How the Dino-Killing Chicxulub Asteroid Impact Was Found Throughout the '80s and '90s, different lines of investigation accumulated evidence that an extraterrestrial impact really did kill off dinosaurs . "I was skeptical at first, but I soon started finding fairly dramatic evidence of plant extinction at the boundary," paleontologist Kirk Johnson at the Denver Museum of Nature and Science told SPACE.com. Geochronologist Paul Renne collects a volcanic ash sample from a coal bed within a few centimeters of the dinosaur extinction horizon. A study by Renne and colleagues confirmed the link between the Chicxulub asteroid impact and dinosaur extinction 65 million years ago. Image released Feb. 7, 2013. Credit: Courtesy of Courtney Sprain Geophysicist Sean Gulick at the University of Texas at Austin noted "the size of the iridium anomaly was such that it was hard to argue that it was anything else but an extraterrestrial impact.

But the concept seemed so fantastical that it took a long time for the scientific community to come around." Then, in 1991, researchers found evidence that the giant crater near the town of Chicxulub (pronounced CHEEK-she-loob) in Mexico came into being about the time of the mass extinction. The explosion that created the crater, which is more than 110 miles (180 kilometers) wide, likely involved a hit from an object about 6 miles (10 km) across. The crash would have released as much energy as 100 trillion tons of TNT, or beyond a billion times the power of the atom bombs that destroyed Hiroshima and Nagasaki. "When that crater was found, for most geologists that wrapped up the question of whether an impact was involved in the mass extinction," Alvarez said. Gulick agreed. "Once the crater at Chicxulub was recognized for what it was, it became the smoking gun for the idea that an extraterrestrial impact caused the mass extinction," Gulick told SPACE.com.

[ Asteroid Impact Threat Explained by NASA's Don Yeomans (Video) ] Big dino-killer: Asteroid or volcano Still, not everyone believes the Chicxulub impact was behind the mass extinction . For instance, geologist Gerta Keller at Princeton University maintains the explosion took place 300,000 years before the end-Cretaceous extinction. Some researchers have explored other possible culprits for the disaster, including other impact sites, such as the controversial Shiva crater in India , or even massive volcanic eruptions, such as those creating the Deccan Flats in India. However, Renne and his colleagues have now discovered the Chicxulubimpact and the end-Cretaceous mass extinction event happened no more than 33,000 years apart. These new findings, appearing in the Feb. 8 issue of the journal Science, support the idea that the extraterrestrial collision dealt the age of dinosaurs its death blow. "I've been involved in a lot of research that's explored huge correlations between mass extinctions and massive volcanism , not impacts, so I've really come at the idea of a cosmic impact from the outside," Renne said.

"A few people have said the crater was the wrong age, but I think these new findings very strongly settle that question," Alvarez said. Asteroids are fascinating for lots of reasons. They contain a variety of valuable resources and slam into our planet on a regular basis, occasionally snuffing out most of Earth's lifeforms. How much do you know about space rocks? Dinosaur Extinction, Cretaceous-Tertiary Extinction Information, Prehistoric Facts -- National Geographic This requires the latest version of Flash Player. Click here to download. Sixty-five million years ago the last of the non-avian dinosaurs went extinct. So too did the giant mosasaurs and plesiosaurs in the seas and the pterosaurs in the skies. Plankton, the base of the ocean food chain, took a hard hit. Many families of brachiopods and sea sponges disappeared. The remaining hard-shelled ammonites vanished. Shark diversity shriveled. Most vegetation withered. In all, more than half of the world's species were obliterated. What caused this mass extinction that marks the end of the Cretaceous and the beginning of the Paleogene? Scientists have yet to find an answer.

The one that does must explain why these animals died while most mammals, turtles, crocodiles, salamanders, and frogs survived. Birds escaped. So did snails, bivalves, sea stars (starfish), and sea urchins. Even hardy plants able to weather climate extremes fared OK. Scientists tend to huddle around one of two hypotheses that may explain the Cretaceous extinction: an extraterrestrial impact, such as an asteroid or comet, or a massive bout of volcanism. Either scenario would have choked the skies with debris that starved the Earth of the sun's energy, throwing a wrench in photosynthesis and sending destruction up and down the food chain. Once the dust settled, greenhouse gases locked in the atmosphere would have caused the temperature to soar, a swift climate swing to topple much of the life that survived the prolonged darkness. Asteroid or Volcanoes? The extraterrestrial impact theory stems from the discovery that a layer of rock dated precisely to the extinction event is rich in the metal iridium. This layer is found all over the world, on land and in the oceans. Iridium is rare on Earth but it's found in meteorites at the same concentration as in this layer.

