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Topic: Earth impacts

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Micrometeor

Tunguska event

Noerdlinger Ries

Meteorite

	Earth Impacts
		The layout of the impact area suggests that the body fell at a shallow angle, and was moving at typical meteorite entry speeds of 40,000 to 60,000 KPH.
		Although it might be assumed that a major impact on the Earth would leave behind absolutely unmistakeable evidence, in fact the gradual processes that change the surface of the Earth tend to cover the effects of impacts.
		The threat of an Earth impact was emphasized by the collision of the comet Shoemaker-Levy 9 with Jupiter on 16 July 1994, resulting in explosive impacts that would have been catastrophic on Earth.
	www.vectorsite.net /taimpact.html (7960 words)

	Impact event - Wikipedia, the free encyclopedia
		Impact events are caused by the collision of large meteoroids, asteroids or comets (generically: bolides) with Earth and may sometimes be followed by mass extinctions of life.
		It was not until 1903–1905 that the Barringer Crater was correctly identified as being an impact crater, and it was not until as recently as 1963 that research by Eugene Merle Shoemaker conclusively proved this hypothesis.
		This has led to the suggestion that the Chicxulub impact was one of several that occurred almost simultaneously, perhaps due to a disrupted comet impacting the Earth in a similar manner to the collision of Comet Shoemaker-Levy 9 with Jupiter in 1994.
	en.wikipedia.org /wiki/Earth_impacts (2338 words)

	Earth Impact Database
		The Earth Impact Database is maintained as a not-for-profit source of information to assist the scientific, industrial, government and public communities around the world in furthering our collective knowledge of impact structures on Earth.
		Presence of an impact melt sheet and/or dikes, and impact melt breccias that were generated due to hypervelocity impact (macroscopic).
		Impact melt sheets are recognized by careful mapping and rock sampling followed by microscopy and geochemical analysis.
	www.unb.ca /passc/ImpactDatabase (1043 words)

	Planetary Society
		Given that no impact craters were recognized as such on Earth until the 1960s and that cratering was thought to be an ancient phenomenon, it is easy to understand our modern sense of security and insulation from cosmic collisions on Earth.
		Assuming that the cosmic impact is not misinterpreted as a hostile nuclear attack set in motion by a real or imagined enemy, the remaining civilizations of the world would presumably remain stable and would be able to supply aid and comfort to the afflicted area.
		Because the damaging effects are dependent on the kinetic energy of the impact (equal to 1/2 mv2, where 'm' is the mass of the projectile and 'v' is its velocity), a comet smaller than 1 kilometer (0.6 mile) across could pack a punch with sufficient energy to initiate a global climate disaster.
	planetary.org /html/neo/ABCsOfNEOs/FrndorFoe.html (2334 words)

	Asteroid impacts
		It now seems that the Earth’s rotational axis has remained largely fixed within a few degrees and that it is unlikely any body large enough to produce catastrophic tides has ever passed close to the Earth.
		Third, the continual rain of impacts during the Flood was the result of breakup of an unstable residual ring.
		The rubble pile disruption-capture model provides a framework for explaining the known impacts of the Earth and the formation of lunar maria, as well as a model that may be extended to other solar system objects.
	www.orgsites.com /oh/evoution-is-a-myth/_pgg7.php3 (1702 words)

	Terrestrial Impact Craters Slide Set (Site not responding. Last check: 2007-10-22)
		Based on apparent correspondences between periodicities observed in the marine extinction record and in the terrestrial impact record, some scientists have suggested that large meteorite impacts might be the metronome that sets the cadence of biological evolution on Earth — an unproved but intriguing hypothesis.
		Impact craters are formed when a large meteoroid (asteroid or comet) crashes into a larger planetary body that has a solid surface.
		On Earth, weathering and erosion of the target rocks quickly alter the surface expression of the structure; despite the crater's initial morphology, crater rims and ejecta blankets are quickly eroded and concentric ring structures can be produced or enhanced as weaker rocks of the crater floor are removed.
	www.lpi.usra.edu /publications/slidesets/craters (1908 words)

	Correlation Found Between Meteorite and Comet Impacts and an Increase in Volcanic Activity Development -- The Earth ... (Site not responding. Last check: 2007-10-22)
		Another question raised by the correlation between impacts and volcanism concerns widely adopted theories that meteorite and comet impacts were the cause of mass extinctions of life on Earth.
		Her primary research focus is the thermal history of the earth, and the manner in which heat transport through the crust and upper mantle influences geological processes, both ancient and present-day.
		The Earth Institute at Columbia University is among the world’s leading academic centers for the integrated study of Earth, its environment, and society.
	www.earth.columbia.edu /news/2003/story01-17-03.html (507 words)

