Products of life on Earth: Some natural raw gem stones including amethyst, tourmaline, ruby and quartz.
Credit: iStockphoto
SYDNEY: Geologists have found that Earth's 'mineral kingdom' has co-evolved with life, and that up to two thirds of the more than 4,000 known types of minerals can be directly or indirectly linked to biological activity.
The authors of the study, published in the current edition of the journal American Mineralogist, say the find could aid scientists in the search for life on other planets.
"For at least 2.5 billion years, and possibly since the emergence of life, Earth's mineralogy has evolved in parallel with biology," said lead author Robert Hazen. "One implication of this finding is that remote observations of the mineralogy of other moons and planets may provide crucial evidence for biological influences beyond Earth."
"Biological influences"
Hazen, Dominic Papineau and colleagues at the Carnegie Institution of Wasington DC, reviewed the physical, chemical, and biological processes that gradually transformed about a dozen different primordial minerals, found in ancient interstellar dust grains, into the thousands of mineral 'species' on the Earth today.
"It's a different way of looking at minerals from more traditional approaches," said Hazen.
"Mineral evolution is obviously different from Darwinian evolution — minerals don't mutate, reproduce or compete like living organisms. But we found both the variety and relative abundances of minerals have changed dramatically over more than 4.5 billion years of Earth's history."
All the chemical elements we are familiar with were present from the start in the Solar System's primordial dust, but they combined together to form comparatively few minerals.
Primordial dust
Only after large bodies such as the Sun and planets were born did there exist the extremes of temperature and pressure required to forge a large diversity of mineral species, the authors said. Many elements were also too dispersed in the original dust clouds to be able to solidify into mineral crystals.
As the Solar System took shape through the "gravitational clumping" of small, undifferentiated bodies (fragments of which are found today in the form of meteorites), about 60 different minerals made their appearance, the study says.
Larger, planet-sized bodies, especially those with volcanic activity and bearing significant amounts of water, could have given rise to several hundred new mineral species. Mars and Venus – which the experts estimate to have at least 500 different mineral species in their surface rocks – appear to have reached this stage in their mineral evolution.
However, Earth is the only planet that we know of where mineral evolution progressed to the next stage.
A key factor was the churning of the planet's interior by plate tectonics, write the authors, the process that drives the slow shifting continents and ocean basins over geological time.
Unique to Earth today, plate tectonics created new kinds of physical and chemical environments where minerals could form, and thereby boosted mineral diversity to more than a thousand types.
What ultimately had the biggest impact on mineral evolution, however, was the origin of life, approximately four billion years ago.
Unique perspective
"Of the approximately 4,300 known mineral species on Earth, perhaps two thirds of them are biologically mediated," says Hazen. "This is principally a consequence of our oxygen-rich atmosphere, which is a product of photosynthesis by microscopic algae."
Many important minerals are oxidized weathering products, including ores of iron, copper and many other metals.
Microorganisms and plants also accelerated the production of diverse clay minerals, the study says. In the oceans, the evolution of organisms with shells and mineralised skeletons generated thick layered deposits of minerals such as calcite, which would be rare on a lifeless planet.
Gary Ernst a geologist at Stanford University in California, USA, who was not involved with the research, called the study "breathtaking," and commented that the "the unique perspective presented in this paper may revolutionise the way Earth scientists regard minerals."
With the Carnegie Institution.
