Peak rings of the recently pulverized Yucatan Peninsula.
Shocked quartz, a result of a high impact force.
Marine fauna of the Cretaceous.
Characteristic: The Mesozoic was marked by a long period of shifting plate tectonics that would heavily affect the climate of its time and the dominate life forms during this period, the Dinosaurs.
Walking through the Mesozoic from beginning to end would take approximately 186 million years, a journey that would usher you through three major geological periods of Earth's history: the Triassic (251 mya - 201 mya), the Jurassic (201 - 145 mya), and the Cretaceous (145mya - 66 mya). The era that included the most impressive animals the world had ever seen, would end in no less dramatic a fashion than a cataclysmic conclusion, during the late-cretaceous mass extinction event where an asteroid or comet punched a 20 mile deep hole in the earth 66 million years ago killing off 75% of life.
During the Mesozoic there was no place on earth you could look to avoid the flourishing abundance of creatures. Antarctica, today's frozen continent, was full of lush forests and water systems teeming with prehistoric crocodiles, giant amphibians, and dinosaurs. Even the skies of the Mesozoic were teaming with life, where a distinct group of flying reptiles known as Pterosaurs dominated, not birds. Often mistaken for dinosaurs, these Pterosaurs, like Pterodactyl, or Quetzalcoatlus, were only closely related and the mistake is akin to calling our human species, marsupials (Smith). They were however, hardly any less awe-inspiring. Some species had an impressive habit of growing to enormity. Quetzalcoatlus was the size of a small airplane, and even sitting on land it stood as tall as a Giraffe, 17 feet, and carried a 5 foot beak.What one could see and feel during this time would be largely alien to what we experience today, but all of today's life forms have a history with this time.
Climates
In the early Triassic, the worlds continents were still a single land mass known as Pangea, where much of the climate consisted of hot, arid desert. However, during the Jurassic when the continents began to break apart, the air patterns and precipitation were able to penetrate further inland, and the following periods became a time of global tropics. Little ice existed on the earth which meant water was not stored on land, and the oceans were more robust. By the cretaceous, the continents had broken apart such that they resembled much of the formation we see today. With the continents of the Cretaceous disassembled, and the higher sea levels, a vast body of water known as the Western Interior Seaway, was able to divide North America in half, stretching from Canada, down to the Gulf of Mexico. Inland seas such as this one were warm, with shallow surface temperatures able to reach over 90 degrees Fahrenheit.
Dominant Aquatic Species - Marine Reptiles
Oceans were a dangerous place to swim. While sharks had already existed for nearly 200 million years, in the Mesozoic, they were not yet the apex predators they are today, then, it was enormous reptiles as large as a city bus, like Tylosaurus, a well known species of Mosasaur. The mosasaurs, and all known aquatic reptiles of this time, with the exception of Spinosaurus, were not dinosaurs. Mosasaurs in particular, evolved from an animal similar to today's monitor lizards, and with similar behaviors, its appetite included anything it could swallow, a feat which sometimes required it to unhinge it's jaw the way a snake would. Marine reptiles like Mosasaurs, or the dolphin shaped Ichtyosaurs, and the Loch Ness looking Pleisasaurs, are just a handful of the formidable fauna that you could find roaming these ancient waters.
Dominant Terrestrial Species - What is a Dinosaur?
North America's warm interior sea, split a continent that was teeming with dinosaurs, but the continent was not utterly unique. Dinosaurs reached every major land mass on Earth, ranging in size from a few feet in length to over 100. But what is a dinosaur exactly? A large lizard, are they reptiles? Are they cold blooded or warm blooded? Questions as to what a dinosaur is have been debated for hundreds of years, even before they were first scientifically defined in 1824 by British paleontologist William Buckland.
Dinosaurs are reptiles, classified as diapsids. A diapsid (especially dinosaurs) are widely identified by having two temporal openings in the roof of their skulls, likely suited for handling additional musculature that bulged when contracting their jaws (DCNH pg. 72).These diapsids branched off of reptiles, which had recently come from amniotes (amphibian like ancestors). Synapsids (which would give rise to mammals) branched off from amniotes as well around this time, 310 - 320mya (DCNH pg. 71). Mammals are therefore distantly related to dinosaurs, and subsequently, humans, are very distantly related to dinosaurs as well. The graphic diagram below shows a simplified progression of their evolution.
