Learning Objectives Differentiate between asteroids, meteoroids, and comets. Describe the physical processes associated with airbursts and impact craters. Suggest the possible causes of mass extinction, and provide examples. Evaluate the evidence for the impact hypothesis that produced the mass extinction at the end of the Cretaceous Period.

Learning Objectives, cont. List the physical, chemical, and biological consequences of impact from a large asteroid or comet. Analyze the risk of impact or airburst of extraterrestrial objects, and suggest how that risk might be minimized.

Chelyabinsk Meteor, February 2013 Small asteroid traveling about 20 times faster than speeding bullet Entered Earth’s atmosphere and exploded People living in Chelyabinsk could feel the intense heat from the fireball as well as the shock wave from the explosion Meteor did not impact Earth Exploded in the stratosphere about 23 km (~15 mi) above the surface Released energy equivalent to 20 to 30 World War II-era nuclear explosions Largest known asteroid to enter Earth’s atmosphere since Tunguska airburst

Meteor Impact Locations

Chelyabinsk Meteor, February 2013, cont. Before entry and explosion, no one knew it was coming Meteor astrophysicists were looking the other way tracking a much larger and completely unrelated asteroid Chelyabinsk meteor damage More than 7000 buildings in six cities damaged About 1500 people required medical attention People were confused and frightened about what was happening Mobile phone networks were overloaded with calls Office buildings evacuated and schools closed Broken windows in homes required immediate attention due to weather

14.1 Earth’s 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 No longer capable of sustaining its mass and collapses inward Explosion scatters mass into space creating a nebula Nebula begins to collapse back inward on itself and new stars are born in a solar nebula

Earth History

14.1 Earth’s Place in Space, cont. Five 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 that added to its formation Bombardment continues today at a lesser rate

Solar Nebula

Sizes in the Solar System

Asteroids, Meteoroids, and Comets Particles in solar system are arranged by diameter and composition Asteroids Found in asteroid belt between Mars and Jupiter Composed of rock, metallic, or combinations Meteoroids are broken up asteroids Meteors are meteoroids that enter Earth’s atmosphere Burn and create “shooting stars” Comets have glowing tails Composed of rock surrounded by ice Originated in Oort Cloud beyond the Kuiper Belt

Meteorites and Related Objects

Diagram of Our Planetary System Showing Asteroid Belt and Kuiper Belt

Comet Hale-Bopp

14.2 Airbursts and Impacts Objects enter Earth’s atmosphere at 12 to 72 km/s (~7 to 45 mi per second) Metallic or stony Heat up due to friction as they fall through atmosphere, produce bright light and undergo changes Meteoroid will either Explode into an airburst Object explodes in atmosphere 12 to 50 km (~7 to 31 mi.) Ex: Tunguska Or collide with Earth as a meteorite If the object strikes Earth Concentrated in Antarctica

Meteoroid Entering Earth’s Atmosphere

Impact Craters Provide evidence of meteor impacts Example: Barringer Crater in Arizona Bowl shaped depressions with upraised rim Rim is overlain by ejecta blanket, material blown out of the crater upon impact Broken rocks cemented together into Breccia Features of impact craters are unique from other craters 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

Extraterrestrial Impact Craters of the United States and Canada

Impact Craters, cont. Can be grouped into two types Simple craters Typically small < 6 km (4 mi.) Ex. Barringer Crater Complex impact craters Larger in diameter > 6 km (4 mi.) Rim collapses more completely Center uplifts following impact Ancient impact craters difficult to identify Usually eroded or filled with sedimentary depostis Examples: Chesapeake Bay in U.S. and Manicouagan Crater in Quebec

Simple Impact Crater in Arizona

Chesapeake Bay Impact Crater

Complex Impact Crater in Quebec

Notable Impacts and Airbursts of Extraterrestrial Objects

Impact Craters, cont. Craters are much more common on Moon Most impact sites on Earth are in ocean where they are buried or destroyed Impact craters on land are now generally subtle features because they have been eroded or buried by debris Smaller meteoroids and comets tend to burn up and disintegrate in Earth’s atmosphere before impact

Uniformitarianism, Gradualism, and Catastrophism Those studying the formation of mountains, large river valleys, and other features had a hard time understanding how they could be formed in 6000 years Based on Archbishop Ussher’s “young Earth” belief, concluded that the processes were catastrophic in nature Gradualism or Uniformitarianism James Hutton introduced concept in 1785, popularized by Charles Hutton Present geological processes may be studied to learn the history of the past Argued Earth must be much older than 6000 years

Uniformitarianism, Gradualism, and Catastrophism, cont. Uniformitarianism lasted into the twentieth century and culminated with plate tectonics Occasionally scientists also discover evidence of catastrophic events Impact craters Rapid extinctions Lead to a new concept Punctuated uniformitarianism Although uniformitarianism explains the long geologic record of gradual mountain building, canyon erosion, and landscape construction, periodic catastrophic events do occur and can cause mass extinctions

14.3 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 Slow process that moves habitats to different locations Volcanic activity Flood basalts produce large eruptions of CO2, warming Earth Silica-rich explosions produce volcanic ash that reflects radiation, cooling Earth Extraterrestrial impact or airburst

14.3 Mass Extinctions, cont. Six major mass extinctions Ordovician, 446 mya, continental glaciation in Southern Hemisphere Permian, 250 mya, volcanoes causing global warming and cooling Triassic-Jurassic boundary, 202 mya, volcanic activity associated with breakup of Pangaea Cretaceous-Paleogene boundary (K-Pg boundary), 65 mya, Asteroid impact Eocene period, 34 mya, plate tectonics Pleistocene Epoch, initiated by airburst, continues today caused by human activity

