LC9C. Stay Current—What Happened to the Dinosaurs?

Life and Climate book cover

Staying current for Chapter 9

{ Life and Climate Contents }

2023-04-26. Do Volcanoes Add More Carbon Than They Take Away?. [] By Saima May Sidik, Eos/AGU. Excerpt: In a new study, Zhong et al. discovered that a volcano in northeast China emits a small net amount of carbon each year. Over geological timescales, that could have a significant impact on our planet’s carbon cycle. Volcanic areas continue to emit carbon dioxide long after eruptions are over. Conversely, atmospheric carbon dioxide (CO2) is constantly locked away into minerals on Earth’s surface through a process called silicate weathering. Whether volcanoes release more CO2 through degassing or capture more CO2 through silicate weathering is an open question. The authors of the new study investigated whether the Changbaishan volcanic area in northeast China is a net source or sink of atmospheric carbon. The region has been active for at least 2.7 million years, but it has not erupted since 1903, making the area a prime spot for analyzing long-term carbon leakage….

2022-10-04. The Asteroid That Killed the Dinosaurs Spawned a Monster Tsunami. [] By Isaac Schultz, Gizmodo. Excerpt: The impact created fast-moving waves nearly 3 miles high, a new study finds. A team modeling the aftermath of the asteroid impact that doomed the dinosaurs 66 million years ago say that the collision also created a global tsunami that devastated coastlines from North America to New Zealand. The researchers studied ancient sediments from over 100 sites around the world, to see how extreme waves resulting from the impact may have disrupted the geological record. Their work was presented at a meeting of the American Geophysical Union in 2018 and is published this week in the journal AGU Advances.…

2022-09-19. Impact Crater off the African Coast May Be Linked to Chicxulub. [] By Katherine Kornei, Eos/AGU. Excerpt: In the world of impact craters, Chicxulub is a celebrity: The 180-kilometer-diameter maw, in the Gulf of Mexico, was created by a cataclysmic asteroid impact at the end of the Cretaceous that spelled the demise of most dinosaurs. But researchers have now uncovered another crater off the coast of West Africa that might well be Chicxulub’s cousin. The newly discovered feature, albeit much smaller, is also about 66 million years old. That’s a curious coincidence, and scientists are now wondering whether the two impact structures might be linked. Perhaps Chicxulub and the newly discovered feature—dubbed Nadir crater—formed from the breakup of a parent asteroid or as part of an impact cluster, the team suggested. These results were published in Science Advances.…

2022-09-02. A Post-Impact Deep Freeze for Dinosaurs. [] By Aubrey Zerkle, Eos/AGU. Excerpt: New research supports the hypothesis that dinosaurs were done in by climate change after an asteroid impact kicked up a massive plume of sulfur gases that circled the globe for several decades. …the Cretaceous-Paleogene (K-Pg) asteroid impact, remains one of the highest-profile cosmic disasters in Earth history—it coincided with a planetwide extinction event that decimated nonavian dinosaurs and wiped out more than three quarters of life on Earth. The long-term biological consequences of this event are well established—the ecological reorganization that followed signified an end to the Mesozoic “Age of Reptiles” and ushered in the Cenozoic “Age of Mammals.” …the impact caused a shock wave that wiped out everything in its immediate path, followed by devastating tsunamis and extensive wildfires. Seismic waves propagated up rivers and onto land, producing landslides that buried anything in their path, including intact fish with well-preserved ear bones that constrained their time of death to Northern Hemisphere spring [During et al., 2022]. …Calculations confirm that dust and soot could have reduced sunlight almost entirely, but these heavier particles would have rained out of the atmosphere in months to years rather than decades [Tabor et al., 2020], limiting their effects to several chilling summers. The key to sustaining a long-term impact winter might lie in where the asteroid hit. …data definitively showed that sulfur from the impact event was thrust into the stratosphere, where it would have prolonged global cooling and intensified the extinction. …In 1991, the eruption of Mount Pinatubo released sulfate aerosols into the stratosphere. This event released about 100,000 times less sulfur than the Chicxulub impact, but it still caused global temperatures to decrease by 0.5°C for 2 years.…

2022-05-09. Discoveries shed new light on the day the dinosaurs died. By Dave Kindy, The Washington Post. Excerpt: …Thescelosaurus panicked and looked to flee — but it was too late. Everything changed in a heartbeat as a 30-foot-high wave of mud and debris came racing up the seaway from the south, sweeping away life and limb in the process. The dinosaur was caught in the destructive deluge, its leg ripped off at the hip by the devastating surge. That moment — 66 million years ago at the end of the Cretaceous period, when an earth-shattering asteroid ended the reign of the dinosaurs — is frozen in time today through a stunning fossil found last year at the Tanis dig site in North Dakota. This perfectly preserved leg clearly shows the skin, muscle and bones of the three-toed Thescelosaurus. …“We’re never going to say with 100 percent certainty that this leg came from an animal that died on that day,” the scientist said. “The thing we can do is determine the likelihood that it died the day the meteor struck. When we look at the preservation of the leg and the skin around the articulated bones, we’re talking on the day of impact or right before. There was no advanced decay.” DePalma and the dinosaur leg will be featured in two episodes of “Nova” on PBS airing back-to-back on Wednesday: “Dinosaur Apocalypse: The New Evidence” and “Dinosaur Apocalypse: The Last Day.” Biologist and natural historian Sir David Attenborough will host the programs, which were produced in conjunction with the BBC. The leg and several other relics discovered at the North Dakota site are the first actual fossils found showing the death and destruction that took place when a 10-mile-long space rock struck the Yucatán Peninsula in the Gulf of Mexico.… []

2021-10-22. Dinosaurs thrived until the moment asteroid hit, excavators of controversial site claim. By Michael Price, Science Magazine. Excerpt: …Two years ago, a paleontologist claimed to have found evidence at a fossil-rich North Dakotan site called Tanis that dinosaurs were alive until moments after the impact, when floodwaters surged over them. But many paleontologists were skeptical, especially because the dinosaur data were first discussed in a magazine story rather than a peer-reviewed journal. Last week, at the annual meeting of the Geological Society of America (GSA) in Portland, Oregon, paleontologist Robert DePalma and colleagues added detail to their claims. They presented evidence of fossils from Tanis—including stunningly well-preserved bones, skin, and footprints from what’s probably a Triceratops—that suggest dinosaurs were indeed witnesses to the asteroid that ushered them out of existence.… []