This led scientists to postulate that the iridium was scattered worldwide when a comet or asteroid struck somewhere on Earth and then vaporized. A 110-mile-wide (180-kilometer-wide) crater carved out of Mexico's Yucatán Peninsula, called Chicxulub, has since been found and dated to 65 million years ago. Many scientists believe the fallout from the impact killed the dinosaurs. But Earth's core is also rich in iridium, and the core is the source of magma that some scientists say spewed out in vast, floodlike flows that piled up more than 1.5 miles (2.4 kilometers) thick over 1 million square miles (2.6 million square kilometers) of India. This bout of volcanism has also been dated to about 65 million years ago and would have spread the iridium around the world, along with sunlight-blocking dust and soot and greenhouse gases. Both hypotheses have merit. Some scientists think both may have contributed to the extinction, and others suggest the real cause was a more gradual shift in climate and changing sea levels.

Regardless of what caused the extinction, it marked the end of Tyrannosaurus rex's reign of terror and opened the door for mammals to rapidly diversify and evolve into newly opened niches. Evolution: Extinction: What Killed the Dinosaurs? What Killed the Dinosaurs? Hypothesis: Asteroid Impact Did a collision with a giant asteroid or comet change the shape of life on Earth forever? It is widely agreed that such an object -- 10 kilometers across -- struck just off the coast of the Yucatan peninsula 65 million years ago. According to scientists who maintain that dinosaur extinction came quickly, the impact must have spelled the cataclysmic end. For months, scientists conclude, dense clouds of dust blocked the sun's rays, darkening and chilling Earth to deadly levels for most plants and, in turn, many animals. Then, when the dust finally settled, greenhouse gases created by the impact caused temperatures to skyrocket above pre-impact levels. In just a few years, according to this hypothesis, these frigid and sweltering climatic extremes caused the extinction of not just the dinosaurs, but of up to 70 percent of all plants and animals living at the time.

Evidence for the Asteroid Impact Hypothesis Impact Crater This 150-kilometer-wide crater lies just off the Yucatan peninsula. Scientists calculate that it was blasted into Earth by a 10-kilometer-wide asteroid or comet traveling 30 kilometers per second -- 150 times faster than a jet airliner. Scientists have concluded that the impact that created this crater occurred 65 million years ago. The date corresponds perfectly to the date of the dinosaur extinction. Rare Metal The metal iridium, which is similar to platinum, is very rare on Earth's surface but is more common in asteroids and in molten rock deep within the planet. Scientists have discovered levels of iridium 30 times greater than average in the Cretaceous/Tertiary (KT) boundary, the layer of sedimentary rock laid down at the time of the dinosaur extinction. Melted Rock These pieces of once-molten rock, called impact ejecta, are evidence of an explosion powerful enough to instantly melt bedrock and propel it more than a hundred miles from its origin.

Ranging in size from large chunks to tiny beads, impact ejecta are common at or near the Cretaceous/Tertiary (KT) boundary, the geological layer that defines the dinosaur extinction. Fractured Crystals These crystals, often called "shocked quartz," show a distinctive pattern of fracturing caused by high-energy impacts or explosions. Some scientists maintain that the fracture pattern in these quartz crystals could only have been caused by a massive asteroid or comet impact. The pattern is prevalent in quartz found at or near the Cretaceous/Tertiary (KT) boundary, the geological layer deposited at the time of the extinction. Fossil Record A gradual decline in the number of dinosaur species would likely mirror an equally gradual cause of their ultimate extinction. Conversely, a sudden "now you see them, now you don't" end to the dinosaurs implies a catastrophic cause. Depending on location and interpretation, the fossil record seems to say different things. Some paleontologists see evidence in the fossil record that dinosaurs were doing quite well prior to the end of the Cretaceous -- that they were in no way declining in abundance when the impact occurred.

The Cretaceous Period Online exhibits : Geologic time scale : Mesozoic Era The Cretaceous Period The Cretaceous is usually noted for being the last portion of the "Age of Dinosaurs", but that does not mean that new kinds of dinosaurs did not appear then. It is during the Cretaceous that the first ceratopsian and pachycepalosaurid dinosaurs appeared. Also during this time, we find the first fossils of many insect groups, modern mammal and bird groups, and the first flowering plants. The breakup of the world-continent Pangea, which began to disperse during the Jurassic , continued. This led to increased regional differences in floras and faunas between the northern and southern continents. The end of the Cretaceous brought the end of many previously successful and diverse groups of organisms, such as non-avian dinosaurs and ammonites. This laid open the stage for those groups which had previously taken secondary roles to come to the forefront. The Cretaceous was thus the time in which life as it now exists on Earth came together. Life No great extinction or burst of diversity separated the Cretaceous from the Jurassic Period that had preceded it. In some ways, things went on as they had.

