GEOL 110 1st Edition Lecture 12Outline of Last Lecture II. Force, Stress, and StrainIII. EarthquakesIV. Locating EarthquakesV. Measuring the size of earthquakesVI. Intraplate earthquakesOutline of Current Lecture VII. Why study Meteor Impacts?VIII. TerminologyIX. History of the Study of GeologyX. CratersXI. Meteors and Humans Current LectureI. Why Study Meteor Impacts?A. Catastrophic events in geologic recordB. Relationship to climate changeC. Fear factor – II. TerminologyA. Meteoroid – an interplanetary chunk of matter that is smaller than a kilometer in diameter, relatively small (think dust sized)B. Meteor – the streak of light that is made when a meteoroid enters the earth’s atmosphere. The friction causes the meteoroid to vaporize or explode. A very large or bright meteor is called a fireball or bolide. C. Meteorite - A natural object of extraterrestrial origin (meteoroid) that survives passage through the atmosphere and hits the ground.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.1. General Classification of MeteoritesI. Iron Meteorites – RARE (5.7%)II. Stony-Iron Meteorites – VERY RARE (1.5%) III. Stony Meteorites – VERY COMMON (92.8%)D. Asteroid - An object ranging in size from sub-kilometer to about 1,000 kilometers in diameter. At the small end, these are meteoroids. At the large end, they are planetoids. Most asteroids orbit the Sun in the Asteroid Belt between the orbits of Mars and Jupiter. Asteroids can exist in any variety of orbits around the Sun, but the largest concentration of asteroids is found in the Asteroid Belt, which is located between the orbits of Mars and Jupiter.III. History of the Study of GeologyA. Geology - the study of Earth’s history and processes as recorded in rocks - is a relatively young field, emerging in the late 1700s and early 1800s.B. Prior to that, both the prevailing consensus of Physicists and Biblical literalism in the mid-1600s constrained the age of the Earth to quite young (thousands of years).C. Renaissance thinkers began to consider the natural environment, questing for processes, guiding principles, physical laws, time constraints.D. Three types of rocks were identified: 1. IGNEOUS - cooled from magma or lava 2. SEDIMENTARY - Sediments from eroded older rocks/ shells, chemical precipitates deposited in basins, deltas, seabeds, ‘lithified’ by pressure and temperature 3. METAMORPHIC - Deformed older igneous or sedimentary rocksE. Principle of Uniformitarianism (created by James Hutton)1. The present is the key to the past. The earth is dynamic, so as rocks are eroded and weathered, new rocks are created. Therefore, the geologic processes observed today were at work in the past, even the distant past. HOWEVER – those processes may have happened at different rates or with different intensity than they do now.2. Older rocks had deposited in a low basin, over a long time; then uplift and tilting occurred, then massive erosion, then down-drop, deposit of new overlying horizontal rocks, now uplifted. THIS TAKES A VAST AMOUNT OF TIME. 3. “No Vestige of a Beginning, No Prospect of an End”4. Therefore the age of Earth, must be hundreds of millions of years, or even thousands of millions of years old.F. Charles Lyell 1. Wrote “Principles of Geology”, Clarified Hutton’s arguments2. The Earth is now understood to be 4.55 Billion Years Old (4,550,000,000 years)3. The Earth formed as the Sun and its planetary system formed, and models of planet formation indicated it grew quickly, in about 30-70 Million years.IV. CratersA. The Declining Impact Flux - The cratering rate for Earth is calibrated from the MoonB. Impactor Hypothesis - A Mars-sized object collides with a young Earth. Material ejected from the collision of the impactor and from the Earth forms the Moon. The differences in chemical composition between the Earth and the Moon are explained. Earth’s highdensity from contribution of the impactor’s core. Moon’s lower density because it originated from Earth’s crust. Mechanics of collision explain Earth-Moon orbit.C. Impacts in Earth’s history1. Earth grew by impact of planetisimals2. Earth was hit by a small planet at the end of its growth; Tilted Earth’s orbit and yielded the Moon3. Earth continued to be bombarded heavily for 600 million years; no oceans/atmosphere/life4. Material continues to hit the Earth5. Impacts have caused mass extinctions, but so far, not totally wiped out life6. Frequencies of ImpactorsI. Pea-size meteoroids - 10 per hour II. Walnut-size - 1 per hour III. Grapefruit-size - 1 every 10 hours IV. Basketball-size - 1 per week V. Car-size - 1 per month (1 kiloton equivalent)VI. 30-m rock (big enough to flatten New Jersey) - 1 per 100 yearsVII. 1-km asteroid - 1 per 100,000 yearsVIII. 2-km asteroid - 1 per 500,000 years7. A well-documented meteor impact occurred at the end of the Cretaceous Period –65 million years ago. Non-avian dinosaurs were not the only animal groups that went extinct.8. Death of the Dinosaurs - All gone by 65 MYA9. The Iridium AnomalyI. Used to find out how long it took the dinosaurs to go extinctII. Assume sedimentation of space dust at a constant rate. The rare earth element Iridium is a proxy for space dust, since Earth’s Ir is in the core. Then the Ir concentration will serve as a proxy for the time spanned by the K/T extinction layer. More Ir, more time. III. To their surprise, spikes in Ir abundance were between 30 and 10,000 times the background level. If cosmic sediment was falling at a constant rate, then the K/T boundary would span several millions of years, AND would require a global shut-down of clay deposition in the oceans. Alternative hypothesis: there was an abrupt spike in cosmic sediment deposition at K/T. A single ~10km diameter meteorite would do the trick!IV. Alvarez et al. Proposed that a 10 km diameter meteorite hit Earth 65 MYA This caused immediate disruption, Rain of fire, Dust and dark Noxious loading of the atmosphere, and Acid Rain10. Cretaceous-Tertiary Event (K-T Boundary): 11. Hypothesis: a ~10km asteriod hit & caused A “global environmental perturbation”, prompting the extinction of surface & shallow ocean life forms.12. Evidence: 1980 Global Iridium Anomalies, 1984: Shocked Quartz, 1988: Mega-tsunami deposits around Caribean, 1989: Candidate crater: Yucatan area (180km diameter)I. Shocked