Natural Disasters Tenth Edition Chapter 17 Impacts with Space Objects Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Impact Scars Surface of the Moon: intense bombardment of first few million years of Solar System history recorded on surface of Moon tens of millions of ancient impact craters Flood basalts on Moon 3.8 3.2 billion years ago created maria few impact scars, so bombardment over by 3.8 billion years ago On geologically dead Moon, craters are preserved Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-2
TABLE 17.1 Frequency of Globally Catastrophic Impacts Average interval between impacts 500,000 years Annual probability a person will be killed 1/500,000 Assumed Fatalities From impact 1/4 of human race Total annual probability of death 1/2,000,000 Source: D. Morrison (1992) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-3
Figure 17.3 Rotations and orbits of the Earth-Moon- Sun system result in tremendous amounts of energy Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-4
Figure 17.4 Moon s surface is ancient and pockmarked by numerous impact craters. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-5
Figure 17.5 Manicouagan impact crater formed about 214 million years ago in northern Quebec, Canada. Crater is 75 km across. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-6
Sources of Extraterrestrial Debris Primarily from fragmented asteroids Secondarily from comets Pieces of asteroids and comets orbiting Sun: meteoroids Meteoroids blazing through Earth s atmosphere: shooting stars or meteors Meteors that hit the Earth s surface: meteorites Irons: metallic meteorites (most of collected meteorites) Stones: rocky meteorites (most of meteorites) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-7
Sources of Extraterrestrial Debris: Asteroids (1 of 2) Solar System: four small, rocky inner planets + four large, gaseous outer planets (+ Pluto) Between Mars and Jupiter: asteroid belt of small (under 1,000 km diameter) rocky, metallic and icy masses Most meteorites come from inner Solar System, from asteroid belt Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-8
Sources of Extraterrestrial Debris: Asteroids (2 of 2) All asteroids together would have formed planet less than half Moon s diameter too strongly influenced by Jupiter s gravitational pull Many asteroids held together with other asteroids by gravity (Ida and Dactyl) multiple impact sites Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-9
Figure 17.7 Solar System from Sun to Jupiter. The asteroid belt contains millions of rocky and metallic bodies Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-10
Table 17.2 Sources of Extraterrestrial Debris Asteroids: Bodies in the Solar System Source: R. T. Dodd (1986) Diameter (miles) Specific Gravity (water =1) Sun 864,886 1.4 27.9 Inner Rocky Planets Mercury 3,024 5.4 0.4 Venus 7,522 5.3 0.9 Earth 7,918 5.5 1.0 Moon 2,160 303 0.2 Mars 4,200 3.9 0.4 Asteroid belt Outer Ice and Gas Plants Jupiter 86,692 1.3 2.6 Saturn 72,352 0.7 1.1 Uranus 29,168 1.3 0.9 Neptune 28,230 1.6 1.2 Dwarf planet Pluto 1,472 1.9 0.06 Ceres 590 2.1 0.03 Gravity (Earth = 1) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-11
Figure 17.8 Asteroid Ida is 56 km long and pockmarked with impact craters. Ida has a near-spherical moon Dactyl 1.6 km diameter. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-12
Sources of Extraterrestrial Debris: Comets (1 of 2) Short-period (orbit less than 200 years) or longperiod Solar System surrounded by: About one billion comets in Kuiper belt flattened disk (in plane of Solar System) from near Neptune to about 50 astronomical units (93 million miles, distance from Earth to Sun) About one trillion comets in Oort cloud spherical orbits far beyond planets Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-13
Sources of Extraterrestrial Debris: Comets (2 of 2) Described as dirty snowballs : composition of ice and rocky debris When passes Saturn toward Sun, affected by sunlight and solar win sublimation releases gas and dust to form tail Nearer Sun, tail becomes larger, always pointing away from Sun Halley s comet: orbit from 74 to 79 years, from Sun to beyond Neptune, last visible near Sun in 1986 Comets contain carbon compounds (CHON carbon, hydrogen, oxygen, nitrogen), building blocks of life brought to Earth by comets? Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-14
Figure 17.12 Comet entering the Solar System heading toward the Sun Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-15
Figure 17.13 Halley s comet (left) streaking through Solar System. Orbit (right) of Halley s comet during its 76 year-long trip. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-16
In Greater Depth: Shoemaker-Levy 9 Comet Impacts on Jupiter ( 1 of 2) Comet named for discoverers (9 th co-discovered comet) Flew too close to Jupiter in 1992, broke into 21 pieces Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-17
In Greater Depth: Shoemaker-Levy 9 Comet Impacts on Jupiter (2 of 2) 1994: Impacted Jupiter s atmosphere, at up to 60 km/sec Initial flash at collision Superheated gas fireball, thousands of kilometers above clouds Radiation as plume crashed back down at high speed Largest (1 km) fragment G impact scar larger than Earth Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-18
