The evolution of minerals on our planet has been propelled by the evolution of life on earth, a sweeping new study demonstrates. While the underlying assumption isn't new, the study is the first to chart how the emergence of algae and then complex microorganisms gave rise to the 4,300 or so minerals that are now present on earth. In the early days of the universe, clouds of gas and dust contained all the naturally occurring elements found in the periodic table, but most were too widely dispersed to form minerals; scientists believe there were only about
a dozen minerals in the interstellar medium. According to the study, around a further 60 different minerals formed 4.5 billion years ago, as clumps of matter collided and coalesced to begin forming the Solar System. The smaller fragments congealed into larger, planet-sized bodies, where volcanism and the effects of water took the mineral count into the hundreds. The planets Mars and Venus have got this far [Nature News],
and have minerals created by hot magma like quartz and zircon. In the study, published in American Mineralogist [subscription required], lead researcher Robert Hazen says that the earth's plate tectonics further increased the mineral count, but it was the origin of life around 4 billion years ago that really boosted the diversity of rocks on our planet.
Photosynthesising organisms created abundant atmospheric oxygen. Under this oxygen-rich environment, the chemical processes of oxidation and weathering generated a swathe of new species of metal-rich minerals, such as iron. "Four billion years ago, metals on the surface like iron and copper remained pure and shiny," says Hazen. "But the new atmosphere oxidised them, creating a host of new minerals" [New Scientist].
As complex microorganisms evolved in the ocean, the calcium-rich shells and bones of marine creatures fell to the seafloor and were compacted into a new mineral known as calcite. Meanwhile, on the land, the roots of plants created acids that converted minerals of volcanic origin into clays. Researchers say that understanding what the presence of certain minerals indicates about the presence of life could yield rich rewards in the study of other planets.
With NASA’s Messenger probe now going into orbit around Mercury, Dr Hazen predicts that it will find only 300 or so minerals on the planet. If there are 500-1,000 detected, then it will suggest that there is a lot more to Mercury than anyone originally thought. And if minerals that depend upon life for their formation show up, then researchers will be flummoxed. The same is true for Mars and other planets—including the exoplanets that have been known about but which have just been seen for the first time orbiting stars outside the Solar System [The Economist].
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Image: flickr/ Gaetan Lee