# Could the dinosaurs have seen the asteroid that killed them?

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Wikipedia says the Chicxulub impactor is thought to have been a 10-15 km diameter object. Would it have been visible to a (human*) naked eye before impact? And if so, would it have appeared like a star that grew brighter and brighter each night?

* I know, there were no humans at the time.

The answer is yes; for a few nights prior to the impact (assuming they had eyes with a similar sensitivity to our own and could look up!). It could also be much longer than this if the object was a cometary body.

Details:

Impacting solar system objects would have relative closing speeds from around 11 to 72 km/s.

We could take the optimal case that the asteroid approaches whilst fully lit by the Sun (which probably precludes the minimum and maximum speed in the range quoted above) and then scale from another similar body - say the asteroid Vesta. This has a diameter of around $$a=520$$ km, gets as close as $$d=1.14$$ au from the Earth and has a maximum brightness of about $$m=5.2$$ apparent magnitude (and is hence just visible to the naked eye) and an observed flux $$f = f_0 10^{-0.4m}$$, where $$f_0$$ is a zeropoint for the magnitude scale.

Thus the flux $$f_n$$ received by a near-Earth asteroid of diameter $$a_n$$, at a distance $$d_n$$ from Earth (in au) and with the same reflectivity would be $$f_n = fleft(frac{a_n}{a} ight)^2 left(frac{1+d}{1+d_n} ight)^2 left(frac{d}{d_n} ight)^2$$

The magnitude of the dinosaur killer would then be $$m_n = m -2.5log (f/f_n)$$

To be an at all conspicuous naked eye object, $$f_n geq f$$. If we assume the dinosaur-killer had $$a_n=10$$ km, then $$d_n^2(1+d_n)^2 leq 0.0022$$

An approximate solution is obtained by assuming $$d_n ll 1$$ and thus we find $$d_n leq 0.047$$ au or 7 million km.

Moving at say 30 km/s, then it gets closer by 2.6 million km per day, thus hitting the Earth about 3 days after becoming a naked eye object. Obviously this would be longer for a slower approach speed or for a larger or more reflective asteroid. But shorter for a smaller, faster asteroid or if the asteroid approached from a direction not fully illuminated by the Sun or had a smaller albedo than Vesta.

Another possibility is that the object is of a cometary origin with an icy composition. If that were so then it could be much brighter as a result of sublimation, outgassing and having a bright cometary nucleus and tail. he answer would still be yes, but the visibility period could be weeks (comets are rather unpredictably bright).

It thus seems to me that there is a plausible range of parameters and trajectories where a dinosaur-killing asteroid could be observed and then observed to grow brighter over a few nights, but probably not much longer than that unless it was a comet.

A carbonaceous condrite has the same reflectivity as the moon at around 7-13%.

If there was ice, if the tail was 10 times smaller than Hale-Bopp, it would have auspiciously covered half of the sky. it could have made an incredible display in the 1-2 days preceding the collision, because it was as close to the sun as Hale-Bopp, the brightest astronomical apparition in history, although it was 100 times closer to the earth in the final days than Hale-Bopp. Hale-Bopp's trail was 1.5 million km long, so the KT asteroid would have needed a tail 100 times smaller, to appear as bright as Hale Bopp in the final 2 days! https://www.google.com/amp/s/www.space.com/amp/20354-dinosaur-extinction-caused-by-comet.html

$$frac{ ext{moon distance}}{ ext{moon diameter}} = 107 ext{ moon diameters}$$ away, so you can cover the moon with a thumb at arms length ( ~1cm/107cm) and the impactor would be nearly thumb sized at: $$ext{comet diameter} cdot107 = 1500 ext{km}$$ away.

If you were 1000km south of Chixculub, it would stay fairly constantly thumb sized for 10-20 seconds as it arrived from the South-East at 60 degrees, and in that time it would travel from 1500km above to 1000km on the horizon. The graph suggests it had a rotation period of about 2 to 10 seconds, so it would have revolved noticeably.

If you were 100km away from the impact, it would grow from thumb size to hand sized for 10-20 seconds. Then it would hit the atmosphere at 50km and the sky would ignite about 5 seconds prior to landfall.

For most of the dinosaurs far away, it would be like holding a pea or a matchstick at arms length.

Perhaps it would be brighter than Venus from 75000 km away; that's about 125 minutes prior to the impact.

It would have been like a fire fly landing slowly on a tennis court if the dino was on the other side of the world.

Mammals were nocturnal previous to the impact which is why mammals have developed whiskers, awesome hearing and only bichromatic photoreceptors of G.B, and mammal skin burns from UV. Only primates have R.G.B. Dinosaurs had R.G.B because birds have the same gene to encode red photoreceptors as tortoises who can also see red, so scientists think that dino's had vision as good as birds, and have better vision than mammals, especially used for detecting movement and for flying.