	Spaceguard Executive Summary
		Although the annual probability of the Earth being struck by a large asteroid or comet is extremely small, the consequences of such a collision are so catastrophic that it is prudent to assess the nature of the threat and prepare to deal with it.
		The greatest risk from cosmic impacts is associated with objects large enough to perturb the Earth's climate on a global scale by injecting large quantities of dust into the stratosphere.
		What is required to assess the population of ECAs and identify any large objects that could impact the Earth is a systematic survey that effectively monitors a large volume of space around our planet and detects these objects as their orbits repeatedly carry them through this volume of space.
	home.earthlink.net /~kstengel226/astro/spacegrd/sg_summary.html (1405 words)

	How Dangerous are Earth-Crossing Objects?
		Asteroid Collisions with Earth summarizes a NASA research project by Owen B.Toon, Kevin Zahnle, and David Morrison to study the environmental repercussions of asteroid and comet impacts on the Earth.
		Asteroid/Comet Earth Impacts by David A. Rideout calculates the approximate kinetic energy of an asteroid and a comet released on impact with the Earth.
		Earth Crossing Objects by Douglas Clarkson briefly summarizes the danger from NEOs, the extinction of the dinosaurs, periodic extinctions and Nemesis, Chiron, and Spaceguard.
	www.pibburns.com /catastro/impacts.htm (6417 words)

	Mars Impacts...The Paper!
		Mars and Earth are very dissimilar planets today, observations of impact craters on the surface of both bodies show they possess similar characteristics.
		Impact craters on Mars are important to our understanding of the evolution of the planet, in that craters can give a good indication of the nature and configuration of the surface content as well as contain a record of erosion and deposition events.
		Earth's surface is comparatively young with the oceanic crust, for example, being only around 250 million years old because it has been completely resurfaced.
	www.oberlin.edu /faculty/bsimonso/group5paper.htm (1540 words)

	News Article: AIAA Position Paper on Protecting Earth from Impacts (Site not responding. Last check: 2007-10-22)
		The cost and disaster relief implications of a NEO impact suggest that disaster relief agencies should utilize hypothetical impact scenarios to examine issues and develop responses to possible emergencies of this type (note: some NEO impact scenarios may already be covered by existing plans for earthquake, tsunami, or other disasters).
		While noteworthy efforts are being made to detect threatening objects, Earth is effectively blind to NEO objects of a size range that could lead to immediate and long term deaths of thousands to millions of people and is unprepared should a short term threat be detected.
		While the probability of an impact of an object of sufficient size to cause major loss of life and property damage is low, it is not zero.
	nai.arc.nasa.gov /impact/news_detail.cfm?ID=153 (1330 words)

	Science News: Shots from outer space: iconoclast links chaos, cosmic impacts, and Earth's internal workings - Cover ...
		Collisions with such cosmic bombs have shaped almost all aspects of Earth's evolution, he contends, from the beatings of its iron heart to the wrinkling of its rocky skin to the dawning and demise of the dinosaurs.
		Earth is not just being shot at by some random gun out there in space like all the.
		The pattern of past impacts, he suggests, determines the positions of the continents, steers the geomagnetic field, creates volcanoes, and occasionally causes mass extinctions.
	www.findarticles.com /p/articles/mi_m1200/is_n4_v147/ai_16679962 (1421 words)

	Meteorite Impacts (Site not responding. Last check: 2007-10-22)
		Since many now "obvious," terrestrial impact craters, like Barringer Crater in Arizona or these Canadian impact craters were known to exist, the impact theory for the extinction of the dinosaurs wasn't such a stretch of the imagination.
		It was obvious that an impact large enough to eliminate 80% of the species on Earth at the end of the Cretaceous would result in a huge crater.
		Impacts, until very recently, were an almost completely neglected class of natural hazards, in spite of the fact that they are not unusual events (consider the Moon, for example!).
	geophysics.ou.edu /impacts (2017 words)

	FAQs About NEO Impacts (Site not responding. Last check: 2007-10-22)
		NEO impacts are the only major natural hazard that we can effectively protect ourselves against, by deflecting (or destroying) the NEO before it hits the Earth.
		The last such impact was in 1908 in Tunguska (Siberia) with an estimated explosive energy of 15 megatons.
		In 2003 NASA completed a study of these sub-km impacts and concluded that it was both technically feasible and cost-effective to to mount an expanded Spaceguard Survey, with much larger telescopes, to search for these smaller asteroids.
	impact.arc.nasa.gov /intro_faq.cfm (1336 words)

	Earth Impacts (Site not responding. Last check: 2007-10-22)
		Unfortunately, that particular conference was under-attended in that year, ironically because most geologists were attending a workshop on Earth impacts, and their report attracted very little attention, though it did get back to Byars.
		However, even Walter Alvarez has acknowledged that there were other major changes on Earth even before the impact, such as drop in sea level and massive volcanic eruptions in India, that may have also contributed to the extinctions.
		Nonetheless, the fact that an impact of an NEA a kilometer or more in size would be a catastrophe unparalleled in human history has kept the idea of a defensive network alive, as well as led to speculations on how to divert objects that might be a threat.
	www.faqs.org /docs/air/taimpact.html (6952 words)