2021-09-16. Small Climate Changes Could Be Magnified by Natural Processes. Source: By Damond Benningfield, Eos/AGU. Excerpt: A new study uses modeling techniques to uncover how small incidents of warming may be turned into hyperthermal events lasting thousands of year. …A little bit of global warming may go a long way. A recent mathematical analysis of the climate of the Cenozoic­—our current geologic era, starting at the demise of the dinosaurs 66 million years ago—says that natural processes may amplify small amounts of warming, turning them into “hyperthermal” events that can last for thousands of years or longer. This finding suggests that human-induced climate change could make our planet susceptible to more extreme warming events in the future…. []

2021-06-04. [] – The rise and fall of the world’s largest lake. By Sid Perkins. Science Magazine. Excerpt: When continental plates smashed together about 12 million years ago, they didn’t just raise new mountains in central Europe—they created the largest lake the world has ever known. This vast body of water—the Paratethys Sea—came to host species found nowhere else, …. At its largest, the body of water—which some scientists consider to have been an inland sea—stretched from the eastern Alps into what is now Kazakhstan, covering more than 2.8 million square kilometers. That’s an area larger than today’s Mediterranean Sea, they write this week in Scientific Reports. …climate shifts caused the lake to shrink dramatically at least four times in its 5-million-year lifetime, with water levels falling by as much as 250 meters between 7.65 million and 7.9 million years ago. …That sent water salinity in the lake’s central basin—which closely matches the outlines of today’s Black Sea—skyrocketing, from about one-third as salty as today’s oceans to a level on par with seawater. …Those shifts wiped out many aquatic species…. Creatures that could survive the brackish water, including some mollusks, survived to repopulate the lake when it expanded during wetter times, …. …The Paratethys soon became home to a wide variety of mollusks, crustaceans, and marine mammals found nowhere else on Earth. Many of the whales, dolphins, and seals living there were miniature versions of those found in open seas…. …One species, the 3-meter-long Cetotherium riabinini—1 meter shorter than today’s bottlenose dolphin—is the smallest whale ever found in the fossil record. Such dwarfism might have helped these animals adapt to a shrinking Paratethys, Gol’din says. The changes to the climate that triggered lake shrinkage also influenced the evolution of land animals, …. As water levels dropped, the newly exposed shorelines became grasslands—and hot spots for evolution…. …Four lengthy dry periods that occurred between 6.25 million and 8.75 million years ago likely drove those creatures to migrate southwestward into Africa, Böhme and her colleagues reported last month in Communications Earth & Environment. Here, they evolved to produce the diversity of creatures for which today’s African savanna is famous… 

2021-05-17. [] – An Unbroken Record of Climate During the Age of Dinosaurs. Source: By Chengshan Wang, Yuan Gao, Daniel E. Ibarra, Huaichun Wu, and Pujun Wang, Eos/AGU. Excerpt: A scientific drilling project in China has retrieved a continuous history of conditions from Earth’s most recent “greenhouse” period that may offer insights about future climate scenarios….

2020-09-15. After an asteroid wiped out the dinosaurs, ocean microbes helped life rebound. By Katherine Kornei, Science Magazine. Excerpt: The asteroid impact that killed most of the dinosaurs 66 million years ago also created conditions for ocean microbes to flourish, according to a new study. In microscopic rock crystals, researchers have found evidence that massive blooms of algae and photosynthetic bacteria covered the world’s oceans, providing food for larger marine creatures soon after the cataclysm. In 2016, researchers working in the Gulf of Mexico drilled into the Chicxulub crater, the scar left behind by the asteroid impact, buried under the sea floor. They found that sediments deposited immediately after the impact were rich in micrite, a calcium carbonate mineral. Calcium carbonate, common in limestone, precipitates in the world’s oceans: Corals and plankton build skeletons of it, microbes such as bacteria produce it, and it can even form directly from seawater…. []

2020-05-29. A Steaming Cauldron Follows the Dinosaurs’ Demise. By Suraiya Farukhi, Ph.D, Universities Space Research Association. Excerpt: Houston, TX and Columbia, MD. A new study reveals the Chicxulub impact crater may have harbored a vast and long-lived hydrothermal system after the catastrophic impact event linked to the extinction of dinosaurs 66 million years ago. The Chicxulub impact crater, roughly 180 kilometers in diameter, is the best preserved large impact structure on Earth and a target for exploration of several impact-related phenomena. …core samples show the crater hosted an extensive hydrothermal system that chemically and mineralogically modified more than 100,000 cubic kilometers of Earth’s crust. The lead author, Universities Space Research Association’s David Kring at the Lunar and Planetary Institute (LPI), explains,“Imagine an undersea Yellowstone Caldera, but one that is several times larger and produced by the staggering impact event that resulted in the extinction of the dinosaurs.”…. [

2020-02-01. Asteroid That Killed the Dinosaurs Was Great for Bacteria.
 By Shannon Hall, The New York Times. Excerpt: The smoldering crater left by the apocalyptic space rock became a nice home for blue-green algae within years of the impact. …New findings published in the journal Geology [] last week revealed that cyanobacteria — blue-green algae responsible for harmful toxic blooms — moved into the crater a few years after the impact. That’s the blink of an eye, geologically speaking, and helps illuminate how life bounces back on Earth following cataclysmic events, even in the most devastated environments…. []  

2020-01-16. Meteorite or Volcano? New Clues to the Dinosaurs’ Demise. By Lucas Joel, The New York Times. [] For GSS Life and Climate chapter 9. Excerpt: Twin calamities marked the end of the Cretaceous period, and scientists are presenting new evidence of which drove one of Earth’s great extinctions. Some 66 million years ago, forests burned to the ground and the oceans acidified after the Chicxulub meteorite hit Earth in the Gulf of Mexico. Around the same time, on the other side of the planet, erupting volcanoes were busy covering much of the Indian subcontinent with lava, forming the Deccan Traps. One of these forces drove all dinosaurs except for the birds extinct, and opened the evolutionary door for mammals until, eventually, humans arose. In the geologic equivalent of a murder mystery, which calamity actually did the deed is a debate that stretches back decades. Now, it seems, the case may finally be cracked. The meteorite, according to a team of scientists, was the chief perpetrator, while the volcanism, driving climate change in the background, might have affected life’s recovery in the wake of the impact….  