Mass Extinction Events

K-Pg Boundary Mass Extinction Dinosaurs disappeared with many plants and animals 70 percent of all genera died Set the stage for evolution of mammals First question, What does geologic history tell us about K-Pg Boundary? Walter and Luis Alvarez decided to measure concentration of Iridium in clay layer at K-Pg 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

K-Pg 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 to 40 km (18 to 25 mi.) Slumps and slides filled crater Drilling finds breccia under the surface Glassy indicating intense heat

Large Impact Crater in Mexico

K-Pg Boundary Mass Extinction, cont. Sequence of events Asteroid moving at 30 km (19 mi.) per second 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

K-Pg Boundary Mass Extinction, cont. Sequence of events, cont. Seconds after impact Ejecta blanket forms Mushroom cloud of of dust and debris Fireball sets off wildfires around the globe Sulfuric acid enters atmosphere Dust blocks sunlight Tsunamis from impact reached over 300 m (1000 ft.)

K-Pg Boundary Mass Extinction, cont. 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-Pg Boundary Mass Extinction, cont. 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 to 100 my Smaller impacts are more probable and have their own dangers

14.4 Linkages with Other Natural Hazards Asteroid or comet impact or airburst direct cause for Tsunamis Most impacting objects land in the world’s oceans Wildfires Superheated clouds of gas and debris reach temperatures capable of drying out then igniting living vegetation Earthquakes Seismic waves created from impact Mass Wasting Earthquakes activate numerous landslides on land and under water Climate Change Inject large quantities of dust into atmosphere and causes cooling Warming then follows from large amounts of greenhouse gases Volcanic Eruptions Impacts cause melting and instability in Earth’s mantle

14.5 Minimizing the Impact Hazard: 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 to 100s of 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 10,000s years

Energy from Impact

Risk Related to Impacts, cont. Risk from impacts is relatively high Probability that you will be killed by Impact: 0.01 to 0.1 percent Car accident: 0.008 percent Drowning: 0.001 percent However, that is AVERAGE probability over thousands of years Events and deaths are very rare!

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 form several 1000s of years from discovery

Asteroid 243 Ida

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 Earth’s 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

The Torino Impact Hazard Scale

Chelyabinsk Meteor, February 2013 – Applying the 5 Fundamental Concepts Largest known asteroid to have entered Earth’s atmosphere since Tunguska event Chelyabinsk meteor, fireball, and blast was video-recorded by numerous people and sensors monitored by the U.S government Explosion of meteor Compression of atmospheric gasses generated massive amounts of heat Meteor erupted into a fireball Then exploded and produced a tremendous shock wave

Damage from Chelyabinsk Airburst

Chelyabinsk Meteor, February 2013 – Applying the 5 Fundamental Concepts, cont. Small meteorites collected from a hole found penetrating a frozen lake Long meteorite fragment found at bottom of lake eight months later Composition and density of the meteor was determined Chondritic in compositions Density about 3.6 g per cm (3.6 times that of water) Total weight estimated to be 11,000 tons Location of explosion was important Catastrophic damage if closer to the ground If over an urban area, millions of deaths could occur

Chelyabinsk Impact

Chelyabinsk Meteor, February 2013 – Applying the 5 Fundamental Concepts, cont. How could the effects of an impact be minimized? Predict when and where a strike may occur so there is enough time to evacuate However, smaller extraterrestrial objects like the Chelyabinsk meteor are not easily identified Scientists were tracking an unrelated larger meteor at the time of the Chelyabinsk meteor Funds appropriated to identify 90 percent of the objects 150 m and larger are insufficient Technology is available and as it improves, it could identify even smaller NEOs

Cosmic Coincidence

Chapter 14 Summary The evolution of Earth most likely started about 14 billion years ago with the so-called explosion of the “Big Bang” that produced atomic particles that later formed galaxies, stars, and planets. Asteroids, meteoroids, and comets are extraterrestrial objects that can intercept Earth’s orbit. A meteoroid entering the atmosphere at about 85 km (~53 mi) above Earth’s surface at a velocity of 12-72 km per second (~7 to 45 mi per second) will become a meteor and emit light.

Chapter 14 Summary, cont. Objects that impact Earths surface produce both simple and complex craters. Large objects can cause local to global catastrophic damage and mass extinction of life. Recent studies suggest that an airburst may have been responsible for the extinction of many large Pleistocene mammals and the disappearance of the Clovis people at the start of the Younger Dryas period 12,800 years ago.

Chapter 14 Summary, cont. Many linkages exist between impacts of comets and asteroids with Earth and other natural hazards. Risk assessment is difficult for events with long return periods. Sufficient studies of comets and asteroids and their interaction with planets enable us to make fairly straightforward predictions of the return time that an object of a particular size would impact Earth.

Chapter 14 Summary, cont. Programs such as Spacewatch and NEAT (Near-Earth Asteroid Tracking) can, with high certainty, identify NEOs of diameters greater than a few hundreds meters at least 100 years before possible impact. The human population of Earth today is about 7 billion, compared to about 1 billion in 1830. Thus, an event in 1830 that might have killed a million people would likely kill more than 10 million people today. The most encouraging note is that a large comet or asteroid would probably be seen a hundred years or more before it is likely to strike Earth.