Tag Archives: andesite

The oldest meteorite ever found is older than the Earth itself

The meteorite, which was discovered in the Algerian part of the Sahara Desert, dates from 4.6 billion year ago — before the Earth was truly formed. It’s one of the first building blocks of our solar system. It’s not just any old meteorite: analysis shows it formed volcanically so it was once part of a proto-planet, maybe even one that never really made it.

A piece of the meteorite. Image in public domain. Credits: A. Irving.

“Numerous stones containing distinctive large greenish crystals were found in May 2020 near Bir Ben Takoul, southern Algeria, within the Erg Chech sand sea,” reads a rather dull entry regarding the meteorite. But right from the get-go, researchers knew something was unusual.

No known asteroid looks like EC 002 (the official name of the meteorite) — because almost none of these ancient relics still exist. Since they were formed so long ago, they’ve been either reintegrated into planets or smashed to bits. Meteorites like EC 002 are also very rare, due to its composition.

Most meteorites we’ve found so far are chondritic: stony (non-metallic) meteorites that haven’t been melted. Meanwhile, EC 002 is essentially an igneous rock — an andesite, to be more precise, which is also unusual. Out of the over 50,000 meteorites discovered so far, just 3,179 are not chondrites. Out of these, most are basalts, which makes EC 002 very rare.

Basalt is a common igneous rock not just on Earth but also elsewhere in the solar system. It’s formed by the rapid cooling of basaltic lava, often at the surface (or very close to the surface).

Andesite shares some similarities to basalt, but it has a different chemical make-up and is characteristic of areas where tectonic plates are either sliding by each other or being destroyed one under another. This makes it even rarer because it takes a very special set of circumstances for andesite to reach meteorites. But the surprises kept coming in.

The rock was once molten, and it solidified some 4.565 billion years ago, in a parent body that accreted 4.566 billion years ago. The Earth is 4.54 billion years old, so it’s already older than the Earth. We’re not sure where it formed, but whatever celestial body it formed on, it must have been in its very early days, a part of its primordial crust.

“This meteorite is the oldest magmatic rock analysed to date and sheds light on the formation of the primordial crusts that covered the oldest protoplanets,” the researchers wrote in their paper.

Further analysis also showed that it took the lava over 100,000 years to solidify, indicating that the lava must have been unusually viscous. A lava’s viscosity is given by its temperature, chemical composition, and volatile gas content, so already, geologists can infer certain properties.

It’s always difficult when studying something so old, but finds like this can help shed new light on how our corner of the universe formed and evolved.

The study was published in PNAS.