2019-10-01. Human Activity Outpaces Volcanoes, Asteroids in Releasing Deep Carbon. By Kimberly M. S. Cartier, Eos/AGU. [] For GSS Climate Change chapter 7 and Life and Climate chapter 9. Excerpt: Of the 1.85 billion billion metric tons of carbon that exist on Earth, 99.8% exists belowground, according to new reports on deep carbon. The research estimates that human activity annually releases into the atmosphere around 40 to 100 times as much carbon dioxide as does all volcanic activity. That’s also a slightly higher rate of carbon emission than Earth experienced just after the asteroid impact that likely killed the dinosaurs, the researchers found. …The new reports summarize 10 years of field data collection, lab experiments, and computer modeling of the origin of Earth’s carbon, how it circulates throughout the Earth system, and extreme events that can upset Earth’s carbon balance…. 

2019-09-10. A New Timeline of the Day the Dinosaurs Began to Die Out. By Katherine Kornei, The New York Times. [] Excerpt: By drilling into the Chicxulub crater, scientists assembled a record of what happened just after the asteroid impact. …Scientists released a new record of this day of chaos in Proceedings of the National Academy of Sciences [] on Monday. Their timeline of the first day of the Cenozoic Era was developed using high-resolution photography, microscopy, computed tomography imaging and magnetic measurements of hundreds of feet of sedimentary rock recently recovered from Chicxulub, one of the largest impact craters on Earth. …The researchers found that the first day of the Cenozoic was peppered with cataclysms. When the asteroid struck, it temporarily carved a hole 60 miles across and 20 miles deep. The impact triggered a tsunami moving away from the crater. It also catapulted rock into the upper atmosphere and beyond. …The largest pieces of debris rained back down to Earth within minutes, Dr. Gulick and his team say, pelting the scarred landscape with solidifying rock. Smaller particles lingered for longer periods, and glassy blobs known as tektites, formed when falling, molten rock cools, have been found across North America and dated to the Chicxulub impact. Within about 30 minutes, ocean water began to flood back into the crater through a gap in its northeastern rim, the researchers suggest. …But this flooding was just ripples in a bathtub compared with what was coming next — the water that had been violently displaced by the asteroid’s impact was returning, the scientists say. Enormous tsunamis, with waves topping several hundred feet, rushed over the crater a few hours after the impact….  

2019-03-29. 66 million-year-old deathbed linked to dinosaur-killing meteor. By Robert Sanders, Berkeley News, UC Berkeley. [] Excerpt: The beginning of the end started with violent shaking that raised giant waves in the waters of an inland sea in what is now North Dakota. Then, tiny glass beads began to fall like birdshot from the heavens. The rain of glass was so heavy it may have set fire to much of the vegetation on land. In the water, fish struggled to breathe as the beads clogged their gills. The heaving sea turned into a 30-foot wall of water when it reached the mouth of a river, tossing hundreds, if not thousands, of fresh-water fish — sturgeon and paddlefish — onto a sand bar and temporarily reversing the flow of the river. Stranded by the receding water, the fish were pelted by glass beads up to 5 millimeters in diameter, some burying themselves inches deep in the mud. The torrent of rocks, like fine sand, and small glass beads continued for another 10 to 20 minutes before a second large wave inundated the shore and covered the fish with gravel, sand and fine sediment, sealing them from the world for 66 million years. This unique, fossilized graveyard — fish stacked one atop another and mixed in with burned tree trunks, conifer branches, dead mammals, mosasaur bones, insects, the partial carcass of a Triceratops, marine microorganisms called dinoflagellates and snail-like marine cephalopods called ammonites — was unearthed by paleontologist Robert DePalma over the past six years in the Hell Creek Formation, not far from Bowman, North Dakota. The evidence confirms a suspicion that nagged at DePalma in his first digging season during the summer of 2013 — that this was a killing field laid down soon after the asteroid impact that eventually led to the extinction of all ground-dwelling dinosaurs. The impact at the end of the Cretaceous Period, the so-called K-T boundary, exterminated 75 percent of life on Earth…. 

2019-03-29. Fossil Site Reveals Day That Meteor Hit Earth and, Maybe, Wiped Out Dinosaurs. By William J. Broad and Kenneth Chang, The New York Times. [] Excerpt: Sixty-six million years ago, a giant meteor slammed into Earth off the coast of modern-day Mexico. Firestorms incinerated the landscape for miles around. Even creatures thousands of miles away were doomed on that fateful day, if not by fire and brimstone, then by mega-earthquakes and waves of unimaginable size. Now, scientists have unearthed a remarkable trove of fossils that appear to date from the very day of the impact. The burial site consists of more than four feet of sediments and organic remains that were dumped in North Dakota almost instantly and transformed into rock over the eons. It evidently captures, in unparalleled detail, the repercussions of the giant doomsday rock…. …When the meteor smashed into waters near what is now Mexico’s Yucatán Peninsula, it left a giant crater known as Chicxulub and prompted upheavals thousands of miles away, including what is now North Dakota. Within hours and perhaps minutes of the titanic collision, sea creatures were swept inland by tsunamis and earthquakes, tossed together and deposited with a diverse array of landlocked life, including trees, flowers and vanished types of freshwater fish. …The jumble was swiftly entombed, and exquisitely preserved. Permeating the deposit were tiny spheres of clay and glass, known as tektites, which formed as molten rock, ejected by the impact, showered from the sky…. See also Science Magazine article Astonishment, skepticism greet fossils claimed to record dinosaur-killing asteroid impact, 4/1/2019 by Colin Barras. []

2019-02-21. Did volcanic eruptions help kill off the dinosaurs? By Paul Voosen, Science Magazine. [] Excerpt: What killed off the dinosaurs? The answer has seemed relatively simple since the discovery a few decades ago of a large impact crater in the Gulf of Mexico. It pointed to a massive asteroid strike 66 million years ago that unleashed towering tsunamis and blotted out the sun with ash, causing a plunge in global temperatures. But the asteroid wasn’t the only catastrophe to wallop the planet around this time. Across what is India today, countless volcanic seams opened in the ground, releasing a flood of lava resembling last year’s eruptions in Hawaii—except across an area the size of Texas. Over the course of 1 million years, the greenhouse gases from these eruptions could have raised global temperatures and poisoned the oceans, leaving life in a perilous state before the asteroid impact. The timing of these eruptions, called the Deccan Traps, has remained uncertain, however. And scientists such as Princeton University’s Gerta Keller have acrimoniously debated how much of a role they played in wiping out 60% of all the animal and plant species on Earth, including most of the dinosaurs. That debate won’t end today. But two studies published in Science have provided the most precise dates for the eruptions so far—and the best evidence yet that the Deccan Traps may have played some role in the dinosaurs’ demise….

