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Chapter 12

Study Guide For EESA05, Chapter 12

2 Pages
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Department
Environmental Science
Course Code
EESB18H3
Professor
Ingrid L.Stefanovic

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Chapter 12: Impacts and Extinctions
12.1 Earth’s Place in Space
- Big bang produced atomic particles that later formed galaxies, stars and planets
- A star’s life depends on its masslarge stars have higher internal pressure and burn up more quickly than
small stars do
- Stars die by releasing huge amts of energy as supernovas; a supernova may have triggered gravitational
collapse of a large molecular cloud from which our sun formed 5 BYA
- Sun grew by accretion of matter from flattened rotating disk of H and He dust called solar nebula. It
condensed under gravitational forces at the centre of the solar nebula. Other particles become trapped in
orbits around the planet Saturn today
- The gravitational forces of the largest, densest particles attracted other particles in the rings until they
condensed to form the planets that orbit the sun
- Bombardment by asteroids and comets contributed to the growth of our planet
Asteroids, Meteoroids and Comets
- asteroids consist of rock, metallic material, or mixtures of the two; most are located in a asteroid belt b/w
mars and Jupiter and would pose no threat if they remained there; but they move around and collide with
one another; some are in orbits that intersect Earth’s orbit
- meteoroids are smaller particles, ranging from dust to objects a few m across
- meteor is a meteoroid ht has entered the Earth’s atm; as it moves thru the atm it becomes hot and gives
off light; meteor showers occur when large # of meteors streak across the night sky
- comets have glowing tail of gas and dust; range from few m to several 100 kms in diameter and are made
of frozen water, solid CO2 (dry ice), rock fragments and dust
- as comet warms in earth’s atm, its ice transform into mixture of gases, producing a characteristic tail
o oort cloud is 500K AU from the sun
o comets also occur in Kuiper Belt in the outer SS
12.2 Aerial Bursts and Impacts
- asteroids and meteoroids made of silicate minerals are referred to as stony; also called differentiated
meaning that they have experienced igneous, and metamorphic processes during their histories
- A, C, M travel at velocities of 12-72 km/s when they enter our atm
- They produce a bright light as they heat up during their descent
- A meteoroid will either explode in an aerial blast at an altitude of less than 50 km or collide with earth as
a meteorite
- Tunguska= aerial blast
Impact Craters
- ejecta blanket is a debris layer that comprises fragments of rock that were blown out of the crater on
impact
- large amts of fragmented rock fell back into crater shortly after impact, forming a type of rock termed
breccia
- impacts involve high velocities and extreme pressures and temperatures that are not achieved with other
geologic processes
- most of the energy of an impact is kinetic energy, energy of movement; this energy is transferred to
earth’s surface thru a shock wave that propagates into the uppermost part of the crust
- the shockwave compresses, heats, melts and excavates crustal rocks, producing a characteristic crater
- the shockwave can metamorphose rocks in the impact area, and melted material may mix with fragments
of the impacting object itself
- most of the meta morphism involves high-pressure modification of minerals such as quartz; such high
pressure metamorphism is produced only by meteorite impacts and thus is helpful in confirming an
impact origin for a crater
- simple craters are small, and do not have uplifted center (e.g. Barringer Crater)
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Description
!"!Chapter 12: Impacts and Extinctions 12.1 Earth’s Place in Space - Big bang produced atomic particles that later formed galaxies, stars and planets - A star’s life depends on its mass—large stars have higher internal pressure and burn up more quickly than small stars do - Stars die by releasing huge amts of energy as supernovas; a supernova may have triggered gravitational collapse of a large molecular cloud from which our sun formed 5 BYA - Sun grew by accretion of matter from flattened rotating disk of H and He dust called solar nebula. It condensed under gravitational forces at the centre of the solar nebula. Other particles become trapped in orbits around the planet Saturn today - The gravitational forces of the largest, densest particles attracted other particles in the rings until they condensed to form the planets that orbit the sun - Bombardment by asteroids and comets contributed to the growth of our planet Asteroids, Meteoroids and Comets - asteroids consist of rock, metallic material, or mixtures of the two; most are located in a asteroid belt b/w mars and Jupiter and would pose no threat if they remained there; but they move around and collide with one another; some are in orbits that intersect Earth’s orbit - meteoroids are smaller particles, ranging from dust to objects a few m across - meteor is a meteoroid ht has entered the Earth’s atm; as it moves thru the atm it becomes hot and gives off light; meteor showers occur when large # of meteors streak across the night sky - comets have glowing tail of gas and dust; range from few m to several 100 kms in diameter and are made of frozen water, solid CO2 (dry ice), rock fragments and dust - as comet warms in earth’s atm, its ice transform into mixture of gases, producing a characteristic tail o oort cloud is 500K AU from the sun o comets also occur in Kuiper Belt in the outer SS 12.2 Aerial Bursts and Impacts - asteroids and meteoroids made of silicate minerals are referred to as stony; also called differentiated meaning that they have experienced igneous, and metamorphic processes during their histories - A, C, M travel at velocities of 12-72 km/s when they enter our atm - They produce a bright light as they heat up during their descent - A meteoroid will either explode in an aerial blast at an altitude of less than 50 km or collide with earth as a meteorite - Tunguska= aerial blast Impact Craters - ejecta blanket is a debris layer that comprises fragments of rock that were blown out of the crater on impact - large amts of fragmented rock fell back into crater shortly after impact, forming a type of rock termed breccia - impacts involve high velocities and extreme pressures and temperatures that are not achieved with other geologic processes - most of the energy of an impact is kinetic energy, energy of movement; this energy is transferred to earth’s surface thru a shock wave that propagates into the uppermost part of the crust - the shockwave compresses, heats, melts and excavates crustal rocks, producing a characteristic crater - the shockwave can metamorphose rocks in the impact area, and melted material may mix with fragments of the impacting object itself - most of the meta morphism involves high-pressure modification of minerals such as quartz; such high pressure metamorphism is produced only by meteorite impacts and thus is helpful in confirming an impact origin for a crater - simple craters are small, and do not have uplifted center (e.g. Barringer Crater) www.notesolution.com !#!- complex craters form in the same way as simple craters but are larger. They can grow to more than 100 km across within seconds of the impact o the crater rim collapses and center of the crater floor rises following this impact - impact craters are much more common on the moon than on earth because o most impact sites on earth are in oceans where craters were not produced or were buried by younger sediment and alter destroyed by plate tectonic processes o most impact craters on land have been eroded or buried and thus are more subtle features than those on the moon o smaller meteoroids and comets burn up and disintegrate before striking the surface of earth - after impact of shoemaker-levy 9 on Jupiter, idea that a C or A could strike earth was accepted 12.3 Mass extinctions - it can be defined as sudden loss of large number of species of plants and animals - it coincides with boundaries of geologic periods or epochs because the geologic timescale was originally organized on the basis of the appearance and disappearance of groups of fossil organisms - 5 major mass extinctions during past 550 MY o 446MYA at end of Ordovician period involved loss of about 100 families of animals, it coincided with continental glaciations in S Hemisphere and may include two extinctions, one when climate cooled and 2nd when climate warmed following glacial interval o End of Permian period! 80% of species died o Boundary b/w Cretaceous and Tertiary period called K-T boundary! impact of large asteroid! ET impact! dinos gone o End of Eocene Epoch! asteroid or comet may have hit the earth; others say it was because of cooling and glaciations; tectonic plate movements allows a cold ocean current to begin to flow around Antarctica sheet to develop there o End of Pleistocene ! rapid increase in human population, deforestation, agriculture, overfishing and pollution K-T Boundary Mass Extinction - iridium is a platinum-group metal found in very small concentrations in meteorites - global rate of accumulation of meteoritic dust and thus iridium on earth is constant - higher rate of sedimentation, the more diluted the iridium becomes - slow sedimentation allow time for more meteorite dust to accumulate, giving higher concentrations of iridium in deep ocean sediments 12.4 Impact Hazards and Risk Risk Related to Impacts - risk of an event is related to both its probability and its consequences Managing the Impact Hazard - we can identify objects in our solar system that could threaten earth; program to identify and categorize comets and asteroids that cross earth’s path is already in progress and could be expanded to include objects in more size classes - spacewatch is producing inventory of near earth objects (NEOs) - near earth asteroid tracking project (NEAT)—studies the size, distribution and movement of NEOs with a focus on objects about 1 km in diameter - both programs use cameras and telescopes to identify and monitor fast-moving objects - chrondritic asteroids are slow moving objects that could penetrate the atm and explode at low altitudes or strike earth’s surface - we cant bring the asteroids but we can change its path; nuclear explosions in the vicinity of the asteroid would alter its path w/o breaking it up www.notesolution.comChapter 12: Impacts and Extinctions 12.1 Earths Place in Space - Big bang produced atomic particles that later formed galaxies, stars and planets - A stars life depends on its masslarge stars have higher internal pressure and burn up more quickly than small stars do - Stars die by releasing huge amts of energy as supernovas; a supernova may have triggered gravitational collapse of a large molecular cloud from which our sun formed 5 BYA - Sun grew by accretion of matter from flattened rotating disk of H and He dust called solar nebula. It condensed under gravitational forces at the centre of the solar nebula. Other particles become trapped in orbits around the planet Saturn today - The gravitational forces of the largest, densest particles attracted other particles in the rings until they condensed to form the planets that orbit the sun - Bombardment by asteroids and comets contributed to the growth of our planet Asteroids, Meteoroids and Comets - asteroids consist of rock, metallic material, or mixtures of the two; most are located in a asteroid belt bw mars and Jupiter and would pose no threat if they remained there; but they move around and collide with one another; some are in orbits that intersect Earths orbit - meteoroids are smaller particles, ranging from dust to objects a few m across - meteor is a meteoroid ht has entered the Earths atm; as it moves thru the atm it becomes hot and gives off light; meteor showers occur when large # of meteors streak across the night sky - comets have glowing tail of gas and dust; range from few m to several 100 kms in diameter and are made of frozen water, solid CO2 (dry ice), rock fragments and dust - as comet warms in earths atm, its ice transform into mixture of gases, producing a characteristic tail o oort cloud is 500K AU from the sun o comets also occur
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