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Natural Disasters Unit 2 Extraterrestrial Threats Impacts and Extinctions Chapter 13

Mar 31, 2015



  • Slide 1

Natural Disasters Unit 2 Extraterrestrial Threats Impacts and Extinctions Chapter 13 Slide 2 Learning Objectives Know the difference between asteroids, meteoroids, and comets Understand the physical processes associated with airbursts and impact craters Understand the possible causes of mass extinction Know the evidence for the impact hypothesis that produced the mass extinction at the end of the Cretaceous period Slide 3 Learning Objectives, cont. Know the likely physical, chemical, and biological consequences of impact from a large asteroid or comet Understand the risk of impact or airburst of extraterrestrial objects and how that risk might be minimized Slide 4 Earths Place in Space Origins of universe begin with Big Bang 14 billion years ago. Explosion producing atomic particles First stars probably formed 13 billion years ago. Lifetime of stars depends on mass Large stars burn up more quickly ~100,000 years Smaller stars, like our sun ~10 billion years Supernovas signal death of star Releases energy and shock waves Click to see movie at right: Slide 5 Earths Place in Space, cont. 5 billion years ago, supernova explosion triggered the formation of our sun. Sun grew by buildup of matter from solar nebula Pancake of rotating hydrogen and helium dust After formation of sun, other particles were trapped in rings. Particles in rings attracted other particles and collapsed into planets Earth was hit by objects, adding to its formation Bombardment continues today Slide 6 Figure 13.2 Slide 7 Asteroids, Meteoroids, and Comets Particles in solar system are arranged by diameter and composition. Asteroids 10m (30ft)1000 km(620 mi). Found in asteroid belt between Mars and Jupiter Composed of rock, metallic, or combinations Meteoroids are broken up asteroids. Meteors are meteoroids that enter Earths atmosphere. We landed a probe on this asteroid: Eros Slide 8 Comets have glowing tails composed of frozen water or carbon dioxide Originated in Oort cloud Slide 9 Slide 10 Figure 13.3 Slide 11 Airbursts and Impacts Objects enter Earths atmosphere at 1272 km/s (27,000161,000 mph) Metallic or stoney Heat up due to friction as they fall through atmosphere, produce bright light Meteorites If the object strikes Earth Concentrated in Antarctica Airbursts Object explodes in atmosphere 12 5o km (7 31 mi) Ex: Tunguska Slide 12 Figure 13.5 Slide 13 Impact Crater Provide evidence of meteor impacts. Bowl-shaped depressions with upraised rim Rim is overlain by ejecta blanket Broken rocks cemented together into breccia Features of impact craters are unique from other craters. Impacts involve high velocity, energy, pressure, and temperature. Kinetic energy of impact produces shock wave into earth. Compresses, heats, melts, and excavates materials Rocks become metamorphosed or melt with other materials. Slide 14 Figure 13.6 Slide 15 Simple Impact Craters Typically small < 6 km (4 mi) Ex. Barringer Crater Figure 13.7 Slide 16 Complex Impact Craters Larger in diameter > 6 km (4 mi) Rim collapses more completely Center uplifts following impact Figure 13.9 Slide 17 Impact Crater, cont. Craters are much more common on Moon. 1. Most impacts are in ocean, buried, or destroyed. 2. Impacts on land have been eroded or buried by debris. 3. Smaller objects burn up in Earths atmosphere before impact. Slide 18 Slide 19 Mass Extinctions Sudden loss of large numbers of plants and animals relative to number of new species being added Defines the boundaries of geologic periods or epochs Usually involve rapid climate change, triggered by Plate tectonics Moves habitats to different locations Volcanic activity Large eruptions release CO 2, warming Earth Volcanic ash reflects radiation, Cooling Earth Extraterrestrial impact Slide 20 Six Major Mass Extinctions 1. Ordovician, 446 mya, continental glaciation in Southern Hemisphere 2. Permian, 250 mya, volcanoes causing global warming and cooling 3. TriassicJurassic boundary, 202 mya, volcanic activity associated with breakup of Pangaea 4. CretaceousTertiary boundary (K-T boundary), 65 mya, asteroid impact 5. Eocene period, 34 mya, plate tectonics 6. Pleistocene epoch, initiated by airburst, continues today, caused by human activity Slide 21 K-T Boundary Mass Extinction Dinosaurs disappeared with many plants and animals. 