Updated 3/2020
Earth Eras
Whether dinosaurs were warm blooded (endothermic) or cold blooded (ectothermic) like crocodiles, lizards, snakes, and turtles, is unclear. Birds are warm blooded, and are the only surviving dinosaurs to date, having evolved from a dinosaur proto-bird similar to aerchyopterix around 150 mya, but they are not an accurate enough measure of what thermal regulatory systems of all dinosaurs would have been. Therefore, this characteristic remains a missing physiological determinant, but other characteristics are more concrete. The most distinguishing identifier of a Dinosaur is that unlike typical modern reptiles, dinosaurs posture had legs situated directly beneath their bodies, not a sprawling stance. Many dinosaurs were better equipped for greater locomotion because of this, where their legs did not flail out to the side at speed.
Estimates for just how fast certain dinosaurs were capable of moving vary, however, there is little dispute as to the advancement in bio-mechanics, diversity, and the overall scale of their thousands of species over any predecessors and even much of today's diverse fauna. Tyrannosaurs, Allosaurus, Giganotosaurus, Utah Raptor, Spinosaurus, these iconic predators of their day each inhabited parts of the globe where they could carve out their niche. Some of these species grew to over 40 feet in length and more than 20,000 pounds: the daily activities of hunting, or territorial disputes, and competition for mates, would have been an intense yet routine experience to behold. Menacing as the carnivores of the Mesozoic were, it is by the age old saying that, necessity is the mother of invention, that it was a requirement, and dually so, since the prey they hunted often came equipped with sizable defense mechanisms, probably using horns, scutes (ossified tissue), thagomizers (stegosaurus tail weapon penetrates bone), and even tail ends equipped with bowling ball style clubs capable of crushing bone. Life, as the fossil record of these animals very visually suggests, was, as often is the case, predominantly about survival.
End of An Era - Mass Extinction
The mesozoic ended cataclysmicly, in what is known as the K-Pg Extinction event, roughly 66 million years ago when an asteroid or comet, roughly the size of Manhattan island, (6.2 - 9.3 miles in diameter) slammed into what is now Mexico's Yucitan peninsula. Around 75% of all plant and animal life was lost, (with no evidence of terrestrial life over 55lbs surviving). Every species of dinosaur was extinguished from existence, except for the smaller feathered ones, the birds.
A new era had arrived on earth, known as the Eocene, or "The Age of Mammals."
Landscapes of the Cretaceous.
A group of Theropods on the hunt while a Ceratopsian dinosaur lays low in the shadows.
An Ammonite wanders in a Jurassic sea.
Marine reptiles in the Jurassic.
The next year, she got the two adversaries, Hildebrand and Sharpton, to sign on as co-authors on a paper in Nature that showed the crater stretched 112 to 124 miles.
Morgan’s next plan was even more ambitious. She wanted to drill Chicxulub. Morgan asked the International Ocean Discovery Program (IODP), a global collaboration of marine research, for more than $100 million to collect six 2-mile-deep cores from around the crater’s center to better understand peak ring formation and the impact’s environmental effects. The IODP sidelined her proposal until she could bring the cost down.
The IODP also called for a 3-D site survey before it would consider Morgan’s proposal. She partnered with University of Texas at Austin geophysicist Sean Gulick, who was already studying the Gulf of Mexico. Again, the researchers towed an array of air guns behind their vessel, this time bouncing more than 35,000 sound waves across a network of 115 land and seafloor seismometers. By 2005, their team had collected enough seismic data to reveal Chicxulub’s exact shape.
Settling the Soot
Fossils from New Mexico and Colorado show that the doomsday asteroid of 66 million years ago may have caused entire forests to burn to the ground. And for decades, some scientists thought that happened because the atmosphere superheated the planet, igniting fires everywhere on Earth as fireballs rained down from the skies.
