Did Life Begin from Space?
Lal (2008) conducted a review of the evidence supporting a variety of theories on the origin of life. After reviewing the current understanding of when life emerged on Earth, noting that evidence for simple unicellular life goes back at least 3.86 billion years, not long after the planet cooled enough to support water. Lal noted that the initial scientific theory of the origin of life was Darwin’s notion of life arising in a warm pond based on the chemistry of the early Earth. This is spontaneous generation.
A second theory, very popular is “RNA World” in which RNA molecules, created randomly, eventually resulted in a version of the molecule that could self-replicate into ribozymes. These in turn generated a form of “peculiar” life that could eventually have resulted in the more complex forms of DNA-based life. RNA World is difficult to initiate, however. While some researchers also consider a “DNA World” there is a chicken-and-egg issue in this hypothesis. While DNA molecules provide the instructions to create proteins, proteins are required to construct DNA (Phillips, 2010).
Another group of theories considers extremophiles (bacteria that survive the harshest conditions on Earth, such as the bacteria around the hot acidic springs at places like Yellowstone Park. Some can reproduce in temperatures up to 113 C (well over the boiling point of water. Since some of these are deep-sea organisms around the volcanic vents, there is the theory that life originated in these deep-sea vents. Other extremophiles survive in highly acidic environments, extremely cold environments (Antarctic), and even deep inside rocks miles underground (Phillips, 2010).
There are theories life also exists elsewhere in the solar system in extreme environments, such as the dark patches in the atmosphere of Venus (“methanogens”). It has been demonstrated that bacteria easily survive the conditions of space vacuum, heat, radiation, and cold, and that methane is a substantial component of atmospheres of Jupiter, Saturn, Uranus and Neptune, plus Titan, Saturn’s largest satellite. Organic molecules have been found in the tail of comets. If even one life-bearing comet made its way to the surface of the Earth, it would be possible to seed the Earth with life. This is particularly true since individual molecules less than 1 micrometer in size are not burned up by entry into the atmosphere, and approximately 10% of interplanetary dust seems to be organic in nature (Lal, 2008).
Even more intriguing recent studies show that liquid water (the one known requirement for life that we know) has recently—perhaps even seasonally—on Mars. Lal (2008) concluded that while the presence of extraterrestrial organics is intriguing, the issue of a panspermia theory has to account for problems in timing regarding when the organics (or bacteria) were delivered to Earth compared to when evidence shows life was established.
The origin of life on Earth is a consistently fascinating question. Are we aliens whose origin is from another planet in our solar system? Are we even more alien than that, being true star children, formed from the seeds from a distant star? Or did life on Earth originate here?
We don’t yet have a firm answer to those questions. What we do know is that the elements of life are not only common, but they are abundant throughout the solar system, Given the known distribution of complex organic materials in comets, it is possible that even a single impact could easily have provided the seed of life on Earth.
Yet impacts are not the only possible bringers of life. Meteors from other planets in our solar system may well have provided the seeds of life. With NASA’s very recent announcement of the presence in at least one meteorite of amino acids and other compounds essential to life as we know it, the potential of transmission of life from, say Mars, becomes more likely. We now know that Mars has flowing water at least at certain times even today (Benson, 13 August 2011). We also know that many meteorites from Mars have landed on Earth. Where there is liquid water on Earth, there is life. Is the same true on Mars? The possibility is exciting and thought-provoking. Is it possible that we’re truly the Martians? Certainly this is an open research question—and one that scientists can now take seriously.
A final source of life from extraterrestrial sources is that life was seeded on Earth from other stars. We know that biological material can survive for eons in space, and with a modest amount of protection from ice and rock, it’s possible that life could survive drifting in from other solar systems. Napier’s 2004 study pointed out that it would be possible to seed an entire galaxy in the space of a few billion years. We may someday meet our cousins if we go out into the stars.
We do not know the answer to the question of the origin of life. There are too many possibilities, and all of them seem possible. What we do know is that it is not at this time valid to exclude the possibility that life on Earth originated elsewhere. Someday we may know the answer to this question, but for now, it is in the realm of fascinating speculation supported by substantial scientific evidence. We just might be star children after all.