Sunday, March 15, 2015

"to seek out new life" even if not carbon-based. . .


To me as a geologist, one of the most intriguing Star Trek (original series) episodes is “Devil in the Dark” (Season 1, Episode 25), which I saw again in rerun last weekend:

Spock: “Life as we know it is universally based on some combination of carbon compounds, but what if life exists based on another element? For instance, silicon.

The "Devil in the Dark" is the "Horta", a mobile living sentient blob that tunnels through rock in the subsurface of planet Janus 6, killing human miners who unknowingly destroyed its spherical eggs. The Horta is not an organic carbon lifeform, but instead is silicon-based. At the time of this episode's first airing in 1967, almost 48 years ago to the day, I had not studied geology yet and was unfamiliar with the silicon basis of most Earth-forming minerals, so the geologic significance was lost on me. Now, however, I appreciate the scientific/geologic foundation behind the concept of the Horta. This story is really an imagination of an alternate or opposite reality, kind of like a planetary Bizarro world (reference either Seinfeld episode, “Bizarro Jerry” Season 8, episode 3, or Bizarro of the Superman universe). 


Mr. Spock (Leonard Nimoy), communicating with the Horta through a Vulcan mind meld.
The home planet of the silicon-based Horta was not a Class M or Earth-like planet; according to the internet fan site Memory Alpha, Janus 6 was geologically inactive and had no atmosphere. Our own knowledge, so far, of unusual chemistry or processes in organic life is from Earth environments beyond the comfort level of humans, such as habitats that lack oxygen or have extreme cold or hot temperatures. "Extreme" biochemistry goes beyond chemical processes and includes incorporation of non-typical elements in genetic material: in saline Mono Lake, California, arsenic has been found to replace phosphorous in DNA and proteins of the bacteria GFAJ-1 (http://www.nbcnews.com/id/41669973/ns/technology_and_science-space/t/definition-life-arsenic-debate-just-wont-die/#.VPu0yMarVe). The arsenic-phosphorous and silicon-carbon exchanges are examples of chemical swaps of elements in the same periodic table group (column) with similar outer electron shells. The article points out, however, that a total substitution of one element for another in Earthly biota would doom an organism.

Is it possible that in other parts of the universe we can find elements we have not imagined, like the Star Trek element pergium mined on Janus 6 or the warp-core fuel dilithium? (Fictional dilithium is an element, not a molecule of two lithiums.) Despite the expanse of the universe, we do understand the formation processes of elements produced during pre-supernova star evolution (hydrogen, helium, carbon, neon, oxygen, silicon, iron) and of higher mass elements in post-iron nova/supernova stellar rebound explosions (http://aether.lbl.gov/www/tour/elements/stellar/stellar_a.html). However, I am guessing there may well be new minerals, not known on Earth, on extraterrestrial planets and moons. As I mentioned in my blog post of November 5, 2014, on the “Deep Carbon Through Deep Time” short course, Robert Hazen described how species of minerals have appeared and evolved on Earth through time in response to surface and subsurface processes. Mineral evolution and resulting mineral assemblages on other extraterrestrial bodies may be different based on element distribution within proto-solar system clouds, resulting initial composition of planetary and lunar bodies, presence or absence of tectonic processes, extremes of temperature and pressure. And this includes organic minerals: Hazen pointed out there are such species since the definition of a mineral is now something that creates a diffraction pattern (Hazen and others, p. 32, Carbon in Earth, Reviews in Mineralogy and Geochemistry, vol. 75, http://www.minsocam.org/MSA/RIM/Rim75.html). Differences in mineral evolution, in addition to non-Earth-like extreme physical conditions, may in turn give rise, I imagine, to different microbes and pre-biotic molecules, since it is known that on Earth minerals serve as electron donors, or energy sources, for lithoautotrophic microbes (Colwell and D’Hondt, p. 558, Carbon in Earth).

Speaking of alien life, Spock's physical make-up also includes an alternate chemistry. Vulcan blood is green because it is copper-based. If analogous to human Earthling blood, the copper would be chelated in the middle of the square porphyrin (tetrapyrrole) molecule in place of iron. In people with lead poisoning, lead replaces the iron, and, logically, a simple blood density test can identify the problem. The porphyrin structure that is part of the chlorophyll molecule in plants has magnesium as the chelated metal. However, during organic diagenesis and petroleum formation, vanadium and nickel from pore waters in sediments replace the magnesium; the proportion of V to Ni [V/(V+Ni)] in petroleum porphyrins depends on the oxidation/reduction potential (oxic vs. anoxic) of the sediments and can be used as a paleoenvironmental indicator.  (The Biomarker Guide: Biomarkers and isotopes in petroleum systems and Earth, 2005, by Kenneth Peters, Clifford Walters, J. Michael Moldowan). 

Chief Mining Engineer Vanderburg in “Devil in the Dark”:  ". . . Look, we didn't call you here so you could collect rocks." 

Geologists on the starship Enterprise? There is one original-series Star Trek episode in which a crew member is identified as a geologist (“That Which Survives”, Season 3, Episode 17). His character name is even listed in IMDB.com as “Lt. D'Amato, Geologist”. But D’Amato, geologist on the Away Team, not in any previous episodes in the series, meets his demise within the first 10 minutes of the story. . . saw that coming light-years away!

When I started college in fall 1969, I had been an avid follower of the US space program and thought I might major in Astronomy, Russian studies or Asian studies. I ended up majoring in History with a minor in Geology, once I realized how interesting mineralogy could be. In hindsight, I think my original interest in majoring in Astronomy was really an interest in Planetary Geology. (I was a bit disappointed to realize that academic astronomy is actually physics and math in disguise, and this was when the college math department computer was a single-job card-loading Fortran machine! Syntax errors-Aaargh!) However, in 1969, despite the first Apollo landing in July, and three years of Star Trek, a separate university concentration in Planetary Geology was not yet off the ground.

I close with a nod to Leonard Nimoy (March 26, 1931 – February 27, 2015): you will “live long and prosper” in the minds and hearts of those who dream of, imagine and yearn to explore the wonders of the universe. An excellent blog post by a geologist on Nimoy/Spock as an inspiration and role model for young scientists can be found at http://blogs.agu.org/magmacumlaude/2015/03/05/importance-fictional-role-models/ . (I actually really separately, before reading Jessica's blog and without mind meld, started writing this post and had included a photo of Spock with the Horta and the reference to geologist D'Amato. Explorers thinking alike!)


No comments:

Post a Comment