01 Nov 2021
The search for our deepest origins is one of the most challenging and yet rewarding endeavours humanity has ever undertaken. For more than half a century now, scientists have strived to find the holy grail; the oldest fossilised living organism or the chemical by-products of such living organisms. As expected, such an endeavour is not without its controversies as it pushes the boundaries of science to the limit and different schools of thoughts have emerged. The two main theories for where life started on Earth are commonly known as Darwin’s Pool, where life originated in pools of water that underwent wet-dry cycles, and the Primordial Soup, where life originated deep within our oceans aided by deep sea alkaline vents.
Yet, scientists searching for the very first traces of life face a formidable adversary; Earth itself. Every few hundreds of millions of years, the very ground upon which we step on gets recycled deep within the mantle where extreme pressures and temperatures erase all traces of organic matter. This recycling of the Earth’s crust is so thorough that rocks older than three billion years old are few and far between. As a result, finding traces of early life is a rare occurrence.
Currently, the oldest undisputed trace of life on Earth are microfossils and stromatolites found in Western Australia that date from 3.5 billion years ago (the Archean era). It is more than likely that life arose before this, and while claims of earlier life are put forward, the evidence is often questionable and our limited knowledge of the conditions of our planet during the early Archean and Hadean eras lead to a lack of consensus in the final interpretation. As such, the oldest disputed trace of life are microfossils 4.3 billion years old found in 2017 in Canada; just a few hundred million years after the formation of our planet.
However, there is another way to search for early life on Earth. Instead of looking down, some researchers think we should look up...at the Moon! Indeed, while Earth is constantly resurfacing itself, the Moon has remained relatively unchanged for billions of years. And since we have found on Earth pieces of the Moon, the planet Mars and even distant asteroid Vesta, the lunar surface should also be littered with Earth rocks. Actually, a rock fragment returned back from the Moon by Apollo 14 was found to be composed of quartz, feldspar, and zircon, all commonly found on Earth and highly unusual on our natural satellite. Some planetary scientists now believe that this rock collected 50 years ago on the lunar surface was indeed formed on Earth 4.0-4.1 billion years ago, during the late heavy bombardment (end Hadean/early Archean), a period where tens of thousands if not millions of Earth rocks were blasted off into space.
Would fossilised life and its by-products be able to survive such an ordeal and then crash onto the Moon unchanged? Some scientists such as Mark Burchell from Kent university have been studying this hypothesis and by putting microscopic fossilised algae (diatoms) under extreme conditions, have shown that it is indeed plausible. (After all, the famous Mars meteorite ALH84001 found in Antarctica was initially thought to show signs of fossilised Martian life).
With nations eager to go back to the Moon (NASA’s Artemis, etc.) and SpaceX’s Starship becoming a reality, humanity is on its way to put boots on the lunar surface once more. It will then only be a matter of time until astronauts pick up more Earth meteorites scattered upon the lunar surface, and if enough of these rocks are found, maybe, just maybe, one of these will hold clues of life’s origins back on Earth.
Who knows? Lunar paleontologist might become a profession in the near future. I’d sign up for that. Would you?