Will Perserverance find it on Mars?
Abiogenesis, the question of the origin of life on Earth, is a fascinating one and on current information we only have one data point on which to base hypotheses. The facts are that life exists on Earth in amazing variety in many different niches from the coldest, darkest oceans to the driest deserts. Yet that life in all its diversity shares much in common.
With few and very interesting exceptions, the genetic code—the way information that terrestrial organisms use to function, grow and reproduce is stored—is shared across all extant species (and in extinct species where DNA is still recoverable). I know of no other plausible explanation for this than life’s diversity radiates from a common ancestor. So far direct fossil evidence takes life back at least 3.75 billion years and molecular phylogeny suggests an even earlier date for the universal common ancestor. It is reasonable to infer that a molten Earth was sterile and that life based on carbon and water could not have existed on this planet before it was cool enough for water to condense on its surface.
So we know life on Earth began around 4 billion years ago but we do not know how. There are religious explanations: divine creation. Life could have begun elsewhere and arrived on Earth embedded in material that transported it. Life could have begun by some natural process in a favoured location, Darwin’s
…warm little pond with all sorts of ammonia and phosphoric salts, light, heat, electricity etcetera present, that a protein compound was chemically formed, ready to undergo still more complex changes…
or perhaps more plausibly in the vortex of a hydrothermal vent (some of the earliest fossils have been found in hydrothermal vent debris dated to 4 billion years ago).
We don’t lack for hypotheses regarding abiogenesis. The Wikipedia article on abiogenesis lists many references to primary sources. What we lack is further evidence to allow us to better choose between hypotheses. Until now!
Is life unique to Earth? Is Earth the only place in the vastness of the observable universe and beyond that living organisms exist or have ever existed? We have learned a lot about elsewhere just from the electromagnetic radiation that arrives from beyond Earth and we have established that exoplanets orbiting other stars are common in our galaxy. Humans have visited our own Moon and brought back rock and soil samples that indicate the Moon is—and always has been—sterile. But NASA and the USSR during the cold war years of the sixties and seventies sent probes to Mars with the Mars Global Surveyor (launched in 1996 and continuing to function until 2006) producing a spectacularly detailed survey of the Martian surface, indicating features that could best be explained by water erosion. Could our nearest planetary neighbour once have supported life? Only by landing a probe on Mars could we begin to answer that question.
The first successful deployment of an unmanned vehicle was Sojourner from the Pathfinder mission launched in 1996. Its success encouraged and informed later missions, Curiosity (which is still operating) and the latest unmanned vehicle, Perserverance.
The hope is to use another unmanned vehicle as yet unlaunched to recover the rock samples prepared by Persereverance. This new vehicle will then deliver them to a lauch vehicle intended to deliver the samples to a satellite (European, whoopee, what could possibly go wrong) and eventually to land on Earth in 2031. Then we shall have our second data point.
|Mars is sterile||Life on Earth is unique hypothesis strengthened|
|Molecules closely related to life on Earth||Panspermia, common source for life on Earth and Mars|
|Evidence of life unrelated to that found on Earth||Life evolved separately on Mars, so life is likely to be teeming across the universe|
Maybe we will not need to wait until samples can be recovered and brought back to Earth. Perserverance is also tasked with “seeking signs of possible past microbial life in those habitable environments, particularly in special rocks known to preserve signs of life over time”.
Unless Perserverance finds signs that can be unequivocally interpreted as evidence of past life, we have perhaps another ten years for those samples to return to Earth and for us to examine the evidence for our second data point. Fingers crossed.