21.The oldest fossils EarthA.show that life began in Africa.B.show that : 1777281
21.The oldest fossils on Earth
A.show that life began in Africa.
B.show that life began in lush regions between large rivers.
C.show that life began in the oceans.
D.are at least 5 billion years old.
E.at most 5 million years old.
22.____ shows that the building blocks of life form naturally under a wide range of circumstances.
A.The Miller experiment
B.The Chicxulub event
C.The earliest fossils
D.The Drake equation
23.Deoxyribonucleic acid is better known as
24.____ is a segment of a chromosome that controls a specific function.
E.An amino acid
25.DNA is coiled into a tight spiral and makes up the ____ that are the genetic material in a cell.
26.A single human cell encloses about 1.5 meters of DNA containing 4.5 billion base pairs. How far apart are these base pairs in the DNA?
A.3.3 ´ 10-10 nm
B.3.3 ´ 1010 nm
C.3 ´ 109 nm
27.What is important about the habitable zone around a star that makes astronomers believe life could exist there?
A.The level of UV radiation from the star is minimal there.
B.Only in the life zone can complex organic molecules be found.
C.Planets in the life zone will always have oxygen atmospheres.
D.In the life zone water can exist as a liquid.
28.When considering the number of technologically advanced civilizations in our Galaxy, it is useful to consider
A.the average life span of an alien.
B.the average life span of the civilization.
C.the distance to the civilization's planet.
D.the type of advanced communication they use.