But David Kring of the Lunar and Planetary Institute has modeled Chicxulub’s immediate aftermath and shown forest fires were likely more regional — some forests lived, while others died. His team proposes that a thermal pulse is to blame, an explosion of heat reaching more than 36,000 degrees Fahrenheit as it spread from the impact site, igniting nearby areas. If that’s correct, forest fires likely spread across southern North America, but stopped before destroying the continent’s northern reaches. The extended fallout also would have started fires on the opposite side of the planet. “There would have been a huge number of ecosystems on Earth at the time, and those ecosystems would have reacted differently,” says Kring.
In research published last year, Joanna Morgan of Imperial College London and her colleagues put that idea to the test by setting pine needles on fire in the lab. The team showed that the thermal pulse from the impact couldn’t ignite the kind of global canopy-replacing wildfires commonly associated with the asteroid. Instead, dry forest litter likely sparked wildfires like the ones forests had evolved with. In Morgan’s version of events, reduced sunlight and re-entering debris may have dried out many of Earth’s plants. Those dead trees and plants later burned as a result.
Either way, we’re sure Earth burned. “What we know is there’s lots and lots of soot, so there must have been lots of fires all across the place,” Morgan says. How did these forests bounce back? A 2014 University of Arizona study of fossilized leaves in North Dakota showed a surprising shift in plant populations. Deciduous plants — those that lose their leaves — fared better than slow-growing evergreens, thanks to their live-fast-die-young strategy. This implies that evergreens were more common before the impact, but fast-growing flowering plants thrived immediately afterward.
Fossil records also commonly show a fern spore spike following the impact, indicating that some spores and seeds survived the fires. This helps explain why some avian dinosaurs lived and others died. A paper published in the journal Current Biology earlier this year looked at birdlike creatures living at the end of the Cretaceous and notes that the survivors — those species that went on to become modern birds — had beaks without teeth, ideal for seeds. Carnivorous species died as their food sources did, but those dinosaurs with toothless beaks could feast on fallen seeds long after plants died. (Dis).
Mesozoic - Eocene
A series of calamities arose during the cretaceous, especially later in the period, that may have resulted in the extinction of animals like the dinosaurs, not merely the singular impact event. Some hypothesis point to a new pulse of volcanic activity, the basalt beds in India are an example, which kicked up masses of c02 into the atmosphere. Climate change as a combination of volcanic activity, the shifting of tectonic plates, coupled with the impact at the very end of the Cretaceous may have all been significant causes of extinction.
The fossil record is not complete enough to confirm, but does show a decrease in speciation in the millions of years leading up to the K-Pg boundary, so it is possible the dinosaurs were already on their way out. However, if one thing is clear, it is that the asteroid/comet impact sealed that fate, as not only did the non-avian dinosaurs vanish, but so did 75% of life on earth, including many sea born reptiles, fish, and other aquatic life along with terrestrial vegetation, 66 million years ago. If there is any question as to the scale of this event one only need to look to the dirt for more clues. The soot and fallout after the impact created what is now known as the K-Pg boundary, about a 1 to 2 inch layer found in soil all over the world. Above the boundary, are 160 million years of dinosaurs and other diverse forms of life, directly after this thin layer, not one dinosaur fossil has ever been found, nor Mosasaur, Ichtyasaur, or other creatures lost to that phenomenal period of time. After the asteroid, no animal on land over 55lbs survived into the new age and the most amazing ocean creatures the world had ever seen were dead.
Tags: 251mya - 201.3mya Name Origin. Climate. Geography. Terrestrial Fauna, Aquatic Fauna.
The Triassic (/traɪˈæs.ɪk/) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.9 million years ago (Mya), to the beginning of the Jurassic Period 201.3 Mya. The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events, the former of which was the Permian-Triassic extinction, in its wake the Earth's biosphere was left impoverished; it was well into the middle of the Triassic before life recovered its former diversity. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic.
Terrestrial Fauna
The first true mammals, themselves a specialized subgroup of therapsids, evolved during this period, as well as the first flying vertebrates, the pterosaurs, who, like the dinosaurs, were a specialized subgroup of archosaurs (Wik). Dinosaurs remained small in stature during this period, like Coelophysis, and did not become dominant until the succeeding Jurassic Period (Wik).
Temnospondryls, the likely ancestors to modern day amphibians, were on the way out by this time after having thrived on land and in water since the Carboniferous. They were suddenly being out competed by reptiles on land, and had largely been relegated to aquatic means of survival.
