The Evidence for Terrestrial Impacts Throughout Geological History

1. The Evidence for Terrestrial Impacts Throughout Geological History Kate Yohay, Jess Yamane, Tram Nguyen, & Courtney Patterson

2. World Map of Large Impacts

3. Europe Crater: Mjolin, Location: Norway Crater: Dellen, Location: Sweden • http://www.unb.ca/passc/ImpactDatabase/europe.html

4. South America Crater: Monturaqui, Location: Chile Crater: Araguainha, Location: Brazil Crater: Chixculub • http://www.unb.ca/passc/ImpactDatabase/SAm.html

5. Africa • http://www.unb.ca/passc/ImpactDatabase/africa.html

6. Asia Crater: Logancha, Location: Russia Crater: El'gygytgyn, Locaction: Russia http://www.unb.ca/passc/ImpactDatabase/asia.html

7. North America • http://www.unb.ca/passc/ImpactDatabase/NAmerica.html Crater: Chesapeake Bay, Location: Virginia, USA Crater: Barringer, Location: Arizonia, USA Crater: Upheaval Dome, Location: Utah, USA

8. Australia http://www.unb.ca/passc/ImpactDatabase/austr.html

9. Terrestrial Impacts on Other Bodies in the Solar System • The surface of the Moon, Mercury, and Mars, where geologic processes have halted millions of years ago, record terrestrial impacts, thus it is beneficial to understand impacts on other solar bodies in the solar system in order to understand terrestrial impacts on Earth.

10. In relation to The Moon • The Earth has been the target of impacting objects about 10 times more than the Moon, yet much less (about 160) has been discovered. • Earth, which has been more heavily impacted than the Moon, is covered with craters that are continuously becoming less evident due to erosin, redeposition, volcanic resurfacing, and tectonic activity. The moon has neither an atmosphere nor water, thus the components in the soil do not weather away chemically as they would on Earth. • The far side of the Moon, in relation to its position facing the Earth, has more craters than the near side because the side facing the Earth is shielded by the Earth.

11. In Relation to Mercury • Mercury has no tectonic plates like Earth. • Mercury is covered by craters that are either classified as intercrater plains or smooth plains, which have been effected by volcanic activity. • After the intense bombardment period (about 4.5 billion years ago), volcanic lava covered the older crust, thus forming the intercrater plains. The lava makes the intercrater plains less saturated with craters and makes the craters appear smaller in size (less than 15 km in diameters). • The smooth plains are even younger, with less craters due to volcanic lava that has further filled the craters.

12. Mars • Mars has symmetry about its equator dividing the planet into the old and young hemispheres. • The older terrain in the southern hemisphere is heavily cratered. • The northern hemisphere has less craters than the southern hemisphere, possibly due to volcanic flows. • Although no one knows exactly why there is a difference between the crater impacts of the two regions, it has been proposed that volcanic plains, huge crustal uplifts, and volcanic shields (i.e., mountains) dominate the northern hemisphere, and thus covers up the potential craters that may have existed there.

13. A Consequence of Asteroid Impact:The Death of the Dinosaurs & End of the Mesozoic Period

14. “Approach of Doom” • Either comet or asteroid about 10 km across traveling @ an estimated velocity of equaling 30km/s • That would make it as wide as San Francisco and taller than Mt. Everest w/ a volume greater than that of all the buildings in the US put together • It would have a destructive equivalent to that of 100 million hydrogen bombs and it’s impact would equal an explosion caused by 100 million megatons of TNT • Aimed at what is now the Yucatan Peninsula of Mexico

15. Moment of Impact 95% of the Atmosphere lies below an altitude of 30 km so depending on the velocity and angle at which the asteroid/comet approached the surface it would have taken 1-2 seconds to penetrate most of the atmosphere Compression heated the air instantly to 4-5x’s that of the sun generating a searing flash of light At the instant of contact with the Earth’s surface where the Yucatan Peninsula lies, 2 shock waves were triggered 1st shockwave plowed forward into the bedrock passing through a 3km thick layer of limestone near the surface and down into the granite crust beneath and crushing shut cracks and pores and destroying much of the crystal structure of minerals 2nd shockwave: flashed backward into the onrushing comet/asteroid reflecting of the back of the body tearing apart its spherical shape

16. Because it’s moving so fast the asteroid/comet would have caused a shock wave, a sonic boom • This compressed the target so intensely that after the shock wave, the decompressing rock flew apart, melted, or vaporized • Whole continents caught fire though firestorms may not have been intense on other continents as N. America • The Earth’s surface became a broiler: cooking, charring, igniting and immolting trees and animals not under rocks/ in holes but in a less immediate area • A gigantic tsunami (about 1km high) spreading outward and across the Gulf of Mexico digging channels in the fine sediment on the sea floor and mixing it w/ impact debris • The Tsunami confined to Gulf of Mexico/Florida area.

