Research conducted by the University of Cambridge suggests that it is highly unlikely for a comet to deliver large volumes of intact molecules to the Earth's surface. This finding casts doubt on an old theory regarding the genesis of life, although it does not rule out other ways these celestial bodies might have contributed.
The study, published in the journal Scientific Reports, focused on analyzing the transport of hydrogen cyanide (HCN), a substance crucial for the chemical reactions that could have preceded the emergence of life.
Historically, comets were viewed as potential sources of raw material for prebiotic chemistry because they carry organic molecules. However, the arrival of these compounds on the Earth's surface depends on very specific circumstances.
The simulations performed indicated that comets frequently struck Earth at high speeds and with excessively inclined angles. The heat and pressure resulting from these collisions could destroy HCN before it reached the soil in an intact state.
Furthermore, even if the molecule survived the impact, its concentration would need to be high enough to drive the investigated chemical reactions. Dilution in the aquatic environment could also decrease the time required for such processes to occur.
Richard Anslow, a researcher at the University of Cambridge Astronomy Institute and the lead author of the work, admitted that the hypothesis cannot be entirely dismissed. He stated that while possible, it would appear to be an extremely rare event, perhaps an isolated coincidence.
The situation becomes even more complex when considering that the rate of comet impacts decreased drastically during the first five hundred million years of Earth's history, thus limiting the chances of delivering significant amounts of HCN.
It is important to note that the research addresses only one specific mechanism and does not determine whether comets had other forms of participation in the early life. There are other viable explanations for the presence of the chemical components necessary for the first reactions, and these were not excluded by the study, as it did not exhaustively evaluate all organic molecules or all chemical consequences of the impacts.
The simulations suggested that Mars would present more favorable conditions for receiving prebiotic molecules brought by comets. Due to its smaller size than Earth and its thinner atmosphere, the planet would offer fewer barriers to the arrival of these compounds during periods of higher impact incidence.
This result does not imply that life originated on Mars; it refers solely to the possibility of transporting chemical inputs, without determining whether these gave rise to living beings.
Additionally, the study may aid in guiding the search for life on other planetary systems, as identifying systems where comets transit between planets is a tactic that can enrich future astronomical observations.
In summary, the research restricts one of the proposed theories for the origin of life on Earth, keeping open the fundamental question of how chemical elements organized themselves to enable the emergence of the first organisms.
