Possibility of Extraterrestrial Life (on Other Planets) and Signs of Life in Meteorites

Starry sky and stargazers. Image Credit: aldoleopoldnaturecenter.org

Since the dawn of humanity we’ve gazed upwards toward the stars above and wondered, where do we come from and is there life beyond the Earth? More recently, we also asked is there proof of alien life to be found in meteorites.

The possibility that meteorites could contain remnants of life from another planet is a staggering thought. For some, that concept could even be interpreted as an attack on their religious beliefs. But “proof of life” on another planet or in another galaxy, in the author’s personal opinion, need not exclude a “higher power”. It would merely prove that we’re not alone in the universe. One could even argue why would a “higher power” create such a vast universe for the the sole purpose of one species, on one planet, in one galaxy, in this one (?) universe if not for the sake of other species away from Earth. To find conclusive evidence of extraterrestrial life in a place other than our planet would catapult us into a new age of learning and knowledge of our universe and our place in the universe that would reshape science, philosophy and theology.

As Carl Sagan once said “The Sky Calls To Us … If we do not destroy ourselves, we will one day, venture to the stars”. The discovery of verifiable proof of life on another moon, asteroid or planet would be a remarkable event rivaling or even surpassing the Apollo 11 landing on the moon.

 

An important note: When reading general science articles like this one or detailed research papers, the reader should always bear in mind that the term “organic” refers to organic chemistry and can be read as carbon-based chemistry. The term “organic” does not imply organisms or living matter are required or exist unless the chemical processes are specifically identified as biotic.

How Did Life Emerge?

Prebiotic molecule methyl isocyanate detected in young star system. Image Credit: www.sciencemag.org

The mysteries regarding the origin of life that scientist are beginning to unravel is how complex organic molecules could have arisen from abiotic processes and then how those molecules assembled into living organisms. The present scientific hypothesis is that life on Earth emerged from a watery primordial soup augmented by the precursor/prebiotic organic compounds necessary to support biogenesis. This prebiotic material came from mostly carbonaceous meteorites that bombarded the Earth after planetary differentiation. The source of planetary water is hypothesized to have been released during planetary formation and from the same bombardment that delivered the prebiotic material.

The Murchison (CM2) meteorite that fell in 1969 is still one of the most studied meteorites and was the first (but not last) meteorite found to contain common amino acids (the building blocks of life) such as glycine, alanine and glutamic acid, along with a wide array of other organic compounds. Later research in carbonaceous meteorites found the presence of nucleobases (components of DNA and RNA). In Nov. 2019, researchers announced the discovery of sugar molecules in the NWA 801 (CR2) and Murchison (CM2) meteorites including ribose, arabinose and xylose. The extraterrestrial origin of these sugars is supported by the significant enrichment of the isotope 13C, above the amount seen in similar sugars that formed via normal biological processes here on Earth. Though the amount found was small (< 200 ppb), their presence further reinforces the hypothesis that various chemical reactions in asteroids can produce complex organic molecules through abiotic processes and that these complex molecules can find their way to Earth.

Though carbonaceous chondrites are the most common source of organic compounds, NASA scientists have found amino acids in other types of meteorites. The Almahata Sitta meteorite that fell in the Sudan desert in Oct. 2008 was comprised of EL, EH, ureilite, CB and even ordinary chondrite types reflecting its rubble pile asteroid origin. The ureilite portion was found to contain 19 amino acids and their enantiomers were identified in Almahata Sitta, along with 4 amines (produced by thermal decomposition of amino acids), plus other unidentified amino acids belonging to the 5-carbon group.

