Earth’s ‘mineral kingdom’ evolved hand in hand with life
* 19 November 2008 by Marcus Chown
AS LIFE evolved in all its abundance and diversity, so too did the minerals that make up Earth’s rocks. Two-thirds of the kingdom of minerals bear the traces of the presence of life – a view that could shake up our picture of Earth’s geological history and even help find life on other planets.
“Rocks and life evolved in parallel,” says Robert Hazen of the Carnegie Institution’s Geophysical Laboratory in Washington DC. “It’s so obvious – you wonder why we geologists didn’t think of it before.”
According to Hazen, the story begins with a mere 12 minerals that existed in the dust grains of the pre-solar nebula – minerals such as diamond, created in the fury of supernova explosions. When the sun ignited, heat boosted the number to around 60. The formation of Earth and subsequent geochemical processes upped that to around 500, and the switching on of the conveyor belt of plate tectonics led to the creation of another 1000. “But it was life, which made its first appearance about 4 billion years ago, that made the biggest difference,” says Hazen. “It boosted the number of minerals to around 5000.”
Life brought profound changes to Earth’s atmosphere and ocean chemistry. Photosynthesising organisms created abundant oxygen, and in this environment the chemical processes of oxidation and weathering generated a swathe of minerals containing metals such as iron. “Four billion years ago, metals on the surface like iron and copper remained pure and shiny,” says Hazen. “The new atmosphere oxidised them, creating a host of new minerals.” Approximately half of all known mineral species owe their existence to oxidation or weathering.
Gary Ernst at Stanford University in California describes the study as “breathtaking” and says it could revolutionise the way minerals are described. “No one until now has put the story together in such a coherent way,” adds David Saja, curator of mineralogy at the Cleveland Museum of Natural History in Ohio.
Anyone want to write the equivalent of the ancestor’s tale that discusses the co-evolution of minerals and life, and not only how coal formed but the feedback mechanisms that led to skeletons, gall stones and gout.