Signatures of life

In this post, I break down the ideas behind a paper I recently read and liked very much. It is written by Sherry Cady, Jack Farmer, John Grotzinger, William Schopf and Andrew Steele, titled “Morphological Biosignatures and the Search for Life on Mars“, published in the journal Astrobiology in 2013. These are well-respected researchers in the astrobiology community, many of whom are working in or closely with NASA on robotic missions on Mars. The goals of these missions are to answer a fundamental question: was there ever life on Mars — a different planet apart from our own Earth?

In order to answer this question, which is, by the way, a question with a definite yes or no answer, many hurdles must be first paved away. Just think logically, how would you answer a question like that, and what kind of evidence you must supply in order to make the case? A lot is actually at stake here in answering this question, because it affects fundamentally how we think of our own position in the universe as a species. It either gives us hope and confidence to venture out into the vast unknowns of the universe or makes us rethink deeper into the reasons for our existence.

Human beings are primarily visual species. This can be made understood in the sense that almost half of our brain is used to process visual information. We are very effective at processing visual data, too. Therefore, there is no doubt that visual or morphological data should be the first to come in when evaluating whether or not a particular piece of evidence suggesting the (past) presence of life on Mars. How can we trust it without seeing it? There is also another saying: “seeing is believing”, which summarized it very well. I think this is another reason behind the idea of looking for “morphological biosignature” on Mars. This is one piece of evidence that is absolutely required.

The paper then opened the discussions on two types of morphological evidence for life: 1) cellularly preserved microorganisms and 2) microbially influenced, laminated sedimentary structures at visible scales. Now both of these are only “morphological clues” that suggest life might have been present. They are certainly still subject to further verification with chemical analysis or ultrastructural analysis — basically using all the tools we’ve got in the box. Even then, after all these work, one questions still will come: how can you prove that they were alive?

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