EDIT: On wiki, the estimated diameter of the comet has been changed to 10-80km. Hale-Bopp comet was 20-40km, and it was visible for months as one of the brightest comets in human history, with a similar aphelion of 0.914AU. That implies that the dinosaur comet may have been visible for many days prior to impact, because it would have been 5 times closer than Hale-Bopp at the end. It's possible that it was very bright in the sky for a week prior to impact.

## Do We Know What Killed the Dinosaurs?

What killed the dinosaurs? Their sudden disappearance 65 million years ago, along with at least 50 percent of all species then living on Earth, is known as the K-T event (Cretaceous-Tertiary Mass Extinction event). Many geologists and paleontologists now think that a large asteroid or comet impacting the Earth must have caused a global catastrophe that led to this extensive loss of life.

The Chicxulub crater in the Yucatan region of Mexico is a good candidate for the ancient point of impact. The crater is the right age – 65 million years old – and it is consistent with the impact of a 6- to 12-mile-wide asteroid. The asteroid would have to have been at least that large to cause global disruptions.

But how could one asteroid kill off over half of the species on Earth? Many scientists originally thought that the heat and dust of the asteroid impact could have caused the K-T extinction. The scalding heat of the impact would have killed off life locally, and then dust kicked up into the atmosphere would have caused the skies to darken worldwide – halting photosynthesis and causing temperatures to drop. Animals that normally fed on plant life would have soon died of starvation. The predators, lacking their traditional prey, would have hunted each other until eventually dying out as well.

But according to Buck Sharpton, planetary geologist with the University of Alaska, Fairbanks and NAI member, this “nuclear winter caused by dust” theory can’t fully explain the K-T extinction.

“Dust itself is fairly benign,” says Sharpton. “We always have dust being sent into the air today, for example, because of volcanic activity. While dust may have initially contributed to changes in the climate at the moment of impact, dust rarely causes fundamental climate changes because it rains out over a few weeks or years.”

Sharpton instead believes that long-term global climate changes were caused by the vaporization of carbonate and sulfate rocks. The increased amounts of sulfur and carbon in the atmosphere would have caused long-term changes in the Earth’s atmospheric chemistry. These changes, he says, lasted for hundreds of years, and probably led to the extinction of many animal species.

The Chicxulub region is especially rich in gypsum and other sulfur-containing materials. After the impact, both dust and the vaporized sulfur smog would have darkened the atmosphere and blocked sunlight. According to Sharpton, the dust would have rained out after the first few weeks or years, while the sulfur would have lasted from several decades to a century. With such a long-lasting sulfur smog, temperatures would have remained cool worldwide and photosynthesis would have been suspended for several lifetimes.

Sulfur was not the only vaporized element that affected the atmosphere. The impact at Chicxulub also vaporized carbonate rocks, releasing a lot of carbon dioxide (CO2) into the atmosphere. Sharpton says that while the sulfur would have been the dominant gas initially, after a century or so the sulfur would have rained out of the atmosphere. Then the CO2 would have been dominant, as it can remain in the atmosphere for 1,000 years without dissipating.

CO2 is a greenhouse gas, so temperatures – which had experienced a period of cooling because of the sulfur – would have immediately started to rise.

“This is the most detrimental swing you can imagine for organisms trying to cope,” says Sharpton. “Just as they begin to get comfortable with colder temperatures, you go and raise the heat on them.”

Sharpton says that temperatures probably only varied by about 10 degrees, but even such a subtle shift can have dramatic effects. A 10 degree variation, for instance, can substantially change how much of the world’s water is locked up in glaciers.

However, Kevin Pope, a geologist and archaeologist with Geo Eco Arc Research, doesn’t think the vaporized CO2 would have greatly affected the atmosphere.

“The amount of vaporized CO2 was not all that significant,” says Pope. “It would have, at most, doubled the amount of CO2 in the atmosphere. That’s the same sort of increase that’s occurred lately from the Industrial Revolution, and there’s a lot of controversy as to whether this current increase in CO2 really has any effect.”

In Pope’s view, the immediate short-term effects of smoke and atmospheric sulfur were the main culprits in causing extinction. Worldwide fires triggered by super-hot ejecta raining down after the Chicxulub impact would have generated smoke, and the combination of smoke and vaporized sulfur would have briefly darkened the skies. Pope says this would have shut down photosynthesis for six months at the most. And while Sharpton says the atmospheric sulfur would have lasted up to a century, Pope thinks it probably rained out much sooner.

“According to our models, the sulfur would have only had significant effects for a maximum of 10 years – but some have suggested it could even be less,” says Pope. “Once the sulfur rained out after a decade, the light levels and temperatures would have rebounded.”