2019-01-17. Moon’s craters reveal recent spike in outer space impacts on Earth. By Paul Voosen, Science Magazine.  [] Excerpt: It has long been thought that as the solar system grows older and stodgier, the number of asteroids and comets colliding with Earth and other planets has steadily gone down. But a new study reveals what appears to be a dramatic 2.5 times increase in the number of impacts striking Earth in the past 300 million years. …Scientists used a thermal camera on NASA’s Lunar Reconnaissance Orbiter to examine the number of large, heat-retaining rocks in the moon’s craters; those rocks are eventually ground to dust by minute meteorite impacts. By looking at previously dated craters, these rocks have been established as a reliable dating technique—the more intact the rocks, the younger the crater. In the new study, the team found a surprising abundance of young craters, seemingly matching the number on Earth. That means, they write today in Science, that in its modern geological history, Earth is much better at retaining the features of impact craters than once thought, and that the recent proliferation coincides with an actual increase in the number of bombarding asteroids or comets. But scientists still don’t know what caused the uptick. Perhaps several large asteroids collided or otherwise broke up some 300 million years ago, their chunks slowly migrating out from the asteroid belt to bombard Earth, the researchers say. And that could have included the giant impact, 66 million years ago, that wiped out most of the dinosaurs….  See also New York Times article, What Happened to Earth’s Ancient Craters? Scientists Seek Clues on the Moon’s Pocked Surface. []

2018-12-20. Huge Global Tsunami Followed Dinosaur-Killing Asteroid Impact. By Katherine Kornei, Eos/AGU. [] Excerpt: The devastating tsunamis that struck the coastlines of Chile, Haiti, Indonesia, and Japan in recent decades produced waves tens of meters high, unimaginable to most people accustomed to gentle seas. But millions of years ago, a truly inconceivable set of waves—the tallest roughly 1,500 meters high—rammed through the Gulf of Mexico and spread throughout the ancient ocean, producing wave heights of several meters in distant waters, new simulations show. The enormous waves were triggered by a large asteroid slamming into the shallow waters of the modern-day Yucatán Peninsula. That asteroid impact, which occurred about 66 million years ago and created the Chicxulub crater, contributed to the demise of the dinosaurs….  

2018-11-14. International Team, NASA Make Unexpected Discovery Under Greenland Ice. NASA RELEASE 18-099. [] Excerpt: The devastating tsunamis that struck the coastlines of Chile, Haiti, Indonesia, and Japan in recent decades produced waves tens of meters high, unimaginable to most people accustomed to gentle seas. But millions of years ago, a truly inconceivable set of waves—the tallest roughly 1,500 meters high—rammed through the Gulf of Mexico and spread throughout the ancient ocean, producing wave heights of several meters in distant waters, new simulations show. The enormous waves were triggered by a large asteroid slamming into the shallow waters of the modern-day Yucatán Peninsula. That asteroid impact, which occurred about 66 million years ago and created the Chicxulub crater, contributed to the demise of the dinosaurs….  

2018-08-08. Dinosaur-Killing Asteroid Impact Made Huge Dead Zones in Oceans. By Lucas Joel, Eos/AGU. Excerpt: About 66 million years ago, an asteroid roughly 10 kilometers wide hit Earth in what is today the Gulf of Mexico. It brought annihilation: All the dinosaurs except for the birds went extinct; forests around the planet vanished temporarily, killing off all bird species that lived in trees; dust and other aerosols blocked the Sun, and global temperatures took a nosedive. The world plunged into a state analogous to nuclear winter. Another fallout effect of the impact, according to new work, was a depletion of oxygen in the oceans triggered by rapid global warming following the impact and nuclear winter. Such anoxia, the researchers behind the work report, devastated marine life. What’s more, this episode of anoxia may have parallels to the rapid global warming and resulting ocean anoxia being wrought by human-driven climate change today. “The global warming following the impact is one of the most rapid warmings in Earth’s history,” said Johan Vellekoop, a geologist at KU Leuven in Belgium who led the new research. “It’s on a human timescale.” He described that the postimpact warming happened over the course of only a few hundred to a few thousand years….

2016-11-17. Updated: Drilling of dinosaur-killing impact crater explains buried circular hills. By Eric Hand, Science. Excerpt: Today, scientists published their first results from a drilling expedition into Chicxulub crater, the buried remnants of an asteroid impact off the Yucatán Peninsula in Mexico that killed off the dinosaurs 66 million years ago. Their discovery of shocked, granite rocks from deep in the crust placed “out of order” on top of sedimentary rocks validates the dynamic collapse theory of formation for Chicxulub’s peak ring, the scientists says. Chicxulub is the only well-preserved crater on Earth with a peak ring, but they abound elsewhere in the inner solar system. Last month, scientists using instruments on a NASA lunar mission showed that the peak rings within the Orientale impact basin were likely to have formed in a similar way as at Chicxulub….

2016-10-13. Comet may have struck Earth just 10 million years after dinosaur extinction. By Paul Voosen, Science. 

