# How loud was the asteroid that killed the dinosaurs?

Asteroid impacts on the Earth can be very loud when they break up in the atmosphere, like Chelyabinsk, captured in this video:

The Chelyabinsk asteroid break-up was estimated to be about 180dB at 3 miles, and was detected as far as 9000 miles away.

If asteroids don't break up, presumably they are extremely loud on impact as well. How loud was the asteroid that killed the dinosaurs either on atmospheric entry or impact with the ocean?

Some estimates which I found worth sharing:

1. For fun, I searched forChixculub TNT equivalentand e.g. ScienceDaily claims

The energy released by the impact that blew out the Chicxulub crater was equivalent to about 100 million megatons, many orders of magnitude greater than the nuclear explosion at Hiroshima, a 15-kiloton blast.

This seems to match up what WolframAlpha uses to rank TNT equivalents.

2. There is a Noise Prediction Calculator which estimates the safe distance from a blast:

This calculator can be used to predict the distance from an open detonation at which 140 decibels (dB) could be expected to be achieved. The 140dB level is widely used as a "safety cutoff" for exposure to impulsive noises while using hearing protection.

Plugging in $$10^{17} { m kg}$$ (of TNT) in that formula (which is probably a rather crude estimate) gives $${460,320 m km} approx 1.4 cdot (2 pi a_oplus)$$ (with $$a_oplus$$ being the Earth's radius), meaning more than equatorial circumference of our planet. In other words, no where on Earth was it safe according to UN safety standards.

So let us approach it the other way round: What is the loudest possible sound?

Strictly speaking, the loudest possible sound in air, is 194 dB. The “loudness” of the sound is dictated by how large the amplitude of the waves is compared to ambient air pressure. A sound of 194 dB has a pressure deviation of 101.325 kPa, which is ambient pressure at sea level, at 0 degrees Celsius (32 Fahrenheit). Essentially, at 194 dB, the waves are creating a complete vacuum between themselves.

You can go louder than 194 dB, but that's not technically a “sound” anymore. The extra energy starts distorting the entire wave, and you end up with something that's more a shockwave and less a soundwave. At that level, sounds don't pass through air - they push the air along, producing pressurized burst (shockwaves).

On the shockwave of Chicxulub, I found the page at the Lunar and Planetary Institute insightful:

The Chicxulub Impact event produced a shock wave and air blast that radiated across the seas, over coastlines, and deep into the continental interior. Winds far in excess of 1000 kilometers per hour were possible near the impact site, although they decreased with distance from the impact site. The pressure pulse and winds would have scoured soils and shredded vegetation and any animals living in nearby ecosystems. An initial estimate of the area damaged by an air blast was a radius 1500 kilometers. There are several factors that can affect this estimate, so the uncertainty might be better reflected in a range of radii from ~900 to ~1800 km. The travel times are quite short, so this effect would have occurred in advance of any falling debris ejected from the Chicxulub crater.

Equipped with all this, we can now try to answer "How loud was the Chixculub explosion?" even if you did not specify where you measure loudness: At the radius of $$approx 1,500 { m km}$$ from the epicenter, the shockwaves "fades" out to become the loudest possible sound of 194dB.

## The asteroid that killed dinosaurs caused the birth of something great

A cataclysmic asteroid impact set the stage for one of Earth’s most diverse ecosystems.

When an asteroid slammed the Yucatán Peninsula 66 million years ago, it was bad news for dinosaurs — and about 75 percent of plant and animal life on the planet. This event marks the Cretaceous-Paleogene boundary and the fiery end of the Mesozoic Era.

But without this cataclysmic impact, we wouldn’t have the iconic neotropical rainforests that spread across Central and South America today. This finding was published Thursday in the journal Science.

Co-lead author Carlos Jaramillo, a paleobiologist at the Smithsonian Tropical Research Institute in Panama, tells Inverse the event “transformed the evolutionary trajectory of the rainforest forever.”

“The forest that we have today is the byproduct of what happened at that precise time.”

What’s new — This large-scale study represents the culmination of about 14 years of work in Colombia, Jaramillo says. Until this point, what happened to tropical forests in South America after the Cretaceous-Paleogene extinction event was relatively unknown.

The study suggests the end of the Cretaceous was a real turning point in the structure and composition of this environment. What we recognize as a lush, biodiverse tropical rainforest today did not exist before the Paleocene.

It also took millions of years for the diversity of the forest to recover after the mass extinction event, which “should be a clear warning against deforestation and the rate at which we are currently intervening on the planet,” says Mónica Carvalho, a postdoctoral fellow at the Smithsonian Tropical Research Institute and co-lead study author.

Background — Neotropical rainforests are unique environments that have what is called a closed canopy.

“You go to the rainforest today, you realize that there is a green carpet at the top of the trees,” Jaramillo says. “Every single space at the top of the canopy is occupied by a leaf because this is where most of the photosynthesis is happening.”

To figure out what forests looked like in the past, paleobiologists need to consult the record of ancient plant life. Analyzing the structure and composition of forests involves a science called palynology, the study of pollen. Counting and identifying thousands of fossil pollen grains across columns and layers of rock gives an idea of how the composition of plants in an area changed broadly over time.

Pollen examination can also determine the abundance of flowering plants, also called angiosperms, versus other plants that release spores, such as ferns. Leaf fossils are useful for determining if the forest had a closed canopy or not.

How they did it — Unraveling records of terrestrial life in deep time isn’t easy: ancient climate records on land are typically lost to decomposition and erosion. Carvalho, Jaramillo, and 19 other study authors worked for over a decade, doing an enormous amount of fieldwork, searching out pollen and thousands of leaf fossils to figure out how Cretaceous forests were impacted by the extinction event.

They looked at 39 different sections of rock and analyzed thousands of microscopic pollen grains found in different layers under the microscope. This, plus the thousands of leaf fossils, allowed the researchers to plot changes in the diversity and composition of flora before, during, and after the extinction event.

What they found — Cretaceous rainforests were quite different than the rainforests today, the findings suggest. There was plenty of light, and many gaps in the forest. Neotropical rainforests, the forests we recognize, made their appearance during the Paleocene — but it took another six million years before plant diversity recovered. Before the extinction event, the forests were about half ferns and half angiosperms, but in the new rainforests of the Paleocene, flowering plants rose to dominance.

