Panspermia
The answer to the question: “where did we come from?” has been sought after by mankind for ages. Many different hypotheses have been crafted over the centuries and have been topics of debate for thousands of years; however we still do not have a definitive answer. Types of theories range from those based on religious doctrine to those which take a strictly scientific approach. One possibility that leans towards the latter is the panspermia theory which suggests that life did not originate on earth; but rather came to earth from somewhere else in the universe. It is the idea that the ingredients for life are found throughout the universe and are able to initiate life given a habitable environment. While this theory may seem improbable to some, increasing evidence suggests that this idea may have more truth to it than some may believe.

In order for life to have come to earth from somewhere else in the universe, it would have had to survive the harshest environment we know of; space. These organisms would have been exposed to massive amounts of radiation, extremely cold temperatures (nearly -273.15ºC), and extreme atmospheric pressure1. When we think of organisms that thrive in the harshest environments on earth we think of extremophiles, and perhaps the most renowned and complex extremophile is the tardigrade. These dry aquatic invertebrates are known to be one of the most resilient species on earth and have received a lot of attention from researchers regarding their potential to survive in space2. Proving that tardigrades have the ability to survive outer space, demonstrates the possibility that life could have traveled through space for extended periods of time without dying. “tardigrades in Space (TARDIS), for example, was the first project planned to evaluate their ability to survive in space. In September 2007 Ingemar Jönsson from the Kristianstad University in Sweden and his team launched tardigrades into the orbit aboard the FOTON-M3 spacecraft for the first time. Tardigrades unshielded from UV were killed by extreme radiations, but others thrived and even laid eggs that managed to hatch1.”This study provides significant evidence supporting panspermia as it exemplifies that life can not only survive in the harsh environment of space, but also reproduce; thus allowing life to continue for extended periods of time while in space.

Another argument that supports the panspermia theory is that life may have come to earth from Mars. Between 4 and 3.8 billion years ago earth endured a tremendously powerful series of meteor showers; however the earliest evidence for life on earth suggests life was present approximately 3.83 billion years ago3. The issue with this is that these observations suggest that life during this period would have gone extinct (further evidence supporting that life did not originate on earth) 3. If life originated somewhere else in the universe, it would have needed to come from a place with an environment that could support it initially. It is well known that water is a primary ingredient for life as we know it and there is evidence supporting that there was liquid water on Mars billions of years ago. There are many other theories suggesting Mars was a much more habitable planet billions of years ago than it is today. ALH84001 is the oldest meteorite ever found to have come from Mars and has been a topic of debate amongst the scientific community since its discovery4. ALH84001 is particularly fascinating compared to the over 50 other meteorites4 that have been identified as coming from Mars. This is due to a number of reasons. Firstly, ALH84001 is by far the oldest meteorite discovered on earth that has come to Mars, forming 4 billion years ago (the next closest is 1.3 billion) 4. Additionally, and even more interesting, is the fact that that it contains 300-micron-wide carbonate globules that make up 1% of the meteorite4. From this, researchers determined that the carbonate was likely formed in the presence of water 4. This was an important discovery as it adds to the evidence that Mars was once a wet planet, thus increasing the odds that life may have once existed on it. Another very interesting feature of the meteorite is the small worm-like fossils within the rock made up of carbonate grains4. “The carbonate grains are associated with organic compounds, contain minute crystals of iron minerals similar in size and shape to those produced by bacteria, and exhibit elongated objects resembling microscopic fossils”5. This evidence suggests the possibility that bacteria could have once lived within this rock, which if true, is a revolutionary discovery. However, in further investigations skeptics argued that these lines found within the meteorite could have been formed from geological processes, or have been contaminated from bacteria living on earth5. In summary, although there are various indications that life may have once existed on Mars, the hypothesis that ALH84001 contains evidence of extraterrestrial life is not generally accepted amongst the scientific community5.

Further evidence supporting that life could have originated on Mars is found when analysing the building blocks for life as we know it. “One of the stumbling blocks to life starting on Earth is the fact that water is almost universally accepted as necessary for the onset of life. Yet RNA—which many consider to be the earliest expression of genetic replication and another essential precursor to life as we know it—falls apart if you try to build it in water6.” The issue with this is that without RNA, it is very unlikely that DNA would have formed and therefore even more unlikely that life would evolve into what we know it as today. According to some, what kept the RNA from falling apart was the presence of a form of boron; however geologists believe boron was too scarce on earth to support the large scale formation of RNA6. Mars on the other hand, is believed to be much more abundant in boron6. Since Mars was believed to be a much wetter planet billions of years ago and also contains significantly more boron than earth did (which was needed for the formation of RNA), does this suggest life begun on Mars? Did RNA lead to DNA on Mars and then travel to earth via rocks catapulted by an impact on Mars? If these life forms that resided on Mars were as resilient as the previously mentioned tardigrades then this could be a possibility.

The Question of how life began is still heavily debated and likely will be for the foreseeable future. The panspermia theory poses more problems that would need to be solved before it is accepted, including how life began elsewhere in the universe in the first place. “At present, panspermia can neither be proved nor disproved. Nevertheless, panspermia is an intellectual idea which holds strong attraction7.” After thousands of years of investigating humans are still attempting to uncover potentially the biggest mystery in the universe of how we got here and regardless of the answer, the fact that we are here is still truly fascinating.

References 1. Wonderofscience, “Surviving Absolute Zero Temperatures”, August 27 2013, http://wonderofscience.com.au/index.php/surviving-absolute-zero-temperatures/ (Oct 20, 2013) 2. K. Ingemar Jönsson, “Tardigrades In Space (TARDIS)” September 29 2008, http://tardigradesinspace.blogspot.ca/ (Oct 20, 2013) 3. Sonali S. Joshi, “Origin of life: The Panspermia Theory” December 2 2008, http://scienceinsociety.northwestern.edu/content/articles/2008/research-digest/student-papers/panspermia/origin-of-life-the-panspermia-theory (Oct 21, 2013) 4. Michael Schirber, “The Continuing Controversy of the Mars Meteorite”October 21 2010, http://www.astrobio.net/exclusive/3653/ (Oct 21, 2013) 5. Harry Y. McSween, Jr. “ALH84001” November 20 2009, http://www.britannica.com/EBchecked/topic/661788/ALH84001 (Oct 21, 2013) 6. Marc Kaufman “Did Life on Earth Come From Mars?” September 5 2013 http://news.nationalgeographic.com/news/2013/09/130905-mars-origin-of-life-earth-panspermia-astrobiology/ (Oct 21, 2013) 7. M.J. Burchell, Panspermia today, (International Journal of Astrobiology, (Cambridge, Dec 24 2004) pp 73-80.