The bulk elemental composition of Earth can’t be fully explained by compositional differences in its initial building blocks, according to a new study by Paul Frossard and colleagues. Instead, they suggest that Earth’s composition was modified as cosmic collisions eroded the crust of Earth and its smaller building blocks as the planet was accreting. Their findings could have implications for how terrestrial planets outside the Solar System may have been modified during their own creation, as Zoë Malka Leinhardt notes in a related Perspective. Stony meteorites called chondrites represent the earliest building blocks of the Solar System. Their elemental composition is similar to that of Earth, but there are some intriguing differences, including an abundance of the isotope neodymium-142 on Earth compared to the meteorites. Frossard et al. analyzed a set of non-carbonaceous and carbonaceous chondrites to determine why this difference might exist. After accounting for the fact that there can be isotope variations in planet-building materials due to which part of the original solar dust cloud these materials came from, the researchers conclude that collisions that eroded crust from Earth’s building blocks are the most likely path to its unique elemental composition.
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