It is theoretically possible that bacteria developed on Mars early in its history and that some were carried to Earth by a meteorite. However, strains of bacteria from different planets would probably have substantial differences in protein structure that would persist over time, and no two bacterial strains on Earth are different enough to have arisen on different planets. So______________________________________________.

(What would be the best option to complete the passage?)

A. Whether or not bacteria actually developed on Mars.
B. Its likely it is that Martian bacteria were transported from Earth.
C. Martian bacteria could have been carried to Earth by means other than meteorites.
D. All bacteria now on Earth could have arisen from transported Martian bacteria.
E. There could have been strains of bacteria that originated on Earth and later died out.

Note: There are two questions available with the similar stimulus and same first line but different question. The other question (criticism) is discussed in: it-is-theoretically-possible-that-bacteria-developed-on-q1-12260.html

D for the same reason as given by Indy

To me it is between B or D. As both option provide clue that it is essentially same bacteria strain in Martian planet as well as Earth.
However D uses word All, so I will say it is extreme.

Hence I will go with B.

Option D and E are very close.
E is relevant but none of the premise are closely related to the existence of bacteria that originated in earth .

I think its D.

this one is a GMAT prep question. read this today and my mind went back to this question. lol - so it was true all along...

NASA: Unearthly bacteria detected on three meteorites

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By Reuters
Monday, March 7, 2011

WASHINGTON -- A NASA scientist reports detecting tiny fossilized bacteria on three meteorites and maintains these microscopic life forms are not native to Earth.

If confirmed, this research would suggest life in the universe is widespread and life on Earth may have come from elsewhere in the solar system, riding to our planet on space rocks like comets, moons and other astral bodies.

The study, published online late Friday in The Journal of Cosmology, is considered so controversial that it is accompanied by a statement from the journal's editor seeking other scientific comment, which is to be published starting today.

The central claim of the study by astrobiologist Richard Hoover is that there is evidence of microfossils similar to cyanobacteria -- blue-green algae, also known as pond scum -- on the freshly fractured inner surfaces of three meteorites.

These microscopic structures had lots of carbon, a marker for Earth-type life, and almost no nitrogen, Hoover said Sunday.

Nitrogen can also be a sign of Earthly life, but the lack of it only means that whatever nitrogen was in these structures has decomposed out into a gaseous form long ago, Hoover said.

"We have known for a long time that there were very interesting biomarkers in carbonaceous meteorites and the detection of structures that are very similar ... to known terrestrial cyanobacteria is interesting in that it indicates that life is not restricted to the planet Earth," Hoover said.

Hoover, based at NASA's Marshall Space Flight Center in Alabama, has specialized in the study of microscopic life-forms that survive extreme environments such as glaciers, permafrost and geysers.

He is not the first to claim discovery of microscopic life from other worlds.

In 1996, NASA scientists presented research indicating a 4-billion-year-old meteorite found in Antarctica carried evidence of fossilized microbial life from Mars.

The initial discovery of the Mars meteorite was greeted with acclaim, and the rock was unveiled at a standing room-only briefing in NASA headquarters in Washington.

Since then, however, criticism has surrounded that discovery, and conclusive proof has been elusive.

Hoover's research may well meet the same fate. In a statement published with the online paper, The Journal of Cosmology's editor in chief, Dr. Rudolf Schild, said in a statement: "Dr. Richard Hoover is a highly respected scientist and astrobiologist with a prestigious record of accomplishment at NASA.

"Given the controversial nature of his discovery, we have invited 100 experts and have issued a general invitation to over 5,000 scientists from the scientific community to review the paper and to offer their critical analysis."

Read more: NASA: Unearthly bacteria detected on three meteorites - Pittsburgh Tribune-Review http://www.pittsburghlive.com/x/pittsbu ... z1Fv6bzPTG