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Chapter 12

Study Guide For EESA05, Chapter 12

by OC2

Environmental Science
Course Code
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
- large amts of fragmented rock fell back into crater shortly after impact, forming a type of rock termed
- 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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