Dinosaurs both great and small moved through forests of ferns, cycads, and conifers. Ammonites, belemnites, other molluscs, and fish were hunted by great "marine reptiles," and pterosaurs and birds flapped and soared in the air above. Yet the Cretaceous saw the first appearance of many lifeforms that would go on to play key roles in the coming Cenozoic world. Perhaps the most important of these events, at least for terrestrial life, was the first appearance of the flowering plants, also called the angiosperms or Anthophyta. First appearing in the Lower Cretaceous around 125 million years ago, the flowering plants first radiated in the middle Cretaceous, about 100 million years ago. Early angiosperms did not develop shrub- or tree-like morphologies, but by the close of the Cretaceous, a number of forms had evolved that any modern botanist would recognize. The angiosperms thrived in a variety of environments such as areas with damper climates, habitats favored by cycads and cycadeoids, and riparian zones.

High southern latitudes were not invaded by angiosperms until the end of the Cretaceous. Ferns dominated open, dry and/or low-nutrient lands. Typical Jurassic vegetation, including conifers, cycads, and other gymnosperms, continued on into the Lower Cretaceous without significant changes. At the beginning of this period, conifer diversity was fairly low in the higher latitudes of the Northern Hemisphere, but by the middle of the period, species diversification was increasing exponentially. Swamps were dominated by conifers and angiosperm dicots. At about the same time, many modern groups of insects were beginning to diversify, and we find the oldest known ants and butterflies. Aphids, grasshoppers, and gall wasps appear in the Cretaceous, as well as termites and ants in the later part of this period. Another important insect to evolve was the eusocial bee, which was integral to the ecology and evolution of flowering plants. The Cretaceous also saw the first radiation of the diatoms in the oceans (freshwater diatoms did not appear until the Miocene ).

The Cretaceous-Tertiary extinction The most famous of all mass extinctions marks the end of the Cretaceous Period, about 65 million years ago. As everyone knows, this was the great extinction in which the dinosaurs died out, except for the birds, of course. The other lineages of "marine reptiles"  the ichthyosaurs, plesiosaurs, and mosasaurs  also were extinct by the end of the Cretaceous, as were the flying pterosaurs, but some, like the ichthyosaurs, were probably extinct a little before the end of the Cretaceous. Many species of foraminiferans went extinct at the end of the Cretaceous, as did the ammonites. But many groups of organisms, such as flowering plants, gastropods and pelecypods (snails and clams), amphibians, lizards and snakes, crocodilians, and mammals "sailed through" the Cretaceous-Tertiary boundary, with few or no apparent extinctions at all. What on Earth  or not  caused this extinction and how can we know? What killed the dinosaurs?

Tectonics and paleoclimate The Cretaceous is defined as the period between 145.5 and 65.5 million years ago,* the last period of the Mesozoic Era, following the Jurassic and ending with the extinction of the dinosaurs (except birds). By the beginning of the Cretaceous, the supercontinent Pangea was already rifting apart, and by the mid-Cretaceous, it had split into several smaller continents. This created large-scale geographic isolation, causing a divergence in evolution of all land-based life for the two new land masses. The rifting apart also generated extensive new coastlines, and a corresponding increase in the available near-shore habitat. Additionally, seasons began to grow more pronounced as the global climate became cooler. Forests evolved to look similar to present day forests, with oaks, hickories, and magnolias becoming common in North America by the end of the Cretaceous. At the end of the Cretaceous Period, 65 million years ago, an asteroid hit Earth in the Yucatan Peninsula, Mexico, forming what is today called the Chicxulub impact crater.

It has been estimated that half of the world's species went extinct at about this time, but no accurate species count exists for all groups of organisms. Some have argued that many of the species to go extinct did so before the impact, perhaps because of environmental changes occuring at this time. Whatever its cause, this extinction event marks the end of the Cretaceous Period and of the Mesozoic Era. Localities Clayton Lake, New Mexico : This Cretaceous site has some of the most extensive and best preserved dinosaur trackways in the United States. Pt. Loma Formation, California : This Cretaceous locality has yielded important fossils for understanding western North American dinosaurs. Resources The Great Mystery: Current Arguments What Killed The Dinosaurs? EXTINCTION THEORIES Two main camps exist in paleontology today, each having a different view of what killed the dinosaurs and other organisms at the K-T boundary. Controversy has surrounded the topic since 1980; it has become difficult for the public (and the scientific world at large) to understand the issue due to the tangled assemblage of data which seems to point in many different directions.

Luckily, the controversy has not harmed the study of mass extinction causation, but rather has made it a dynamic and interesting area. Every groundbreaking new hypothesis makes new headlines in the media, and excites researchers to delve further into the mystery. The major sides of the schism can be broken down (greatly simplifying the issue, but making it more accessible) into "intrinsic gradualists" and "extrinsic catastrophists." We'll describe each generalized group in turn, and then try to synthesize the available information so you can form your own opinion. But first, let's outline what scientists generally agree that we know about the K-T boundary. The common ground There was global climatic change; the environment changed from a warm, mild one in the Mesozoic to a cooler, more varied one in the Cenozoic. The cause of this climate change, and the speed at which it proceeded, are the major concerns of both schools of thought. As well as a permanent global climatic change, there is evidence that there were less lasting changes at the end of the Cretaceous period.