Why did the forests shift from open to closed canopies across the end of the Cretaceous to the beginning of the Paleocene? Jaramillo says there are potentially three reasons why, and all of these factors could have been happening at the same time.

• It could have been that dinosaurs, especially large plant-eating ones, ate so much biomass it kept lighting shining through the forest during the Cretaceous.
• The change in the structure of the environment could have been from an increase in soil nutrients. It is even possible the ash fall from the asteroid impact provided a layer of fertilizer.
• Angiosperms may have been able to rise to dominance because there was selective extinction of ferns and other non-flowering plants due to their lack of ecological diversity.

Why it matters — Rainforests in Central and South America are some of the most biologically diverse locations on Earth, and this study shows how they got their start. The study also illustrates the fact that major changes to an environment can completely upend an ecosystem. It's an ominous lesson in the age of anthropogenic climate change.

More broadly, this research matters because it makes a critical discovery about deep time in an area of the world, South America, that is often underrepresented in paleontology. Jaramillo says many of the researchers who participated in this study are from Colombia and shows that “if you create a critical mass, we can produce good science.”

6 million years. Paleocene forests resembled modern Neotropical rainforests, with a closed canopy and multistratal structure dominated by angiosperms. The end-Cretaceous event triggered a long interval of low plant diversity in the Neotropics and the evolutionary assembly of today’s most diverse terrestrial ecosystem.

## Comet or Asteroid: What Killed the Dinosaurs And Where Did it Come From?

New theory explains possible origin of the Armageddon-causing object.

Cambridge, MA - It forever changed history when it crashed into Earth about 66 million years ago.

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

The enduring puzzle: Where did the asteroid or comet originate, and how did it come to strike Earth? Now, a pair of researchers at the Center for Astrophysics | Harvard & Smithsonian believe they have the answer.

In a study published today in Nature’s Scientific Reports , Harvard University astrophysics undergraduate student Amir Siraj and astronomer Avi Loeb put forth a new theory that could explain the origin and journey of this catastrophic object.

Using statistical analysis and gravitational simulations, Siraj and Loeb calculate that a significant fraction of long-period comets originating from the Oort cloud, an icy sphere of debris at the edge of the solar system, can be bumped off-course by Jupiter's gravitational field during orbit.

"The solar system acts as a kind of pinball machine," explains Siraj, who is pursuing bachelor's and master's degrees in astrophysics, in addition to a master's degree in piano performance at the New England Conservatory of Music. "Jupiter, the most massive planet, kicks incoming long-period comets into orbits that bring them very close to the sun."

During close passage to the sun, the comets — nicknamed "sungrazers" — can experience powerful tidal forces that break apart pieces of the rock and ultimately, produce cometary shrapnel.

"In a sungrazing event, the portion of the comet closer to the sun feels a stronger gravitational pull than the part that is further, resulting in a tidal force across the object," Siraj says. "You can get what's called a tidal disruption event, in which a large comet breaks up into many smaller pieces. And crucially, on the journey back to the Oort cloud, there’s an enhanced probability that one of these fragments hit the Earth."

The new calculations from Siraj and Loeb'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 sungrazers.

The pair say 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.

"Our paper provides a basis for explaining the occurrence of this event," Loeb says. "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."

Evidence found at the Chicxulub crater suggests the rock was composed of carbonaceous chondrite. Siraj and Loeb's hypothesis might also explain this unusual composition.

A popular theory on the origin of Chicxulub claims that the impactor originated from the main belt, which is an asteroid population between the orbit of Jupiter and Mars. However, carbonaceous chondrites are rare amongst main-belt asteroids, but possibly widespread amongst long-period comets, providing additional support to the cometary impact hypothesis.

Other similar craters display the same composition. 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 the timing of these impacts support their calculations on the expected rate of Chicxulub-sized tidally disrupted comets.

Siraj and Loeb say their hypothesis can be tested by further studying these craters, others like them, and even ones on the surface of the moon to determine the composition of the impactors. Space missions sampling comets can also help.

Aside from composition of comets, the new Vera Rubin Observatory in Chile may be able to observe tidal disruption of long-period comets after it becomes operational next year.

"We should see smaller fragments coming to Earth more frequently from the Oort cloud," Loeb says. "I hope that we can test the theory by having more data on long-period comets, get better statistics, and perhaps see evidence for some fragments."

Loeb says understanding this 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.

"It must have been an amazing sight, but we don't want to see that again," he said.

This work was partially supported by the Harvard Origins of Life Initiative and the Breakthrough Prize Foundation.

## Contents

In 1978, geophysicists Glen Penfield and Antonio Camargo were working for the Mexican state-owned oil company Petróleos Mexicanos, or Pemex, as part of an airborne magnetic survey of the Gulf of Mexico north of the Yucatán Peninsula. [10] Penfield's job was to use geophysical data to scout possible locations for oil drilling. [11] In the offshore magnetic data, Penfield noted anomalies whose depth he estimated, and mapped. He then obtained onshore gravity data from the 1940s. According to Penfield, "The old data showed a large concentric set of onshore gravity anomalies. When I laid it next to my No. 2 pencil mapping of the offshore magnetic anomalies, the fit was perfect: a shallow, 180-kilometer diameter gravity-magnetic bullseye on the almost non-magnetic, uniform carbonate background of the Yucatan platform! We recognized the crater as the likely Cretaceous-Paleogene boundary event." [4] [11] A decade earlier, the same map suggested an impact feature to contractor Robert Baltosser, but he was forbidden to publicize his conclusion by Pemex corporate policy of the time. [12]

Pemex disallowed release of specific data but let Penfield and company official Antonio Camargo present their results at the 1981 Society of Exploration Geophysicists conference. [13] That year's conference was underattended and their report attracted scant attention. Coincidentally, many experts in impact craters and the K–Pg (Cretaceous–Paleogene) boundary were attending a separate conference on Earth impacts. Although Penfield had plenty of geophysical data sets, he had no rock cores or other physical evidence of an impact. [11]

He knew Pemex had drilled exploratory wells in the region. In 1951, one bored into what was described as a thick layer of andesite about 1.3 kilometers (4,300 ft) down. This layer could have resulted from the intense heat and pressure of an Earth impact, but at the time of the borings it was dismissed as a lava dome—a feature uncharacteristic of the region's geology. Penfield tried to secure site samples, but was told such samples had been lost or destroyed. [11] When attempts at returning to the drill sites and looking for rocks proved fruitless, Penfield abandoned his search, published his findings and returned to his Pemex work.

