Mineralogy’s link to ecology makes an Earth twin unlikely

PHILADELPHIA — The odds of finding another planet with Earth’s exact mineral composition are astronomically long, a mineralogist using tools borrowed from ecology calculates.

Reproducing Earth’s mineral makeup elsewhere has a 1 in 10²⁰⁰ chance of success, Robert Hazen of the Carnegie Institution for Science in Washington, D.C., said December 6 at the annual meeting of the American Society for Cell Biology. That is because the evolution of minerals has been so closely tied to the development of life.

Hazen and colleagues first proposed in 2008 that about two-thirds of minerals couldn’t exist if it weren’t for living organisms (SN: 12/6/08, p. 10). The new calculations have implications for astronomers looking for signs of life on other planets.

“There basically aren’t any Earth-like planets from a mineralogical point of view,” Hazen said. Planets that harbor life are likely to have a wider variety of minerals than barren planets do. But no other life-bearing planet is likely to have had the same chemical, physical and biological conditions that led to the creation of Earth’s 4,937 known minerals —rocks that have specific chemical formulas and crystal structures.

Even replaying Earth’s own history would probably change the identity of about 25 percent of the planet’s minerals, Hazen said.

Hazen and colleagues conducted a survey of minerals using a method similar to how ecologists canvas species: They cataloged the types and abundance of minerals in about 125,000 locations around the world.

About 22 percent of minerals are found in only one locality, Hazen and colleagues discovered. One of those, Hazenite, named for Hazen, is a phosphate mineral made only by microbes that live in Mono Lake in California. More than half of known minerals are found in five or fewer spots.

About 1,500 minerals remain to be discovered, Hazen said he and his colleagues predict. Using ecological strategies may help mineralogists learn where to look for new types and even predict which types of minerals should be found in any given location, he said.

There’s no question that biology and geology are intimately tied to each other, says Jennifer Lippincott-Schwartz, a cell biologist at the National Institute of Child Health and Human Development in Bethesda, Md., and the president of the cell biology society. “All of the major metabolic pathways have minerals at their core,” she said.