These changes may have been the result of a massive terrestrial disturbance, which threw up soot into the air, causing short term acid rain, emission of poisonous gases, and cooling (similar to a nuclear winter). Long term consequences would have been a global greenhouse effect (warming and reduced sunlight). As discussed before , many organisms; both marine and terrestrial, vertebrate and invertebrate; went extinct. The reason for this extinction was probably this climate change. At or near the K-T boundary in several places around the globe, we have a thin layer of clay with an unusually high iridium (a rare metal similar to platinum) content. This may be evidence for the dust cloud in #2 above. The "intrinsic gradualists" Those scientists falling into this category believe that the ultimate cause of the K-T extinction was intrinsic; meaning of an Earthly nature; and gradual, taking some time to occur (several million years). Two main hypotheses exist today: Volcanism: We are quite certain that the end of the Cretaceous period that there was increased volcanic activity. Over a period of several million years, this increased volcanism could have created enough dust and soot to block out sunlight; producing the climatic change.

In India during the Late Cretaceous, huge volcanic eruptions were spewing forth floods of lava which can be seen today at the K-T boundary (these ruptures in the Earth's surface are called the Deccan traps). The chemical composition of the lava rocks in India shows that they originated in the Earth's mantle, which is also relatively rich in iridium. This richness would explain the iridium layer. Plate Tectonics: Major changes in the organization of the continental plates (continental drift) were occurring at the K-T boundary. The oceans (especially the Interior Seaway in North America) were experiencing a regression; they were receding from the land. A less mild climate would have been the result, and this would have taken a long time. Large scale tectonic events did occur in the Mesozoic several times, and no extinction events have been conclusively associated with them yet. Note that these two above hypotheses are inextricably tied together; volcanism cannot occur without the action of plate tectonics, and vice versa. If the extinction was intrinsic and gradual, both processes probably played a role.

Also note that the basic theory here is an elaboration of the 'dinosaurs faded away' hypothesis from the invalid hypotheses section; it adds a factor of causation that is quite convincing. The "extrinsic catastrophists" This side of the controversy holds that the ultimate cause of the K-T extinction was extrinsic, meaning of an extraterrestrial nature, and catastrophic, meaning fairly sudden and punctuated. The main hypothesis was proposed in 1980 by (among others) Luis and Walter Alvarez of the University of California at Berkeley. The Alvarez Hypothesis: The original hypothesis is the basis for several subsequent variations on the theme that a large extraterrestrial object collided with the Earth, its impact throwing up enough dust to cause the climatic change. The iridium layer is what prompted the Alvarez team to blame an asteroid impact for the extinction  asteroids and similar extraterrestrial bodies are higher in iridium content than the Earth's crust, so they figured that the iridium layer must be composed of the dust from the vaporized meteor. No crater was found, but it was assumed that one existed that was about 65 million years old and 100 kilometers (about 65 miles) in diameter.

Later research found a likely candidate for the crater at Chicxulub, on the Yucatan Peninsula of Mexico. Other evidence was also reported: the presence of shocked quartz in the rocks of the K-T boundary (indicating the passage of a shock wave so powerful that it actually rearranged the crystal structure of quartz grains), glassy spheres that looked like impact ejecta (molten rock that solidified into droplets when cooled), and a soot layer was found in many areas (evidence for widespread forest fires). The likelihood that massive hurricanes and firestorms would have raged across the Earth was also hypothesized, adding to the destructive power of the catastrophe. To reconcile the hypothesis with gradual data, it was suggested that rather than one impact, several impacts (of comets or meteors) could have occurred over a period of many years. Some evidence supported this  a hint of periodicity of mass extinctions in the fossil record was reported; mass extinctions seemed to occur roughly every 26 million years. Astronomers theorized that the Oort cloud of comets could cross the path of our solar system every 26 million years, and would possibly rain comets on our planet for a few million years.

The existence of a tenth, as-yet unseen planet  or Nemesis, the twin star to our sun  both with large orbits were also contemplated. To date, no reliable evidence for periodicity or Nemesis-type celestial bodies has been found, but this does not render the hypothesis obsolete; it is accepted that any large extraterrestrial body impacting the Earth's surface could and would produce climatic changes similar to those thought to have occurred around the K-T boundary. All of this work was not without its detractors, of course; we'll discuss that in the final section. Conclusions? There has been no settlement to the issue so far, and no clear one is foreseeable. Both sides claim to hold the majority of proponents in science; it seems that (greatly over-generalizing) many paleontologists lean towards the intrinsic side, while many astronomers and physicists favor the extrinsic side, and geologists are probably evenly split between the two.