Perhaps even more tantalizing is research that indicates that complex organic molecules can be found in all meteorite types including highly shocked ordinary chondrites and even iron meteorites. In the research paper titled “Indigenous Amino Acids in Iron Meteorites” by J. E. Elsila et al, the author identified the presence of various amino acids (< 100 ppb) some of which are rare in the terrestrial biosphere (unlikely to be contaminants) and therefore suggestive of an indigenous origin and therefore extraterrestrial. Interestingly, previous research referenced in this paper indicates that surface-catalyzed reactions of gases could form amino acids on metal surfaces. If these amino acids are verified as having extraterrestrial origins, then this research could usher in a new age in astrobiology. One of the major unanswered questions in this research is how do these amino acids survive these extreme conditions when the decomposition temperature of most (all?) amino acids is well below 350 oC.

To date, there is no conclusive evidence of anyone finding indigenous proteins within meteorites. If we ever discover that an abiotic process can form such complex molecules like proteins under the extreme conditions of space, then we would be one step closer to unlocking the secrets of life and its emergence here on Earth and possibly throughout the universe.

As a sobering thought, we should consider the words of Conel Alexander, a geochemist at the Carnegie Institution of Washington, regarding the source(s) of organic molecules. “It really comes down to quantitative arguments about how much was made on Earth [and] how much was brought in from space,” he says. “Any honest person would keep an open mind about the whole issue.” (Scientific American, 2008)

Do Meteorites Contain Proof of Alien Life?

The idea of life spreading throughout the galaxy, transported by bits of other planets, asteroids and comets is not new, it’s called Panspermia, and was proposed by the 5th century Greek philosopher, Anaxagoras. The theory today presupposes that life exists throughout the universe and that life on Earth and possibly other planets originated from space debris that itself contained life in the form of simple microscopic organisms like extremophiles.

To date, there is no conclusive scientific proof that extraterrestrial life or remnants of extraterrestrial life such as fossils have ever been found in any meteorites here on Earth, or on any planet in our solar system including Mars. Some papers may refer to “strong evidence” or “proposes presence of”, but this is not a conclusive statement. This situation may change in the future, but proof will have to come from research published and peer-reviewed by respected researchers and institutions, and in recognized journals. Claims of finding life in meteorites have all been based on misinterpreted results that can be traced back to either terrestrial contamination or weathering byproducts. What scientist do believe is that meteorites contain prebiotics that could, under the right circumstances, support the genesis of life. This hypothesis is referred to as Molecular Panspermia.

As we normally focus on the organic chemistry required as a precursor to life, one can easily forget that a broad range of minerals are also required to sustain life. For example, phosphorus in its mineral forms is a crucial element required to support life and is contained in every living cell. Isaac Asimov’s book Asimov on Chemistry went as far as to state that based on Liebig’s Law of the Minimum, “life can multiply until all the phosphorus has gone and then there is an inexorable halt which nothing can prevent.” Though phosphorus represents only 0.09% of the earth’s crust, we are likely to run out of living room before we run out of phosphorus, but the point is well made. Phosphorus, with its origins in the furnace of stars, could only have made it to Earth through early accretion processes and the continuous bombardment of meteorites throughout Earth’s early history. Of all meteorites, iron meteorites contain the most most phosphorus in the form schreibersite. Yet again, Carl Sagan says it best, “the cosmos is within us. We are made of star-stuff. We are a way for the universe to know itself.”

A Brief History of Announcements of “Life” Found on Mars

Purported “fossil” in ALH 84001 and later discredited. Image Credit: NASA

NASA itself has caused confusion on this topic when in 1996, a group of scientists led by David McKay, Everett Gibson and Kathie Thomas-Keprta of NASA’s Johnson Space Center (JSC) in Houston published an article in Science announcing the discovery of biogenic evidence in the ALH84001 meteorite.In the 2009 paper titled “Origins of magnetite nanocrystals in Martian meteorite ALH84001“, scientists used more advanced analytical instruments to conduct more thorough testing on ALH 84001, and came to the following noncommittal conclusion, “This origin [of magnetite nanocrystals] does not exclude the possibility that a fraction is consistent with formation by biogenic processes, as proposed in previous studies.”

