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Where Did Life on Earth Originate?
Life on Earth has existed for billions of years, but did it all start here? Hundreds of millions of years before there were any fish or plants as we know them, single-cell organisms occupied the oceans of our world.
All of the necessary building blocks have existed on Earth nearly from the start. Early bombardment during the formation of the Solar System, however, made conditions far from safe for life.
But the bombardment of Earth by meteors may have started it all off. One theory states that simple hydrocarbon compounds riding on meteoroids crashed into Earth giving rise to more complex chemicals—a step closer to life itself. Experiments in the laboratory have shown that such chemicals indeed increase in complexity after hypervelocity impact. An alternate version states that the chemicals resided on Earth and simple meteor collision added the needed energy to transform the chemicals.
In one series of Japanese experiments, a pellet made of iron and carbon was shot at a stainless steel container at 4,500 miles per hour, generating temperatures of about 5,000 degrees Fahrenheit (2,800°C). The container held a solution of ammonia and water. This "shock" impact produced amines, fatty acids and glycine (an amino acid). These are important components of life.
But there is another theory that life originated elsewhere and was carried to Earth.
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What is Panspermia?
The American Heritage Dictionary defines panspermia as, "The theory that microorganisms or biochemical compounds from outer space are responsible for originating life on Earth and possibly in other parts of the universe where suitable atmospheric conditions exist." This field of study is divided into three more specific ideas:
- Directed Panspermia. This is the highly controversial idea that an advanced extraterrestrial civilization spread life to other young star systems, including our own.
- Ballistic Panspermia. From a comet or asteroid collision with a life-bearing planet, biological material is carried to another planet in the same star system.
- Lithopanspermia (sometimes referred to as interstellar panspermia). This is the same as ballistic panspermia except that the end target is a planet in a different star system.
While it is entirely possible that aliens seeded our planet 4 billion years ago, such an idea cannot be proven without access to that hypothetical alien civilization. It might be interesting to speculate about such an alien expedition. What could have been their purpose in seeding other star systems? Could they have come to realize that life is too rare and needed help to start elsewhere? If such a hypothesis turns out to be true, then that alien civilization, if it still exists, would be some four billion years older than our own. Would they consider us their children?
And while it is entirely possible that life may have formed on another planet in this star system and was later transported to Earth, we have as yet not found any evidence of life on another planet.
For these reasons, we will discuss only the idea of interstellar panspermia (lithopanspermia).
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Showing Panspermia is Possible
A number of experiments have already been performed which support the possibility that panspermia can happen.
Fajardo-Cavazos, et al, published an article in 2005 in Astrobiology showing that microbes can survive hypervelocity entry into Earth's atmosphere.
Another article by de La Torre Noetzel, published in 2008, showed that lichens could survive some of the harsh conditions in space. After ten days in low Earth orbit, during which lichens were subjected to vacuum, cold, heat and UV radiation, the samples of lichen showed rapid recovery to biological activity.
But can material be knocked off of one planet and into space later to land on Earth? Yes it can. In fact, NASA scientists have determined that a number of meteorites found on Earth originated on Mars.
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While these experiments show that panspermia can happen, proving that interstellar panspermia was the source of life on Earth would be close to impossible. Such proof would require access to other star systems, which are found to contain life similar to that on Earth. And that would require a method of interstellar travel that could be done in a reasonable amount of time—say within a few lifetimes. Current spacecraft that have left the Solar system are traveling far too slowly. Voyager 1, for instance, will take about 40,000 years to reach the distance of a nearby star in the Camelopardalis constellation. Though Voyager 1 is not headed directly for that star, it will pass within about one and a half light years of that system.
One future day, when humanity has cracked the "light barrier" (if that is even possible), then we might travel to other star systems in months, weeks or even days. Only then will we be able to test adequately the ideas of interstellar panspermia. Only then will we be able to see if there is life in other star systems similar to our own.
And yet, if life did originate in another star system, we must ask, "How did life start there?"
Any system that may have been the panspermia source of life in ours would be very far away by now. Nearly every star in our solar neighborhood would likely be many thousands of light years away from us after 4 billion years.
- Jet Propulsion Laboratory, "Mars Meteorites," http://www2.jpl.nasa.gov/snc/
- de La Torre Noetzel, Rosa, "Experiment lithopanspermia: test of interplanetary transfer and re-entry process of epi- and endolithic microbial communities in the FOTON-M3 Mission," http://adsabs.harvard.edu/abs/2008cosp...37..660D
- Fajardo-Cavazos, Patricia, et al, "Bacillus subtilis Spores on Artificial Meteorites Survive Hypervelocity Atmospheric Entry: Implications for Lithopanspermia," http://www.liebertonline.com/doi/abs/10.1089/ast.2005.5.726
- Keim, Brandon "Proof That Meteors Could Have Sparked Life on Earth," http://www.wired.com/wiredscience/2008/12/in-a-vat-primor/
- Panspermia Theory, http://www.panspermia-theory.com
- Houghton Mifflin, "Definition of panspermia," http://education.yahoo.com/reference/dictionary/entry/panspermia