- Steinbach meteorite
- 4,565,470,000 year(s)
- Germany ()
Achondrites are a relatively rare group of meteorites that lack chondrules (small round grains that form in space then accrete into a larger body) - instead forming under igneous processes such as melting and recrystallisation, lending them a similar appearance to terrestrial rocks such as basalts. Many of them are ancient, forming in the early years of the Solar System as planets and moons began to emerge, offering us vital insights into that little-understood period. The oldest known example of an achondrite meteorite is the Steinbach meteorite - a 98-kg (216-lb) IVA iron meteorite found in Germany in 1724. Using Pb-Pb radiometric dating, scientists established an age of 4,565.47 million years (give or take 0.3 million years). This is older than Earth itself, which is thought to have formed c. 4.5 billion years ago. The findings were published in Earth and Planetary Science Letters on 13 August 2019.
There are several types of achondrite meteorite, which include both stony and stony-iron examples, classified by their chemical, mineralogical and textural characteristics. The main classification groups are: primitive, asteroidal, lunar and Martian.
It is rare to find such ancient rocks on Earth, as plate tectonics have continuously recycled the planet’s crust. To put the discovery in context, the oldest rock formed on Earth – samples of bedrock from the Nuvvuagittuq greenstone belt on the eastern shore of Hudson Bay in Canada – is c. 4.28 billion years old.
The oldest igneous rock found on Earth is also an achondrite meteorite: Erg Chech 002 (EC 002), found in the desert of south-west Algeria in May 2020, was dated at c. 4.565 billion years old, as reported in Proceedings of the National Academy of Sciences on 16 March 2021.
The research was conducted by the Centre for Star and Planet Formation at the University of Copenhagen, Denmark, by J N Connelly, M Schuller and M Bizzarro.