What Is The Panspermia Hypothesis And How Does It Explain The Beginning Of Life On Earth?

This article on Panspermia is a guest article by Anja Sjöström, an IB diploma student from Switzerland.

Panspermia is the astrobiological hypothesis that life exists elsewhere in the universe due to a distribution of microorganisms being inadvertently transported on asteroids, other traveling planetoids, or even spacecraft. Hypotheses of panspermia could both allow us to explain abiogenesis or in other words the origin of life, and how it may travel from places known to hold living organisms to populate distant galaxies or planets.

Earth was said to be uninhabitable 4 billion years ago, and the first life forms were signs detected from up to 3.8 billion years ago. However, scientists argue that in the span of 0.2 billion years, life would not have had the time to evolve from no-life into the single-cellular form, as evolution is a slow process. Thus, panspermia becomes a viable option in explaining the apparition of relatively developed life which would have come from another planet, potentially Mars, delivered by comet or object having escaped Mars’ atmosphere with on it, simple forms of life, microorganisms.


Mechanisms of Panspermia

Panspermia has been proposed by scientists to take place in a plethora of ways. Amongst the schemes by which life could leave Earth or a planet, find themselves two main scales of transport: interstellar panspermia and interplanetary panspermia. In order to achieve the former and the latter, three main mechanisms are considered.

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First of all, is the mechanism of Radiopanspermia in which microorganisms are propelled through space thanks to the radiation pressure of stars until reaching an object on which conditions might be favorable or not for it to develop into larger and more elaborate forms of life. However, this hypothesis was refuted due to the long exposure of bacteria to radiation during interplanetary travel which would denature any form of DNA or RNA and reduce any chances of successful Radiopanspermia to almost nil.


Secondly, is the hypothesis of Lithopansmermia. In this case, the interplanetary transfer of life would occur thanks to the presence of microorganisms on or in asteroids, comets, and other planetoids large and resistant enough to withstand planetary ejection, lengthy intergalactic, planetary, or stellar, travel as well as atmospheric reentry.

What Is The Panspermia Hypothesis And How Does It Explain The Beginning Of Life On Earth? 1

Finally, hypotheses of directed Panspermia, or the intentional implementation of life on Earth, are also being held as plausible. According to Nobel Prize winner, Francis Crick, life on Earth could have originated through the deliberate targeting of our planet by an advanced extraterrestrial civilization.

An extension of directed Panspermia would be the case of accidental panspermia, also conducted by an alien civilization. In the scenario, the intention of this extraterrestrial civilization would not have been to populate Earth of living organisms but more that of accidental disposal of its organic waste which would have landed on planet Earth.

Read all the articles of the History of Life series here

Organisms Prone To Panspermia

The first condition for organisms to survive exposed space travel is their ability to survive in the absence of sunlight. However, up until the 1970s, such living organisms were unfathomable, until in the depths of the Galapagos Rift were discovered organisms which only required water and energy synthesized from the oxidation of reactive chemicals found in Earth’s soil to exist.

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This shed light on a new category of bacteria now known as extremophiles. These microorganisms would develop cysts and spores to protect and shield themselves when exposed to high stress (gamma radiation, temperature, ultraviolet…). However, once viable conditions restored, these spores and cysts would germinate and allow for the organism to become metabolically active once again.


Finally, panspermia fails to be widely accepted or respected throughout the scientific community due to the fact that it merely delays the answer to the question: ‘How did life originate?’, by placing it on another celestial body than our own. Even though it might be conclusive in explaining abiogenesis on Earth, it fundamentally fails to explain how, from a generic perspective, life arose anywhere in the universe.

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