What Killed the Dinosaurs

What killed the dinosaurs

INTRODUCTION: It is one of the greatest puzzles in paleontology. For more than 150 million years, dinosaurs rule the Earth. They were so successful than other animals groups, mammals included, had little change of taking over. Then, 65 million years ago, the dinosaurs disappeared from the world altogether. Did they meet a quick and catastrophic end, or did they fade away gradually? What happened 65 million years ago? In the search for answers to what killed the dinosaurs at the end of the Cretaceous Period in the Mesozoic Era, scientists have looked beyond fossils. Geological evidence also holds clues and has led to many hypotheses, working explanations, of how dinosaurs may have become extinct. The extinction mystery is far from a simple “whodunit.” The same piece of evidence is sometimes subject to multiple interpretations. And, as yet, there is no obvious answer, no piece of evidence that strongly supports only one hypothesis while showing that all others are incorrect. So what do we know about dinosaur extinction, and how do we know it.

EVIDENCE: Scientific evidence and observations are the building blocks of hypotheses. At first the same evidence and observations may support different hypotheses. As more evidence becomes available, some hypotheses are proven, others are disproved, and new ones are formed.

HYPOTHESES: A dinosaur extinction hypothesis is a testable statement describing factors that may have played a part in the dinosaur’s extinction and how long the process may have taken. Evidence, observations, and experimentation can serve to support or disprove a hypothesis. Regardless of its acceptance or rejection, through, a good hypothesis provides direction for future scientific study. Several hypotheses will be considered in the following readings: . Continental Drift . Asteroid Impact . Volcanism . Mammal Competition Earth and Life History 1 Adapted from M. Archer 2004 HYPOTHESIS: CONTINENTAL DRIFT It is difficult to imagine a process more slow than continental drift. But some scientists say that, slow or not, this moving of the world’s continents was a disaster for dinosaurs. As continents moved, ocean currents were changed and the world’s sea levels fell. The Interior Seaway, for example which once divided North America in half, simply emptied as the continent rose thousands of feet. According to this hypothesis, climates in many parts of the world became drier and cooler. The resulting ecosystems produced less food than the ecosystems in which dinosaurs evolved and were unable to fee them.

EVIDENCE FOR THE CONTINENTAL DRIFT HYPOTHESIS Fossil Record A gradual decline in the number of dinosaur species would likely show that there would be a gradual cause of their extinction. But, a sudden decline of the dinosaurs implies a catastrophic cause. Depending on location and interpretation, the fossil record seems to say different things. According to some scientists, fossil evidence clearly shows a decline in the number of dinosaur species for several million years leading up to the end of the Cretaceous Period. Sea Level The presence of 65- to 70 million year old fossilized ocean creatures thousands of feet above presented-day sea level shows that ocean levels feel dramatically as the Cretaceous Period came to a close. According to many scientist, continental drift and sea level decrease would have caused continents to become drier, cooler, and less friendly to dinosaur life than had been previously.

Earth and Life History 2 Adapted from M. Archer 2004 HYPOTHESIS: VOLCANISM Did dinosaurs become extinct suddenly or gradually? Some scientists think the answer lies lacked within long-dormant volcanoes. Large areas of old lava found around the world show an Earth 65 to 70 million years ago when volcanic eruptions were common. According to the volcanism hypothesis, this sudden global-scale volcanic activity put so much gas, ah, ad dust into the atmosphere that it kept sunlight from reaching Earth’s surface. Temperature and plant production dropped quickly, and dinosaurs and many other living things that were not used to the new climate died out.