17. Aftermath • W/in days fires and wind were dying and Tsunami was spent, but the Earth was becoming dark and cold • In the zone where bedrock was melted/vaporized no living thing could have survived even w/in a radius of 100km • Fine dust from the comet/asteroid settled through the upper atmosphere around the world and blocking out the sunlight –lasted for a few months • The greenhouse gases, water vapor and carbon dioxide, were released raising temperatures above normal levels for probably thousands of years • Acid rain was formed from sulfur in the limestone in the Yucatan area • Nitrogen gas breaks up when in extreme temperatures, thus vast quantities of NO were produced which would form nitric acid when in gaseous form killing plants and animals and dissolving rock when it rained

18. Retrospect • 180 km wide collision scar “the great ‘K-T’ mass extinction” • Chicxulub crater • Peligic limestone (neritic limestone is built up by fossils of organisms that live on the sunlit bottom of shallow water) are sediments that are deposited in the darkness of the deepest eroding waves and lie undisturbed for 10’s of millions of years

19. The Barringer Meteorite Crater aka Meteor Crater • Occurred 50,000 years ago during an ice age • Arizona: Cool wet forest • Inhabited by mammoths, mastodons, giant ground sloths, bison • Impact blast caused local extinction providing a new habitat for other plants and animals • The bowl shaped depression filled with water creating a fresh water lake for vegitation and aquatic animals

20. Evidence During the early 1900s there was a race to see who could prove the cause of the crater The leading theories, provided by Grove Karl Gilbert stated that the crater was either formed by a meteorite or that it was the result of a massive explosion of steam produced by volcanic heat at a great distance below the surface. No evidence of volcanic rock was found in the area Barringer’s papers were based on observations Gilbert made but whose significance Gilbert had missed

21. Barringer’s Findings • The presence of a vast amount - probably in the millions of tons - of finely pulverized silica. The pressures required to produce such a material, Barringer argued, were too great to be the product of any known volcanic force. • The large quantities of magnetic iron oxide, in the form of globular "shale balls", scattered around the rim and the surrounding plain. Some of the large balls, when split open, displayed the "Widmanst䴴en patterns" characteristic of iron meteorites. Much of the rest consisted of a fine blackish-gray powder, crystalline in structure, "with intensely fine grains of silica powder adhering so closely to its surface as to suggest adhesion." This powder, Tilghman noted, was "not a constituent of any of the rocks in the neighborhood", and furthermore was "different from any terrestrial magnetite known." • The random mixture of chunks of meteoritic material with the ejected rocks on the crater rim, and its symmetrical distribution around the crater, both of which demonstrated that the material must have been deposited simultaneously with the creation of the crater. • The fact that the different types of rock in the rim and "ejecta blanket" (material thrown out of the crater) appeared to have been deposited in the opposite order from their order in the underlying rock beds - as if the beds themselves had been overturned. • The absence of any naturally occurring volcanic rock in the vicinity of the crater. Regarding Gilbert's failure to find any magnetic anomalies, Tilghman noted that while the presence of a single large mass of iron should produce such an anomaly, a mass of small magnetized fragments would not. He found it difficult to discuss Gilbert's steam explosion hypothesis, since no one had ever seen or known of such a process in actuality, except in association with an ordinary volcano. (Hoyt, pp. 89-99)

22. Tunguska • June 30th, 1908 “something” exploded 8 km high on the river Stony Tunguska destroying 2,150 km^2 of Siberian taiga • Fires burned for weeks destroying 1,000km^2 • “Ash and powdered tundra fragments sucked skyward by the fiery vortex were caught up in the global air circulation and carried around the world. Meanwhile, bursts of thunder echoed across the land to a distance of some 800 kilometers. “ (Southworth Planetarium) • Unclear whether it was a comet or asteroid

23. Tunguska region in 1938:Portion of one of the photos from Kulik's aerial photographic survey (1938) of the Tunguska region. The parallel fallen trees indicate the direction of the blast wave.

24. Effects • Following the explosions unusually colorful sunsets and sunrises were reported in W. Europe, Scandinavia, and Russia • Magnetic “storms” similar to ones produced by nuclear test explosions in the atmosphere occurred 900km southeast • Following the blast there was accelerated growth of biomass in the region of the epicenter as well as an increased rate of biological mutations