Although Pope says the smoke and sulfur would not have lasted long, he thinks they could have triggered significant long-term global changes.

“You shut down photosynthesis for just one year, and the ecosystem collapses,” says Pope. 󈭓.9 percent of all life on the Earth is dependent on the Sun. Take out the Sun, and you knock out the first tier of life. The brief cold spell could have pushed the Earth into a new regime, altering the atmosphere and the ocean’s circulation, leading to changes in the carbon cycle that lasted hundreds to millions of years.”

Sharpton does not agree with Pope’s assertion that short-term darkness could have caused global extinctions, however.

“As those of us who live in the Arctic know, plants and animals can tolerate several months of darkness quite easily,” says Sharpton. “Paleobotanical studies of the Canadian High Arctic, for example, show that during the Early Tertiary, stands of maple trees, crocodiles, and other temperate and even tropical species existed. These times were warm but they were characterized nonetheless by extended periods of darkness where photosynthesis was not possible.”

Whatever global climate changes occurred, more than just the dinosaurs were affected. Almost all large land vertebrates and tropical invertebrates were wiped out. Many water-dwelling organisms died as well. Acid rains – created by the mixing of vaporized sulfur and water – acidified lakes and streams.

According to Sharpton, the acid rains also acidified the top layers of the oceans, especially near the impact site. This killed off the plankton-like microscopic foraminifera, which lived in the top ocean layers.

“The calcium carbonate-shelled microorganisms were in trouble when it began to rain sulfuric acid, because acid dissolves limestone,” says Sharpton. “Those organisms found themselves in a world of hurt.”

Pope disagrees with this assessment however, and says the acid rains could not have acidified the top layers of the oceans.

“There definitely was acid rain,” says Pope, “and clearly a lot of microorganisms were hit hard. The acid rains would’ve acidified the lakes and streams, and it would have also acidified the soil, affecting plant life. But there just wasn’t enough acid to acidify the top layers of the oceans they’re too vast.”

Pope instead thinks the forminafera were harmed by the decrease in sunlight when smoke and sulfur darkened the sky.

“Darkness either directly caused the organisms to shut down, or it affected the photosynthesizing plankton that they ate,” says Pope. “These organisms lived in the top 30 to 100 meters of the ocean, where sunlight can pass through. There is no energy reserve – when you shut off the sunlight, they just die, and everything dependent on them dies. It’s not like the mammals that were able to scavenge on the dead and thereby survive.”

But Sharpton argues that planktonic lifeforms merely become inactive during periods of darkness.

“The Arctic and Bering Sea, as well as much of the southern ocean, are continuously dark six months every year and yet plankton abound,” says Sharpton.

Regardless of how they died, many scientists now look to foraminifera rather than dinosaurs and other land animals to record the rate of extinction at the K-T boundary.

“Dinosaur fossils are very rare,” explains Pope. “Of all the dinosaurs that were once on the planet, we have only found a fraction of a percent. Because they’re so rare, tracing the dinosaur fossil record is hard. A better fossil record to trace is the marine microfossils. They are very diverse, evolve quickly, were superabundant, and so much easier to track. They show a clearer story of extinction at the K-T boundary.”

Sharpton says that although the Chicxulub impact seems to be the logical cause of the K-T extinction, there’s still a lot we don’t know. In fact, he says we may never know the exact cause of extinction.

“We have good circumstantial evidence,” says Sharpton. “In a general sense, we have it nailed down, the case is closed. But as to the particular cause of the extinction, be it dust, sulfur, CO2, or smoke, we don’t know. When you roll all those things up together, it’s a wonder that anything on the planet survived!

“It makes me think sometimes that we’re all out to lunch – that there’s something critical that we’re overlooking.”

It’s possible, he suggests, the impact could have affected just a few key organisms that were somehow interconnected with many other species.

“It’s like the stack of cans at the grocery store – remove a few of the top cans, and the structure remains sound, but take out a bottom can – a load-bearing can – and the whole thing will come tumbling down,” says Sharpton. “It could be that the interconnection between organisms is so absolute – and yet so subtle – that removing only a few organisms would cause the whole biosphere to collapse.”

Studying impact events like the Chicxulub crater can help astrobiologists understand the close connection between life, geology, chemistry – and how such impacts may disrupt this relationship. Sharpton, for one, doesn’t see such impacts as a completely destructive force.

“The Earth is such a complex and fragile structure, but it managed to withstand the Chicxulub event,” says Sharpton. “Life rebounded. These impacts destroy life, but they can also promote evolution. If it weren’t for the Chicxulub impact, where would we be today?”

Sharpton will be drilling at Chicxulub this summer with a team of scientists. He is also studying a crater in Siberia that he thinks will help planetary scientists better understand impact events on Mars.