All of the evidence cited for the extrinsic catastrophist side is claimed as evidence by the intrinsic gradualists for their side or against the opposite side  volcanoes could create the iridium layer, shocked quartz, soot, and impact ejecta; the makeup of the iridium layer is not uniform in all areas, so it could be meaningless; and so on. The main problem with both hypotheses is the issue of the selectivity of the mass extinction; as you saw before in the background section , some organisms were wiped out, while others were unaffected. Can climate change really explain the differential selectivity of the K-T event? Our lack of understanding of the physiology of dinosaurs makes the issue more complex; if they were endothermic, why did they not survive like birds and mammals? If they were ectothermic, why did small dinosaurs not survive like small reptiles? Also, many studies have focused on the extinction of dinosaurs alone, and have forgotten about the more substantial marine ecosystem collapse. The fossil record suggests that some marine reptiles died out several million years prior to the K-T boundary.

Other major problems with the issue are that it is not easy to prove (test) causation (as noted before), and that most of the ages of the rocks that different evidence comes from are questionable. It is not certain whether there is a gradual decline in the global fossil record, or if there was a sudden catastrophe; some studies in some areas show evidence pointing to different answers. Ultimately, we just don't know yet for sure. The two main schools of thought are split fairly evenly among scientists familiar with them. Either an intrinsic or extrinsic cause for the extinction would have complex biotic effects on ecosystems which would look confusing in the fossil record. There could well have been different, even separate extinctions in the oceans and on land; the marine fossil record does support a slightly rapid decline, while the terrestrial record (especially in North America) strongly suggests a more gradual decline (but again, has a fragmentary fossil record). If an extraterrestrial impact occurred during a gradual decline, that might explain the seemingly contradictory evidence.

If you are looking for an opinion here from a paleontologist's point of view, it seems that the simplest explanation is that the climatic changes induced by the shifting continents and the regression of the continental seaways were the ultimate cause (at least in North America), but this has not been (and may not ever be) proven. There is much work to be done, and much value to this work  understanding the K-T extinction would help us to understand mass extinctions in general, and might provide a glimpse into the fleeting, evanescent nature of our own mortality. Explore the Issue: Jurassic Period Facts: Rise of the Dinosaurs | Exploring Lifes Mysteries Home > History > Dinosaurs > Jurassic Period Facts: Rise of the Dinosaurs Jurassic Period Facts: Rise of the Dinosaurs 9 E-mail Total: 19 How do we keep this site running? This post may contain affiliate links — the cost is the same to you, but we get a referral fee. Compensation does not affect rankings. Thanks! The Mesozoic era saw some incredibly amazing life forms that continue to puzzle paleontologists today.

The Mesozoic era was divided in to three individual periods: the Triassic period, the Jurassic period and the Cretaceous period. Smack in the middle of the Mesozoic area, the Jurassic period itself was also divided in to three sections, the early, middle and late Jurassic periods. The Jurassic period brought some amazing changes that bred some amazing prehistoric beasts in a time which fell between 146 and 200 million years ago. The Early Jurassic Period: the Liassic Epoch (176 to 200 Million Years Ago) The early Jurassic period, known also as the Liassic epoch came about 176 to 200 million years ago and was divided in to the Hettangian age, the Sinemurian age, the Pliensbachian age, and the Toarcian age. The beginning of the Jurassic period saw a rise of the dinosaurs after the Triassic period saw the extinction of many of the animals that thrived during that time. The early Jurassic period also brought a much warmer and wetter rainforest type of climate and as such it encouraged reptile expansion.

The early Jurassic period saw a variety of other life as well including the Ammonites, marine reptiles and terrestrial animals. While the Triassic period saw the end of many creatures due to extinction it only saw the near extinction of Ammonoids. As the continents shifted during the early Jurassic period the initial continent break up was in motion and this wasn’t the only activity in the world’s oceans. Ammonoid life began to evolve. It did so so quickly that Ammonites alone can be used as markers of fossil zones. Marine reptiles also saw the early Jurassic period as a prime time to evolve and Ichthyosaurs and Plesiosaurs continued to grow giving birth to new marine reptiles such as the Ichthyosaurus, Temnodontosaurus, Eurycleidus, Macroplata and Rhomaleosaurus. Terrestrial animals which made their appearance during the early Jurassic period include the Heterodontosaurids, Scelidosaurs, Tetanurae, Stegosaurs.

Also showing their faces at this time were the smaller carnivores: Sphenosuchid and Protosuchid crocodilians, the new flying Pterosaur species and early mammals such as the Tritylodonts, Sphenodonts, and Lissamphibians. The Middle Jurassic Period: The Dogger Epoch (176 to 161 Million Years Ago) The Separation of Pangea and the Rise of the Atlantic The middle Jurassic period, known as the Dogger epoch came about 176 to 161 million years ago and was divided in to the Aalenian age, the Bajocian age, the Bathonian age, and the Callovian age. The middle of the Jurassic period saw the beginning of the separation of Pangea in to Laurasia and Gondwana and the formation of the Atlantic Ocean. The middle Jurassic period saw both growth and reduction in life; however, it was certainly not as dramatic of a change as that during the beginning of the Jurassic period. The reason for such explosive growth at the beginning of the Jurassic period was the extinction of so many species during the Triassic period.