Then in 2012, in a paper titled “Martian Meteorite Compendium: ALH 84001“, Charles Meyer from the NASA Johnson Space Center, made the following observations:

  1. After considerable research by various team, it now seems that various inorganic processes can reproduce all of the features found in ALH84001 and that there is no compelling evidence for life on Mars from this important (albeit complicated) sample.
  2. The exact nature of the black rims on the carbonate “rosettes” has not been properly characterized, which is surprising, considering that it is where the claim of evidence for life in this rock is to be found.

Is There or Can There be Life Beyond Planet Earth?

Ethiopia’s Danakil Depression. Image Credit: National Geographic

The answer is … probably. Life, albeit in the form of simple organisms like extremophiles, is able to exist under the most extreme conditions here on Earth and in places we would least expect. For example, Ethiopia’s Danakil Depression could easily be mistaken for an extraterrestrial landscape. Yet, even in an environment of acidic hot springs, bubbling lavas, salty sands and toxic vapours, microorganisms thrive within the sulphuric pools and mineral chimneys.

If we expand our perspective, then according to the Drake Equation, there is a non-zero probability that life does exist somewhere out in the universe. Unfortunately, the only way to determine its existence outside our solar system is to look for intelligent life that developed technology capable of transmitting detectable radio frequencies like TV, radio, satellite or cellular communication signals. Complicating matters further, radio frequencies travel at the speed of light and could take millions if not billions of years to reach Earth depending how from from us this civilization is located. Finally, there is the added challenge that our electronic receivers must be sensitive enough to detect an incredibly small signal that is likely buried under cosmic noise.

As part of an interesting philosophical discussion, we should also consider the anthropic principle. The definition of the “anthropic principle” from Wikipedia states that “The principle was formulated as a response to a series of observations that the laws of nature and parameters of the universe take on values that are consistent with conditions for life as we know it rather than a set of values that would not be consistent with life on Earth.” In simpler terms, it is the observation that, since we exist, the conditions of the universe must be such as to permit life to exist. The “weak anthropic principle” holds that the conditions necessary for the development of intelligent life will be met only in certain regions that are limited in space and time. That is, the region of the Universe in which we live is not necessarily representative of a purely random set of initial conditions; only conditions favorable to intelligent life would actually develop creatures who wonder what the initial conditions of the Universe were, and this process can only happen at certain times through the evolution of any given universe. The “strong anthropic principle” argues that that if the laws of the Universe were not conducive to the development of intelligent creatures to ask about the initial conditions of the Universe, intelligent life would never have evolved to ask the question in the first place. In other words, the laws of the Universe are the way they are because if they weren’t, no intelligent beings would be able to consider the laws of the Universe at all.

The anthropic principle appears to be (at least this author) a philosophical extension of Rene Descartes’ famous quote, “I think, therefore I am.” originally in French as ” je pensedonc je suis” as published in 1637 in his book Discourse on the Method.  As he explained, “We cannot doubt of our existence while we doubt.” While Descartes looked within himself, the anthropic principle seeks an external perspective to explain our place in the universe.

Two Trillion Galaxies

One Million Out of Two (2) Trillion Galaxies. Image Source: Astronomy Photo of the Day

Based on the deep-sky census assembled from surveys taken by NASA’s Hubble Space Telescope and other observatories, astronomers now estimate there are 2 trillion galaxies in the observable universe with each galaxy averaging between 200 billion and 400 billion stars. Trying to fathom numbers this large is nearly impossible, however look at this image on the left. Those aren’t stars, but strings and clusters of galaxies, each with hundreds of billions stars.

Therefore, based on these incredibly large numbers, the possibility that we are alone or unique in the universe seems very unlikely. Unfortunately, the odds are also astronomically against encountering intelligent extraterrestrial life without one of us being able to travel faster than the speed of light.

Hubble Ultra Deep Field slowly zooms out to reveal the larger Hubble Legacy Field, containing 265,000 galaxies.
Credits: NASA, ESA, G. Illingworth (University of California, Santa Cruz) and G. Bacon (STScI)

 

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