Let me put this out in front: Carl Sagan is a hero of mine. How could he not be? He was a scientific communicator par excellence. His ability to make complex scientific concepts accessible and engaging inspired countless individuals, including myself, to understand the wonders of the universe better. Despite any critiques or challenges to his ideas, his legacy as a visionary and educator remains unchallenged.
However, I have always struggled with one of his most renowned quotes: “Extraordinary claims require extraordinary evidence.” Known as the Sagan standard, this phrase was first introduced by Sagan in his 1979 book Broca's Brain and reiterated in his 1980 television series Cosmos. Since then, it has been a guiding principle in scientific and sceptical discourse, suggesting that claims that deviate significantly from established understanding must be supported by equally exceptional proof. The problem stems from the subjectivity behind the word extraordinary. The online dictionary states that extraordinary means very unusual, unexpected, strange, or special. And yet, I'd argue that the quality of scientific evidence should be consistent, regardless of a claim's perceived extraordinariness. As such, evidence, no matter how exceptional, should be grounded in methodological soundness, reliability, and the applicability of the scientific process, not an arbitrary standard.
Let's take the latest development on Mars: the possible discovery of fossilized microbial life. Recently, the Perseverance rover was studying an ancient river valley, more precisely on the northern edge of the Neretva Vallis that emptied into Jezero Crater, when it stumbled upon a large rock with puzzling features - see image. The rock, named Cheyava Falls, is billions of years old and is Perseverance's most important find since it landed in Jezero Crater in February 2021 as it has "distinctive colorful spots indicative of chemical reactions that microbial life could use as an energy source, and clear evidence that water — necessary for life — once passed through the rock." said Ken Farley, Perseverance project scientist of Caltech in Pasadena, in a press release.
Cheyava Falls has been studied extensively by Perseverance since its discovery, revealing large white calcium sulfate and hematite veins covered with dozens of tiny off-white splotches, each ringed in black, which look reminiscent of leopard spots. The black rings contain iron and phosphate. Organic compounds, the building blocks of life, have been found as well. The rock seems to have been mud mixed with organic compounds and later altered by water creating the calcium sulfate veins. The "leopard spots" might have resulted from an abiotic process, most likely linked to olivine, a type of mineral. Yet, on Earth, such features would have been thought as biological in origin. To be clear, we don't know what formed these rings and we would need further studies in labs back on Earth to better understand how they formed.
Therefore, we are not yet able to claim that we have discovered life on Mars. However, just imagine, dear reader, if further analysis shows that these spots are indeed indicators of past microbial activity. Could these tiny, coloured chemical deposits found on a rock—whose origins were uncertain for many years—be considered extraordinary evidence of extraterrestrial life, the most remarkable of all claims? I'm certain not everyone would agree. So, let us set aside the "extraordinary evidence" requirement and focus on what truly matters: solid, well-earned evidence, regardless of its proportions or how it might be perceived.
Comments