Marine life during the Dogger epoch saw some thinning of marine life as Icthyosaurs diversity reduced; however this reduced diversity was met with increased numbers of existing species. Also during this period Pliosaurs grew to mammoth proportions, matching killer whales in mass. It is during this time also that Plesiosaurs made their appearance even more known by multiplying in numbers and the Metriorhynchid crocodilians also stepped on to the scene. The Dogger epoch also saw the appearance of new terrestrial life including Cetiosaurs, Hypsilophodonts, Megalosaurs, and Brachiosaurs. As Cynodonts continued to grow during this time the Trithelodont Cynodonts saw the end of the line at the end of the epoch. In terms of mammals it is the middle of the Jurassic era that saw the evolution of what we consider “real” mammals.

The end of the Jurassic Period: the Malm Epoch (161 to 146 Million Years Ago) The True Pinnacle of Dinosaur Life The end of the Jurassic period, known as the Malm epoch came about 161 to 146 million years ago and was divided in to the Oxfordian age, the Kimmeridgian age and the Tithonian age. The end of the Jurassic period is known to many as the true pinnacle of dinosaur life and it also saw the true break up of Pangea in to Laurasia and Gondwana. The late Jurassic period saw some simply amazing creatures come to form as well as the growth of existing dinosaurs from the middle Jurassic period. One of the most abundant dinosaurs to roam the Earth during the end of the Jurassic period was the Sauropods. The Cetiosaurids of the middle Jurassic period come to be replaced by the Camarasaurs, Brachiosaurs and Diplodocids many of which were absolutely gargantuan in size.

Along with the humongous beasts which began roaming the Earth during this time crocodiles, lizards, frogs, turtles, marine reptiles, flying reptiles and the first birds in existence graced the Earth as well. Jurassic Period Facts: Commonalities Among Dinosaurs While the Jurassic period is neatly divided by and for paleontologists in to three eras, which are in turn divided in to their own periods, Jurassic facts are not. Jurassic facts, species and artifacts are, in fact, often given the label of Jurassic without having a specific period of the Jurassic age pinned to them. There are many facts that relate to broader concepts and events that occurred during the Jurassic period which do not specifically apply to one section or the other and instead can be applied to the entire stretch of time from the early to the late Jurassic era. Such facts and artifacts cover geography, tectonics, fauna and flora as well as common misconceptions or this time as well. The Breaking of Pangea into Laurasia and Gondwana As already mentioned above, during the Jurassic period the massive continent Pangea broke in to Laurasia and Gondwana; however, during the Jurassic period there were many other geographic changes afoot.

The breaking of Pangea also brought the Gulf of Mexico in to existence and the North Atlantic Ocean came in to being. The Rise of North America, the Atlantic, the Gulf of Mexico, and the Rocky and Sierra Nevada Mountains The Atlantic Ocean of the beginning Jurassic period was a narrow ocean which bore very little resemblance to the Atlantic Ocean we know today. The lower Atlantic did not show itself until Gondwana broke apart during the Cretaceous period. Due to the rainforest like climate of the Jurassic era there was no evidence of either ice caps or glaciers and due to the larger continents still being in existence there was not yet any evidence of land near the poles at this time either. The larger continents at this time were also rotating; however, different sections of the continent rotated at different rates and directions causing rift valleys which went on to cause what is now the North American continent to drift westwards. It is also during this time that the beginnings of the Rocky Mountains and Sierra Nevada mountains saw their beginnings. During the Jurassic period the sea levels also rose and caused flooding over large sections of the continents leaving behind shallow seas and rich sediment across the land.

Plate Tectonics Help Dinosaurs Rule the World As plates continued to collide over this period not only were mountains created but so too were volcanoes which would, according to today’s paleontologists, assist dinosaurs in ruling the earth by eliminating the competition of other land roaming creatures. Fauna during the Jurassic period became more abundant for the most part following the extinction that occurred during the Triassic period with the exception of a few species which became less diverse but more numerous. Despite depictions in Steven Spielberg’s film “Jurassic Park” dinosaur life during the Jurassic period was not filled with Tyrannosaurus Rex living alongside Velociraptors and Brachiosaurus. Despite the depictions of the Hollywood inspired dino park the truth of the matter is that many of the dinosaurs depicted in Spielberg’s Jurassic Park were not even in existence during the Jurassic period. Take for example the Tyrannosaurus Rex and the Velociraptor, neither of which were walking the Earth until the Cretaceous period. There were, however, many large as well as vicious dinosaurs which roamed the Earth during the Jurassic period and they fell in to three families, the Sauropods, the Theropods, and the Ornithopods.

