrophic happened on land."
However, analysis of a unique set of molecules found in rocks taken from the Dolomites in Italy has enabled scientists to build up a picture of what actually happened. The molecules are the remains of polysaccharides, large sugar-based structures common in plants and soil, and they tell the story of the extinction.
The molecules date from the same time as the major volcanic eruption that caused the great outpouring of basalt lava over vast swathes of land in present day Siberia. The researchers believe that the volcanic gases from the eruption, which would have depleted Earth's protective ozone layer and acidified the land and sea, killed rooted vegetation. This meant that soil was no longer retained and it washed into the surrounding oceans.
The chemistry of the rocks reveals that although the sugar molecules were found in marine sediments, they were derived from land, supporting the theory that massive soil erosion caused them to end up in the sea.
Soil materials in the oceans would have blocked out light and soaked up oxygen. Analysis of rock chemistry suggests that after the soil crisis on land, the marine ecosystem succumbed to the stresses of environmental change and oceanic life faltered, completing a global catastrophe.
Professor Henk Visscher of Utrecht University, also part of the research team, commented: "The soil crisis could have caused a worldwide expanse of uninhabitable low-oxygen conditions in shallow marine waters. So what began on land ended in the sea. It seems there was no place to hide at this time of great dying."
Did the Dino Killing Asteroid Have Help From Super Volcanos?
The asteroid that slammed into the ocean off Mexico 66 million years ago and killed off the dinosaurs probably rang the Earth like a bell, triggering volcanic eruptions around the globe that may have contributed to the devastation, according to a team of UC Berkeley geophysicists.
Specifically, the researchers argue that the impact likely triggered most of the immense eruptions of lava in India known as the Deccan Traps, explaining the “uncomfortably close” coincidence between the Deccan Traps eruptions and the impact, which has always cast doubt on the theory that the asteroid was the sole cause of the end-Cretaceous mass extinction.
“If you try to explain why the largest impact we know of in the last billion years happened within 100,000 years of these massive lava flows at Deccan … the chances of that occurring at random are minuscule,” said team leader Mark Richards, UC Berkeley professor of earth and planetary science. “It’s not a very credible coincidence.”
While the Deccan lava flows, which started before the impact but erupted for several hundred thousand years after re-ignition due to the impact, probably spewed immense amounts of carbon dioxide and other noxious, climate-modifying gases into the atmosphere, it’s still unclear if this contributed to the demise of most of life on Earth at the end of the Age of Dinosaurs, Richards said.
“This connection between the impact and the Deccan lava flows is a great story and might even be true, but it doesn’t yet take us closer to understanding what actually killed the dinosaurs and the forams,” he said, referring to tiny sea creatures called foraminifera, many of which disappeared from the fossil record virtually overnight at the boundary between the Cretaceous and Tertiary periods, called the KT boundary. The disappearance of the landscape dominating dinosaurs is widely credited with ushering in the age of mammals, eventually including humans.
He stresses that his proposal differs from an earlier hypothesis that the energy of the impact was focused around Earth to a spot directly opposite, or antipodal, to the impact, triggering the eruption of the Deccan Traps. The “antipodal focusing” theory died when the impact crater, called Chicxulub, was found off the Yucatan coast of Mexico, which is about 5,000 kilometers from the antipode of the Deccan traps.
Richards proposed in 1989 that plumes of hot rock, called “plume heads,” rise through Earth’s mantle every 20 to 30 million years and generate huge lava flows, called flood basalts, like the Deccan Traps. It struck him as more than coincidence that the last four of the six known mass extinctions of life occurred at the same time as one of these massive eruptions.
“Paul Renne’s group at Berkeley showed years ago that the Central Atlantic Magmatic Province is associated with the mass extinction at the Triassic/Jurassic boundary 200 million years ago, and the Siberian Traps are associated with the end Permian extinction 250 million years ago, and now we also know that a big volcanic eruption in China called the Emeishan Traps is associated with the Guadalupian extinction 260 million years ago,” Richards said. “Then you have the Deccan eruptions – including the largest mapped lava flows on Earth – occurring 66 million years ago coincident with the KT mass extinction. So what really happened at the KT boundary?”