70% of all genera died Set the stage for evolution of mammals First question: What does geologic history tell us about K-T Boundary? Walter and Luis Alvarez decided to measure concentration of Iridium in clay layer at K-T boundary in Italy. Fossils found below layer were not found above. How long did it take to form the clay layer? Iridium deposits say that layer formed quickly. Probably extinction caused by single asteroid impact. Slide 22 K-T Boundary Mass Extinction, cont. Alvarez did not have a crater to prove the theory. Crater was identified in 1991 in Yucatan Peninsula. Diameter approx. 180 km (112 mi) Nearly circular Semi-circular pattern of sinkholes, cenotes, on land defining edge Possibly as deep as 30 40 km (18 25 mi) Slumps and slides filled crater Drilling finds breccia under the surface Glassy indicating intense heat Slide 23 Figure 13.12 Slide 24 Sequence of Events a) Asteroid moving at 30 km (19 mi) per second b) Asteroid impacts Earth, produces crater 200 km (125 mi) diameter, 40 km (25 mi) deep Shock waves crush, melt rocks, vaporized rocks on outer fringe Figure 13.13b Figure 13.13a Slide 25 Sequence of Events, cont. c) Seconds after impact: Ejecta blanket forms Mushroom cloud of dust and debris Fireball sets off wildfires around the globe Sulfuric acid enters atmosphere Dust blocks sunlight Tsunamis from impact reach over 300 m (1000 ft) Figure 13.13c Slide 26 Sequence of Events, cont. Month later No sunlight, no photosynthesis Continued acid rain Food chain stopped Several months later Sunlight returns Acid rain stops Ferns restored on burned landscape Figure 13.13d Figure 13.13e Slide 27 K-T Extinction, Final Impact caused massive extinction, but allowed for evolution of mammals. Another impact of this size would mean another mass extinction probably for humans and other large mammals. However, impacts of this size are very rare. Occur once ever 40 100 my Smaller impacts are more probable and have their own dangers. Slide 28 Linkages with Other Natural Hazards Tsunamis Wildfires Earthquakes Mass wasting Climate change Volcanic eruptions Slide 29 Risk Related to Impacts Risk related to probability and consequences Large events have consequences, will be catastrophic Worldwide effects Potential for mass extinction Return period of 10s 100s millions of years Smaller events have regional catastrophe Effects depends on site of event Return period of 1000 years Likelihood of an urban area hit every few 10,000 years Slide 30 Risk Related to Impacts, cont. Risk from impacts is relatively high. Probability that you will be killed by Impact: 0.01%-0.1% Car accident: 0.008% Drowning: 0.001% However, that is AVERAGE probability over thousands of years. Events and deaths are very rare! Slide 31 The Torino Impact Scale Slide 32 What is it for? A "Richter Scale" for newly discovered asteroids and comets. A communication tool for astronomers and the public. Why is it needed? Predictions for newly discovered NEOs are naturally uncertain. For most objects, even the initial calculations are sufficient to show that they will not make any close passes by the Earth within the next century. However, for some objects, 21st century close approaches and possible collisions with the Earth cannot be completely ruled out. Slide 33 Minimizing the Impact Hazard Identify nearby threatening objects. Spacewatch Inventory of objects with diameter > 100 m in Earth crossing orbits 85,000 objects to date Near-Earth Asteroid Tracking (NEAT) project Identify objects diameter of 1 km Use telescopes and digital imaging devices Most objects threatening Earth will not collide for several 1000s of years from discovery. Slide 34 Minimizing the Impact Hazard, cont. Options once a hazard is detected Blowing it up in space Small pieces could become radioactive and rain down on earth Nudging it out of Earths orbit Much more likely since we will have time to study object Technology can change orbit of asteroid Costly and need coordination of world military and space agencies Evacuation Possible if we can predict impact point Could be impossible depending on how large an area would need to be evacuated Slide 35 End Natural Disasters Unit 2 Extraterrestrial Threats Impacts and Extinctions Chapter 13