The Sauropods The Sauropods of the Jurassic period were the dinosaurs that were characterized by long necks and long tails. Sauropods are also known by paleontologists as the largest living things to ever walk the Earth, some reaching as large as 190 feet long! Some of the most recognized Sauropods of the Jurassic era include: Diplodocus, Apatosaurus, Brachiosaurus, and the Amygdalodon. The Theropods of the Jurassic period were the dinosaurs that were bipedal and almost all of them were carnivorous. Some of the most recognized Theropods of the Jurassic era include: Ceratosaurus, Megalosaurus, Magnosaurus, and Archaeopteryx. The Ornithopods of the Jurassic period were the dinosaurs who had bird like hips (characterized by a backwards pointing pelvis), were herbivores, had a beak and switched from being quadrupedal to being bipedal. Some of the most recognized Ornithopods of the Jurassic era include the Iguanodon, Agilisaurus and the Phyllodon.

Jurassic Period Plant Life: Age of Cycads Flora during the Jurassic period was abundant and conducive to thriving dinosaur populations. As the warmer seas rose to cover continents in shallow seas fertile and moist ground gave way to thick and tall plant life. Cycads were especially abundant during the Jurassic period which is why many paleontologists refer to this time as the “Age of Cycads”. Cycads are plants which grow from seeds and flourish into plants whose leaves resemble palms. The moist environment of the Jurassic period also provided ideal conditions for thriving jungles which grew to cover large portions of land. Conifers also thrived during the Jurassic era growing large tall trees as well as taking over low latitude vegetation with the Mesozoic era Cheirolepidaceae. Other shrubs and ferns which took over forest life include the Cycads, Ginkgos and Dicksoniaceous tree ferns. Rich Plant Life Helps Dinosaurs Grow and Expand It is not only the land which was conducive to flora life though, as the oceans underwent change. So too did ocean life, and algae became more sparse. It is during the Jurassic period that Coralline algae made its first appearance.

As a result of such luscious and thick plant life during the Jurassic era dinosaurs were able not only to rule the Earth but they were able to diversify to allow the coming of the Cretaceous period which brought with it many more fierce creatures. It is even thought by some that such rich a dense plant life and vegetation gave rise to the gigantic size of the dinosaurs which were to come during the last age of the dinosaurs – the Cretaceous period. When and How did the Jurassic Period End? As the Jurassic period came to a close it ended in a similar way to which it began. The Jurassic period began with a huge mass extinction which eliminated some of the biggest dinosaurs of the Triassic period. While the end of the Jurassic period did not bring such a dramatic change it did, in fact, bring a closing of doors for some major dinosaur species. The extinction, or “dying out” that came to be at the end of the Jurassic period obviously fell short of the mass extinction at the end of the Cretaceous period in magnitude as well; however, it did create some rather huge changes for dinosaur life.

Dinosaurs continued to remain dominant over the land during the following Cretaceous period, although the smaller dinosaurs that saw the end of the Jurassic period had no idea of the mammoth dinosaurs that were to be ushered in with their small extinction event. While it is unknown as to what caused the minor mass extinction that accompanied the end of the Jurassic period it is known that it brought the end to quite a few species of dinosaur. Among the dinosaurs that saw their end ushered in with the end of the Jurassic era were the majority of the giant Sauropods such as Mamenchisaurus, Diplodocus and Brachiosaurus. The transition in to the Cretaceous period also saw the end of the majority of Stegosaurids including the Stegosaurus, Kentrosaurus and Tuojiangosaurus. Additionally many genera of ammonoids, marine reptiles and bivalves saw their end of days as the Jurassic period drew to a close. While unfortunate for these species that did not live through to the beginning of the Cretaceous period their extinction played a role in the evolution of the real kings of dinosaurs who trod the Earth during the age of gigantism – the Cretaceous period.

Lean More Find out more about Jurassic period at the Smithsonian either in person at the National Museum of Natural History or online at their Department of Paleobiology . Mesozoic Era: Age of the Dinosaurs Mesozoic Era: Age of the Dinosaurs By Tia Ghose, Senior Writer | January 7, 2015 10:26pm ET MORE New research suggests that reptiles that lived during the Dinosaur age were hard-hit. Here, the carnivorous lizard Palaeosaniwa chases a pair of young Edmontosaurus while the snake Cerberophis and the lizard Obamadon look on. Credit: Carl Buell During the Mesozoic, or "Middle Life" Era, life diversified rapidly and giant reptiles, dinosaurs and other monstrous beasts roamed the Earth. The period, which spans from about 252 million years ago to about 66 million years ago, was also known as the age of reptiles or the age of dinosaurs. Boundaries English geologist John Phillips, the first person to create the global geologic timescale, first coined the term Mesozoic in the 1800s.

