Scientists have nearly doubled the kinds of known minerals on Earth in two studies that could help solve the mystery of how life emerged on Earth, and whether it exists elsewhere in the universe.
Minerals are a diverse group of compounds that act as the building blocks of planets, making them an essential part of the story of life’s emergence on Earth and, potentially, other habitable worlds. Roughly 6,000 mineral species are recognized by the International Mineralogical Association, but a pair of scientists have now expanded that number to more than 10,500 by introducing what they call a “evolutionary system of mineralogy,” in twin studies published on Friday in the journal American Mineralogist.
“The tradition in mineralogy has been to consider each mineral species” by its “idealized chemical composition and idealized crystal structure,” said Richard Hazen, a mineralogist at the Carnegie Institution for Science and lead author of the studies, in a call. “But that tells you nothing about when the minerals formed, how they formed, or the context of each mineral specimen in planetary evolution” which can include “the coevolution of life and rocks.”
Hazen added that there is value in this traditional minimalist system for many scientific fields, but that researchers interested in the interactions of minerals with each other, and with life, require a richer framework that incorporates the origin stories of these assorted materials. With that in mind, Hazen and co-author Shaunna Morrison, who is also a mineralogist at the Carnegie Institution for Science, meticulously cataloged 57 formation pathways for minerals—or “paragenetic modes,” in the words of the studies—that include being boiled, crushed, transformed by life, or forged by human activities.
The team found that about 59 percent of minerals form from only one known paragenic mode, but that some of them can spring up from all kinds of different processes. Water is the dominant driver in the formation of a whopping 80 percent of minerals, whereas life is involved in about half of all pathways, with a third of minerals only derived from biological processes. More than 600 minerals arise from human activities, mostly from mining and coal mine fires, and guano—the poop of birds and bats—helps to create 72 minerals.
Pyrite, also known as fool’s gold, holds the record with 21 different formation pathways, while diamonds have nine different origins here on Earth, and in space. The new classification system includes these mineral mode counts—for instance, there are 21 entries for pyrite—which is why the researchers ended up with more than 10,500 “mineral kinds” that each reflect a unique “mineral genome,” Hazen said.
“When you talk about the mineral genome, we're talking about all the attributes, all the properties, that make each mineral a historic object,” he explained. “Every mineral is a time capsule just waiting to be opened. It's got a history and that history is embedded in the rocks.”
“The thing that amazes me about minerals is they're the only objects you can hold in your hand that are hundreds of millions, or billions, of years old,” Hazen continued. “If we're interested in planetary history that goes back in our case, more than 4.56 billion years, the only way we can know about that, through a tangible object that we can study in the laboratory, is with minerals. Times in history are really important in the context of minerals, and understanding not just where planets came from, but where we came from.”
To that point, Hazen and Morrison hope that their new research will help explain how life arose from natural minerals on Earth, and inform the search for aliens on other worlds. One big insight included in their studies, along these lines, is that about 3,500 minerals are thought to have formed within the first 250 million years of Earth’s lifespan, which demonstrates that our planet was mineralogically rich at a young age.
This finding raises the question of how many other extraterrestrial worlds are also seeded with the mineral ingredients for life, and whether it is likely that any of them have likewise nurtured aliens with these abiotic materials.
“This has to do with the whole philosophical question of: Are we unique?” Hazen said. “What this suggests to me is that a great deal of the chemistry that occurs at, or near, the surface of an Earth-like planet is deterministic. It is going to happen over and over and over again and anytime you replay the tape, you're going to see the same things.”
“My gut feeling, knowing how diverse the environments are on Earth, and how early so many different mineral-forming environments arose, that probably is true for organic chemistry as well,” he concluded. “If you do get life very readily on an Earth-like planet if the right kind of chemistry occurs, I think there's no impediment to that kind of chemistry occurring.”