How did life begin on Earth? That question has intrigued humanity for millennia. In this paper I will investigate only one fairly recent theory about the origins of life on Earth: That life came from space. This theory is referred to as the “panspermia” theory because it presumes that life may be seeded from space throughout many worlds and many solar systems. By implication, the panspermia theory supposes that life should be common wherever there are physical conditions that are capable of supporting life. This report addresses the possibility that life may have originated in space rather than on Earth, and considers the evidence in support of the various theories about how that may have happened, if it did. Such theories are called “panspermia” theories from the Greek for “all seeds”—the seeds of life existing everywhere in space.
One of the critical issues in any discussion of life from beyond the Earth is how we define life at all. In most scientific circles, the modern definition of life has become “life as we currently recognize it” rather than “any possible type of life imaginable.” Yet even the definition of what we declare to be recognizable is constantly updated as we discover life here on Earth that survives in extreme conditions of heat, radiation, extreme acids, unusual chemistries (sulfur-based), and even inside rocks buried deep underground. The bottom line condition for life “as we know it” seems at this point to be the presence of liquid water at least at some time in the past, if not the present. (Sonali S. Joshi 2008)
Panspermia Theories of the Origin of Life
Most theories of the origin of life assume that it developed from some type of organic molecule “soup” which spontaneously developed into self-replicating molecules and from there into primitive cells. Where the organic molecules came from to initiate the process? Did they spontaneously form as the Earth cooled, perhaps by a conjunction of lightning, water, and heat acting on a warm pool of chemicals? Or, possibly, did the organic molecules—even the self-replicating molecules of RNA and DNA—derive from someplace else? Did those molecules come from outer space? The concept that life derived from space sounds very modern and trendy, but in fact, it was originally proposed in the 17th Century by both Sir Isaac Newton and Edmond Halley (of Halley’s Comet). Their theories were not quite the same, however. Halley believed that a cometary impact on Earth could have caused the Biblical flood; Newton believed that when the Earth passed through the tail of comets it could have collected water which in turn would become the source of life on Earth.
Modern life-from-space theories take a leaf from both Newton and Halley in that it is now believed that the organic chemicals found in the tails of comets could indeed have been accreted through both cometary impacts and near-misses. It is also believed that in the early Earth, massive numbers of cometary impacts could have delivered substantial amounts of water, and may have delivered enough water to the newly formed Earth to create the oceans Today, however, there are a number of variations on the idea that life may have come from space. The first type of theory is that life developed initially on another planet in the solar system, and then was transmitted to Earth in the form of rocks ejected from that planet which eventually fell to Earth as meteorites (i.e., a transpermia theory of “transmission” of the seeds of life from other planets). A second set of theories considers whether any life transmission to Earth might have happened only once, at the time the early Earth was forming (i.e., a panspermia theory), or whether it is ongoing today (a neopanspermia theory). Finally, an additional set of theories considers whether life might have transmitted across interstellar space (interstellar panspermia). Each of these types of panspermia theories