In the spring of 2020, an amazing relic was discovered in a remote region of the Sahara desert: an ultra-rare chunk of an embryonic planet that existed before Earth was born.
Known as Erg Chech 002 (EC 002), the meteorite was forged within the crust of an ancient protoplanet, a small celestial body that serves as a building block for planets. The volcanic space rock is “the oldest known lava” that has ever fallen to Earth and offers an unprecedented glimpse of planetary formation in the early solar system, according to a study published on Monday in Proceedings of the National Academy of Sciences.
Scientists led by Jean-Alix Barrat, a professor of geochemistry at the University of Western Brittany in France, jumped at the opportunity to examine this extraordinary time capsule from the infancy of the solar system, which belongs to the andesitic family of volcanic rocks and is unlike anything that has been seen before.
“When we saw the first descriptions of this rock, it was really obvious that this rock was unusual,” Barrat said in an email. Given his past research on another rare andesitic meteorite, described in a 2014 study, Barrat and his colleagues were also aware that the EC 002 was potentially very old.
“The age was not the sole point of interest,” he noted. “We were extremely interested by the genesis of such extraterrestrial andesitic melts and on the processes of formation of primordial crusts. Such samples are extremely precious.”
Named after its landing site within Algeria’s Erg Chech dune sea, EC 002 consists of several meteorites that collectively weigh about 70 pounds. The stones, which contain stunning crystals, were found in May 2020, but earthly erosion of the extraterrestrial rocks suggests that they fell in the desert much earlier.
“It is not a meteorite freshly fallen on Earth,” confirmed Barrat. “It is slightly weathered, but we know since the study of the Tatahouine meteorite that terrestrial weathering is fast even in the Sahara.”
After procuring samples of the meteorite, Barrat and his colleagues were able to pin down when this piece of protoplanet crust, which was partially melted as lava, crystallized into a solid form.
Analysis of magnesium and aluminum isotopes in the rock revealed that it dates back about 4.566 billion years, making it “the oldest known piece of an igneous crust” ever found, reports the study. For comparison, the next oldest igneous meteorite, called NWA 11119, is about 1.24 million years younger than EC 002, while Earth itself began to emerge several million years after the formation of these rocks.
In addition to its unrivaled age, EC 002 is also notable for its unusual composition. The meteorite is 58 percent silicon dioxide, a telltale sign that its ancient parent body had a crust made of andesite rock, which is distinct from basalt, a more familiar igneous material that is common in volcanically active regions on Earth.
Barrat and his colleagues note that these andesitic crusts were probably abundant in asteroids and protoplanets during the solar system’s early days, but that they have become extremely scarce in the billions of years since that bygone era. Ancient protoplanets were either incorporated into larger bodies such as Earth or were blasted apart by collisions with other rocks in the tumultuous and crash-prone period of our solar system.
“EC 002 is clearly distinguishable from all asteroid groups, and no object with spectral characteristics similar to EC 002 has been identified to date,” the team said in the study, adding that remnants of primordial crusts are “not only rare in the meteorite record, but they are also rare today in the asteroid belt.”
“This suggests that the earliest differentiated protoplanets that populated the solar system, as well as most of their debris, were certainly destroyed or subsequently accreted to the growing rocky planets, making the discovery of meteorites originating from primordial crusts an exceptional occurrence,” the researchers noted.
The team estimates that EC 002 was ejected from its parent body by one of these encounters mere decades after the protoplanet’s crust cooled and crystallized, revealing amazing new details about the evolving embryos of planets during a time before Earth existed.
Barrat said that he and his colleagues, as well as other teams, are working to confirm the age of EC 002 with other isotopic studies. Researchers also want to study the crystals inside the rock, which are older than the surrounding volcanic material.
“If we know the compositions of the magmas produced during the early magmatic activity of a protoplanet,” he concluded, “we can deduce a lot of things on the building of its crust.”
Update: This article has been updated to include comments from study lead Jean-Alix Barrat.