“The impact [in Siberia] was made in volcanic rocks very similar to the rocks in the upper layers of Mars,” says Sharpton. “ The crater has a nice lake, and at the bottom of the lake are sediments that record the climatic history over 3.5 million years. We should start drilling there with the Russians in a few years.”

Pope is currently studying the hydrothermal system associated with the Sudbury crater in Canada. The crater is the same size as the Chicxulub crater, but it is much older – about 1.85 billion years old. It was formed when there was no multi-cellular life on Earth. Like Sharpton, Pope thinks his studies of impact craters could have implications for Mars research.

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## Ferns and Conifers

Forests used to look a lot different in the Cretaceous Period. Dinosaurs would have roamed through ecosystems that were a mixture of ferns, conifers like the curious-looking monkey puzzle tree and others. Only about half of the flora was constituted of flowering plants.

Fossil evidence shows that the forests were relatively open back then, with a lot of light likely reaching the forest floor. “Trees were actually growing really far apart,” Carvalho says.

It’s unclear what happened immediately after Chicxulub. Photosynthesis would have largely shut down for up to a century or so as dust from the initial impact blocked sunlight. Ash from the numerous fires triggered by flaming debris also helped to clog up the atmosphere.

“Whatever was able to survive were seeds that would have been a lot more resistant,” Cavalho says.

Overall, there was a 45 percent loss in tropical plant diversity that took nearly 7 million years to recover, her research shows.

## Still believe an asteroid killed the dinosaurs? Think again—new theory suggests

Psychology professor Gordon Gallup (left) and his former student Michael Frederick (right) claim that due to a psychological deficit, the dinosaurs were dying off long before the notorious asteroid hit. Credit: University at Albany

Some experts have long believed that a massive asteroid was a primary cause of dinosaurs' extinction some 65 million years ago, but new analysis from a University at Albany psychology professor suggests that the dinosaurs were in trouble long before the asteroid hit.

Professor and evolutionary psychologist Gordon Gallup and his former student Michael J. Frederick, now of the University of Baltimore, assert that the emergence of toxic plants combined with dinosaurs' inability to associate the taste of certain foods with danger had them already drastically decreasing in population when the asteroid hit.

"Learned taste aversion" is an evolutional defense seen in many species, in which the animal learns to associate the consumption of a plant or other food with negative consequences, such as feeling ill. To explain the defense mechanism, Gallup offers the example of rats.

"A reason why most attempts to eliminate rats have not been successful is because they, like many other species, have evolved to cope with plant toxicity," said Gallup. "When rats encounter a new food, they typically sample only a small amount and if they get sick, they show a remarkable ability to avoid that food again because they associate the taste and smell of it with the negative reaction."

The first flowering plants, called angiosperms, appear in the fossil record well before the asteroid impact and right before the dinosaurs began to gradually disappear. Gallup and Frederick claim that as plants were evolving and developing toxic defenses, dinosaurs continued eating them despite gastrointestinal distress. Although there is uncertainty about exactly when flowering plants developed toxicity and exactly how long it took them to proliferate, Gallup and Frederick note that their appearance coincides with the gradual disappearance of dinosaurs.

In addition to studying the proliferation of toxic plants while dinosaurs were alive, Gallup and Frederick examined whether or not birds (considered to be a descendant of dinosaurs) and crocodilians (also considered to be descended from dinosaurs) could develop taste aversions. They found that the birds, rather than forming aversions to taste, developed aversions to the visual features of whatever made them sick. Still, they knew what they shouldn't eat in order to survive. In a previous study in which 10 crocodilians were fed different types of meat, some slightly toxic, Gallup discovered that like dinosaurs, crocodilians did not develop learned taste aversions.

"Though the asteroid certainly played a factor, the psychological deficit which rendered dinosaurs incapable of learning to refrain from eating certain plants had already placed severe strain on the species," said Gallup. "The prevailing view of dinosaur extinction based on the asteroid impact implies that the disappearance of dinosaurs should have been sudden and the effects should have been widespread, but the evidence clearly shows just the opposite: Dinosaurs began to disappear long before the asteroid impact and continued to gradually disappear for millions of years afterward."

The full paper is published in the peer-reviewed Ideas in Ecology and Evolution.

It was tens of miles wide and forever changed history when it crashed into Earth about 66 million years ago.

The Chicxulub impactor, as it’s known, was a plummeting asteroid or comet that left behind a crater off the coast of Mexico that spans 93 miles and goes 12 miles deep. Its devastating impact brought the reign of the dinosaurs to an abrupt and calamitous end, scientists say, by triggering their sudden mass extinction, along with the end of almost three-quarters of the plant and animal species then living on Earth.

The enduring puzzle has always been where the asteroid or comet originated, and how it came to strike the Earth. And now a pair of Harvard researchers believe they have the answer.

