Why can studies of carbon isotopes be used to detect the presence of past biological activity in rocks?
A) living organisms absorb only the most common carbon isotope
B) living organisms remove all carbon from rocks
C) living organisms absorb certain carbon isotopes more easily than others
D) carbon isotopes are found only in living organisms
C
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The ecliptic is
a. the centerline of the zodiac. b. the projection of Earth's orbit on the sky. c. the apparent path of the sun around the sky. d. all of the above e. none of the above
When a parcel of air expands against the environment and no heat enters or leaves, its temperature
A) increases. B) decreases. C) remains unchanged.
The principal greenhouse gases in our present atmosphere are:
A) hydrogen and helium. B) hydrogen sulfide and carbon disulfide. C) water vapor and carbon dioxide. D) methane and ammonia. E) sulfuric acid vapor and carbon dioxide.
If we had sent a radio signal to an advanced civilization in 2006 which is located in the zeta reticuli star system approximately 39 light-years away and the signal was immediately replied to, when would the reply arrive back at Earth?
A) 2084 B) 2012 C) 2045 D) 2039