It is difficult to estimate current rates of extinction, but we know that extinction rates have risen dramatically in recent years because
A) the fossil record is unreliable.
B) current rates of extinction are much higher than that of background rates.
C) new species are evolving as fast as species are becoming extinct.
D) background extinction rates have increased.
E) most species in danger of extinction are microscopic.
B
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Which of the following animals would have a placenta?
A. the marsupial mammal, opossum B. the platypus C. the rat D. the bullfrog E. a fish
What properties of estuaries make them highly productive areas?
What will be an ideal response?
When the amount of water in soil exceeds what the pore space can hold, the soil is
A) at field capacity. B) at the wilting point. C) saturated. D) desiccated.
Pikaia gracilens is an extinct invertebrate animal described from the wonderful pre-Cambrian soft-bodied fossils of the Burgess Shale in British Columbia. Examinations by paleontologists have revealed that organisms belonging to this species had a prominent notochord and segmental muscles. From this information, you could conclude that it is closely related to __________.
Fill in the blank(s) with the appropriate word(s).