At the same time, in 1980, geologist Walter Alvarez and his father, Nobel Prize–winning scientist Luis Walter Alvarez, put forth their hypothesis that a large extraterrestrial body had struck Earth at the time of the Cretaceous–Paleogene boundary. In 1981, unaware of Penfield's discovery, University of Arizona graduate student Alan R. Hildebrand and faculty adviser William V. Boynton published a draft Earth-impact theory and sought a candidate crater. [14] Their evidence included greenish-brown clay with surplus iridium containing shocked quartz grains and small weathered glass beads that looked to be tektites. [15] Thick, jumbled deposits of coarse rock fragments were also present, thought to have been scoured from one place and deposited elsewhere by a megatsunami resulting from an Earth impact. [16] Such deposits occur in many locations but seem concentrated in the Caribbean basin at the K–Pg boundary. [16] So when Haitian professor Florentine Morás discovered what he thought to be evidence of an ancient volcano on Haiti, Hildebrand suggested it could be a telltale feature of a nearby impact. [17] Tests on samples retrieved from the K–Pg boundary revealed more tektite glass, formed only in the heat of asteroid impacts and high-yield nuclear detonations. [17]

In 1990, Houston Chronicle reporter Carlos Byars told Hildebrand of Penfield's earlier discovery of a possible impact crater. [18] Hildebrand contacted Penfield in April 1990 and the pair soon secured two drill samples from the Pemex wells, stored in New Orleans. [19] Hildebrand's team tested the samples, which clearly showed shock-metamorphic materials.

A team of California researchers including Kevin Pope, Adriana Ocampo, and Charles Duller, surveying regional satellite images in 1996, found a cenote (sinkhole) ring centered on Chicxulub that matched the one Penfield saw earlier the cenotes were thought to be caused by subsidence of bolide-weakened lithostratigraphy around the impact crater wall. [20] More recent evidence suggests the crater is 300 km (190 mi) wide, and the 180-kilometre (110 mi) ring is an inner wall of it. [21]

Researchers at the University of Glasgow dated tektite samples from the impact as 66,038,000 ± 11,000 years old. [22]

The Chicxulub impactor had an estimated diameter of 11–81 kilometers (6.8–50.3 mi), and delivered an estimated energy of 21–921 billion Hiroshima A-bombs (between 1.3×10 24 and 5.8×10 25 joules, or 1.3–58 yottajoules). [23] For comparison, this is

100 million times the energy released by the Tsar Bomba, a thermonuclear device ("H-bomb") that remains the most powerful human-made explosive ever detonated, which released 210 petajoules (2.1×10 17 joules, or 50 megatons TNT). [24] The impact created a hole 100 kilometers (62 mi) wide and 30 kilometers (19 mi) deep, leaving a crater mainly under the sea and covered by 600 meters (2,000 ft) of sediment by the 21st century. [25] In addition, the impact created winds in excess of 1,000 kilometres per hour (620 mph) near the blast's center. [26]

One example of recent parameter estimates is in a 2020 study, [9] informed by data from crater core samples (taken by IODP-ICDP Expedition 364 in 2016). The authors simulate one scenario using an impactor that is 17 km in diameter, with a density of 2,650 kg/m 3 and therefore a mass of about 6.82×10 15 kg, striking Earth at 12 km/s with an angle of 60⁰ from horizontal. In another scenario that also approximately matches the evidence they analyzed, they simulate an impactor that is 21 km in diameter, with a mass of 1.28×10 16 kg, a speed of 20 km/s, and an impact angle of 45⁰. These values illustrate one set of experts' estimates based on current evidence and density parameter approximating that of a carbonaceous chondrite asteroid, often considered the likely type of the impactor.

### Effects Edit

The impact would have caused a megatsunami over 100 meters (330 ft) tall [27] that would have reached all the way to what are now Texas and Florida. [28] The height of the tsunami was limited by the relatively shallow sea in the area of the impact in deep ocean it would have been 4.6 kilometers (2.9 mi) tall. [27] Nonetheless, the most recent simulations show that waves may have been up to 1.5 kilometers (

1 mi) tall, able to reach the coastal lines all over the world. In reality, many types of tsunamis were triggered, with two main megatsunamis generated, respectively, by the direct blast and expansion of the transient crater and by the outward expansion of oceanic water after filling the crater (both 100–300 meters tall) two other kind of tsunamis, tens of meters tall, were triggered by massive slumps and landslides for seismic waves around the Gulf of Mexico and directly by seismic waves. There may have been back and forth tsunamis in time. [29] [30] [31] [32] A cloud of hot dust, ash and steam would have spread from the crater as the impactor burrowed underground in less than a second. [33] Excavated material along with pieces of the impactor, ejected out of the atmosphere by the blast, would have been heated to incandescence upon re-entry, broiling the Earth's surface and possibly igniting wildfires meanwhile, colossal shock waves would have triggered global earthquakes and volcanic eruptions. [34] Fossil evidence for an instantaneous die-off of diverse animals was found in a soil layer only 10 centimeters (3.9 in) thick in New Jersey 5,000 kilometers (3,100 mi) away from the impact site, indicating that death and burial under debris occurred suddenly and quickly over wide distances on land. [25] Field research from the Hell Creek Formation in North Dakota published in 2019 [35] shows the simultaneous mass extinction of myriad species combined with geological and atmospheric features consistent with the impact event. According to researchers, the impact triggered a seismic event equivalent to a Magnitude 12 earthquake at the impact site, with shockwaves generating the equivalent of Magnitude 9 earthquakes across the globe. In addition, the ensuing shockwaves likely triggered large-scale volcanic eruptions across the Earth the shockwaves probably contributed to the Deccan Traps flood basalt eruption, which was estimated to have occurred around the same time. [36]

