Despite making up more than a third of our planet, the world’s most abundant mineral has remained nameless because scientists couldn’t find a natural sample of it to characterize. Now, concluding 50 years of dogged searching, scientists have discovered a specimen inside a meteorite that slammed into Earth in 1879, meaning that the anonymous mineral could finally be given a name. The mineral, which has been characterized in the journal Science, will now be known as bridgmanite in honor of Percy Bridgman, an American physicist and Nobel laureate.
The Earth’s lower mantle comprises more than 50% of the planet by volume and extends from 670 to 2,900 kilometers (416 to 1,802 miles) in depth. Pressures in this region begin at 237,000 times the atmospheric pressure (24 gigapascals) and even reach 1.3 million times atmospheric pressure.
Although scientists don’t know a great deal about the lower mantle, it’s thought to be largely composed of a super-dense version of magnesium iron silicate. Until now, this mineral has been nameless because scientists couldn’t find a natural sample, and the International Mineralogical Association requires that a mineral can only be named after it has been analyzed in its natural state. The reason it has been so difficult to find is that, while it makes up some 38% of Earth’s entire volume, it is extremely rare at the Earth’s surface, and it’s only typically stable at pressures found more than 670 kilometers below the surface.
Scientists were finally able to get their mitts on a natural sample thanks to an asteroid collision that took place hundreds of millions of years ago. The event created a meteorite that slammed into Australia in 1879. This meteorite was subjected to temperatures of around 2100oC (3632oF) and pressures of 24 gigapascals, which are similar to the conditions experienced deep inside our planet. After thoroughly examining the specimen, the researchers discovered microscopic pieces of the mineral buried in the meteorite’s veins. The mineral should have decayed when the rock returned to ambient temperature and pressure, but the icy temperatures of space acted like a preservative, essentially freezing it into place.
Alongside allowing scientists to finally give the mineral a name, its discovery is important because it should help further our knowledge of the region of Earth that it is found in. By analyzing the elements that fit into its crystal structure, scientists should be able to improve existing models on how the lower mantle behaves.
The mineral’s new name, bridgmanite, is in honor of Percy Bridgman, a scientist who won the 1946 Nobel Prize in Physics. Bridgman pioneered techniques that allowed scientists to synthesize and analyze minerals at pressures akin to those experienced deep within our planet.