EVIDENCE OF THE VOLCANISM HYPOTHESIS Lava Flows Huge lava flows cover nearly 200,000 square miles of the Deccan region of India, and are more than 6,500 feet in places. Lava flows like these are evidence of a lot of volcanic activity for at least 500,000 years leading up to the extinction of the dinosaurs. 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 melted rock deep within the planet. Some scientist think the presence of high of high concentrations of iridium in the surface rock layer at the time of the dinosaur mass extinction could be the result of a lot of volcanic activity. Cracked Crystals These crystals, often called “shocked quartz”, show a special pattern of cracking caused by high-energy impacts or explosions. Although geologists generally agree that a comet or asteroid impact would cause these fractures, some scientists conclude that they could also be the result of volcanic eruptions. Fossil Record A gradual decline in the number of dinosaurs species would likely show that there would be a gradual cause of their extinction. But a sudden decline of the dinosaurs implies a catastrophic cause. Depending on location and interpretation, the fossil record seems to say different things.

Earth and Life History 3 Adapted from M. Archer 2004 HYPOTHESIS: ASTEROID IMPACT Did a crash with a giant asteroid, comet, or meteorite cause the mass extinction of dinosaurs? 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 believe that dinosaur extinction came quickly, the impact must have spelled a quick end. For months, thick clouds of dust blocked the sun’s rays, darkening and chilling Earth to deadly levels for most plants and many animals. Then, when the dust finally settled gasses created by the impact caused temperatures to dramatically increase above pre-impact temperatures. In just a few years, according to this hypothesis, these freezing and very hot climate changes caused the extinction of not just dinosaurs, but also of up to 70 percent of all plants and animals living at the time.

EVIDENCE FOR THE ASTEROID IMPACT HYPOTHESIS Impact Crater The 150 kilometer wide crater from an asteroid impact lies just off the Yucatan peninsula. Scientists calculate that it was created by a 10-kilometer wide asteroid or meteorite traveling 30 kilometers per second, that’s 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 melted rock deep within the planet. Scientist have discovered levels of iridium thirty (30) times greater than normal in the Cretaceous/Tertiary (K/T) boundary, the layer of rock laid down at the time of the dinosaur extinction. Melted Rock These pieces of once-melted rock, called impact ejecta, are evidence of an explosion powerful enough to immediately melt rock and throw it more than a hundred miles from where it started.

Earth and Life History 4 Adapted from M. Archer 2004 Ranging in size from large chicks to tiny beads, impact ejecta are common at, or near the K/T boundary, the rock layer that defines the dinosaur extinction. Cracked Crystals These crystals, often called “shocked quartz”, show a special pattern of cracking caused by high-energy impacts or explosions. Some scientists believe that the crack pattern in these quartz crystals could only have been caused by a huge asteroid or meteorite impact. The pattern is common in quartz found at or near the K/T boundary, the rock layer deposited at the time of dinosaur mass extinction. Fossil Record A gradual decline in the number of dinosaurs species would likely show that there would be a gradual cause of their extinction. But a sudden decline of the dinosaurs implies a catastrophic cause. Depending on location and interpretation, the fossil record seems to say different things. Some scientist see evidence in the fossil record that dinosaurs were doing well before the end of the Cretaceous Period and Mesozoic Era that they were in no way gradually declining when the impact occurred.

Earth and Life History 5 Adapted from M. Archer 2004 HYPOTHESIS: MAMMAL COMPETITION Extinction implies that the living things that die could not change to survive in a changing environment. Faced with an evolving group of competing animals, the mammals, maybe the dinosaurs were driven slowly over time to extinction by competition with mammals for food. Packs of small mammal would have competed with dinosaurs for food and carnivorous mammals would have eaten dinosaur eggs. Not only did mammals likely compete with dinosaurs for resources, many mammal species survived the end of the Mesozoic extinction (65 mya) and then came to dominate Earth in the Tertiary Period of the Cenozoic Era.

EVIDENCE FOR THE MAMMAL COMPETITION HYPOTHESIS Fossil Record A gradual decline in the number of dinosaur species would likely show that a gradual cause of their extinction. But, a sudden decline of the dinosaurs implies a catastrophic cause of their extinction. Depending on location and interpretation, the fossil record seems to say different things. While mammals certainly did well after the dinosaur extinction, it is unclear whether mammals and dinosaurs competed with each other for food.

Earth and Life History 6 Adapted from M. Archer 2004