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Natural Hazards Impacts and Extinctions Chapter 14 Learning Objectives Know the difference between asteroids, meteoroids, and comets Understand physical processes associated with airbursts and impact craters Understand possible causes of mass extinction Understand the process of mass extinction caused by extra-terrestrial collisions with earth Learning Objectives 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 Understand how impact risk might be minimized Earth’s Place in Space The universe may have begun with a “Big Bang” 14 billion years ago 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 may last ~10 billion years Supernovas signal death of star Releases energy and shock waves Earth’s Place in Space 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 Hydrogen fuses into helium, releasing electromagnetic energy, some of which is visible light. After formation of sun, other particles were trapped in rings (orbits). Particles in rings attracted other particles and collapsed into planets Earth was hit by inter-stellar debris, adding to its formation Bombardment continues today Anthropocene (human) epoch now? Asteroids, Meteoroids, and Comets Asteroids (10m –1000 km) - asteroid belt between Mars and Jupiter Composed of metals Meteoroids are broken-up asteroids Meteors are meteoroids that enter Earth’s atmosphere Meteorites actually hit the earth’s surface Chondrite – a meteorite with more stone than metal - 85% of all meteorites Comets have glowing tails – dirty snowball composed of frozen water or carbon dioxide May have originated in Oort cloud far from our solar system Comets are soft - gas and/or ice. Asteroids are rocky or metallic. Meteors and meteorites travel at relatively high speed – collision with earth atmosphere causes immediate combustion: intense heat and flame. The energy of colliding with earth is converted to heat and flame. Asteroid - larger Meteoroid – smaller fragments Meteor fully or partially vaporized on atmospheric entry Meteorite Very small remnants that survive to land on earth Oort cloud is extremely far away – most knowledge of it is inferential or theoretical Figure 13.3 Pluto has been relegated to association with the Kuiper belt Airbursts and Impacts Objects enter Earth’s atmosphere at 27,000 to 161,000 mph Meteorites Metallic or stony Flash to flame on striking the atmosphere - bright light Small pieces that did not vaporize but instead survive to hit the earth Airbursts Meteor explodes on striking the atmosphere at high speed (Tunguska 1908) Chelyabinsk (2013) included hundreds of meteorites large enough to be collected. Impact Craters Provide evidence of meteor impacts. Bowl-shaped depressions with upraised rim Rim is overlain by ejecta blanket of debris 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 Soil and water may vaporize from vast heat produced by collision Other rocks may metamorphose or melt. Severity of meteorite impact: Worst = vaporize into basic elemental gases Very bad = completely melt into new rocks Bad = metamorph into a modified rock Not bad = be thrown into the air and broken apart Note: Being blown into the air and broken into pieces is similar to a student not finishing an ePortfolio before the final exam. Simple Impact Craters Typically small less than 6 km Arizona’s Barringer Crater A “shatter cone” may form under the impact zone. Complex Impact Craters Larger in diameter than 6 km Rim collapses more completely Center uplifts following impact leaving a peak Impact Rebound Source: joerenaissanceman.blogspot.com Impact Crater Details Craters are much more common on the Moon because: Moon has no atmosphere to incinerate incoming objects On earth, most impacts are in the ocean, buried, or eroded Impact alteration of rocks can occur in collisions between asteroids as well - - they hit each other - - a few are bumped toward the earth. Intense heat and pressure may metamorphose rocks. “Contact metamorphosis” can also occur on earth by tectonic force, including volcanism and pyroclastics. Add Chelyabinsk – 2013 – estimated 20-meters wide before exploding arrived at speed of 12 miles per second – 12 x 60 x 60 = 43,200 mph Estimates of energy released vary widely, but include: - A 7-meter (22 feet) wide meteorite striking the atmosphere releases energy equivalent to an atomic bomb. - 5-meter meteors arrive about every year. - 50-meter rocks arrive once a thousand years. (Source: en.wikipedia.org/wiki/Impact_event The Chelyabinsk meteorite event knocked people off their feet. Others were seriously burned or even blinded by the bright light of combustion. The effects were much more than just breaking glass. Scientists are now considering that impacts of that size may occur more frequently than previously believed. (Source:www.theguardian.com/science?across-the-universe/2013/feb/15/russianmeteorite . . ) Mass Extinctions Sudden loss of large numbers of plants and animals Sudden climate change Define the boundaries of geologic periods or epochs Mass extinctions can also be caused by meteorites and: Plate tectonics Volcanic activity Moves habitats to different locations Large eruptions release CO2, warming Earth Volcanic ash reflects radiation, cooling Earth Changes in solar energy can also be attributed to weather and/or catastrophic effect. Six Major Mass Extinctions 1. Ordovician, 446 million years ago (mya), continental glaciation in Southern Hemisphere 2. Permian, 250 mya, volcanoes causing global warming and cooling 3. Triassic–Jurassic boundary, 202 mya, volcanic activity associated with breakup of Pangaea 4. Cretaceous–Tertiary boundary (K-T boundary), 65 mya, meteorite impact 5. Eocene period, 34 mya, plate tectonics 6. Pleistocene epoch, initiated by airburst meteor, continues today, more recently enhanced by human activity Now, consider that aside from earth change caused by meteorites and volcanoes, human power arose when the Pleistocene “ice age” withdrew. The earth warmed enough to provide space for people to start farming and burning fossil fuel. So, the “Anthropocene epoch” makes sense. We are ‘human bulldozers” powered by ancient solar energy stored for millions of years as oil, coal and natural gas. Let’s look a little more at the “K-T Boundary Mass Extinction” 65 million years ago. Dinosaurs disappeared with many plants and animals. 