The emission of dust and particles could have covered the entire surface of the Earth for several years, possibly a decade, creating a harsh environment for living things. Production of carbon dioxide caused by the destruction of carbonate rocks would have led to a sudden greenhouse effect. [37] Over a decade or longer, sunlight would have been blocked from reaching the surface of the Earth by the dust particles in the atmosphere, cooling the surface dramatically. Photosynthesis by plants would also have been interrupted, affecting the entire food chain. [38] [39] A model of the event developed by Lomax et al. (2001) suggests that net primary productivity (NPP) rates may have increased to higher than pre-impact levels over the long term because of the high carbon dioxide concentrations. [40]

In February 2008, a team of researchers led by Sean Gulick at the University of Texas at Austin's Jackson School of Geosciences used seismic images of the crater to determine that the impactor landed in deeper water than previously assumed. They argued that this would have resulted in increased sulfate aerosols in the atmosphere. According to the press release, that "could have made the impact deadlier in two ways: by altering climate (sulfate aerosols in the upper atmosphere can have a cooling effect) and by generating acid rain (water vapor can help to flush the lower atmosphere of sulfate aerosols, causing acid rain)." [41] This was borne out by the results of a drilling project in 2016 which found that sulfate-containing rocks found in the area were not found in the peak ring (the rocks found were from deep within the earth's crust instead), the interpretation being that they had been vaporized by the impact and dispersed into the atmosphere.

A long-term local effect of the impact was the creation of the Yucatán sedimentary basin which "ultimately produced favorable conditions for human settlement in a region where surface water is scarce." [42]

### Geology and morphology Edit

In their 1991 paper, Hildebrand, Penfield and company described the geology and composition of the impact feature. [43] The rocks above the impact feature are layers of marl and limestone reaching to a depth of almost 1,000 m (3,300 ft). These rocks date back as far as the Paleocene. [44] Below these layers lie more than 500 m (1,600 ft) of andesite glass and breccia. These andesitic igneous rocks were only found within the supposed impact feature, as is shocked quartz. [44] The K–Pg boundary inside the feature is depressed to 600 to 1,100 m (2,000 to 3,600 ft) compared with the normal depth of about 500 m (1,600 ft) measured 5 km (3 mi) away from the impact feature. [45]

Along the edge of the crater are clusters of cenotes or sinkholes, [46] which suggest that there was a water basin inside the feature during the Neogene period, after the impact. [45] The groundwater of such a basin would have dissolved the limestone and created the caves and cenotes beneath the surface. [47] The paper also noted that the crater seemed to be a good candidate source for the tektites reported at Haiti. [48]

### Astronomical origin of impactor Edit

The impactor is widely agreed to be of carbonaceous chondritic composition, based on geochemical evidence. [5] In 1998 a 2.5 mm sized meteorite was described from the North Pacific from sediments spanning the Cretaceous-Paleogene boundary, that was suggested to represent a fragment of the Chicxulub impactor. Analysis suggested that it best fit the criteria of CV, CO and CR carbonaceous chondrites. [49]

In September 2007, a report published in Nature proposed an origin for the asteroid that created the Chicxulub crater. [38] The authors, William F. Bottke, David Vokrouhlický, and David Nesvorný, argued that a collision in the asteroid belt 160 million years ago resulted in the Baptistina family of asteroids, the largest surviving member of which is 298 Baptistina. They proposed that the "Chicxulub asteroid" was also a member of this group. The connection between Chicxulub and Baptistina is supported by the large amount of carbonaceous material present in microscopic fragments of the impactor, suggesting the impactor was a member of an uncommon class of asteroids called carbonaceous chondrites, like Baptistina. [50] According to Bottke, the Chicxulub impactor was a fragment of a much larger parent body about 170 km (106 mi) across, with the other impacting body being around 60 km (37 mi) in diameter. [50] [51]

In 2011, new data from the Wide-field Infrared Survey Explorer revised the date of the collision which created the Baptistina family to about 80 million years ago. This makes an asteroid from this family highly improbable to be the asteroid that created the Chicxulub crater, as typically the process of resonance and collision of an asteroid takes many tens of millions of years. [52] In 2010, another hypothesis was offered which implicated the newly discovered asteroid 354P/LINEAR, a member of the Flora family of asteroids, as a possible remnant cohort of the K/Pg impactor. [53]

In February 2021, Avi Loeb and a colleague published a study in Scientific Reports suggesting the impactor was a fragment from a disrupted comet, rather than an asteroid which has long been the leading candidate among scientists. [54] [55] This was followed by a rebuttal in June of the same year, which charged that the paper ignored key geochemical evidence that made a comet incompatible with known data, and suggested based on multiple lines of evidence that the impactor was either a CM or CR carbonaceous chondrite asteroid. [5]

### Chicxulub and mass extinction Edit

The Chicxulub Crater lends support to the theory postulated by the late physicist Luis Alvarez and his son, geologist Walter Alvarez, that the extinction of numerous animal and plant groups, including non-avian dinosaurs, may have resulted from a bolide impact (the Cretaceous–Paleogene extinction event). Luis and Walter Alvarez, at the time both faculty members at the University of California, Berkeley, postulated that this enormous extinction event, which was roughly contemporaneous with the postulated date of formation for the Chicxulub crater, could have been caused by just such a large impact. [56] The age of the rocks marked by the impact shows that this impact structure dates from roughly 66 million years ago, the end of the Cretaceous period, and the start of the Paleogene period. It coincides with the K–Pg boundary, the geological boundary between the Cretaceous and Paleogene. The impact associated with the crater is thus implicated in the Cretaceous–Paleogene extinction event, including the worldwide extinction of non-avian dinosaurs. This conclusion has been the source of controversy.

