# CH 19

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According to fossil evidence how far back in time did life on Earth exist?
D) About 3.5 billion years or more.
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Terms in this set (35)
Why do scientists say that evolution is a "theory"?
A) Because they are not very confident that it really happened.
B) Because it is supported by only a small amount of evidence.
C) Because it's really just a guess about how life developed on Earth.
D) Because it explains a great deal about life and is supported by an enormous body of evidence.
Which of the following best describes what we mean by a habitable world?
A) a planet or moon that lies within its star's habitable zone
B) a planet or moon that could support life, if any life happened to be on it
C) a planet or moon with life
D) a planet or moon on which humans could survive if we happened to go there
The Sun's habitable zone
A) extends from just beyond the orbit of Mercury to just beyond Earth's orbit.
B) extends from some place a little beyond the orbit of Venus to some place near the orbit of Mars.
C) consists only of Earth, since Earth is the only planet known to be inhabited.
D) extends from the orbit of Earth to the orbit of Jupiter.