In a study published in Scientific Reports, Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard, and Amir Siraj ’21, an astrophysics concentrator, put forth a new theory that could explain the origin and journey of this catastrophic object and others like it.

Using statistical analysis and gravitational simulations, Loeb and Siraj say that a significant fraction of a type of comet originating from the Oort cloud, a sphere of debris at the edge of the solar system, was bumped off-course by Jupiter’s gravitational field during its orbit and sent close to the sun, whose tidal force broke apart pieces of the rock. That increases the rate of comets like Chicxulub (pronounced Chicks-uh-lub) because these fragments cross the Earth’s orbit and hit the planet once every 250 to 730 million years or so.

“Basically, Jupiter acts as a kind of pinball machine,” said Siraj, who is also co-president of Harvard Students for the Exploration and Development of Space and is pursuing a master’s degree at the New England Conservatory of Music. “Jupiter kicks these incoming long-period comets into orbits that bring them very close to the sun.”

It’s because of this that long-period comets, which take more than 200 years to orbit the sun, are called sun grazers, he said.

“When you have these sun grazers, it’s not so much the melting that goes on, which is a pretty small fraction relative to the total mass, but the comet is so close to the sun that the part that’s closer to the sun feels a stronger gravitational pull than the part that is farther from the sun, causing a tidal force” he said. “You get what’s called a tidal disruption event and so these large comets that come really close to the sun break up into smaller comets. And basically, on their way out, there’s a statistical chance that these smaller comets hit the Earth.”

The calculations from Loeb and Siraj’s theory increase the chances of long-period comets impacting Earth by a factor of about 10, and show that about 20 percent of long-period comets become sun grazers. That finding falls in line with research from other astronomers.

The pair claim that their new rate of impact is consistent with the age of Chicxulub, providing a satisfactory explanation for its origin and other impactors like it.

Understanding Chicxulub impactor is not just crucial to solving a mystery of Earth’s history but could prove pivotal if such an event were to threaten the planet again, contends Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard. Kris Snibbe/Harvard file photo

“Our paper provides a basis for explaining the occurrence of this event,” Loeb said. “We are suggesting that, in fact, if you break up an object as it comes close to the sun, it could give rise to the appropriate event rate and also the kind of impact that killed the dinosaurs.”

Loeb and Siraj’s hypothesis might also explain the makeup of many of these impactors.

“Our hypothesis predicts that other Chicxulub-size craters on Earth are more likely to correspond to an impactor with a primitive (carbonaceous chondrite) composition than expected from the conventional main-belt asteroids,” the researchers wrote in the paper.

This is important because a popular theory on the origin of Chicxulub claims the impactor is a fragment of a much larger asteroid that came from the main belt, which is an asteroid population between the orbit of Jupiter and Mars. Only about a tenth of all main-belt asteroids have a composition of carbonaceous chondrite, while it’s assumed most long-period comets have it. Evidence found at the Chicxulub crater and other similar craters that suggests they had carbonaceous chondrite.

This includes an object that hit about 2 billion years ago and left the Vredefort crater in South Africa, which is the largest confirmed crater in Earth’s history, and the impactor that left the Zhamanshin crater in Kazakhstan, which is the largest confirmed crater within the last million years.

The researchers say that composition evidence supports their model and that the years the objects hit support both their calculations on impact rates of Chicxulub-sized tidally disrupted comets and for smaller ones like the impactor that made the Zhamanshin crater. If produced the same way, they say those would strike Earth once every 250,000 to 730,000 years.

## How dinosaurs could have survived killer asteroid

The space rock that wiped out most of the dinosaurs may have had a colossal case of bad timing. If the impact had occurred a few million years earlier or later, more of the majestic beasts may have survived, scientists say.

A global team of researchers examined the evidence for different extinction scenarios and concluded that an asteroid or comet almost certainly triggered the abrupt annihilation of all dinosaurs, except for birds, some 66 million years ago.

Skull of a T. rex dinosaur. CBS News

But a period of low diversity among herbivorous dinosaurs, at least in North America, may have set the stage for the massive die-off, according to a study published today (July 28) in the journal Biological Reviews. [Wipe Out: History's Most Mysterious Extinctions]

"The dinosaur extinction is one of the great mysteries in all of science," said study co-author Stephen Brusatte, a paleontologist at the University of Edinburgh in Scotland. "A group of us decided to come together and present a consensus."

Brusatte and 10 other recognized dinosaur experts from around the world convened and reviewed the latest fossil evidence from North America at the end of the Cretaceous Period, which spanned from 146 million to 66 million years ago. A geological layer known as the K-Pg boundary (formerly known as the K-T boundary) marks the end of this period, and with it, the age of Earth's most charismatic beasts.

