From Early Earth Biogeodynamics to Exoplanet Geoastronomy

Abstract

Experiencing an international childhood, and an innate curiosity of learning the origin of himself and his surroundings, Steve Mojzsis set out to try his best to make sense of the universe he was born into. This quest will never be fulfilled, but it doesn’t prevent him from trying. The ultimate prize is to figure out how the biosphere came into being. The path towards learning began with adventures mostly in North America and Central and Western Europe. To find himself still further meant going, to Africa, Asia and Australia, with expert guidance from the best mentors along the way. Ever the bridge builder, he was not satisfied with staying within one narrow discipline of science for very long before trying a hand at something else, albeit related. In this way he stumbled into biogeodynamics and geoastronomy; we will probably not see spectacular developments in either of these nascent fields until the end of 21^st century or long after he is returned to some mineral salts, CO₂ and H₂O. Back on his home world, it is evident that in its first 500 Myr (q.v. Hadean eon) Earth’s crust co-existed with liquid water; it was affected by late accretion bombardments and harboured chemically diverse hydrothermal systems. Globally active volcanism powered by a hotter mantle, impact generated topography and inherent differential buoyancy of the crust means that scattered emergent land masses existed irrespective of different estimates for plausible Hadean ocean volumes. Consequently, land surfaces in the first few hundred million years – with diverse subaerial and (sub-)aqueous environments – could bring prebiotic chemical ingredients to reactive concentrations. This active chemistry led to the first life. Yet, the inferred complexity for even the minimum biological entity probably means that both operative and persistent biology in a planetary environment is the most difficult developmental stage to reach. Soon after Earth’s formation, its surface had the capacity to host fully fledged (i.e. living) biochemistry. While life emerged at the dynamic interface of the planet’s primordial geosphere, hydrosphere and atmosphere, nobody knows whether any Hadean environment was ideally suited, or merely good enough, to facilitate its emergence. Given that we do not have time machines to go back and see what happened on Earth, or anywhere else for that matter, we are compelled to tell stories that fit the data. That said, comfortable fictions about what “might” have happened, just because somebody said something (without evidence), ought to be taken with a grain of salt. If we ever are to come up with a plausible pathway to a life giving world, it will be more metaphorical than literal. All of this will likely change if we find an independent origin of life, either on purpose or, more likely in Mojzsis’ opinion, by accidental discovery of something strange in the data.