Aquatic Fauna
Triassic seas were vast, especially when Pangea existed, and were inhabited by a variety of new and growing number of species such as Ichthyosaurs (pictured right), Nothosaurs, and Plesiosaurs.
Ichthyosaurs (which resembled modern day dolphins) sometimes grew to immense sizes of more than 70ft, though these were thought to only be filter feeders, whereas smaller species ate larger prey like fish. While they were also reptiles, they gave birth to live young, as did the Plesiosaurs, a long necked fat bodied flipper bearing animal noted for looking identical to the Loch Ness Monster.
Animals like Ammonite's, (closely related to the modern day Nautilus) survived the Permian extinction and would prove a valuable contribution to the food chain as a major source of prey for many marine reptiles until the end of the cretaceous 186 million years later. Modern types of coral also evolved in the Triassic.
Triassic - Jurassic Extinction Event
The Triassic–Jurassic extinction event marks the boundary between the Triassic and Jurassic periods, 201.3 million years ago, and is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans. In the seas, a whole class (conodonts) and 23–34% of marine genera disappeared. On land, all archosaurs other than crocodylomorphs (Sphenosuchia and Crocodyliformes) and Avemetatarsalia (pterosaurs and dinosaurs), some remaining therapsids, and many of the large amphibians became extinct. The cause of this extinction remains unclear, but some hypothesis have considered the massive outpouring of c02 from a sudden pulse of volcanic activity, an asteroid impact (though no appropriately sized and timed crater has yet been discovered), or, the less thematic gradual affects of climate change. The transition to the Jurassic would be the beginning to an even more diverse and prolific period in earth's history than ever before, and would begin with new life on land and sea.
Tags: 201.3mya - 145.5mya Name Origin. Climate. Geography. Terrestrial Fauna, Aquatic Fauna.
The Jurassic Period (/dʒʊəˈræs.ɪk/; from Jura Mountains, a range in Switzerland) is a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago (Mya) to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles. The start of the period was marked by the major Triassic–Jurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian-Toarcian extinction in the Early Jurassic, and the Tithonian event at the end; neither event ranks among the "Big Five" mass extinctions, however.
Terrestrial Fauna
The Jurassic was a golden age for the large herbivorous dinosaurs known as the sauropods—Camarasaurus, Apatosaurus, Diplodocus, Brachiosaurus, and many others—that roamed the land late in the period; their foraging grounds were either the prairies of ferns, palm-like cycads and bennettitales, or the higher coniferous growth, according to their adaptations. The smaller Ornithischian herbivore dinosaurs, like stegosaurs and small ornithopods were less predominant, but played important roles. They were preyed upon by large theropods, such as Ceratosaurus, Megalosaurus, Torvosaurus and Allosaurus. All these belong to the 'lizard hipped' or saurischian branch of the dinosaurs. During the Late Jurassic, the first avialans, like Archaeopteryx, evolved from small coelurosaurian dinosaurs. In the air, pterosaurs were common; they ruled the skies, filling many ecological roles now taken by birds, and may have already produced some of the largest flying animals of all time. Within the undergrowth were various types of early mammals, as well as tritylodonts, lizard-like sphenodonts, and early lissamphibians. The rest of the Lissamphibia evolved in this period, introducing the first salamanders and caecilians. (Wik).
Aquatic Fauna
During the Jurassic period, the primary vertebrates living in the sea were fish and marine reptiles. The latter include ichthyosaurs, which were at the peak of their diversity, plesiosaurs, pliosaurs, and marine crocodiles of the families Teleosauridae and Metriorhynchidae. Numerous turtles could be found in lakes and rivers.
In the invertebrate world, several new groups appeared, including rudists (a reef-forming variety of bivalves) and belemnites. Calcareous sabellids (Glomerula) appeared in the Early Jurassic. The Jurassic also had diverse encrusting and boring (sclerobiont) communities, and it saw a significant rise in the bioerosion of carbonate shells and hardgrounds. Especially common is the ichnogenus (trace fossil) Gastrochaenolites.
During the Jurassic period, about four or five of the twelve clades of planktonic organisms that exist in the fossil record either experienced a massive evolutionary radiation or appeared for the first time. (Wik).
