For centuries, scientists believed that animals and minerals lived in two separate worlds. Then, four years ago, a groundbreaking study led to a dynamic realization: Life on Earth radically altered the way minerals formed on our planet. Last year, a major research journal devoted an entire issue to analyzing the idea, and now the science of studying minerals and understanding Earth as a planet has been radically shaken up.
Nearly
3,000 minerals that contain significant oxygen atoms would not have
existed on Earth without life making large amounts of oxygen available
in the "Great Oxidation Event," some 2.5 billion years ago. This
includes many attractive species like rhodochrosite, a collector's
favorite (this specimen, 14.5 cm, comes from the Pincushion II Pocket,
Fluorite Raise, Sweet Home Mine, Mount Bross, Alma Dist., Park Co.,
Colorado). Photo credit: David J. Eicher.
The evidence shows that microbes on Earth exploded the number of mineral species beginning about 2.45 billion years ago in what has come to be known as the “Great Oxidation Event.” Prior to that time, microbial photosynthesis happily produced lots of oxygen, but organic matter and dissolved iron captured it. The tipping point came when these minerals became saturated and lots of free oxygen atoms began to accumulate in the atmosphere — about 1 percent of the oxygen in our present-day atmosphere.
That brought on momentous change. With so much oxygen now able to combine with existing minerals (and boy, does oxygen like to react), the number of species exploded over time from about 1,500 (about the number that could exist on Mars) to our present-day 4,400+. On came numerous oxides, carbonates, sulfates, silicates, and many others that were now hydrated in new combinations. Over time, the mineral world tripled in size. Other effects came, too: By producing so much free oxygen, cyanobacteria unleashed the greatest extinction event in Earth’s history by killing off a huge percentage of the planet’s anaerobic microbes.
We know that chemistry is consistent throughout the universe. Temperatures, pressures, and other local conditions change, but the laws of chemistry — of how atoms combine in crystal lattices — are the same. So on one level, Earth minerals give us a glimpse of what minerals on other planets may look like. But we can now suggest that living planets host a much broader and far more complex suite of minerals than nonliving ones. On alien planets, could we recognize whether life exists or once existed there by the minerals that inhabit its landscape?
Stay tuned for coverage of this amazing subject of planetary science in a future issue of Astronomy. And thanks to my friend Paul Pohwat of the Smithsonian Institution, manager of the world’s largest mineral collection, for emphasizing this research to me. It’s an incredible chapter now opening up in understanding how planets work.