In March 2010, forty-one experts from many countries reviewed the available evidence: 20 years' worth of data spanning a variety of fields. They concluded that the impact at Chicxulub triggered the mass extinctions at the K–Pg boundary. [57] [58] In 2013 a study compared isotopes in impact glass from the Chicxulub impact with the same isotopes in ash from the boundary where the extinction event occurred in the fossil record the study concluded that the impact glasses were dated at 66.038 ± 0.049 Ma, and the deposits immediately above the discontinuity in the geological and fossil record was dated to 66.019 ± 0.021 Ma, the two dates being within 19,000 years of each other, or almost exactly the same within experimental error. [22]

The theory is now widely accepted by the scientific community. Some critics, including paleontologist Robert Bakker, argue that such an impact would have killed frogs as well as dinosaurs, yet the frogs survived the extinction event. [59] Gerta Keller of Princeton University argues that recent core samples from Chicxulub prove the impact occurred about 300,000 years before the mass extinction, and thus could not have been the causal factor. [60] This conclusion is unsupported by radioactive dating and sedimentology. [57] [22]

The main evidence of such an impact, besides the crater itself, is contained in a thin layer of clay present in the K–Pg boundary across the world. In the late 1970s, the Alvarezes and colleagues reported that it contained an abnormally high concentration of iridium. [61] Iridium levels in this layer reached 6 parts per billion by weight or more compared with 0.4 for the Earth's crust as a whole [62] in comparison, meteorites can contain around 470 parts per billion of this element. [63] It was hypothesized that the iridium was spread into the atmosphere when the impactor was vaporized and settled across the Earth's surface among other material thrown up by the impact, producing the layer of iridium-enriched clay. [64] Similarly, an iridium anomaly in core samples from the Pacific Ocean suggested the Eltanin impact of about 2.5 million years ago. [65] [66]

A more recent discovery is believed to demonstrate evidence of the scope of the destruction from the impact. In a March 2019 article in the Proceedings of the National Academy of Sciences, an international team of twelve scientists revealed the contents of the Tanis fossil site discovered near Bowman, North Dakota that appeared to show the destruction of an ancient lake and its inhabitants at the time of the Chicxulub impact. In the paper, the group claims that the geology of the site is strewn with fossilized trees and remains of fish and other animals. The lead researcher, Robert A. DePalma of the University of Kansas, was quoted in the New York Times as stating that "you would be blind to miss the carcasses sticking out. It is impossible to miss when you see the outcrop." Evidence correlating this find to the Chicxulub impact included tektites bearing "the unique chemical signature of other tektites associated with the Chicxulub event" found in the gills of fish fossils and embedded in amber, an iridium-rich top layer that is considered another signature of the event, and an atypical lack of scavenging of the dead fish and animals that suggested few other species survived the event to feed off the mass death. The exact mechanism of the site's destruction has been debated as either an impact-caused tsunami or lake and river seiche activity triggered by post-impact earthquakes there has yet been no firm conclusion upon which researchers have settled. [67] [68]

In recent years, several other craters of around the same age as Chicxulub have been discovered, all between latitudes 20°N and 70°N. Examples include the disputed Silverpit crater in the North Sea, and the Boltysh crater in Ukraine. [69] [70] [71] Both are much smaller than Chicxulub, but are likely to have been caused by objects many tens of meters across striking the Earth. [72] This has led to the hypothesis that the Chicxulub impact may have been only one of several impacts that happened nearly at the same time. [73] Another possible crater thought to have been formed at the same time is the larger Shiva crater, though the structure's status as an impact crater is contested. [74] [75]

The collision of Comet Shoemaker–Levy 9 with Jupiter in 1994 demonstrated that gravitational interactions can fragment a comet, giving rise to many impacts over a period of a few days if the comet should collide with a planet. Comets undergo gravitational interactions with the gas giants, and similar disruptions and collisions are very likely to have occurred in the past. [74] [76] This scenario may have occurred on Earth at the end of the Cretaceous, though Shiva and the Chicxulub craters might have been formed 300,000 years apart. [73] [74]

In late 2006, Ken MacLeod, a geology professor from the University of Missouri, completed an analysis of sediment below the ocean's surface, bolstering the single-impact theory. MacLeod conducted his analysis approximately 4,500 kilometers (2,800 mi) from the Chicxulub crater to control for possible changes in soil composition at the impact site, while still close enough to be affected by the impact. The analysis revealed there was only one layer of impact debris in the sediment, which indicated there was only one impact. [77] Multiple-impact proponents such as Gerta Keller regard the results as "rather hyper-inflated" and do not agree with the conclusion of MacLeod's analysis, arguing that there might only be gaps of hours to days between impacts in a multiple-impact scenario (cf. Shoemaker-Levy 9) which would not leave a detectable gap in deposits. [78]

Chicxulub is the only known Earth crater with a remaining impact peak ring, but it is under 600 m (2,000 ft) of sediment. [79] During April and May 2016, a joint IODP-ICDP [80] [81] Mission Specific Platform Expedition no. 364 obtained the first offshore core samples from the peak ring, surrounding the central zone of the crater. [82] During Expedition 364, DES [83] drillers on the L/B Myrtle [84] collected core samples to enable ECORD [85] Science Party members to study how the peak ring formed and calculate the total impact energy.

Their target depth was 1,500 m (4,900 ft) below the bottom of the ocean, [86] but they reached an acceptable 1,335 m (4,380 ft). [82] Sample preparation and analysis were performed in Bremen, Germany. [79]

It was announced in November 2016 that pink granite, usually found deep in the Earth's crust, had been found in drilling samples. [6] [87] It suggests the impact was so great it shocked and melted rocks found deep in the crust, causing them to shoot up before falling back down to produce the peak rings. [6] [87] The granite samples were also found to be lighter and weaker than normal granite, a result of the shock and extreme conditions of the impact. [88] The findings confirmed that the rock comprising the peak ring had originated deep in the earth, and was ejected to the surface. [6] It had been subjected to immense pressures and forces and had been melted by heat and shocked by pressure from its usual state into its present form in just minutes the fact that the peak ring was made of granite was also significant, since granite is not a rock found in sea-floor deposits, originating much deeper in the earth, and had been ejected to the surface by the immense pressures of impact. [87]

Gypsum, a sulfate-containing rock usually present in the shallow seabed of the region, had been almost entirely removed and likely vaporized to enter the atmosphere, an event immediately followed by a megatsunami sufficient to lay down the largest-known layered bed of sand, around 100 m (330 ft) deep and separated by grain size, directly above the peak ring. [89] These types of sand deposits are caused by extreme water movement, where the larger and heavier sand grains settle first, followed by lighter and smaller grains.

