Is Panspermia Occurring Right Now?
June 22, 2010 9 Comments
Panspermia is said to be one of the possible ways for evolution of life on Earth. The theory of panspermia suggests that life did not originate on Earth, but instead came from space. The possibility that life originated here on Earth, but was supplemented by space-derived microorganisms also cannot be ruled out. Another variant of panspermia, “neopanspermia” refers to the contemporary arrival of life from space. The idea that life originated from space has a long history, while the theory of neopanspermia is relatively new. However, the entire concept of panspermia, in its modern guise is based on the seminal work of Sir Fred Hoyle and Chandra Wickramasinghe. Until recently most of the work on panspermia has been theoretical. However, there is now laboratory evidence to support the view that microbes can be transferred across the cosmos, and which suggests that, at this moment, life is entering the Earth’s atmosphere from space.
One might imagine that the proposition that life is incoming to Earth from space could be easily be demonstrated, simply by sampling space at a height above the Earth where there is no possibility of contamination from below. One also might have assumed that NASA or another space agency would have looked for the presence of microbes in near space and would have determined at what height above the Earth’s surface they eventually peter out. This has not happened. Surprisingly, despite all the billions spent of space research we still do not know how high the Earth’s biosphere extends into space, nor have answers been provided to the apparently simple question- are microorganisms present in near space?
The highest point at which we know that microbial life exists is 77 km. However, we know nothing about the biology, if it exists, at heights above this. If microorganisms continue to be isolated as at even greater heights then there must come a point when it is acknowledged that they are incoming to Earth from space. The existence of a stratospheric biosphere may have had an important effect on the evolution of life on Earth. Any bacteria transferred from Earth to the stratosphere will be exposed to high levels of mutagenic UV rays and other forms of radiation. Such exposure will induce mutations in bacteria passing into the stratosphere. The ability of UV to cause mutations in microbial genome has long been recognised, and is used in biotechnology to improve the production of important biochemicals like penicillin. Moreover, the ability of the effected host to survive in varied environments can also be impacted. For example, UV induced mutations in Lactobacillus enables them to survive high concentrations of sodium chloride and sodium nitrate. Thus, mutations may pave the way for bacteria to colonize even toxic planets.
Therefore, naturally enhanced mutation in the stratosphere may speed up evolution rates in microbes which survive a period of UV exposure in this region and then return to Earth. This would also be true of microbes which arrive on Earth from space. Such mutagenesis will be far greater than that which occurs on Earth, where the amount of UV is reduced by the atmosphere, clouds, and the ozone layer.
The high cold biosphere may therefore act as a huge mutation- generator, a vast laboratory where new microbial genomes are created and returned to Earth where this new “information” can be promiscuously transferred to microbes which have not journeyed to the stratosphere. This process may be ongoing with microorganisms being continually returned to the stratosphere for a new dose of mutagenic radiation.
The acquisition of an atmosphere and ozone layer was absolutely essential for the development of complex multicellular life on Earth, thereby allowing life to explore and conquer diverse environments and to evolve and diversify. However, this protective layer also reduced the level of mutagenesis in prokaryotes and eukaryotes. Given that the protective ozone layer was not sufficiently established until around 540 million years ago, coupled with the explosion of complex life which followed, it could be said that UV-induced mutagenesis may have promoted microbial evolution and diversity for the first 4 billion years of Earth’s history, but hindered eukaryotic evolutionary development.
Critics of panspermia often erroneous claim that it is impossible for naked bacteria to survive the transfer from space to Earth, because of problems related to ionising, and, particularly, UV radiation. There is now considerable evidence demonstrating that bacteria can survive UV radiation, and a journey from Earth to space and back again. Resistance to UV for even a short period of time would allow a bacterium to survive when the protective cosmic dust covering is partially exposed, until a new UV-protective dust cover is formed. In this way, a bacterium which can survive direct exposure to UV would be at a competitive advantage over one that was not; of course, if a bacterium remained permanently covered by an impenetrable UV-protective layer of cosmic dust or carbonised cells then it could remain viable in the absence of any native UV resistance.
In a research paper by Jeff Secker published in arxiv.org suggest that the traditional idea of radiopanspermia is valid if micro-organisms (bacteria and viruses) are shielded inside grainswhose material blocks significant UV radiation, and are ejected into space in the late stagesof a (one-solar-mass) star’s life. Coupled with recent discoveries supporting other aspects of panspermia and their result suggested that the probability for life in any given solar system has increased.
Three different micro-organisms were considered in these calculations. The Micrococcusradiophilus is the most radiation-resistant bacteria known at this time, and it is therefore alogical candidate for this radiopanspermia. The Staphylococcus minimus is a very commonbacteria which is much smaller than the Micrococcus radiophilus. As well, the virus weconsidered combined properties of both the T1 Bacteriophage and the phage C-36. Sun’s UV radiation is considerably more harmful than its ionizing radiation, and it is so intense at the present time that it effectively inactivates all exposed micro-organisms. This situation might be avoided if the micro-organisms are embedded in dust grains. This might be a natural thing, depending on how they are put into space, through UV processing of a thin surface skin of organic matter, or through interactions and accretion of carbon-rich interplanetary dust particles. It is noteworthy that in interstellar space the intensity of radiation is many orders of less than it is in the vicinity of sun.