A theoretical biologist and a mineralogist are at a Christmas party. The former turns to the later and asks: “Were there clay minerals during the Archean Era?”
This isn’t the setup to a joke, but rather a real event that occurred in 2006 when Harold Morowitz (the theoretical biologist) pressed Robert Hazen (the mineralogist) on what kinds of elements might have been present during the origin of life on Earth. Morowitz wanted to know this because clay minerals have long been thought important for sequestering and protecting the organic molecules that would eventually self-assemble into early microbes. But the question ended up being pivotal for another reason.
“To my knowledge, no mineralogist had ever asked, ‘Did Mineral X occur at Period Y,’” recalls Hazen, a researcher at the Carnegie Institution for Science in Washington D.C.
After some sleepless nights, and a year of development with other collaborators, Hazen produced a paper in 2008 tracing the evolution of minerals on our planet, showing how an initial group of roughly 420 mineral species turned into the 5,000 types seen today. Perhaps most importantly the research suggested that, directly or indirectly, living organisms were responsible for greatly increasing this diversity; biological processes were necessary in creating more than two-thirds of the known minerals on Earth.
“As a mineralogist that’s a shocking statement,” says Hazen. “We were trying to think about how minerals contributed to the origin of life but ended up learning how life contributed to the origin of minerals.”
Along with blowing everyone’s mind, the idea of mineral evolution has proven to be a fruitful avenue of research. Subsequent work has shown that the Earth possesses a unique mineralogical pattern; many minerals can be found all over our planet, but thousands of rare species are confined to only one or two places. Mathematical models have estimated the number of ‘missing minerals’ still waiting to be discovered. Such ideas could also help in the search for life on other worlds. A place like Mars, for instance, would display different mineral characteristics if it once had a biosphere or if it didn’t. Perhaps more than anything, the field has illuminated an important aspect of the universe — the drive to diversification and complexity extends beyond living organisms; it seems to be a fundamental process acting on many scales and substances.
Just after the Big Bang, there were no minerals; the cosmos was filled with little more than hydrogen and helium. But once the first generation of stars exploded as supernovas, they ejected elements like carbon out into the universe, allowing crystals of the first ur-minerals to form.
“Perhaps a dozen mineral species emerged, including graphite (a form of pure carbon that’s used as pencil ‘lead’), corundum (most familiar as ruby and sapphire in its colored forms), and moissanite (a tough compound of silicon and carbon that’s often used as a cheap substitute for diamond gemstones). These ancient species of crystals still fall to Earth today in the form of microscopic interstellar dust, left over from the great nebula that formed the Sun and planets more than 4.5 billion years ago,” wrote Hazen in a piece for Aeon in 2014.
When our Sun was born, it heated and melted dust grains in the proto-solar nebula that gave rise to our solar system, generating about 60 different minerals that are now commonly found in chondrite meteorites. As these bits collided and stuck together, the impact, melting, and accreting created around 250 mineral species — the raw mineralogical material for the Earth and other terrestrial planets. Quartz (beach sand) and the first clay minerals appeared around this time. After our planet coalesced and differentiated into a core, mantle, and crust, internal pressure and plate tectonics began reworking rocks into ever more complicated forms over the course of about a billion years, leading to about 1,500 minerals.
Primitive microbial communities formed around 3.8 billion years ago and began altering their local environments, leaving behind banded iron formations in rocks as well as other mineralogical records of their behavior. When photosynthesizing algae released oxygen into the atmosphere roughly 2.5 billion years ago, copper, iron, manganese, uranium, and countless other elements could now combine with oxygen into new states. This “likely represents the single most important event in the diversification of Earth’s mineralogy,” Hazen and his co-authors wrote in their 2008 paper, leading to thousands of never-before-seen mineral species.
Later biological evolution allowed even more minerals to form. The advent of shells, bones, and teeth in complex life after the Cambrian explosion created new minerals containing calcium carbonate and calcium phosphate. When plants conquered the land, their root systems broke apart the ground, increasing the number of clay minerals by an order of magnitude. Many microbial communities precipitate out uncommon minerals of gold, iron, and copper through their activity. Today, the geochemical cycle of almost every element on Earth is affected by living creatures in some way.
The varied, intricate forces shaping minerals in the timeline above suggest that a significant number are the result of historical accident. “Were Earth’s history to be replayed, and thousands of mineral species discovered and characterized anew, it is probable that many of those minerals would differ from species known today,” wrote Hazen and his co-authors in a 2015 paper examining this issue. Another paper published that year looked at the number of minerals yet to be discovered on Earth, finding that perhaps 1,500 minerals — a whopping one-quarter of the total estimated mineralogical diversity on our planet — are currently unaccounted for.
To that end, researchers have organized efforts to scope out rare minerals deep in the Earth’s crust. The longest-running is the Deep Carbon Observatory (DCO), a project Hazen started that is dedicated to characterizing how carbon moves through both the biological and geological realms of our planet. The DCO has found eight new carbon minerals; including one, tinnunculite, that only forms when falcon poop bakes in the hot gases of a coal fire.
Earth is not the only planet with applications from mineral evolution. Hazen recently joined the Mars Curiosity rover’s CheMin instrument team, where he hopes to use statistical methods to predict the mineralogical patterns of the Red Planet. A world that once had life would display very different results than one that was always dead.
“You can look at a planet and never find a fossil,” says Hazen. “Yet the distribution of minerals on the surface might be a kind of fossil record of a biosphere. That’s an astonishing statement.”
This story was originally published on the defunct website now.space on 02/06/2017