A paper published in August 2015 by scientists at the Harvard-Smithsonian Center for Astrophysics theorizes life on Earth may have originated on other planets. This exciting revelation comes at a time when the scientific community feasts on data from the Rosetta mission to a nearby comet, as orbiting satellites continue to probe exoplanets outside of our solar system, and when projects searching for extraterrestrial intelligence are receiving greater funding. This theory is known as panspermia.
One of the study's lead researchers, Dr. Avi Loeb, said, “Life could spread from host star to host star in a pattern similar to the outbreak of an epidemic.” In other words, over the span of millions or billions of years, one planet may accidentally send the building blocks of life to other planets, according to Mirror.
This works due to asteroid impacts on worlds that already have life. Suppose that a gigantic ball of rock strikes the surface of a planet teeming with plants, animals, and microbes. Some of these microscopic life forms, embedded in soil, eject into space as a new asteroid, according to Discovery News. That asteroid goes off in another direction and eventually lands on a planet that doesn't contain life. Over hundreds of millions of years, those microbes evolve into more complex life forms as dictated by the conditions on the new planet.
Another theory proposed by Loeb's team speculates that more advanced civilizations may colonize other planets deliberately, and these advanced life forms adapt to different conditions. These races would have the ability to move entire civilizations in huge ships that could take tens of thousands of years to travel between stars.
How Researchers Did the Math
Loeb, and co-author Henry Lin, used a complex computer model to show how panspermia could occur under the right conditions. First, chunks of rock must fling into space and then land on another planet. Life from the new planet, after hundreds of millions of years, may eject into space and go to another world further away from the first one. In a way, complex life spreads through a galactic region similar to a virus.
Over time, these star systems spread further from each other due to the motion of the Milky Way galaxy. This makes detecting other life more difficult. However, current technology allows satellites to possibly detect the atmospheric composition of some exoplanets, giving astrobiologists hope that life may occur around other stars. In Lin and Loeb's model, if as few as 25 planets harbor biological activity, scientists have a chance of detecting such life, and these odds increase as time moves forward, according to The Astrophysical Journal Letters.
Panspermia, as a theory, has been around for a few generations. Lord Kelvin and a few of his colleagues observed the effects of the massive volcanic eruption from Krakatoa in the 1880s. Kelvin noted in a speech that although the island became sterile directly after the explosion, a few months later seedlings developed and plants began to grow, according to i09.
Naturalists who traveled to Indonesia to see the after-effects of the eruption speculated seeds drifted in the ocean or through the air to land on the volcanic island. Perhaps some humans unknowingly took seeds to the island to aid in the flora's growth. Kelvin extrapolated that interstellar space could serve as a medium similar to that of an ocean or air. Large asteroids, carrying frozen life forms, could travel to distant planets and eventually spread life.
Panspermia gained more popularity in 1972 when Francis Crick, one of the scientists who discovered DNA, published a paper with Leslie Orgel speculating that aliens could send automated exploratory probes to distant planets. These probes could contain microbial life, and distribute their payload on the distant planet for it to evolve over millions of years.
Although discussions of advanced alien life remain controversial, space rocks do travel from one planet to another. Meteors from Mars have landed on Earth. Scientists know this by studying the chemical composition of the rock versus what astronomers know of the Martian surface.
If the theory of panspermia bears out and scientists can prove the origin of life on Earth in such a way, it would provide a fundamental shift in the way humans perceive themselves. Instead of a planetary island adrift in a lonely galactic sea, Earthlings may find themselves in an interstellar ocean full of life. After all, life finds a way to exist in even the harshest environments on Earth, so why not during a journey through outer space? Read more amazing stories about life on this planet at Greater Good.Whizzco