The Morrison Formation is exposed in the western United States and represents a nonmarine deposit with abundant dinosaur fossils. Much of the Morrison is pure mudstone, yet it is common to find highly polished pebbles and cobbles in the mud
Which of the following do you think is the best explanation of these cobbles?
A) They represent meteorites that killed the dinosaurs.
B) They were placed in the mud by space aliens.
C) They are impossible; people must have put them there.
D) They are gastroliths, a trace fossil.
D
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A fish propels itself through water mainly by
A. deflecting water downward. B. pushing water backward. C. wiggling its tail. D. pushing forward.
What reasons cause the downwelling and upwelling of ocean water?
a. Winds that drive water surplus or deficit b. Contrasts in water density c. Tidal effect d. Both a and b
In the demographic transition model, death rates fall while birth rates remain high ____ stage.
A. during the preindustrial B. during the industrial C. during the postindustrial D. during the transitional E. following the postindustrial
Any stream may lengthen its valley by ________ and delta formation
A) headward erosion B) siltation C) saltation D) alluvial deposition E) delta erosion