Taken together, analyses indicate that the impactor was large enough to create a 190-kilometer (120 mi) peak ring, to melt, shock and eject granite from many kilometers within the earth, to create colossal water movements, and to eject an immense quantity of vaporized rock and sulfates into the atmosphere, where they would have persisted over years to decades. [6] [89] This global dispersal of dust and sulfates would have led to a sudden and catastrophic effect on the climate worldwide, large temperature drops, and devastated the food chain. The researchers stated that the impact generated an environmental calamity that extinguished life, but it also induced a vast subsurface hydrothermal system that became an oasis for the recovery of life. [87] [90]

A program on British television in 2017 [91] described that the drilling revealed, from top down: thick Cenozoic limestone, about 600 m (2,000 ft) a graded sediment deposit from the megatsunami, over 100 m (330 ft) thick the impact melted basement granite from the Earth's midcrust with shocked quartz. The peak ring itself did not contain the calcium sulfate that the rocks in the area around contain, leading the program makers to conclude that all the calcium sulfate in the crater area had been vaporized into the atmosphere and had become a dense sulfur dioxide veil stopping the sunlight. As additional clues of the resulting megatsunami found in a New Jersey, US quarry, a dense marine bone bed was found on the Cretaceous–Paleogene boundary containing a mixture of dead sea animals with little or no damage from scavengers or predators. Also related to this tsunami was a dense dinosaur bone bed on the Cretaceous–Paleogene boundary found in Patagonia.

A 2020 study mentioned that Expedition 364 drilled to a depth of 1,335 m (4,380 ft) below the sea floor to reach the peak ring, and discovered a massive hydrothermal system filled with magma, which modified

1.4 × 10 5 km 3 of Earth's crust and lasted for hundreds of thousands of years in addition, those hydrothermal systems might support the impact origin of life hypothesis for the Hadean, [92] when the entire surface of Earth was affected by impactors enormously larger than the Chicxulub impactor. [93]

## Case Closed! We Finally Have Proof of What Actually Killed the Dinosaurs

According to new research, there is finally solid proof that an asteroid did in fact kill the dinosaurs around 66 million years ago. While the most talked about theory was that an asteroid killed them, there have been other hypotheses such as volcanic eruptions or other global catastrophes.

Back in the 1980s, researchers discovered asteroid dust in the geological layer from the time of the dinosaur extinction. Then in the 1990s, experts confirmed that the Chicxulub impact crater was the same age as the geological rock layer. And now, it has been confirmed that asteroid dust has been found inside of the impact crater. “The circle is now finally complete,” stated Steven Goderis, who is a geochemistry professor at the Vrije Universiteit Brussel and who led the study.

Researchers involved with the International Ocean Discovery Program mission took almost 3,000 feet of rock core samples from the impact crater that was buried beneath the seafloor. (A picture of a piece of the rock core can be seen here.)

They were able to confirm that the dust did come from an asteroid because it contained several elements associated with space rocks – specifically iridium which is found in some asteroids but uncommon in the crust of our planet. The largest amounts of iridium were discovered in a piece of the rock core that measured just 5 centimeters and was located at the top of the peak ring of the crater. The sediment layer found in the crater from the impact was so thick that the researchers were able to date it all the way back to two decades following the strike.

To make sure that they were correct in their study, additional analysis was conducted in several different labs around the world – Belgium, Austria, the United States, and Japan. Goderis reiterated this by stating, “We combined the results from four independent laboratories around the world to make sure we got this right.”

Immediately after the impact, dust would have flown into the atmosphere but researchers believe it only lasted for a couple of decades at the most, which is approximately how long it would have taken many of the species to completely die out.

Additional studies are being planned for the summer with the focus being in the center of the crater where experts are hoping to find additional materials from the asteroid.

The study was published in Science Advances where it can be read in full.

## Would dinosaurs survive?

Research indicates that if the impact happened elsewhere on the globe, life's destiny on Earth might have been very different. If it had sunk just minutes later, the asteroid would have landed in deeper water, vaporizing less rock and rising to block the light and warmth of the Sun. It would have reduced mass extinction odds.

But if an asteroid hadn't suddenly ended the dinosaurs' reign, Paul thinks we may have had some (other than birds) around today.

'I suspect some are still around. We don't know much about their last 10 million years of reign, and what we know is focused on one place in the world, West North America. There's a pretty good record of the last classic non-bird dinosaurs like Tyrannosaurus, Triceratops.

'From that part of the planet, it looks like dinosaurs flourish in numbers, but the number of different dinosaur forms is limited. If that trend held elsewhere, we don't know - it's still a major mystery.'

If not for the meteor, dinosaurs may have lived a little longer, but with the advent of modern birds, mammals and reptiles, they would not have ruled as they once did.

How did asteroids and meteors really kill the dinosaurs?
Wildlife presenter Steve Backshall is back with a bang. The award-winning presenter is on the hunt for the most deadly animals to have walked the Earth: dinosaurs. Razor-sharp claws, axe-like heads and giant whipping tails are hunted down in the quest to find the world’s top Triassic terror. In his explorer’s Dino-Den, Steve brings dinosaurs back to life with cutting-edge CGI.

Welcome to Earth Unplugged! We make films about the incredible natural world, we investigate the conundrums, quirks and beautiful science of our amazing planet, delving into the BBC vaults and mixing it up with our own stuff to take a brand new look at Earth.

## What killed the dinosaurs? Harvard astronomers revisit asteroid theory

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### Asteroid: Animation shows how dinosaurs were &lsquowiped out&rsquo

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About 66 million years ago, the dinosaurs' dominance on Earth was cut short when a major body from space came crashing into our planet. The object is believed to be about 10-miles (16 kilometres) wide and left a crater across the coast of Mexico which runs 63 miles wide and 12 miles deep. The impact wiped out a vast majority of dinosaurs, while an ensuing climate shift which lasted thousands of years led to the demise of three-quarters of all life on Earth.

### Related articles

Where this major space rock came from has been a mystery, but Harvard University scientists believe they now have the answer.

When most think of the major space rock, they state it was an asteroid.

However, new research has claimed the body was more likely a comet which swung in from the edge of the solar system in a region known as the Oort Cloud - where billions of comets, as well as dust and debris still resides - which circles the entire solar system.

The main difference between an asteroid and a comet is the former is made up of metals and rocks, while the latter is more composed of ice, dust and rock.

What killed the dinosaurs? Harvard astronomers revisit asteroid theory (Image: GETTY)

Was it an asteroid or comet which wiped out the dinosaurs? (Image: GETTY)

This means it is easier for a comet to break up, especially as it passes by the Sun.