2015-10-01. Volcano-asteroid combo may have done in the dinosaurs. By Sid Perkins, Science. Excerpt: Scientists have for decades hotly debated what killed the dinosaurs. One long-held hypothesis blames immense and long-lasting volcanic eruptions that drastically altered Earth’s climate. Another more recent hypothesis suggests that the dino die-offs occurred after a massive asteroid hit the planet near the Yucatán Peninsula. Now, research finds that the extraterrestrial impact may have led to increased volcanism in the Indian subcontinent, providing a double whammy that took out Tyrannosaurus rex and his kin. …The new study finally provides dates for those eruptions. Using an argon-argon radioactive dating technique, a team led by geochronologist Paul Renne of the University of California, Berkeley, sampled materials from ancient lava layers at sites in the Deccan Plateau of central and western India. They found that the Deccan eruptions started at least 173,000 years before the asteroid hit and continued for at least 500,000 years after the impact. What’s more, the researchers were able to determine the size and strength of each major eruption, based on lava flow estimates. Before the impact, the eruptions produced about 71,000 cubic kilometers of lava—an average rate of about 400 million cubic meters each year. But starting about 50,000 years after the asteroid impact, Deccan volcanoes and fissures began spewing lava at an average rate of about 900 million cubic meters per year, the researchers report online today in Science. …How the asteroid impact half a world away from India bumped up lava production is a mystery, Renne says. He speculates that its effects rippled along the boundaries of nearby tectonic plates until they reached the volcanoes, expanding the size of subterranean magma chambers and thus increasing the volume of magma they could spew during any given eruption. Not all scientists are convinced.  …Ironically, by more closely linking the date of the impact with the increase in Deccan volcanism, Renne and his team may have made it more difficult to tease out the relative contribution of each phenomenon to the die-offs, Melosh says. “These findings will add greatly to the controversy of volcanism versus impact.”  See also

2013-03-27.  New Evidence Ancient Asteroid Caused Global Firestorm On Earth.   Excerpt: A new look at conditions after a Manhattan-sized asteroid slammed into a region of Mexico in the dinosaur days indicates the event could have triggered a global firestorm that would have burned every twig, bush and tree on Earth and led to the extinction of 80 percent of all Earth’s species, says a new University of Colorado Boulder study. …the collision would have vaporized huge amounts of rock that were then blown high above Earth’s atmosphere. The re-entering ejected material would have heated the upper atmosphere enough to glow red for several hours at roughly 2,700 degrees Fahrenheit — about the temperature of an oven broiler element — killing every living thing not sheltered underground or underwater. …there was enough infrared radiation from the upper atmosphere that reached Earth’s surface to create searing conditions that likely ignited tinder, including dead leaves and pine needles. If a person was on Earth back then, it would have been like sitting in a broiler oven for two or three hours…. …The asteroid-Earth collision is thought to have generated about 100 million megatons of energy…. Science News.

2013-02-07.  New evidence comet or asteroid impact was last straw for dinosaurs | Robert Sanders, UC Berkeley News Center. Excerpt: The demise of the dinosaurs is the world’s ultimate whodunit. Was it a comet or asteroid impact? Volcanic eruptions? Climate change? …In an attempt to resolve the issue, scientists at the Berkeley Geochronology Center (BGC), the University of California, Berkeley, and universities in the Netherlands and the United Kingdom have now 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 say, that they now believe the comet or 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, BGC director and UC Berkeley professor in residence 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. He and his colleagues will report their findings in the Feb. 8 issue of the journal Science…. Read the full article:

2012 May 27. It Took Earth Ten Million Years to Recover from Greatest Mass Extinction | ScienceDaily. Excerpt: Life was nearly wiped out 250 million years ago, with only 10 per cent of plants and animals surviving…recovery from the crisis lasted some 10 million years…There were apparently two reasons for the delay, the sheer intensity of the crisis, and continuing grim conditions on Earth after the first wave of extinction.The end-Permian crisis, by far the most dramatic biological crisis to affect life on Earth, was triggered by a number of physical environmental shocks — global warming, acid rain, ocean acidification and ocean anoxia. These were enough to kill off 90 per cent of living things on land and in the sea…Current research shows that the grim conditions continued in bursts for some five to six million years after the initial crisis, with repeated carbon and oxygen crises, warming and other ill effects.Some groups of animals on the sea and land did recover quickly and began to rebuild their ecosystems, but they suffered further setbacks. Life had not really recovered in these early phases because permanent ecosystems were not established…. 

2012-06-25. ‘Nature’s Masons’ Do Double Duty as Storytellers.  By Sean B. Carroll, New York Times. An article relevant to GSS Climate Change chapter 8, Life and Climate chapter 9, and A Changing Cosmos chapter 1. Excerpt: GUBBIO, Italy — …Limestone is composed largely of crystallized calcium carbonate. Some of it comes from the skeletal remains of well-known creatures like corals, but much of the rest comes from less appreciated but truly remarkable organisms called foraminifera, or forams for short. Forams have been called “nature’s masons,” … these single-celled protists construct surprisingly complex, ornate and beautiful shells to protect their bodies. After forams die, their shells settle in ocean sediments…. While tiny relative to ourselves …, forams are extremely large for single-celled organisms, … largest forams can reach a few centimeters. … forams are particularly valuable to geologists and paleontologists in telling us about Earth’s history. The forams in the limestone just outside Gubbio provided the first clues to … an asteroid that struck earth at the end of the Cretaceous period, 65 million years ago…about the size of Mount Everest and traveling at about 50,000 miles an hour when it hit the earth, drilling a 120-mile-wide crater and ejecting so much material into (and even out of) the atmosphere that food chains on land and in the oceans were disrupted for thousands of years. The impact caused one of the greatest mass extinctions in history, from the largest animals to tiny forams. Read the full article:

2012-04-05. Bus-Size Dinosaurs, Fuzzy as Chicks | by John Noble Wilford, The New York Times. An article relevant to GSS Life and Climate chapter 9. Excerpt: Fossils discovered in northeastern China of a giant, previously unrecognized dinosaur show that it is the largest known feathered animal, living or extinct, scientists report. …The adult was at least 30 feet long and weighed a ton and a half, …. The two juveniles were a mere half ton each. The new species was a distant relative of Tyrannosaurus rex …. Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, who was the lead author of the paper, said …that it was “possible that feathers were much more widespread, at least among meat-eating dinosaurs, than most scientists would have guessed even a few years ago.” Dr. Xu said the feathers were simple filaments, more like the fuzzy down of a modern baby chick than the stiff plumes of an adult bird. Such insubstantial feathers, not to mention the animal’s huge size, would have made flight impossible. The feathers’ most important function was probably as insulation. The species has been named Yutyrannus huali, which means “beautiful feathered tyrant” in a combination of Latin and Mandarin. Mark A. Norell, a curator of paleontology at the American Museum of Natural History in Manhattan, who had no part in the research, said the findings were significant because they swept aside a longstanding argument that perhaps dinosaurs had feathers only when they were small and shed them as they grew…. Read the full article:

2012 Feb 3. Global Extinction: Gradual Doom as Bad as Abrupt. NSF Press Release 12-019. Excerpt: The deadliest mass extinction of all took a long time to kill 90 percent of Earth’s marine life–and it killed in stages–according to a newly published report. It shows that mass extinctions need not be sudden events. Thomas Algeo, a geologist at the University of Cincinnati, and 13 colleagues have produced a high-resolution look at the geology of a Permian-Triassic boundary section on Ellesmere Island in the Canadian Arctic.