Figure 17.15 Impact scar of Shoemaker-Levy 9 comet on Jupiter Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-19
Figure 17.16 Path and impact plume of Comet fragment G Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-20
Figure 17.14 Frequency versus size of impacting space debris on Earth Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-21
Rates of Meteoroid Influx (1 of 2) 100,000 million or more meteoroids enter Earth s atmosphere every day Smaller meteoroids greater abundance Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-22
Rates of Meteoroid Influx (2 of 2) At 115 km above ground, atmosphere is dense enough to heat meteoroids to glowing (shooting star) Meteoroids typically visible 100 km above ground, vaporized before reaching 60 km above ground Adds 100 to 1,000 tons of material to Earth s surface each day Speeds of 11 30 km/sec atmosphere behaves like solid Most meteoroids destroyed on impact, deflected back into space or slowed down by friction Meteoroids larger than 350 tons largely unaffected by atmosphere Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-23
Rates of Meteoroid Influx: Cosmic Dust Smallest meteoroids unaffected by atmosphere settle on surface as gentle rain Shooting Stars Sand grain sized debris (1 mm diameter) Friction-generated flash about 35 km above ground as debris melts to tiny droplets of glassy rock spheres Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-24
Rates of Meteoroid Influx: Meteorites (1 of 2) Meteoroids 1 gram or more pass through atmosphere to Earth s surface Frictional resistance of atmosphere melts away exterior, protecting interior glazed, blackened crust Violently compresses air mini-sonic boom Atmospheric frictional heat may raise surface temperature to 3,000 o C, creating tail to fireball Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-25
Rates of Meteoroid Influx: Meteorites (2 of 2) 1954: stony meteorite crashed through roof of Alabama home, bounced off walls then hit woman in hip, severely bruising her October, 1996: meteorite streaked over New Mexico and Texas, bounced into space, pulled back and fell in California March, 2003: meteorite flashed over midwest as it broke apart more than 60 pieces found, hitting homes, cars and fire department September, 2003: large meteorite broke apart over Orissa, India, raining debris that injured three people and set house afire Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-26
Figure 17.17 A meteor hitting the top of the atmosphere sends off sonic shock waves that might be heard on the ground Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-27
The Crater-Forming Process (1 of 3) Energy release of impact depends on object s speed, mass Asteroids impact at 14 km/sec, comets at 70 km/sec Impacts of smaller meteorites form simple craters (Meteor Crater, Arizona) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-28
The Crater-Forming Process (2 of 3) Impacts of larger bodies form complex craters Examples: buried Chicxulub crater on Yucatan Peninsula, Mexico; Manicouagan crater in Canada; Yuty crater on Mars Miniature corollaries: falling drop of water hitting still body of water, bullet into soft sand Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-29
The Crater-Forming Process (3 of 3) Impacts of larger bodies form complex craters Central uplifts, collapsed and fractured outer rims Much of asteroid and crater rock is melted and vaporized In first instant: shock wave with temperatures thousands of degrees, pressures more than 100 gigapascals new minerals created (diamond, stishovite), ground pushed downward and outward Still initial second: release wave deflects material upward and outward forms central uplift, transient crater Later: fractured walls of empty crater slide in final enlarged crater with central peak, circular trough, outermost fractured rim Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-30
Figure 17.18 Meteor Crater, Arizona Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-31
Figure 17.21 Drop of water hitting a body of water note the central rebound Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-32
Figure 17.20 Yuty crater on Mars has well-developed central peak (rebound) and surrounding circular trough Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-33
Impact of a meteoroid (a) Incoming at 30,000 mph (b) Impact high temperatures and pressures vaporize and melt meteoroid (c) Release wave causes center of crater to rise (d) Fractured walls slide into crater Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-34
Figure 17.19 Impact of a meteoroid Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-35
Figure 17.22 Impact crater locations Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-36