### Trending News

Despite some differences, the researchers agreed unequivocally that a meteor impact -- from an asteroid, or, some say, a comet -- most likely killed the dinosaurs, and that the die-off happened quickly, not gradually, as some researchers believe.

"The extinction was abrupt," happening within a few tens of thousands to hundreds of thousands of years, or even quicker, Brusatte told Live Science. "Dinosaurs weren't wasting away for tens of millions of years." [Crash! 10 Biggest Impact Craters on Earth]

Volcanic eruptions, fluctuating temperatures and changes in sea level were sculpting the planet a few million years before the giant space rock pummeled the planet and carved out the 110-mile-wide (180 kilometers) Chicxulub crater in Mexico. A giant sea once bisected North America from the Gulf of Mexico to the Arctic, but a drop in sea levels exposed more land, which means dinosaur species that once thrived separately would have had to compete with one another.

So why did most dinosaurs die out, when a few -- namely, birds, as well as mammals and other creatures -- survived? In fact, many birds did go extinct, so it may have been random, Brusatte said. The truth is, scientists don't know what made most dinosaurs so susceptible to extinction.

However, computer simulations suggest that changes in the climate and landscape reduced the number of different plant-eating dinosaurs in North America, which formed the base of the dino food chain.

When the asteroid or comet hit, it may have come at a really bad time. The impact would have triggered tsunamis, earthquakes, wildfires and temperature fluctuations, and the loss of dinosaurs at the bottom of the food chain would have had a domino effect on the dinosaurs that fed on them.

Dinosaur evolution and extinction Brusatte et al, Biological Reviews

Could they have survived?

If the meteor had hit a few million years before, when a richer array of herbivorous dinosaurs populated North America, or a few million years later, when the salad-munching giants had recovered some diversity, the space rock may not have triggered a dinopocalypse, the researchers said.

Experiencing the meteor impact was a bit like getting hit by a bus, Brusatte said. Having low herbivore diversity would be like limping across the road with a sprained ankle -- you're more likely to get run over, he said.

Still, the researchers only looked at the winnowing of herbivore species in North America, said study co-author Richard Butler, a paleontologist at the University of Birmingham in England.

"The great uncertainty at this stage is whether what we see in the North American fossil record really reflects what was going on in the rest of the world," Butler told Live Science.

At any rate, the findings in North America suggest that ecosystems are deeply interconnected, the researchers said. Perhaps that's a lesson for humanity today, as human activities continue to threaten biodiversity.

"I think dinosaurs are a cautionary tale," Brusatte said. "When you mess with diversity," he said, "you can be even more susceptible to a knockout blow."

## Asteroid that Killed the Dinosaurs Hit at Worst Possible Angle

A round 66 million years ago, an asteroid larger than Mt. Everest ripped through the atmosphere of Earth, striking our planet at the Yucatán Peninsula, on the southeastern coast of Mexico. This event set off fires around the globe, and the dust kicked into the air blocked out the Sun over large portions of the world. Soon, the era of dinosaurs, which lasted 175 million years, was snuffed out.

Simulations show the asteroid that killed the dinosaurs struck Earth at an angle around 60 degrees to the surface of Earth. Striking at this angle, the asteroid kicked up the greatest possible amount of dust, maximizing climate change, killing off the clade of animals, as well as 75 percent of other species on Earth.

The dust lifted into the atmosphere, including millions of tons of sulfur, blocked out the Sun, creating a “nuclear winter” worldwide.

“For the dinosaurs, the worst-case scenario is exactly what happened. The asteroid strike unleashed an incredible amount of climate-changing gases into the atmosphere, triggering a chain of events that led to the extinction of the dinosaurs. This was likely worsened by the fact that it struck at one of the deadliest possible angles,” said Professor Gareth Collins of Imperial’s Department of Earth Science and Engineering, lead researcher on the study.

Researchers developed the first-ever 3D computer simulations modeling the entire event from initial impact to the formation of the Chicxulub Crater which marks the spot where the asteroid hit Earth. The simulation examined the effects of an asteroid having a diameter of 17 kilometers (10.5 miles) traveling at 43,200 kilometers per hour (26,800 MPH).

The study found the asteroid that killed the dinosaurs came in from the northeast at a 60-degree angle, maximizing the amount of material thrown into the atmosphere. Following the impact, crustal material fell back into the initial crater, forming the geological feature we see today.

The computer simulation showing the beginning and end of impacts at 30 degrees (left) and 60 degrees (right). Image credit: Imperial College London

“We considered four impact trajectory angles, measured relative to the target surface: 90∘ (vertical), 60∘, 45∘ and 30∘. Simulations were performed at two impact speeds: 20 and 12 km/s. The slower speed was used for computational expediency and to afford direct comparison of the vertical impact case with previous 2D simulations. The higher impact speed is approximately the average speed that asteroids encounter Earth and is hence more representative of the likely impact speed of the Chicxulub impact,” researchers describe in an article announcing their findings, published in Nature Communications.

