For decades, astronomers have been trying to understand the origin of the material that makes up Earth and the other rocky planets in our solar system. Two models have been proposed: the Wetherill-type accretion model, which suggests that most of the building material comes from the inner solar system, and the Pebble accretion model, which suggests that the raw materials come from the outer solar system. To determine which model is correct, researchers have compared the isotopic abundances of certain elements on Earth to those in different types of meteorites.

• Isotopic signatures in meteorites

Anomalies in the isotopic abundances of certain elements can serve as a signature of the origin of a planet's building material. To determine if the building blocks of Earth come from the inner or outer solar system, researchers have analyzed the isotopic abundances of certain elements in samples of Earth and in different types of meteorites. Carbonaceous and non-carbonaceous chondrites are particularly useful for this purpose because they formed in different parts of the solar system.

• Potassium and zinc in meteorites

Two recent studies have focused on the origin of potassium and zinc on Earth. In the first study, researchers measured the isotopic abundances of three potassium isotopes in 28 meteorites (10 carbonaceous and 18 non-carbonaceous) and compared them to those on Earth. They found that the isotopic signature of potassium-40 on Earth matches that of non-carbonaceous meteorites, suggesting that most of Earth's potassium comes from the inner solar system, with less than 20% coming from carbonaceous meteorites from the outer solar system.

• The origin of zinc on Earth

In the second study, researchers measured the isotopic abundances of five stable isotopes of zinc in 18 meteorites (7 carbonaceous and 11 non-carbonaceous) and compared them to those on Earth. They found that the isotopic signature of zinc on Earth suggests that it comes from a mixture of carbonaceous and non-carbonaceous meteorites, with roughly half coming from each type. This is in contrast to the findings for potassium, which suggests that it mainly comes from non-carbonaceous meteorites.

• Implications for the formation of the solar system

These studies provide new insights into the origin of Earth's elements and the formation of the solar system. The finding that potassium mainly comes from non-carbonaceous meteorites supports the Wetherill-type accretion model, which suggests that the building blocks of the inner solar system formed through collisions of planetesimals made of grains from this region. The finding that zinc comes from a mixture of carbonaceous and non-carbonaceous meteorites supports the Pebble accretion model, which suggests that the building blocks of the solar system formed from pebbles that migrated from the outer solar system.

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