The new research from the Center for Astrophysics at Harvard & Smithsonian has suggested a comet was likely pulled in from the Oort Cloud and passed through the solar system.

As the comet got close to the Sun - comets which do so are known as 'sungrazers' - it likely broke up, with the chunks of the comet taking on different directions.

Unfortunately for Earth and the dinosaurs, the larger chunk of the comet ended up on a collision course with the planet after a game of tug-of-war between the Sun and Jupiter, the largest planet in the solar system.

An illustration of the solar system and the Oort Cloud (Image: NASA)

### Related articles

Harvard University astrophysics undergraduate student Amir Siraj said: "The solar system acts as a kind of pinball machine.

"Jupiter, the most massive planet, kicks incoming long-period comets into orbits that bring them very close to the Sun.

"In a sungrazing event, the portion of the comet closer to the sun feels a stronger gravitational pull than the part that is further, resulting in a tidal force across the object.

"You can get what's called a tidal disruption event, in which a large comet breaks up into many smaller pieces.

"And crucially, on the journey back to the Oort Cloud, there's an enhanced probability that one of these fragments hit the Earth."

Asteroids, comets and meteors (Image: EXPRESS)

### Trending

What adds more weight to the Oort Cloud theory is that rock traces found in the crater site suggest the comet was made of carbonaceous chondrite.

Carbonaceous chondrite is rare in objects from the asteroid belt - located between the orbits of Jupiter and Mars - but could be widespread in objects from the Oort Cloud, according to Mr Siraj and Harvard's Avi Loeb.

Professor Loeb said: "I hope that we can test the theory by having more data on long-period comets, get better statistics, and perhaps see evidence for some fragments."

The Harvard astronomy professor said not only could the new study solve a long-standing theory, but it could help protect Earth from similar disasters.

He said: "It must have been an amazing sight, but we don't want to see that again."

## How the Dinosaur-Killing Asteroid Spurred the Evolution of the Modern Rainforest

Before an asteroid lit the world on fire 66 million years ago, massive dinosaurs barged through tropical South American forests with airy, open canopies that were dominated by conifers and other seed-bearing gymnosperms—a group of plants that don’t flower or bear fruit. Flowering plants or angiosperms, which make up roughly 80 percent of our modern flora, were there, too, but existed mainly in the margins.

After the impact, three-quarters of all plant and animal species on Earth went extinct. But new research suggests that out of the ashes of this destruction, sprang the closed-canopy, flower-packed South American rainforests that now host the greatest diversity of plants and animals on Earth. The study, published today in the journal Science, uses thousands of fossilized remnants of South American flora from before and after the world-changing asteroid impact to reveal two very different forests on either side of a fracture in the history of life.

“What makes this paper so dramatic and elegant is that they’re addressing two questions that nobody could ever solve and solving them simultaneously,” says Peter Wilf, a paleobotanist from Pennsylvania State University who was not involved in the research.

Those two questions, says Wilf, are what happened in the tropics at the time the dinosaurs went extinct, and when did modern neotropical rainforests first appear.

Until now, scant fossil records have obscured what effects the cataclysm had on the rainforests of South America. The oldest traces of the neotropics as scientists know them today—with closed canopies dominated by flowering angiosperms—date to roughly 60 million years ago, which still leaves millions of years of evolution unaccounted for. But the fact that a modern-looking rainforest was apparently thriving just six million years after the asteroid, only begged the second question of when these ecosystems first originated.

To fill in the six million year gap in the fossil record, paleobiologist Carlos Jaramillo of the Smithsonian Tropical Research Institute and the co-authors of the new study assembled a massive database of fossilized pollen grains that spanned both sides of the asteroid impact and paired the pollen with a trove of new and old leaf fossils from sites in Colombia.

These leaf fossils from Colombia formed in the Paleocene epoch, after an asteroid impact led to the planet’s fifth mass extinction event. (Fabiany Herrera)

Leaf fossils are hugely informative but relatively rare. They can usually be identified to the species level and reveal other things such as which plants lived in a particular area, how much sunlight a plant got or which types of insects ate its leaves. Pollen, on the other hand, can often only be identified to the family level and might have blown in from a long way off, making it less reliable as a localized census. But what pollen lacks in biological detail it more than makes up for with its ubiquity.

Fossil pollen grains are abundant and easy to find in an array of different sediment types spanning nearly all time periods. Collecting tens of thousands of fossil pollen grains from 39 different sites allowed Jaramillo and his team to fill in the missing millions of years right around the mass extinction.

Over more than a decade, Jaramillo worked with his collaborators and trained several crops of South American researchers to excavate and catalog the ancient flora of their home continent, amassing more than 6,000 fossil leaves and more than 50,000 grains of fossilized pollen.

The scientists dated the pollen and leaf fossils using the previously established ages of the geological strata they were found in. Then, the scientists identified the specimens to the extent possible by comparing them to a huge library of living and previously studied extinct plant species.

Identifying the plants represented in the fossils was a massive labor of taxonomy that Jaramillo says eventually allowed the team to determine which species were lost and gained following the asteroid impact. But to get at the question of how these fossil forests were structured, the researchers studied the fossil leaves using three newer techniques.

In the first method, the scientists measured the density of the small veins that the leaves once used to transport nutrients to and from the rest of the plant. In living rainforest plants, canopy leaves have a high density of veins to make the most of the sunlight, while leaves from the understory, even on the same plant, have a lower density of veins. So, if an assortment of a forest’s leaves sports a big range of leaf venation densities, it suggests that the forest has a dense, stratified canopy. By contrast, forest leaf litter that exhibits relatively consistent vein densities typically comes from an ecosystem with an open canopy.

For the second method, the researchers checked the ratio of a pair of carbon isotopes—carbon-13 and carbon-12—to infer how much sun beat down on a leaf when it was alive. If a collection of a forest’s leaves has roughly consistent ratios of carbon-12 to carbon-13 isotopes, then the forest probably had an open canopy. But if the forest’s leaves display a big range of carbon isotope ratios, that suggests a closed canopy where some leaves got blasted by solar radiation and others lived in near-darkness.

Finally, the team also inspected each fossil leaf for signs of insect damage. Different insects damage leaves in different ways and so the researchers could use these tell-tale chomps and piercings to approximate the diversity of insects supported by the forest.

