In 2027, an Unmanned Rover Lands on Mars, Scoops Pieces

question 86

Multiple Choice

In 2027, an unmanned rover lands on Mars, scoops pieces of ancient sedimentary rock into its interior, and then makes careful chemical analyses. Back on Earth, scientists are astonished to find that the rocks contain traces of RNA, much like that in ribosomes. Some of the scientists conclude that the rover has found evidence of Martian life, while others interpret the presence of RNA as evidence that the rover was contaminated by microorganisms on Earth before launch. Statements 1-4 below list four possible outcomes of a molecular phylogenetic test of the two hypotheses. Rank the outcomes in order of INCREASING support for the hypothesis that life originated independently on Earth and Mars.
1) The RNA found by the rover has no close resemblance to that found in terrestrial organisms.
2) Molecular phylogenetic analyses place the Martian RNA close to that of the bacterium E. coli.
3) Molecular phylogenetic analyses place the Martian RNA as a sister group to all known RNAs of bacteria, archaea and eukaryotes.
4) Molecular phylogenetic analyses place the RNA near the bottom of the bacterial branch of the tree of life.

• A)1, 2, 3, 4
• B)1, 2, 4, 3
• C)1, 3, 2, 4
• D)1, 3, 4, 2
• E)1, 4, 3, 2

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