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
Scientists have proposed panspermia 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. To achieve the former and the latter, three main mechanisms are considered.
First 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.
Second 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.
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 our planet’s deliberate targeting 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, this extraterrestrial civilization’s intention would not have been to populate Earth with living organisms but more that of accidental disposal of its organic waste that would have landed on planet Earth.
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 that only required water and energy synthesized from the oxidation of reactive chemicals found in Earth’s soil to exist.
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 are 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 because 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.