Scientists have long debated where the raw material that formed Earth originally came from. Although our planet sits in the inner Solar System, many researchers have proposed that 6-40 percent of its building material arrived from the outer Solar System, beyond Jupiter. That idea has been especially important for explaining how Earth acquired volatile substances such as water.
If those materials came from farther out, then matter must have moved between the outer and inner regions of the Solar System while Earth was forming. New research now challenges that picture. Planetary scientists Paolo Sossi and Dan Bower of ETH Zurich compared existing measurements of isotope ratios from a wide range of meteorites, including samples associated with Mars and the asteroid Vesta, with the isotopic composition of Earth.
Isotopes are sibling atoms of the same element (same number of protons) that have a different mass (different number of neutrons). Using a new approach to analyze those data, the researchers reached a striking conclusion. Their results indicate that the material that formed Earth came entirely from the inner Solar System.
Material from the outer Solar System appears to account for less than two percent of Earth's total mass, and possibly none at all. The study was published in Nature Astronomy. "Our calculations make it clear: the building material of the Earth originates from a single material reservoir," says Sossi.
His colleague Bower adds: "We were truly astonished to find that the Earth is composed entirely of material from the inner Solar System distinct from any combination of existing meteorites." The ETH Zurich team based its analysis on existing measurements from ten different isotope systems found in meteorites. Earlier studies typically focused on only two isotope systems. "Our studies are actually data science experiments," says Sossi.
"We carried out statistical calculations that are rarely used in geochemistry, even though they are a powerful tool." Meteorite Isotopes Reveal Earth's Origins Scientists have used isotopes in meteorites for decades to trace where celestial objects formed, including which region of the Solar System they came from. For many years, however, oxygen isotopes were the main tool available for identifying that origin. That changed in the early 2010s, when an American researcher showed that isotopes of other elements, including chromium and titanium, could also reveal where meteorites formed.
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