4.6-Billion-Year-Old Chunk Of Protoplanet Landed In The Sahara

A piece of the Erg Chech 002 meteorite. Image credit: Maine Mineral and Gem Museum/Darryl Pitt.

A meteorite discovered less than a year ago in the Sahara desert might be the oldest example of crystallized lava in the Solar System. Analysis of the many fragments of this space rock suggests that they become solid million of years before Earth formed, giving us clues to what the very beginning of planetary formation must have been like.

A study published in the Proceedings Of The National Academy Of Sciences details the properties of meteorite Erg Chech 002, which was found in the Algerian region of the Sahara known as Erg Chech in 2020. This region is well known for its meteorites. Back in 2007, 100 kilograms (220 pounds) of meteorites were discovered there. Erg Chech 002 weighs in at 32 kilograms (70.5 pounds). Fun fact: space rocks or material become meteors if they enter (and burn up) in Earth's atmosphere, and meteorites if they hit the ground. 

The team has estimated the age of the space fragments to be 4.565 billion years, about 20 million years older than our own planet, and older than the previous record-holder by 1 million years. The Solar System was just 2 million years old when this rock formed.

The researchers believe that what we are seeing is a chunk of the crust of a protoplanet. If our understanding of planetary formation is correct, gas and dust that surrounded the young Sun grew into pebbles, and by smacking into each other those rocks became protoplanets.

Protoplanets are objects that are far too small to be fully-fledged planets but large enough that interesting geological processes take place. In the case of Erg Chech 002, the protoplanet was similar in composition to carbon-rich asteroids but its crust was lava for a period before this meteorite solidified. Finding bits of the crust of these ancient bodies is rare because eventually, the Solar System's protoplanets ended up colliding and turning into Mercury, Venus, Earth, and Mars.

About 3,100 known meteorites are from the crust or mantle of these ancient celestial bodies. The vast majority of these are made of basalt. Erg Chech 002 is instead made of a mineral known as andesite. The finding suggests that these protoplanets with crusts of andesite were not rare, but they most likely ended up being the building blocks of the major rocky planets. There is no other object like this meteorite in our record.

“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 authors wrote in the paper.

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