Crater-Forming Impacts (1 of 2) Meteor Crater, Arizona World s classic meteorite crater over 1 km wide, excavated 175 m below Colorado Plateau, rim 35 to 60 m above Colorado Plateau Evidence that formed by meteorite impact: Steep-sided, closed crater Surrounding rock rim of uplifted, tilted sedimentary rock layers of region Surrounded by hills of inverted regional sedimentary sequence, limestone blocks 265 m of shattered rock on crater floor Nearly 30 tons of nickel-iron metallic meteorite collected in area Evidence of high temperature and pressure: coesite, stishovite, cooled droplets of metal, fused sand grains, shatter cones Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-37
Crater-Forming Impacts (2 of 2) Meteor Crater, Arizona Formed about 50,000 years ago: nickel-iron metallic meteorite with 40 m diameter, weighing around 110,000 tons, traveling about 12 km/sec Impact melted 80% of meteorite and surrounding ground in less than 1 second Shock wave leveled all trees in region, started wildfires, released enough dust to darken sky Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-38
Figure 17.23 Meteor Crater, Arizona Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-39
Impact Origin of Chesapeake Bay Impact 35.5 million years ago formed 90 km diameter crater, 25 km diameter central peak, 400 m deep trough Spread tektites (glassy spherules formed by inair cooling of impact-melted rock) over southeastern U.S., Gulf of Mexico, Caribbean Sea 9,000,000 km 2 area Impact crater formed topographic low spot rivers flowed toward crater, drowned today by Chesapeake Bay Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-40
Figure 17.24 Outline of the buried impact crater in lower Chesapeake Bay, Virginia Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-41
The End-Cretaceous Impact Study of latest Cretaceous age rocks near Gubbio, Italy by father and son Alvarez team disclosed high levels (300 times normal) of iridium in end- Cretaceous limestone layer Iridium is associated with iron abundant in core, very sparse in crust, abundant in meteorites could have been supplied by meteorite Popular theory: asteroid with diameter equivalent to height of Hawaii (from seafloor to peak of Mauna Kea) hit Earth about 66 million years ago, causing mass extinctions and leaving excess iridium deposited in global clay layer Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-42
Figure 17.25 The end-cretaceous Impact Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-43
The End-Cretaceous Impact: Evidence of the End-Cretaceous Impact (1 of 3) End-Cretaceous boundary clay layers around world searched for evidence of Earth-like vs. meteoritelike components Clay layer found on continents iridium enrichment End-Cretaceous boundary clay minerals have different composition than clays in limestones above and below in rock sequences explained by mix of one part asteroid to ten parts Earth crust Shocked quartz grains present Spherules present, suggesting melting and resolidification Microscopic diamonds (found in some meteorites) found in end Cretaceous boundary clay layer Carbon-rich grains with fluffy structures indicative of fire are abundant in end-cretaceous boundary clay layer Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-44
The End-Cretaceous Impact: Site of the End Cretaceous Impact (2 of 3) Evidence compelled scientists to agree that impact had occurred, but crater had to be found Could have been subducted, buried under glacier, hidden under continental or oceanic sediment, covered by flood basalt, eroded and erased, destroyed by continent collision 65 million year old sediment layers with shocked quartz grains, spherules, huge angular blocks, and tsunami deposits found throughout eastern North America and Caribbean Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-45
The End-Cretaceous Impact: Site of the End Cretaceous Impact (3 of 3) Mexican national petroleum company (PEMEX) in Yucatan Peninsula: Discovered layer of shattered rock with shocked quartz and spherules in exploratory wells Ground surface with circular pattern of sinkholes Circular patterns of gravity and magnetic anomalies Seismic survey shows 80 km diameter raised inner ring and 195 km diameter outer ring Chicxulub structure formed 64.98 (+/- 0.06) million years ago when asteroid slammed in shallow tropical sea Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-46
The End-Cretaceous Impact: Size and Velocity of Impactor Impactor diameter estimated to be about 10km Impactor velocity estimated to be about 21 km/sec (47,000 mph) Angle of Impact: Subsurface features show opening to northwest result of asteroid coming from southeast Oblique impact: concentrated energy into vaporizing surface rocks yielding mammoth dust cloud Worldwide effects: significant role in extinctions Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-47
Figure 17.26 Buried impact crater (top) on tip of Yucatan Peninsula, Mexico Approximate path (bottom) of incoming asteroid Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-48
Problems for Life from the End- Cretaceous Impact (1 of 2) Earthquake of monumental magnitude with numerous aftershocks extrapolated impact magnitude of 11.3 Wildfires raged regionally or even globally Huge amounts of nitrogen oxides in atmosphere probably fell as acid rain, acidified surface waters Dust and soot in atmosphere blocked sunlight, inhibiting photosynthesis Dust settled but water vapor and CO 2 remained in atmosphere global warming for years Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-49