Phillips found ways to correlate sediments found around the world to specific time periods, said Paul Olsen, a geoscientist at the Lamont-Doherty Earth Observatory at Columbia University in New York. The Permian-Triassic boundary, at the start of the Mesozoic, is defined relative to a particular section of sediment in Meishan, China, where a type of extinct, eel-like creature known as a conodont first appeared, according to the International Commission on Stratigraphy . The end boundary for the Mesozoic Era, the Cretaceous-Paleogene boundary , is defined by a 20-inch (50 centimeters) thick sliver of rock in El Kef, Tunisia, which contains well-preserved fossils and traces of iridium and other elements from the asteroid impact that wiped out the dinosaurs. The Mesozoic Era is divided up into the Triassic, Jurassic, and Cretaceous periods. Life and climate The Mesozoic Era began roughly around the time of the end-Permian extinction, which wiped out 96 percent of marine life and 70 percent of all terrestrial species on the planet.

Life slowly rebounded, eventually giving way to a flourishing diversity of animals, from massive lizards to monstrous dinosaurs. The Triassic Period , from 252 million to 200 million years ago, saw the rise of reptiles and the first dinosaurs, the Jurassic Period , from about 200 million to 145 million years ago, ushered in birds and mammals, and the Cretaceous Period , from 145 million to 66 million years ago is known for some of its iconic dinosaurs, such as Triceratops and Pteranodon . Coniferous plants, or those that have cone-bearing seeds, already existed at the beginning of the era, but they became much more abundant during the Mesozoic. Flowering plants emerged during the late Cretaceous Period. The lush plant life during the Mesozoic Era provided plenty of food, allowing the biggest of the dinosaurs , such as the Argentinosaurus, to grow up to 80 tons, according to a 2005 study in the journal Revista del Museo Argentino de Ciencias Naturales. Earth during the Mesozoic Era was much warmer than today, and the planet had no polar ice caps.

During the Triassic Period, Pangaea still formed one massive supercontinent. Without much coastline to moderate the continent's interior temperature, Pangaea experienced major temperature swings and was covered in large swaths of desert. Yet the region still had a belt of tropical rainforest in regions around the equator, said Brendan Murphy, an earth scientist at St. Francis Xavier University in Antigonish, Canada. Extinctions The Mesozoic Era was bookended by two great extinctions, with another smaller extinction occurring at the end of the Triassic Period, Olsen said. Around 252 million years ago, the end-Permian extinction wiped out most life on Earth over about 60,000 years, according to a February 2014 study in the journal Proceedings of the National Academy of Sciences (PNAS). At the end of the Triassic Period, roughly 201 million years ago, most amphibious creatures and crocodile-like creatures that lived in the tropics were wiped out. About 65 million years ago, a giant asteroid blasted into Earth and formed a giant crater at Chicxulub in the Yucatan Peninsula.

Because the fossil record is incomplete, it's difficult to say exactly what caused the extinctions, or even how rapidly they occurred. After all, certain species or traces of catastrophic events could be missing in the fossil record simply because the sediments may have disappeared over tens of millions of years, Olsen said. "Nature is very efficient at getting rid of its corpses," Olsen told Live Science. However, there are a few prime suspects in each of the extinctions. At the end of the Permian, the Siberian Traps underwent massive volcanic eruptions, which most geologists believe caused the world's biggest extinction . Exactly how, however, is up for debate. The volcanic eruptions caused a spike in carbon dioxide in the atmosphere, though the 2014 PNAS study suggests that the spike was brief. The eruptions may have increased sea surface temperatures and led to ocean acidification that choked out sea life. And another study published in March 2014 in PNAS proposed that the eruptions released huge troves of the element nickel , which fueled a feeding frenzy by nickel-munching microbes known as Methanosarcina. Those microbes may have belched out huge amounts of methane, superheating the planet.

Most scientists agree that an asteroid impact wiped out the dinosaurs at the end of the Cretaceous Period. The impact would have kicked up so much dust that it blocked the sun, halted photosynthesis, and led to such a huge disruption in the food chain that everything that wasn't a scavenger or very small died. But the Deccan Traps , in what is now India, were spewing massive amounts of lava both before and after the asteroid impact, and a few scientists believe these flows either directly caused or accelerated the dinosaurs' demise. Volcanism may also be to blame for the end-Triassic extinction. Though volcanism in general leads to global warming, after an initial volcanic eruption, huge amounts of sulfur spew into the air and cause a brief period of global cooling. Such cooling-heating cycles may have occurred hundreds of times over 500,000 years. Similar cold snaps have been tied to huge crop failures in historical times, such as in Iceland in the 1700s, Olsen said.

As a result, animals used to constant, balmy temperatures in the tropics were wiped out, while animals that were insulated with proto-feathers, such as pterosaurs, or that lived at higher latitudes and were already adapted to big temperature variations, did just fine, Olsen said. "When you have these volcanic winters, where temperatures may have dropped even below freezing in the tropics, it was devastating," Olsen said.

Question: What name is given to the age at the end of which the extinction event happened which saw the end of the dinosaur?
Answer: Cretaceous