The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary (K–T) extinction, was first found to be the result of an asteroid strike when geologist Walter Alvarez found a thin layer of iridium around the world in the late 1970’s. This element is normally rare on Earth, but fairly common in asteroid, suggesting its extraterrestrial origin.

In the era leading up to the time of impact, massive volcanoes in the Deccan Traps in northwestern India were erupting, sending massive quantities of gas and dust into the atmosphere, greatly altering the climate of the planet.

Sulfur, and Thanks for All the Fish

“Dinosaurs are extinct today because they lacked opposable thumbs and the brainpower to build a space program.”
― Neil deGrasse Tyson

Geological examination of the Chicxulub Crater lent further evidence to findings made using the computer simulation. Central to this evidence was examination of a ring of mountains found inside the crater rim and dense, uplifted rock found 30 km (19 miles) beneath the surface of the crater. The simulation, when set to impact at 60 degrees, produced nearly identical features as those seen in the real world.

A gravity map, showing the density of rocks beneath the Chicxulub Crater. Image credit: Imperial College London

“Despite being buried beneath nearly a kilometre of sedimentary rocks, it is remarkable that geophysical data reveals so much about the crater structure — enough to describe the direction and angle of the impact,” Dr. Auriol Rae of the University of Freiburg stated.

The ground around the asteroid impact site is rich with water, as well as porous carbonate and evaporite rocks. The heat and diffusion of material would have sent massive quantities of water vapor, carbon dioxide, and sulfur into the atmosphere.

Once in the air, sulfur would form aerosols, minuscule particles capable of blocking sunlight, triggering the nuclear winter. A rapidly cooling climate and forest fires around the world, paired with the loss of photosynthesis feeding plants, resulted in the extinction of most of the life on Earth, researchers suggest.

Earlier studies only examined the earliest stages of the impact. This new study could help researchers better understand the nature of massive craters on other worlds.

#### James Maynard

James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.

## Explosive timing

That paper's authors also uncovered a surprise: Their new dating showed that about 75 percent of the lava created by the Deccan Traps erupted after the impact. If further research confirms it, that's a novel finding, as previous studies suggested that only 20 percent of the lava flowed after the asteroid or comet hit.

The scientists used a precise dating method called argon-argon dating to measure rocks formed around the same time as the mass extinction at the end of the Cretaceous and beginning of the Tertiary period. This area in the geological record is called the K-Pg boundary (formerly known as the K-T boundary).

In the new paper, this team built on previous research they'd done pinpointing the date of the impact, which rocks collected in Montana suggested occurred 66,052,000 years ago, give or take 8,000 years.

They have also tackled the Deccan Traps dating conundrum before, in a 2015 investigation of Indian samples that showed that in at least one location, the eruptions happened within 50,000 years of the impact. Now, the scientists have obtained similar dates from a total of 19 rocks found at other locations in the Deccan Traps.

If most of the lava shot out after the impact, this has large implications for how the extinction played out. Here's what the standard narrative has been: If most of the Deccan Traps lava burst out before the impact, then the gases it generated could have caused global warming during the last 400,000 years of the Cretaceous. Observations show that global temperatures increased by about 14.4 degrees Fahrenheit (8 degrees Celsius), which would have forced species to evolve to live in these warmer temperatures. Then the disturbed ecosystem would have collapsed amid sudden global cooling after the impact kicked up dust (blocking the sun) or the volcanic gases cooled the climate.

The new scenario suggests climate change happened even before the eruptions peaked. If this happened, gases would have trickled out from underground magma chambers over a long period , similar to what is observed today at Mount Etna in Italy and Popocatepetl in Mexico. [In Pictures: The Giant Crater Beneath Greenland Explained]

"This changes our perspective on the role of the Deccan Traps in the K-Pg extinction," lead author Courtney Sprain, a former Berkeley doctoral student who is a postdoctoral researcher at the University of Liverpool in the United Kingdom, said in the same statement. "Either the Deccan eruptions did not play a role — which we think unlikely — or a lot of climate-modifying gases were erupted during the lowest volume pulse of the eruptions."

There are many open questions with this research, though, particularly since volcanoes can produce both cooling and warming gases. And scientists have never been able to measure the output of a massive flood basalt eruption like the one at Deccan Traps in real time — the last such eruption finished about 15 million years ago, in the Pacific Northwest.)

The second new study also complicates matters, calculating slightly different date estimates for the Deccan Traps eruption. (The two groups analyzed different minerals furthermore, one focused on the lava flows themselves, and the other on sediments found between lava flows.)

The research is described in two papers published today (Feb. 21) in the journal Science.