2010 May 17. Ancient mass extinction of fish may have paved way for modern species. By Amina Khan, LA Times. Excerpt: …”It’s clearly one of the most important papers published in recent years” in paleontology, said John Long, a paleontologist at the Natural History Museum of Los Angeles County who was not involved in the study. “Forty-four percent of all vertebrate life went extinct at that point, and that was not recognized before.” 

…That event was one of the most devastating in Earth’s history, on a par with the one that killed off the dinosaurs 65 million years ago, said Lauren Sallan, a paleontologist at the University of Chicago and lead author of the paper.

…And just as the fall of the dinosaurs made room for mammals to rise, she said, this extinction made way for modern marine life such as sharks and the ancestors of modern fish — as well as for tetrapods, ancestors of terrestrial vertebrate life. 

2010 March 23. Dinosaurs’ dominance ‘helped by mass volcanism’. By Paul Rincon, BBC News. Excerpt: Immense volcanic activity helped the dinosaurs rise to prominence some 200 million years ago, a study suggests.
Dinosaurs were the dominant vertebrates on land for some 135 million years.
While it is widely accepted that an asteroid or comet wiped them out, there has been less agreement on the factors which led to their ascendancy.
Research in PNAS journal suggests volcanic eruptions changed the climate, causing a mass extinction that wiped out the dinosaurs’ main competitors.
The scientific paper…looked at several lines of evidence such as the remains of plant wax and wood from sedimentary rocks interbedded with lava flows. From these, they were able to extract vital data about the climate at this time.
The lava flows are dated to the end-Triassic extinction, 201.4 million years ago, which wiped out 50% of tetrapods (four-limbed animals) on land, 50% of terrestrial plants and 20% of marine families….

2010 March 9. Alvarez Theory on Dinosaur Die-Out Upheld: Experts Find Asteroid Guilty of Killing the Dinosaurs. By Lynn Yarris, Lawrence Berkeley National Laboratory. Excerpt: In the March 5, 2010 edition of the journal Science, an international panel of 41 experts in geology, paleontology and other related fields, after an exhaustive review of the data, declared an end to a 30 year controversy over what triggered the extinction of the dinosaurs – an asteroid or volcanoes. The panel ruled in favor of the asteroid, a theory first put forth in 1980 by one of Berkeley Lab’s greatest scientists, the late Nobel laureate Luis Alvarez, and his son Walter, a geologist with UC Berkeley….

2009 April 28. New Blow Against Dinosaur-killing Asteroid Theory, Geologists Find. ScienceDaily. Excerpt: The enduringly popular theory that the Chicxulub crater holds the clue to the demise of the dinosaurs, along with some 65 percent of all species 65 million years ago, is challenged in a paper to be published in the Journal of the Geological Society on April 27, 2009.
The crater, discovered in 1978 in northern Yucutan and measuring about 180 kilometers (112 miles) in diameter, records a massive extra-terrestrial impact.
When spherules from the impact were found just below the Cretaceous-Tertiary (K-T) boundary, it was quickly identified as the “smoking gun” responsible for the mass extinction event that took place 65 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.
The newest research, led by Gerta Keller of Princeton University in New Jersey, and Thierry Adatte of the University of Lausanne, Switzerland, uses evidence from Mexico to suggest that the Chicxulub impact predates the K-T boundary by as much as 300,000 years.
…From El Penon and other localities in Mexico, says Keller, “we know that between four and nine meters of sediments were deposited at about two to three centimeters per thousand years after the impact. The mass extinction level can be seen in the sediments above this interval.”
…The scientists also found evidence that the Chicxulub impact didn’t have the dramatic impact on species diversity that has been suggested.
…”We found that not a single species went extinct as a result of the Chicxulub impact,” says Keller.
…Keller suggests that the massive volcanic eruptions at the Deccan Traps in India may be responsible for the extinction, releasing huge amounts of dust and gases that could have blocked out sunlight and brought about a significant greenhouse effect….

2008 December 15. Fight over dinosaur death flares anew in S.F. By David Perlman, San Francisco Chronicle. Excerpt: SAN FRANCISCO — The age of the dinosaurs ended abruptly about 65 million years ago when some catastrophic event drove them to extinction, and now a vehement controversy over their disappearance is emerging anew.
…An international group of scientists is arguing that poisonous fumes from violent waves of volcanic eruptions in India millions of years ago killed off the beasts, not – as UC Berkeley scientists first proposed nearly 30 years ago – the impact of a giant meteorite that blasted a huge undersea crater in Mexico and touched off a kind of “nuclear winter” that darkened the skies with a pall of dust and debris that the creatures could not possibly have survived.
The origins of the big debate began nearly 30 years ago when the geologist Walter Alvarez at UC Berkeley and his father, Luis, a Nobel physics laureate, proposed that a cosmic collision by an object from space at least six miles wide crashed just off Mexico’s Yucatan peninsula about 65 million years ago and created what is known as the Chicxulub crater.
…Gerta Keller of Princeton University…, joined by Vincent Courtillot of the University of Paris and Sunil Bajpai, of the Indian Institute of Technology, …insisted that the impact crater was formed at least 300,000 years before the great extinction and “caused no species extinctions” – certainly not to the dinosaurs. She came to her conclusion, in part, by age-dating clusters of mineral spherules that presumably spewed out of the Chicxulub crater and landed in Texas, where Keller said she gathered and tested them.
Instead, she argued, the extinction coincided with three or four waves of volcanism in a region of northwest India known as the Deccan traps….
…Walter Alvarez…rejected the idea that volcanism in India was the sole cause of the mass extinction.
…”Few experts on the mass extinction would agree with Keller that the Chicxulub impact is older than the mass extinction,” he said….

