EESB18H3 Chapter 12: Study Guide For EESA05, Chapter 12
19 Jul 2010
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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 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)
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Document Summary
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. Meteoroids are smaller particles, ranging from dust to objects a few m across.
