The idea that life on Earth originated on Mars is a scientific hypothesis. This idea suggests that life’s building blocks, or early life forms, may have emerged on Mars before reaching Earth. Exploring this possibility involves examining Mars’s past conditions, understanding how life could traverse interplanetary space, and analyzing chemical clues in extraterrestrial samples.
Mars’s Early Conditions
Billions of years ago, Mars was a very different world than the cold, arid planet observed today. Geological evidence indicates that early Mars hosted extensive liquid water, with features like dried riverbeds, ancient lakebeds, and deltas visible on its surface. During the ancient Noachian period (approximately 4.1 to 3.5 billion years ago), Mars likely possessed a thicker atmosphere. This early atmosphere, rich in carbon dioxide and hydrogen, would have contributed to a warmer climate. Such conditions, including temperatures warm enough for liquid water, are considered favorable for the emergence of microbial life.
How Life Could Travel Between Planets
The scientific concept known as lithopanspermia proposes a mechanism for life’s journey between planets. This hypothesis suggests that microscopic life forms or their precursors could travel encased within rock fragments ejected from a planet’s surface. Such ejection events would be caused by powerful impacts from asteroids or comets. Once launched into space, these rock fragments, potentially harboring resilient microorganisms, would then endure the harsh conditions of interplanetary travel.
Space presents challenges such as extreme vacuum, intense radiation, and wide temperature fluctuations. However, certain extremophilic microorganisms, like bacterial spores, have demonstrated significant survival capabilities in laboratory simulations of these conditions. After their journey through space, the rock fragments would then undergo atmospheric entry into another planet. Evidence for this interplanetary transfer of material exists in the form of Martian meteorites found on Earth. Over 270 such meteorites have been identified, demonstrating interplanetary transfer from Mars to Earth.
Clues Pointing to a Martian Origin
Specific chemical arguments lend support to the idea of a Martian origin for Earth’s life, particularly concerning the formation of RNA. RNA, a molecule thought to be a precursor to DNA, is considered fundamental for early life. Its formation requires certain elements, including boron and molybdenum. Boron, when present in its oxidized form (borate), is important because it stabilizes ribose, a sugar component of RNA, preventing its degradation in water. High concentrations of boron have been detected in Martian meteorites and by the Curiosity rover on Mars.
Molybdenum, specifically in a highly oxidized state, is also believed to be necessary for the chemical reactions that form RNA. Conditions on early Earth, with its very low oxygen levels, would have made this oxidized form of molybdenum scarce. In contrast, early Mars is thought to have had a more oxygen-rich atmosphere or environments conducive to the formation of this necessary molybdenum type. Earth’s early abundance of water might have diluted boron, which concentrates in drier environments, whereas Mars’s less pervasive surface water could have allowed for higher concentrations of both boron and oxidized molybdenum.
Other Theories and Unanswered Questions
While the Martian origin hypothesis is one theory, it exists alongside others for life’s genesis on Earth, collectively known as abiogenesis. The prevailing scientific hypothesis suggests that life arose from non-living matter through a process of increasing complexity. One prominent idea, the “primordial soup” hypothesis, posits that life began in shallow, chemically rich pools on early Earth, where organic molecules formed spontaneously from inorganic precursors. Another significant theory suggests life originated around deep-sea hydrothermal vents, where chemical energy and unique geological conditions could have supported the formation of organic compounds and early metabolic pathways.
Despite arguments for a Martian origin, the hypothesis faces several unanswered questions and challenges. A primary criticism is that panspermia, while explaining how life could spread, does not explain how life initially formed. It shifts the question of origin to another celestial body without providing the fundamental answer to abiogenesis itself. Proving panspermia definitively is also difficult, as it requires demonstrating that microorganisms could survive ejection, the harshness of space, and re-entry, and then successfully initiate life on a new planet. The ongoing search for important evidence of past or present life on Mars continues.