2008 Mar 25. Theory on Dinosaurs and Volcanic Activity 65 Million Years Ago. By HENRY FOUNTAIN, NY Times. Excerpt: An asteroid or comet impact gets most of the credit for the event that wiped out the dinosaurs 65 million years ago. But massive volcanic activity around the same time might have played a role, too, by pumping enormous amounts of gases containing sulfur and chlorine into the atmosphere. An analysis by Stephen Self of the Open University in Milton Keynes, England, and colleagues lends new support to that idea. By looking at tiny bits of glass that formed inside the lava flows, they’ve been able to reconstruct how much sulfur and chlorine were released. The volcanic activity over thousands of years produced a flood of lava, now known as the Deccan Trapps, that is thousands of feet thick over thousands of square miles of central India. The researchers’ analysis, reported in Science, suggests the eruption could have produced …on an annual basis, …the amount of SO2 … at least 10 times greater than the current amount released by worldwide volcanic activity. The environmental impact of that much gas, they add, was probably severe.

2007 November 6. Rethinking What Caused the Last Mass Extinction. By JOHN NOBLE WILFORD. NY Times. Excerpt: FREEHOLD, N.J. – Splashing through a shallow creek in suburban New Jersey, the paleontologists stepped back 65 million years to the time of the last mass extinction, the one notable for the demise of the dinosaurs. …At the time, sea levels were higher and New Jersey was warmer. The proto-Atlantic waters reached the center of the current boundaries of New Jersey, standing more than 60 feet deep here, where on a recent day the paleontologists were up to their ankles in a creek. They had their eyes on the sediments in the bank just above the iridium clay. They call this the Pinna layer.
On previous visits, they had found in the Pinna rock and soil a surprising number of marine fossils, including small clams, crabs and sea urchins. There was an abundance of ammonites, considered index organisms of the uppermost Cretaceous environment. Somehow, here at least, life appeared to have not only persisted but also flourished for tens, perhaps hundreds, of years after the putative asteroid impact.
…”It is undeniable that the iridium spike at the base of the Pinna layer was produced by the impact,” Dr. Landman said. “That’s amazing and makes it hard to explain the ammonite abundances we find above the iridium anomaly.”
Gerta Keller, a paleontologist and professor of geosciences at Princeton University, said the research by Dr. Landman’s group “shows the complexity of this extinction event and the difficulty explaining it by the currently popular impact theory.”….

28 November 2006. New York Times. Marine Life Leaped From Simple to Complex After Greatest Mass Extinction. By Andrew C. Revkin. Excerpt: At least five mass extinctions, most presumably caused by asteroids that struck the earth, have transformed global ecology in the half-billion years since the emergence of multicelled life, lopping entire branches from the evolutionary tree and causing others to flourish. The greatest “great dying,” 251 million years ago, erased 95 percent of species in the oceans (and most vertebrates on land). But new research suggests that it was followed by an explosion of complexity in marine life, one that has persisted ever since. Moreover, it happened quite suddenly… The shift to complicated, interrelated ecosystems was more like a flip of a switch than a slow trend. The researchers detected the change by analyzing records of marine fossils from 1,176 sites around the world, which are part of a new international archive, the Paleobiology Database (

23 September 2006. DINOSAURS’ CLIMATE SHIFTED TOO, REPORT SHOWS. Ancient rocks suggest dramatic climate changes during the dinosaur-dominated Mesozoic Era, a time once thought to have been hot and humid. NASA Earth Observatory.

20 September 2005. Fossils Offer Support for Meteor’s Role in Dinosaur Extinction. By WILLIAM J. BROAD. For more than a decade, the standard view has envisioned a speeding object from space that crashed into the earth and kicked up enough dust and rock around the globe to blot out the sun. The smoking gun seemed to be the discovery beneath the Yucatán peninsula of Mexico of a 110-mile-wide crater called Chicxulub, after a nearby town. But lately, doubters have argued that Chicxulub formed 300s,000 years before the mass extinction – too early to have played a role in the demise of the dinosaurs and hundreds of other plant and animal species that vanished at the end of the Cretaceous. …Now, in the September issue of Geology, the scientists, from Spain, Cuba and Mexico, report that they have discovered a highly disturbed bed of fossils that bears numerous signatures of Chicxulub’s mayhem. The date of the disturbance, 65 million years ago, is exactly at the end of the Cretaceous. …Starting around 2000, Dr. Alegret and her European colleagues repeatedly sought work permits for a nearby hill but always met with stultifying delays, if not outright rejections. Finally, they slipped into the site with their Cuban colleagues, going in late 2000, 2002 and 2003. …A rocky outcrop on the hill showed an exposed bed of sedimentary rock made up of broken bits of minerals and fossils. It was more than 30 feet thick. The team took 66 samples. Examination with microscopes showed numerous signs of cosmic violence, including quartz deformed by high temperatures and pressures, as well as tiny spheres of glass, both clearly debris from a spectacular fireball. Microscopic study also revealed the presence of thousands of tiny fossil creatures, most especially foraminifera. … Forams, as they are known, evolve so fast that geologists, paleontologists and oil companies use their shifting appearance as reliable guides to geologic dating. “They told the age of the sediments,” Dr. Alegret said. “So we’ve definitely confirmed the age of these deposits.” At the end of the Cretaceous, the rocky bed now in Cuba formed on the ocean bottom at a depth of perhaps 3,300 feet, over a few days or weeks as tons of debris rained down from the sky and huge waves generated by the Chicxulub event washed land out to sea. “It was geologically instantaneous,” Dr. Alegret said of the deposit’s formation.

10 March 2005. Mass extinction comes every 62 million years, UC physicists discover. David Perlman, SF Chronicle Science Editor. Excerpt: With surprising and mysterious regularity, life on Earth has flourished and vanished in cycles of mass extinction every 62 million years, say two UC Berkeley scientists who discovered the pattern after a painstaking computer study of fossil records going back for more than 500 million years. Their findings are certain to generate a renewed burst of speculation among scientists who study the history and evolution of life. Each period of abundant life and each mass extinction has itself covered at least a few million years — and the trend of biodiversity has been rising steadily ever since the last mass extinction, when dinosaurs and millions of other life forms went extinct about 65 million years ago….Richard Muller and his graduate student, Robert Rohde, are publishing a report on their exhaustive study in the journal Nature today, and in interviews this week, the two men said they have been working on the surprising evidence for about four years. “We’ve tried everything we can think of to find an explanation for these weird cycles of biodiversity and extinction,” Muller said, “and so far, we’ve failed.” But the cycles are so clear that the evidence “simply jumps out of the data,” said James Kirchner, a professor of earth and planetary sciences on the Berkeley campus who was not involved in the research but who has written a commentary on the report that is also appearing in Nature today..