Triassic - Cretaceous
There weren't any mass extinctions to speak of that lead into the Cretaceous, it was a gradual occurrence defined by a new layer of chalk like sediment in the fossil record.
6.2 mile wide asteroid collides in what is today the Yucatan Peninsula off Mexico.
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Tags: 145.5mya - 66mya Name Origin. Climate. Geography. Terrestrial Fauna, Aquatic Fauna.
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.
Terrestrial Fauna
On land, mammals were generally small sized, but a very relevant component of the fauna, with cimolodont multituberculates outnumbering dinosaurs in some sites. Neither true marsupials nor placentals existed until the very end.
The apex predators were archosaurian reptiles, especially dinosaurs, which were at their most diverse stage. Pterosaurs were common in the early and middle Cretaceous, but as the Cretaceous proceeded they declined for poorly understood reasons (once thought to be due to competition with early birds, but now it is understood avian adaptive radiation is not consistent with pterosaur decline[25]), and by the end of the period only two highly specialized families remained.
The Liaoning lagerstätte (Chaomidianzi formation) in China is a treasure chest of preserved remains of numerous types of small dinosaurs, birds and mammals, that provides a glimpse of life in the Early Cretaceous. The coelurosaur dinosaurs found there represent types of the group Maniraptora, which is transitional between dinosaurs and birds, and are notable for the presence of hair-like feathers.
Insects diversified during the Cretaceous, and the oldest known ants, termites and some lepidopterans, akin to butterflies and moths, appeared. Aphids, grasshoppers and gall wasps appeared.
Temnospondryls, the likely ancestors to modern day amphibians, were on the way out by this time after having thrived on land and in water since the Carboniferous. They were suddenly being out competed by reptiles on land, and had largely been relegated to aquatic means of survival.
Aquatic Fauna
In the seas, rays, modern sharks and teleosts became common.[27] Marine reptiles included ichthyosaurs in the early and mid-Cretaceous (becoming extinct during the late Cretaceous Cenomanian-Turonian anoxic event), plesiosaurs throughout the entire period, and mosasaurs appearing in the Late Cretaceous.
Baculites, an ammonite genus with a straight shell, flourished in the seas along with reef-building rudist clams. The Hesperornithiformes were flightless, marine diving birds that swam like grebes. Globotruncanid Foraminifera and echinoderms such as sea urchins and starfish (sea stars) thrived. The first radiation of the diatoms (generally siliceous shelled, rather than calcareous) in the oceans occurred during the Cretaceous; freshwater diatoms did not appear until the Miocene.[26] The Cretaceous was also an important interval in the evolution of bioerosion, the production of borings and scrapings in rocks, hardgrounds and shells.
K-Pg Extinction (The End)
For billions of years, it waited. A city-sized chunk of primordial space rock circled the solar system somewhere between the orbits of Mars and Jupiter. Earth took shape. Life evolved. And all the while, the space rock just drifted, tumbling end over end like a poorly thrown football. Then, some unknown celestial mechanics shoved this 9-mile-wide projectile out of its orbit. Destination: Earth.
The asteroid belt escapee arrived 66 million years ago. In those last dinosaur days, any skygazing T. rex might have tilted its head in curiosity as a strange, new star grew dozens of times brighter than the sun. Burning through the atmosphere at 45,000 mph, the asteroid’s leading edge hit the Gulf of Mexico while its other end was still higher than the cruising altitude of a 747 (40,000ft).
It excavated a hole nearly 20 miles deep, ripping fault lines down to Earth’s mantle. For two minutes, land behaved like liquid. The open hole left behind by the asteroid quickly filled back in as material rebounded from the depths, building a great ring of peaks around the crater’s center. Twelfth-magnitude earthquakes rocked the region. Cliffs crumbled. A blast of air surged at speeds exceeding 600 mph, bringing hurricane-force winds to what is now North America. Vegetation vaporized. Within the hour, waves hundreds of feet high pounded Texas and Florida. A debris plume erupted above Earth’s atmosphere and rained back down around the globe, creating regional infernos. These were just the opening salvos of hell on Earth. A crater 126 miles in diameter was left in its wake.