## Dinosaur-Killing Space Rock Created Dramatic Temperature Drop

Dinosaurs such as Tyrannosaurus rex and Triceratops became extinct about 66 million years ago, after an asteroid strike resulted in plunging temperatures. According to a new study, the frigid weather that ultimately led to their extinction was far worse than earlier models suggested.

At the end of the Cretaceous era, a massive asteroid — approximately 7 miles (12 kilometers) wide — crashed into a limestone- and gypsum-rich region, now known as the Yucatán Peninsula in the Gulf of Mexico. A new study estimates that the sun-absorbing sulfur — which vaporized into the atmosphere after the asteroid hit the gypsum — was three times more abundant than previous models estimated.

Of course, the asteroid impact itself was terrible for local animal inhabitants, which may have perished in the crash's immediate aftereffects such as tsunamis and landslides. But the asteroid's impact site was an extra stroke of bad luck for the rest of the planet, according to Natalia Artemieva, a senior scientist at the Planetary Science Institute in Tucson, Arizona, and co-author of the new study.

"The impact site in the current Gulf of Mexico had 3-km [of] thick sedimentary cover, a combination of limestone… and sulfur-bearing evaporites," Artemieva told Space.com in an email. "It's kind of a joke that 66 million years ago the asteroid fell into the worst possible place on Earth . "would impact [have] occur[ed] into the ocean or into silicate rocks (such as granite), dinosaurs would be still alive."

The so-called Cretaceous-Paleogene extinction event wiped out many species, including all of the non-avian dinosaurs, according to a 2012 study by Paul Renne et al. According to a statement released by the American Geophysical Union, researchers often attribute that extinction event — to the asteroid collision that hit the Yucatán Peninsula, which combined with other forces of climate change - like the Deccan Plateau volcanic eruptions - to make for hostile global environments.

The space rock would have thrown enormous amounts of dust, sulfur and carbon dioxide into the atmosphere, and it was the abundance of sulfur in these clouds that may have caused Earth's average surface air temperatures to drop by as much as 47 degrees Fahrenheit (26 degrees Celsius) in the long term. According to the new study, detailed Oct. 30 in the journal Geophysical Research Letters, the dramatically cooler temperatures lasted about three years after the asteroid impact.

Artemieva, co-author Joanna Morgan of Imperial College London and their team came across these findings by using a model that, according to the study, had "the capability to simulate the dynamics of different materials within the impact plume." The different materials displaced by the space rock each act differently when shock-waves hit them, so by fine-tuning the ejection models, the team could predict how much of each temperature-altering gas was ejected high enough to linger in the atmosphere upon impact.

The team calculated only the gases that flew with a minimum velocity of 1 kilometer per second (0.62 miles per second, or 2,200 mph) into the atmosphere, because gases thrown at slower speeds were likely unable to reach a high enough altitude to influence the climate, Artemieva said. Older models with less computing power are therefore less accurate, she added, because they didn't isolate for a material's chances of staying in the atmosphere. Instead, the older models calculated all of the material that turned into vapor upon impact. Researchers now know that if material is vaporized, it doesn't mean it reached the atmosphere and caused climatic change, since much of it actually stayed near the crater.

Recent geophysical studies, including more up-to-date information on how rocks behave under extreme conditions and various impact angle models, suggest the Chicxulub crater formed when hit at an approximately 60-degree angle. The revised data means more sulfur was ejected into the sky, the researchers said. According to Artemieva, volcanoes may offer insight into the effect this mineral has on Earth's climate when it gets pummeled into tiny solid particles known as aerosols.

"Sulfur aerosols … cause cooling as they block incoming sunlight. Currently, the amount of CO2 and SOx [sulfur oxide] in Earth's atmosphere are balanced somehow, and we have our current (quite comfortable) climate," Artemieva said. Volcanic eruptions, for example, release a lot of sulfur into the atmosphere, which can cause local cooling, and even global cooling for one to two years, she added.

## Human Impact on the Amazon Rainforest

Today’s rainforests are under serious threat from human activity. The Amazon, for example, saw its highest rate of deforestation in 12 years during 2020. There are concerns that if enough trees are felled, much of the forest would pass a tipping point at which it would no longer be able to make its own rain and would degrade into grassland. ﻿ ﻿

Worldwide, biodiversity is also under threat to such an extent that scientists have said we are in the midst of the sixth mass extinction. ﻿ ﻿ Carvalho says that the 45% of plant species that were wiped out when the asteroid hit is roughly equivalent to the number of species predicted to go extinct by the end of the century if habitat destruction continues.

A loss like that cannot be recovered easily. Jaramillo says it took around seven million years for tropical forests to regain the amount of biodiversity it had before the asteroid hit. We can expect a similar lag if we wipe out the unique species now flourishing in the Amazon.