26 December 2004. About tsunami from asteroidal impacts: Deep-sea waves generated at contact by asteroids varying in diameter from 1-100km (unaffected by interaction with sea floor) could reach heights of about 1 km, according asteroidal impact modeling studies (e.g. Gisler, Weaver, et al. 2002). This would translate into multi-km wave heights upon arrival in shallow/shore waters. Thankfully, these are rather rare events, even by geological standards. 

26 August 2004. Ground Zero for the “Great Dying”? – J. KELLY BEATTY, Sky & Telescope magazine. Excerpt: IT’S BEEN NEARLY a quarter century since geologists realized that a colossal impact contributed to (and probably caused) the demise of the dinosaurs and most of Earth’s other species 65 million years ago. …In the years since, researchers have sought evidence linking impacts with other mass extinctions throughout geologic history. The worst of these die-offs brought an abrupt end to the vibrant Permian period 251 million years ago, nearly sterilizing Earth by wiping out 90 percent of all marine species and 70 percent of those on land in less than 160,000 years. No compelling explanation for the Permian-Triassic extinction – widely called the “Great Dying” – has yet gained favor. But recent research suggests that, coincidence or not, the Great Dying was accompanied by a Great Wallop. Fallout from a major blast has been found at the Permian-Triassic boundary in Antarctica, Australia, China, and Japan (S&T: June 2001, page 26). Now seven geoscientists, led by Luaim Becker (University of California, Santa Barbara), think they’ve found “ground zero” on the northwest margin of Australia. In the online journal ScienceExpress for May 13th, they argue that the Bedout High, a broad, lava-covered dome that today lies deeply buried beneath sea-floor sediment, is actually the uplifted center of a crater comparable in size to the huge Yucatan scar….But some impact specialists are skeptical For example, Andrew Glikson (Australian National University) found no evidence for impact-induced shock when he examined one of the Bedout drill cores. And none of the Permian-Triassic boundary layers show a pronounced excess of iridium, a telltale trace element that’s rare in Earth’s crust but common in meteorites. Meanwhile, debate continues over whether the Permian-Triassic extinction was instead caused by a massive outflow of lava in what is now Siberia. All told, volcanoes disgorged some 2 million cubic kilometers of molten rock and inundated an area the size of Europe. That eruption, proponents argue, set off an abrupt green house effect or other climatic upheaval.

14 May 2004. Did an Impact Trigger the “Great Dying”? By J. Kelly Beatty, Sky & Telescope magazine. It’s been nearly a quarter century since geologists realized that a colossal impact contributed                    to (and probably caused) the decimation of the dinosaurs and vast numbers of Earth’s other species 65 million years ago. Eventually this event’s smoking gun, a crater some 180 kilometers across, was discovered beneath what is now Mexico’s Yucatán Peninsula. In the years since researchers have sought evidence linking impacts with other mass extinctions of life throughout geologic history. The biggest of these, 251 million years ago, ended the vibrant Permian period and nearly left Earth sterile: 90 to 95 percent of all species died within a geologic blink of an eye. No compelling explanation for the Permian-Triassic extinction – widely called the “Great Dying” – has yet gained favor. Now seven geoscientists, led by Luann Becker (University of California, Santa Barbara), believe they’ve identified evidence of a huge impact on the northwest margin of Australia. In the May 13th ScienceExpress, they claim that the Bedout High, a broad plateau now deeply buried beneath seafloor sediment, is actually the uplifted center of an impact crater comparable in size to the Yucatán’s huge scar.

13 May 2004 NASA RELEASE: 04-159 — Evidence Of Meteor Impact Found Off Australian Coast. An impact crater believed to be associated with the ” Great Dying,” the largest extinction event in the history of life on Earth, appears to be buried off the coast of Australia.

24 February 2004. Scientists want to be ready to block asteroid from hitting Earth. GARDEN GROVE, California (AP) — The asteroid believed to have wiped out dinosaurs 65 million years ago was rare but hardly unique, say scientists gathered to discuss ways of aggressively defending our planet from another such space rock, including by detonating nukes in space. Asteroids capable of inflicting damage on a global scale hit the Earth roughly every million years, and we shouldn’t dawdle in developing a method of deflecting them, say the scientists attending a four-day planetary defense conference in suburban Orange County.

17 January 2003. Columbia University Research Finds Correlation Between Meteorite and Comet Impacts and an Increase in Volcanic Activity Development. 10 Major Episodes of Extraterrestrial Impacts Found to Correlate with 9 Major Episodes of Volcanism. Earth Institute at Columbia University; Mary Tobin; 845-365-8607

11 December 2002. New Scientist — Earth’s volcanism linked to meteorite impacts. Large meteorite impacts may not just throw up huge dust clouds but also punch right through the Earth’s crust, triggering gigantic volcanic eruptions. The idea is controversial, but evidence is mounting that the Earth’s geology has largely been driven by such events. This would also explain why our planet has so few impact crater remnants.

December 2002. Did a Comet Swarm Kill the Dinosaurs? by DAVID TYTELL, Sky & Telescope magazine, p. 24. IN 1991 A MODERN SCIENTIFIC “WHODUNIT” WAS SOLVED WHEN geologists identified a deeply buried, 180-kilometer-Wide crater in the Yucatan peninsula. Now known as Chicxulub, the scar resulted from the impact of a 10-km asteroid or comet nucleus 65 million years ago. Geologic evidence indicates that the impact triggered global tidal waves, worldwide firestorms, and massive earthquakes. It also left a worldwide layer of extraterrestrial dust. When Earth finally returned to normal, the dinosaurs and the majority of all then-living species had gone extinct, opening the way for mammals to diversify and dominate Earth. …Now a new study suggests that Chicxulub may not have been an isolated event. Rather, the dinosaurs may have been the victims of a one-two punch.