By chance, the asteroid struck a shallow sea over a sulfur-rich shelf. Once vaporized, the chemicals formed a climate-altering blanket that enveloped the planet and fell as acid rain. Photosynthesis nearly stopped. As forests died, wildfires turned the world’s plants into a layer of soot now found all around the planet. Most of the remaining creatures — from the tiniest plankton to the largest dinosaurs — froze or starved. On land, nothing larger than 55 pounds survived.
“Most damaging were the sulfur and the dust. Those two things made the Earth very dark and cold for an extended period of time,” says Joanna Morgan of Imperial College London, who’s spent her career studying the calamity. Some 75 percent of life vanished, ending the 180 million-year reign of the dinosaurs. But life couldn’t be snuffed out so easily. The survivors emerged from the ash to repopulate the planet. A different kind of creature soon flourished in the dinosaurs’ absence — mammals.
Now scientists have returned to the scene of the crime, seeking answers to fundamental questions about what happened that day. How exactly did that limestone shelf behave like a liquid? Where did the peak ring rocks come from? And what kinds of life were the first to return to ground zero? Researchers are turning back time, layer by layer, drilling down to the time of the Cretaceous — the final dinosaur era — examining rocks and tiny fossils for new details that could solve decades-old controversies.
“It’s the most important natural event on Earth in the last 100 million years,” Morgan says. “It changed the course of evolution.” And if the researchers can find those first species to recolonize the crater, the discovery could teach us not only more about the dinosaurs’ demise, but also how life survived similar events billions of years earlier.
Spotting Ground Zero
Under the fierce May sun, Morgan steps into an open-air basket on a supply vessel floating 19 miles off the Yucatán Peninsula. A crane operator pulls her high above the rough ocean waves, giving her the asteroid’s final view of the Gulf of Mexico.
But there’s no evidence of the apocalypse from here; the coastline isn’t even in sight. Her landing target is the Liftboat Myrtle, a drill rig parked over the planet’s best-preserved large impact scar, now dubbed Chicxulub (pronounced CHICK-soo-loob), after a tiny nearby town. The rig’s feet stand on the shallow seafloor, just 65 feet underwater, and its platform
(Above) Fragment of the asteroid that ended the 186 million years of the Mesozoic. (Below) Shocked quartz.
rises well above the waves, providing a stable base for the drill crew. Morgan is here to sink a diamond-tipped drill bit through nearly a mile of Earth’s crust and collect samples. Her journey began in 1994. Three years earlier, scientists had linked the Chicxulub crater to Luis and Walter Alvarez’s incredible theory that a 66 million-year-old worldwide layer of iridium — a material common in asteroids, but not on Earth’s surface — proved a space rock’s crash killed the dinosaurs. Clues from around the Caribbean had helped them home in on this missing crater. First, sandy tsunami sediment was found in Texas. Then tiny tektites — glass bits formed during impacts — turned up in Haiti. Eventually, oil-hunting Mexican geologists handed over drill cores from a strange circular feature they’d found in the Yucatán. Inside was shocked quartz, the smoking gun for impact craters. Scientists had started to assume the impact happened in the open ocean. Chicxulub’s surprisingly sulfur-rich location helped explain the environmental devastation. But that was just the beginning.
Voodoo Physics
By the time Morgan became involved, most experts agreed that an asteroid killed the dinosaurs and that it landed in Mexico. But debate still raged over the size of the Chicxulub crater. Some estimated it was nearly twice as big as it really is. Few scientists were studying impacts at the time, and knowing how much energy the asteroid carried depended on knowing the crater’s diameter. Morgan watched as two geologists — Alan Hildebrand of the University of Calgary and Buck Sharpton of the Lunar and Planetary Institute in Houston — sparred over the details. “There were accusations of voodoo physics from one and the other saying your parents were not married,” Morgan jokes. The scientists were trying to tease out gravitational and magnetic anomalies buried beneath more than half a mile of sediment. The young seismologist saw an opportunity. In 1996, Morgan began a three-month seismic study of the site — the first of its kind. Her team towed a large air gun behind a research vessel, blasting the seafloor with seismic waves that would bounce back, revealing a clearer picture of the crater.