The researchers used all these methods across thousands of samples from more than 40 sites in Colombia to establish a broad, regional picture of how the neotropics looked before and after the asteroid impact.

“All individual components of our analysis told us the same story,” says Jaramillo.

In the time of the dinosaurs, the rainforests of South America had open canopies dominated by conifers and other seed-bearing gymnosperms. Members of the Araucariaceae genus, ancestors of today’s Kauri pine and Norfolk Island pine, were common.

In 2007, co-author Mauricio Gutierrez collects fossil leaves inside a coal mine in Colombia. (Courtesy of Carlos Jaramillo )

Following the asteroid’s blast, the study finds roughly 45 percent of all plant diversity disappeared, particularly the gymnosperms. Amid the roughly six-million-year recovery, the flowering plants that reign supreme in today’s neotropics quickly came to account for 85 to 90 percent of plant diversity, says Jaramillo.

The leaves of the fossilized angiosperms that repopulated South American rainforests exhibited wide ranges of leaf vein density and disparate ratios of stable carbon isotopes, suggesting the new forests had thick canopies that created a tiered hierarchy of access to sunlight. Though these early iterations of the modern neotropics were similar in structure and in the plant families that dominated their ranks compared to today, the overall diversity of species remained low until roughly six million years after the impact.

“This gives us a whole new window on where these hyper-diverse tropical rainforests in South America came from,” says Bonnie Jacobs, a paleobotanist at Southern Methodist University who co-authored a commentary on the new paper for Science. “With this paper you can kind of visualize the most amazing plant communities on Earth recovering and going down this deviated path after a mass extinction.”

A post-asteroid leaf fossil identified as a legume from Colombia’s Cerrejón Formation (58-60 million years ago). Legumes are absent from the South American landscape before the asteroid impact but are integral parts of the region’s rainforests today. (Fabiany Herrera)

Jaramillo and his team propose three potential explanations for why flowering plants rose to prominence after the asteroid that put a period on the age of the dinosaurs.

The first explanation draws on a hypothesis that has been kicking around for decades, positing that the big-bodied dinosaurs maintained the forest’s open floor plan simply by trampling the space between the large conifer trees and eating or snapping any saplings that sprang up. Then, once the dinosaurs were gone, the angiosperms closed ranks and filled in the forest’s gaps.

A second explanation has to do with a change in soil nutrients. Some researchers think the asteroid impact might have dramatically increased the availability of nutrients in the soil, perhaps by raining down particulate and through the ashes of incinerated life. This would have given angiosperms a competitive advantage because they tend to grow faster than gymnosperms and outperform them in nutrient-rich soils.

The third explanation is that before the extinction event, conifers specialized in being the biggest trees around. This narrow life strategy might have made conifers more vulnerable to dying out, and if the group had no shrubby understory representatives to fill the ecological gap via evolution, the door would have been wide open for angiosperms to step in.

A graph showing the rise and fall of species diversity in the South American tropics on either side of the asteroid impact that caused the end-Cretaceous extinction event. On the right are a pair of illustrations showing the differing forest structures that defined each epoch. (Carvalho et al., Science 2021)

Jaramillo says these explanations aren’t mutually exclusive, and it could have easily been some combination of all three that allowed flowering plants to become the dominant group in today’s South American rainforests.

But even as these findings highlight how a mass extinction gave rise to the modern pinnacle of biodiversity, researchers say it should also be a cause for reflection as humans cause what many call a sixth mass extinction event.

“This asteroid impact and the mass extinction it caused is actually a good analog for what’s happening today,” says Wilf. “The asteroid and what humans are doing in terms of driving extinctions are instantaneous in geological time. This work shows how an ecosystem evolved and recovered after catastrophe, but it took millions of years,” he says. “That should really give us pause because we can’t wait that long.”

Molten material has now been blasted into the atmosphere at speeds of more than 100,000 miles per hour.

The burning debris coming from the newly formed Chicxulub crater is now hotter than the Sun so everything nearby is on fire.

Dinosaurs nearby would have starting boiling and bursting open with steam as temperatures reached over 300 degrees Celsius.

Other creatures would have been incinerated instantly.

A huge tsunami that's hundreds of feet high then forms.

## How long was the asteroid that killed the dinosaurs?

The mass extinction event of 65 million years ago, which wiped out most of Earth’s species (including dinosaurs) has been widely publicized and is probably the most famous event in prehistory, and also, one of the most fascinating.

A painting of an asteroid slamming into tropical, shallow seas of the sulfur-rich Yucatan Peninsula in present-day Mexico.
Donald Davis/NASA

What do we know about that killer rock that darkened the skies for dozens of years, raised the volume of the sea above the heads of large animals, and caused earthquakes and violent volcanic events?

To begin with, scientists long ago calculated that the large rock was about 15 kilometres in diameter. This means that, at the time of the collision with the Earth, this asteroid had the height in the sky of a passenger plane .

Thanks to experts from NASA and ESA, we know that rocks of different sizes are integrated into the Earth’s atmosphere on a daily basis. Most do not reach the surface as they disintegrate on their journey to the surface others, the size of bricks, cause little damage. But it would be enough for a rock to have a diameter of at least 10 kilometers to compromise life on Earth as we know it.

The force with which it struck the Earth was a billion times greater than that of the atomic bombs of Hiroshima and Nagasaki. It created earthquakes greater than 10 on the Richter scale created monstrous tidal waves, raising the entire depth of the sea it left a crater, or “ground zero”, 200 kilometres in diameter and it released materials into the atmosphere , enough to create a global winter that blocked the sun’s rays.

Life on Earth was reeling animals died directly or indirectly from the impact and here, the big winners were the smallest and most versatile animals: small mammals that were able to take refuge low in the ground and feed on grains. These animals were the most intelligent, understanding intelligence in its original definition, as the ability to adapt to changes. Thus, the mammals inherited the Earth, and the hegemony of the great saurians came to an end.

Despite the fact that we know a lot about this catastrophe, and there is sufficiently solid evidence to know that it did indeed happen, there are currents of scientists who believe that it was volcanism, and not the impact of the asteroid , that had more weight than the time to provoke mass extinction regardless of whether both facts were true.