Problems for Life from the End- Cretaceous Impact (2 of 2) Tsunami up to 300 m high Bubble of steam up to 500 km 3 volume blows rock and asteroid debris into upper atmosphere End-Cretaceous asteroid landed in shallow sea underlain by limestone vaporized to contribute even more CO 2 to atmosphere, raised temperature as much as 10 o C Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-50
Figure 17.27 Problems for life from the end- Cretaceous Impact Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-51
Biggest Events of 20 th and 21st Centuries (1 of 2) Tunguska, Siberia, 1908 Massive fireball from east exploded about 8 km above ground in blast heard 1,000 km away Killed many reindeer in area (no humans nearby) Nearly ignited shirt of man 60 km away before air blast threw him 2 m Knocked people off their feet 480 km away 20 km high column of fire was visible 650 km away Ground shaking was registered in Russia and Germany Barometric anomalies from air blast traveled around world twice Years of speculation before expedition to remote area Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-52
Biggest Events of 20 th and 21 st Centuries (2 of 2) Tunguska, Siberia, 1908 Forest in more than 1,000 km 2 area destroyed, 80 million trees knocked down over 5,000 km 2 area No impact crater or broken ground only globules of once-melted metal and silicon-rich rock (collected 1958) Meteoroid (fragment of icy comet Encke or large, stony meteorite) racing through atmosphere at 15 km/sec broke up and exploded 8 km above ground Fortunately occurred over uninhabited area Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-53
Figure 17.28 The Tunguska event devastated more than 400 square miles, knocking down trees. What if it hit Washington D.C.? Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-54
Biggest Near Events March 1989: asteroid 1989FC missed Earth by six hours, less than 700,000 km (impact would have created 7 km crater) May 1996: 150 m asteroid missed Earth by 453,000 km March 1998: reports that asteroid 1997XF11 might hit Earth in 2028 Also March 1998: movies Deep Impact and Armageddon Torino scale developed Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-55
TABLE 17.4 The Torino Scale Assessing Comet and Asteroid Impact Hazards Events with No Likely Consequences (white zone) 0 No collision hazard, or object is small Events Meriting Careful Monitoring (green zone) 1 Collision is extremely unlikely Events of Concern (yellow zone) 2 Collision is very unlikely 3 Close encounter with > l % chance of local destruction 4 Close encounter with > l % chance of regional devastation Threatening Events (orange zone) 5 Significant threat of regional devastation 6 Significant threat of global catastrophe 7 Extremely significant threat of global catastrophe Certain Collisions (red zone) 8 Collision will cause localized destruction (one event each 50 to 1,000 years) 9 Collision will cause regional devastation (one event each 1,000 to 100,000 years) 10 Collision will cause global catastrophe (one event each 100,000 years) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-56
Frequency of Large Impacts (1 of 2) Determined by examination of Moon s maria: one major impact every 110 million years Extrapolated to Earth s 80 times larger surface area: 2,400 impacts leaving craters bigger than 25 km diameter (720 of them on land) More than 160 craters discovered so far, most smaller than 25 km diameter (remainder probably buried or destroyed) Extremely small odds that Earth will be hit by large asteroid during human lifetime Very large numbers of people killed when impact occurs Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-57
Frequency of Large Impacts (2 of 2) Prevention of Impacts Could alter NEO s collision course by: Blowing apart with nuclear explosion Attaching rocket engine to drive it away Using big mirror to focus sunlight to vaporize rock Scooping rock mass and tossing it away Putting a body (gravity tractor) near the potential impactor to let gravity alter its path Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-58
TABLE 17.5 Frequency of impacts and annual Risk of Death Tunguska-size Events: Average interval between impacts Average interval for populated areas only Average interval for urban areas Average interval for U.S. urban areas only 300 years 3,000 years 100,000 years 1,000,000 years Total annual probability of death 1/30,000,000 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-59
TABLE 17.6 Odds of Dying in the United States from Selected Causes (2007) Cause of Death Odds of Happening Motor vehicle accident 1 in 90 Murder 1 in 185 Falls 1 in 250 Fire 1 in 1,100 Firearms accident 1 in 2,500 Drowning 1 in 9,000 Flood 1 in 27,000 Airplane crash 1 in 30,000 Tornado 1 in 60,000 Asteroid/Comet Impact(global) 1 in 75,000 Earthquake 1 in 130,000 Lightning 1 in 135,000 Asteroid/Comet Impact(regional) 1 in 1,600,000 Food poisoning by botulism 1 in 3,000,000 Shark attack 1 in 8,000,000 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-60