Metal Planet

Abstract

Just as we are reminded of our aquatic origins when we taste the salt of our tears, each time we reflexively lift a cut finger to our mouths, the metallic taste of blood is a reminder of our origins in an iron-rich environment. We carry many other metals, most notably copper and zinc, which also refer us back to elements available to our distant ancestors. Metals are fascinating because while some are simply toxic like lead, others like zinc and copper are both essential and toxic. For humans, metals are essential not only physiologically, particularly for proper protein function, but also economically, as these elements played key roles in the advancement of civilizations. Our idolatry of gold, silver, titanium, and other metals has, for better or worse, dramatically changed the types and amounts of metals available in the biosphere. Yet, when it comes to the history of the chemistry of metals on Earth, humans are far from the most important agents of change. We know that life evolved in an iron-rich aquatic environment relatively devoid of other metals and minerals now recognized as essential. We also know that as the earth’s atmosphere changed with the introduction of oxygen, dramatic changes in metal availability occurred as well. Metals once plentiful turned insoluble, dropping out of solution and away from life’s grasp, while others became increasingly soluble and washed into the sea, more available than ever before.

Earth formed as a heavy metal planet.

Robert Williams and J.J.R. Frausto da Silva

Life’s “addiction” to iron is thought to reflect this early evolution in an iron-rich reducing environment.

Jennifer S. Cavet, Gilles P.M. Borrelly, and Nigel J. Robinson