70% of all genera died Set the stage for evolution of mammals (humans are mammals) 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 indicate that layer formed quickly. Extinction probably caused by a single meteorite impact. K-T Boundary Mass Extinction Alvarez did not have a crater to prove the theory. But we later found a crater in Yucatan Mexic0. Diameter approx. 180 km (112 mi) Nearly circular Semi-circular pattern of sinkholes on land define the edges Possibly as deep as 30–40 km (18–25 mi) Slumps and slides filled crater Drilling located breccia under the surface Glassy, indicating intense heat Notice the center uplift – consistent with large, complex crater. Iridium is part of the platinum group – it is more common in meteorites than in native earth. Iridium rivals Osmium as the most dense natural element known in the universe and the most resistant to heat and corrosion. Most of our Iridium may have come from a meteorite. The Iridium ‘layer’ of rock points toward a meteorite strike. Iridium metal Beautiful, strong, expensive Source: en.wikipedia.org/wiki/Iridium Sequence of Events a) Asteroid moving at 30 km (19 mi) per second b) Asteroid hit the Earth, producing a crater 200 km (125 mi) diameter, 40 km (25 mi) deep c) Shock waves crushed, melted and vaporized rocks Sequence of Events, cont. 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) 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 K-T Extinction, summary Impact caused massive extinction of plants and animals, 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 million years Smaller impacts are more probable and have their own dangers. Linkages with Other Natural Hazards Tsunamis Wildfires Earthquakes Mass wasting Climate change Volcanic eruptions All of these events can result from a major meteorite strike on earth Event Frequency and Risk Risk related to probability and consequences Large events have consequences, will be catastrophic Worldwide effects Potential for mass extinction Return period of 10’s–100’s millions of years Smaller events have regional catastrophe This outlook is from the textbook and is being re-evaluated by scientists. Effects depends on site of event Return period of 1000 years Likelihood of an urban area hit every few 10,000 years Local events every 100 years (Tunguska, Chelyabinsk) Micro events – many daily Risk Related to Impacts, cont. Risk from impacts is relatively high. Emerging risk assessment may be altered upward: Probability that you will be killed by Impact: 0.01%-0.1% Car accident: 0.008% Drowning: 0.001% Meteorite hazards to humans may be greater than we thought. However, that is AVERAGE probability over thousands of years. Events and deaths are very rare. Minimizing the Impact Hazard Identify nearby threatening objects. Spacewatch Near-Earth Asteroid Tracking (NEAT or NEO) project Inventory of objects with diameter larger than 100 meters in Earth-crossing orbits 85,000 objects found so far Identify objects diameter of 1 km or larger Use telescopes and digital imaging devices Most objects threatening Earth will not collide for thousands of years from discovery. Minimizing the Impact Hazard Consider our options once a hazard is detected Use nuclear explosion to fragment the object in space Nudge it out of Earth’s orbit Small pieces could rain radioactivity down on earth Much more likely because we will have time to prepare Technology can change orbit of asteroid Expensive process will require coordination of world military and space agencies Evacuation A good idea only if we can predict impact point Could be impossible depending on how large an area would need to be evacuated Bolide Meteor? Large enough to cause a sonic “boom” Note the debris trail. The 1974 event also appeared to include visible flame and smoke Source: Astronomy.wonderhowto.com/inspiration/sonic-boom Do regular meteor ‘showers’ occur? Yes. Lyrid, Geminid, Leonid and other regular meteor “showers” occur, based on routine intersection of orbits about the sun. Comets exhibit similar habits. Clark Planetarium at the Gateway < The planetarium has a selection of meteorites and vast other resources for ePortfolios> The planetarium also has very cool light shows set to rock music -- hah hah - no pun intended. Impact craters Source: clarkplanetarium.org/venue/cosmic-light-shows Why does the “dark” side of the moon have much more cratering? Because the moon’s rotation is earth-synchronous, so that it keeps the same face to the earth at all times. So, the side facing away from the earth is not shielded from meteorites. Chelyabinsk – 2013 a major meteorite strike in Russia This meteor was tracked en-route to earth, supporting the concept of prediction and protection NEO and NEAT space programs are tracking other dangerous asteroids and comets Conclusion Current science suggests that if an asteroid is large enough to cause world-wide damage, then there is probably enough time to identify the hazard and take action at least 100 years before the collision.