Life Raining Down from Space?

Not likely

The "diatom" in question. Wainwright et al.

Last week the University of Sheffield in England issued a press release claiming that a group of scientists from the university believe they’ve found life in Earth’s stratosphere that arrived from space. The associated paper is published in the Journal of Cosmology.

That would be a significant find, wouldn’t it? Yes, if only it held up. The researchers, led by Milton Wainwright, sampled the stratosphere from a balloon and found a particle that appears to be a fragment of a diatom. This is not that unusual, since there have been reports of microbes and even spiders found in the stratosphere. The usual explanation is that some atmospheric conditions lifted them up to high altitudes, although an extraterrestrial origin has been claimed in some cases.

I guess I’m one of the “unthinking critics” mentioned in the paper, and here’s why: At best, the claim is extremely premature. As the lead author says in the press release, the isotopic fractionation rate still has to be determined, which would help settle whether the sample is of terrestrial origin. Also, the researchers don’t appear to have done a detailed study of the alleged diatom.

They go on to suggest that the diatom probably originated “in the watery environment of a comet,” which only raises more problems. True, comets contain amino acids and organic compounds, but this is a far cry from evidence for biology, as these compounds can form without leading to life or the involvement of organisms. And based on our admittedly limited current understanding, comets are not suitable places for the origin of life (I would argue that a terrestrial planet is needed for that). Even if my conjecture doesn’t hold, I would find it extremely unlikely that diatoms originated in a comet or came from space in general. Diatoms are relatively advanced life forms; they developed on Earth most likely at the beginning of the Mesozoic period—very late during evolution, probably at least three billion years after life appeared on Earth. Diatoms typically live in an aquatic environment, and use photosynthesis as a metabolic strategy. These kinds of conditions don’t fit the environment on a comet, where liquid water is not present (except perhaps for a short period of time when the comet is very close to the Sun and is heating up). I would expect an extraterrestrial organism to be quite different from what we see on Earth in some significant way, and certainly not likediatom species on Earth.

Many other possible tests come to mind that might have been done before publication, from mineralogical analysis to screening for trace organic compounds to the analysis of amino acids and their chirality (handedness). The only in-depth analysis that seems to have been conducted was to look at typical particle residence times in the atmosphere and to exclude ground-based contamination. It’s difficult for people not involved in the study to assess whether the fragment actually came from the stratosphere, or whether it might be contamination. But basing a conclusion on a limited analysis of one particle seems quite odd. And inferring (and publicizing) an extraterrestrial origin is completely off base, in my view. Much more evidence is needed for this kind of extraordinary claim. To make the claim with such limited data does a disservice to astrobiology, and feeds the skeptics who say it’s a science based only on speculation.

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