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Chapter 2: Biochemistry

Size of Nanobacteria

Dear Dr. SETI:
This question should actually go "Dr. Astrobiology", but I couldn't locate any such website. For that reason I'll take a chance and ask you:
are the purported microbes found on mars meteorite ALH 84001 smaller than any similarly shaped organisms found here on Earth? I've heard the argument that the "wormlike" fossils found in ALH 84001 are too small to be living organisms. Is that true? If the "wormlike" objects in ALH 84001 are not micro fossils, what else could they be? Are there non-organic objects on earth that resemble these Martian structures? Finally, assuming that rocks from the surface of Earth have found their way to the surface of Mars, is it possible that primitive Earth organisms could have survived the trip?

Robert (submitted via The SETI League website)

The Doctor Responds:
First off, please remember that SETI can be considered a sub-branch of Astrobiology. At one time, the acronym SETI was thought to encompass all scientific research into life in the Universe. Then, the political winds blew foul, and SETI became a four-letter word. Eventually, NASA had to excise the term entirely from its various missions, lest it run afoul of the bugetary watchdogs. The recent popularity (in NASA circles, at least) of the new label, Astrobiology, is a reflection of pragmatic thinking within the agency. If anyone is to lay claim to the Dr. Astrobiology monicker, it should be somebody within the NASA Astrobiology Institute. But, I am not affiliated with NASA; hence it is still safe for me to designate myself Dr. SETI!

Now, on to your question. The assertion you cite was certainly believed to be true, Robert, at the time the structures in ALH 84001 were first announced. In fact, the size issue was one of the strongest arguments against these artifacts being biological in nature. Shortly after NASA made its big-splash announcement, however, nanobacteria of similar size were discovered on Earth, apparently giving some credence to claims that these structures were fossilized microorganisms.

Unfortunately for astrobiology, other arguments against the microfossil hypothesis have since surfaced, and they are compelling. So, the jury is still out as to the true nature of these structures. If they do indeed represent crude, unicellular life, then the theories of panspermia articulated by Hoyle, Wickramasinghe, and others gain added strength. But if the ALH 84001 evidence is refuted, this in no way refutes the theory of interstellar panspermia -- it merely means we will have to look elsewere for direct physical evidence.

The detractors suggest that the structures found in the meteorite could be inorganic byproducts of some chemical process. But, to my knowledge, no similar structures have been observed on Earth, originating from inorganic processes. And yes, of course, exchange of biological material from Earth to Mars is theoretically possible. But the trip from Earth to Mars is "uphill", while that from Mars to Earth is "downhill". That is, the energy required to carry ejecta mass from Earth to Mars is considerably greater than the opposite direction. Thus, I consider it more likely for life to have originated on Mars and spread to Earth than vice-versa.

Bear in mind, however, that these are merely my opinions, and not necessarily authoritative. After all, I am not "Dr. Astrobiology"!

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