	Impacts - Natural History Museum
		Some of these impacts can be so powerful that they blast huge craters into the Earth's surface, generating enough heat to vaporise the crashing object.
		The impact flux has been fairly constant throughout Earth's history except for a violent period (known as the great bombardment) shortly after the solar system formed when there were twice as many impacts.
		However, impacts during the great bombardment may also be responsible for creating the conditions for life in the first place, bringing essential water and carbon to our planet.
	www.nhm.ac.uk /nature-online/space/impacts/test.html (401 words)

	Cosmic Impacts: Is the Sky Falling? (Skeptical Inquirer May 1997)
		Most scientists first thought about the role of impacts in Earth history in response to the now-famous paper published in Science in 1981 by Luis and Walter Alvarez and their colleagues, suggesting that an impact sixty-five million years ago produced the mass extinction that terminated the Cretaceous era.
		Impacts are the ultimate environmental disasters, more important than volcanic eruptions or other more familiar events in shaping the history of life on the planet.
		Her short, well-illustrated (in fl and white) book is a straightforward introduction to cosmic impacts, beginning with solar-system formation, moving to comets and asteroids, then to Earth impacts (including the K-T event), Tunguska, current ideas about the impact hazard, and possible planetary defense.
	www.csicop.org /si/9705/asteroid.html (5109 words)

	Risks to the Earth from impacts of asteroids and comets
		There seemed to be little evidence for such a risk: the craters on the Earth and the moon were generally thought to be of volcanic origin, not made by impacts; and while, since prehistoric times, comets must always have aroused interest, or even dread, their true danger was not understood.
		The near Earth asteroids usually have orbits rather similar to that of the Earth, with periods of the order of a year; they are often stony (perhaps as groups of rocks held together only by their own weak gravitational forces), but can be carbonaceous or metallic.
		Taking all sizes and impact frequencies into account, the risk of an individual’s dying from NEO impacts over his or her lifetime is estimated at about 1 in 20,000.
	www.europhysicsnews.com /full/10/article3/article3.html (2689 words)

	PSR Discoveries:Hot Idea: Origin of the Earth and Moon
		The giant impact hypothesis is consistent with our ideas for how planets were assembled and explains some important features of the Earth-Moon system, such as why the Moon has only a tiny metallic core.
		Such a monumental impact would cause a large amount of material to be lofted into orbit around the Earth, and the Moon could form from that debris.
		The growing Earth is the larger of the two objects; the smaller object is the projectile whose impact led to the formation of the Moon.
	www.psrd.hawaii.edu /Dec98/OriginEarthMoon.html (2186 words)

	Directory - Society: Future: Catastrophes: Large Near Earth Object Impacts (Site not responding. Last check: 2007-10-22)
		Asteroid impact scale endorsed · iweb · cached · A new scale that will quantify the risk of an asteroid or comet hitting the Earth has been adopted by the International Astronomical Union.
		Earth Impact Database · cached · Assembled since 1985 by researchers at the Geological Survey of Canada (a division of Natural Resources Canada), this site also includes an article on impact cratering, a FAQ, and images.
		Impact · cached · Describes the threat posed by a comet or asteroid impact and provides disaster preparedness planning for such an event.
	www.incywincy.com /default?p=314632 (374 words)

	Age of Dinosaurs Bracketed by Asteroid or Comet Impacts--The Earth Institute at Columbia University (Site not responding. Last check: 2007-10-22)
		An asteroid or comet impact on Earth may have paved the way for the sudden rise of the great Jurassic dinosaurs, according to a paper to be published this week in the journal Science.
		The scientists postulate that the asteroid or comet impact and the resulting death of Triassic competitors allowed a few groups of carnivorous dinosaurs to evolve in size very quickly and dominate the top of the terrestrial food chain globally.
		The Earth Institute at Columbia University is the world's leading academic center for the integrated study of Earth, its environment and society.
	www.earth.columbia.edu /news/story05_16_02.html (911 words)

	Catastrophic Impacts and Mass Extinctions
		Such an impact would trigger global fires and fill the atmosphere with dust which would take years to settle out.
		The manner in which solar systems form suggests that impacts are a factor on planets everywhere in the universe.
		Impacts were more frequent in the distant past, but continue today.
	www.astro.virginia.edu /class/skrutskie/astr121/notes/massext.html (918 words)

	Armageddon Online - Asteroid Impacts & Meteor Impacts with Earth
		It is thought that 65 million years ago in what is now Yucatan the impact at a velocity of 11 km/second of a 10-kilometer wide asteroid is what helped to bring about the K-T extinction, whereas no land animal with a size greater than the size of a small chicken was able to survive.
		It is an estimate that impacts of asteroids as large as the one thought responsible for the K-T extinction occur about once every hundred million years.
		While most of the recent recorded impacts have happened in places that were barely inhabited, we won't always be that lucky.
	www.armageddononline.org /asteroid.php (1343 words)

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