Two billion years ago, radioactive heat production was
A) half of what it is today.
B) twice what it is today.
C) the same as it is today.
D) four times what it is today.
Answer: D
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Briefly explain passive and active satellite systems.
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Purple martins are the largest species of swallow in North America. In the Eastern United States, they breed almost exclusively in large colonies in artificial martin houses and hollowed-out gourds hung by martin enthusiasts
Given this information, which of the following would be a valid inference? A) Purple martins and martin enthusiasts exhibit a relationship that can best be described as commensalism. B) In the eastern United States, purple martins have a size advantage over other swallows and are able to outcompete them for nest sites. C) In the eastern United States, purple martins are specialists because they rely almost solely on humans for nesting sites. D) In the eastern United States, purple martins are generalists with a broad ecological niche.
List the five principal themes of modern geographic education
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The Oort cloud is ________
A) another name for the inner solar system, just before the Sun became hot enough for nuclear fusion B) the asteroid belt C) the outer solar system where planetesimals, rocky debris and comets orbit outside beyond the outer planets but cross into the inner solar system at times D) an unusual type of cloud formed when meteorites strike the earth