Exam 18: Asteroid and Comet Impacts

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A) about 2 to 3 km per minute
B) about 60 km per minute
C) about 2 to 3 km per second
D) about 60 km per second
E) about 500 km per second

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D

A) 10 m
B) 100 m
C) 1 km
D) 5 km
E) 15 km

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Stony-iron meteorites make up less than ...

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The same energy that blasts out a crater also has an effect on rocks in the area. Rocks on the receiving end of an impact show distinctive characteristics, especially shatter cones. These cone-shaped features, with rough striations radiating downward and outward from the shock effect, range from 10 centimeters to more than a meter long and are considered proof of asteroid impact. They form most readily in fine-grained massive rocks. Apexes of shatter cones point upward toward the shock source. Cones directly under the impactor should be vertical; those off to the sides flair down and outward from the source in "horsetail" fashion. Thus, the distribution of shatter cone orientations provides evidence for the location of the center of an impact site. Individual cones are often initiated at a point of imperfection, sometimes a tiny pebble. Sometimes melting of the asteroid produces glass; sometimes glass forms by melting the target material. Molten glass droplets sprayed out during impact form tiny, hollow spherules. These droplets of glass, generally a millimeter or two in diameter, and often altered to green clay, are typically the most obvious signatures of an impact feature found in sediments. In silicate target rocks, the impact melt may also form sheets, dikes, and ejecta fragments, and be disseminated in breccias. The melt develops under extremely high impact pressures. Impact-melt compositions are a mixture of the compositions of target rocks shocked above their melting temperatures. Because the impacting meteorite is often melted as well, impact melt may contain small but extraordinary amounts of nickel, iridium, platinum, and other metals that are abundant in iron meteorites. ​

A) 20
B) 100
C) 500
D) 1500
E) 5200

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A) the gravitational influence of planets
B) the gravitational attraction of the sun
C) a change in magnetic characteristics due to its age
D) only the collision with another asteroid.
E) the slow loss of water, causing a change in path

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A) tsunamis
B) earthquakes
C) volcanic eruptions
D) floods far from coastal areas
E) fires

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chlorophyll

A) none
B) only one
C) only a few (less than five or so) ​
D) about 15
E) about 50 (one every couple of years)

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A) 5 million years
B) 15 million years
C) 35 million years
D) 45 million years
E) 70 million years

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A) funnel-shaped cones of rock with apex pointing downward, with striations radiating downward and outward
B) funnel-shaped cones of rock with apex pointing upward, with striations radiating downward and outward
C) cone-shaped depressions in and around the crater, caused by hypervelocity impact
D) vertical cracks in rocks, radiating outward from the point of impact
E) rocks that shattered at impact, leaving cone-shaped depressions where the rocks once were

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A) They range far beyond the planetary part of our solar system and loop past the sun and back into outer space.
B) Their path is the same as Earth.
C) They have a circular orbit around the sun.
D) They orbit Earth, not the sun.
E) They don't orbit the sun; they are pulled to the sun by its gravity and eventually crash into it. ​

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