Richards teamed up with experts in many areas to try to discover faults with his radical idea that the impact triggered the Deccan eruptions, but instead came up with supporting evidence. Paul Renne, a professor in residence in the UC Berkeley Department of Earth and Planetary Science and director of the Berkeley Geochronology Center, re-dated the asteroid impact and mass extinction in 2013 and found them essentially simultaneous, but also within approximately 100,000 years of the largest Deccan eruptions, referred to as the Wai subgroup flows, which produced about 70 percent of the lavas that now stretch across the Indian subcontinent from Mumbai to Kolkata.
Michael Manga, a professor in the same department, has shown over the past decade that large earthquakes – equivalent to Japan’s 9.0 Tohoku quake in 2011 – can trigger nearby volcanic eruptions. Richards calculates that the asteroid that created the Chicxulub crater might have generated the equivalent of a magnitude 9 or larger earthquake everywhere on Earth, sufficient to ignite the Deccan flood basalts and perhaps eruptions many places around the globe, including at mid-ocean ridges.
“It’s inconceivable that the impact could have melted a whole lot of rock away from the impact site itself, but if you had a system that already had magma and you gave it a little extra kick, it could produce a big eruption,” Manga said.
Similarly, Deccan lava from before the impact is chemically different from that after the impact, indicating a faster rise to the surface after the impact, while the pattern of dikes from which the supercharged lava flowed – “like cracks in a souffle,” Renne said – are more randomly oriented post-impact.
“There is a profound break in the style of eruptions and the volume and composition of the eruptions,” said Renne. “The whole question is -- Is that discontinuity synchronous with the impact?”
Reawakened Volcanism
Richards, Renne and graduate student Courtney Sprain, along with Deccan volcanology experts Steven Self and Loyc Vanderkluysen, visited India in April 2014 to obtain lava samples for dating, and noticed that there are pronounced weathering surfaces, or terraces, marking the onset of the huge Wai subgroup flows. Geological evidence suggests that these terraces may signal a period of quiescence in Deccan volcanism prior to the Chicxulub impact. Apparently never before noticed, these terraces are part of the Western Ghats, a mountain chain named after the Hindu word for steps.
“This was an existing massive volcanic system that had been there probably several million years, and the impact gave this thing a shake and it mobilized a huge amount of magma over a short amount of time,” Richards said. “The beauty of this theory is that it is very testable, because it predicts that you should have the impact and the beginning of the extinction, and within 100,000 years or so you should have these massive eruptions coming out, which is about how long it might take for the magma to reach the surface.”
Since the team’s paper was accepted for publication, a group from Princeton University published new radioisotopic dates for the Deccan Traps lavas that are consistent with these predictions. Renne and Sprain at UC Berkeley also have preliminary, unpublished dates for the Deccan lavas that could help solidify Richards’ theory, Renne said.
Co-authors of the paper, in addition to Richards, Renne, Manga and Sprain, are Walter Alvarez, a UC Berkeley Professor Emeritus of Earth and Planetary Science and the co-originator of the dinosaur-killing asteroid theory; Stephen Self, an Adjunct Professor in the same department at UC Berkeley; Leif Karlstrom of the University of Oregon; Jan Smit of Vrije Universeit in Amsterdam; Loyc Vanderkluysen of Drexel University in Philadelphia; and Sally A. Gibson of the University of Cambridge in the UK.
For more information:
https://news.berkeley.edu/2019/03/29/66-million-year-old-deathbed-linked-to-dinosaur-killing-meteor/
https://ucmp.berkeley.edu/diapsids/extinctheory.html
https://www3.open.ac.uk/media/fullstory.aspx?id=18308
https://pr.princeton.edu/pwb/03/0922/
http://www.imperial.ac.uk/college.asp?P=7101
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