Here’s what you’ll learn when you read this story:

• There have been ongoing arguments about whether the components of Earth originated from the inner or outer Solar System.
• Researchers who analyzed variations in isotopes from meteorites found that Earth almost exclusively matched the variants found in the inner Solar System.
• Jupiter is probably to blame for this, since the formation of the gas giant likely created a gravitational barrier that almost no materials from the outer Solar System could pass.

Earth is a rocky amalgamation of materials. As far as we can tell, the formation of Earth took one of two primary paths. On the first, debris from the inner Solar System formed our young planet billions of years ago (along with terrestrial worlds such as Mars and Venus). On the second, the stuff of Earth was flown over by comets and asteroids from our cosmic backyard’s furthest reaches.

Planets form primarily by accretion. It is thought that Earth took around 30 to 40 million years to accrete, slowly collecting planetesimals and other space rocks that slammed into each other. After all of that was said and done, whatever was left over would have become asteroids and meteorites.

Planetary scientists Paolo Sossi and Dan Bower, of ETH Zurich, wanted to know if the rocks that built Earth originated within the inner Solar System, or if there was interference from the outer Solar System. So, they turned to nucleosynthetic isotope anomalies to figure this out. Because of the different components of stardust scattered throughout the cloud that birthed our planet, anomalies occur in meteorites and planets that bear those chemical signatures. Sossi and Bower analyzed variations in anomalies found in meteoritic, planetary, and other space rocks—including fragments from the asteroid Vesta and meteorites that broke off from early Mars.

“The identification of two, distinct populations of meteorites from their mass-independent isotopic compositions, the ‘isotopic dichotomy’, has precipitated a revolution in our understanding of the provenance of planetary materials and, in turn, the spatio-temporal evolution of the early Solar System,” the team said in a study recently published in the journal Nature Astronomy.

Meteorites come in two main flavors—carbonaceous (high in carbon) or non-carbonaceous (low in carbon)—and are generally typed through isotope analysis. Carbonaceous chondrites are generally from the outer Solar System, are high in water, and are studded with chondrules (embedded fragments) of other carbonaceous rocks like diamond and graphite. Non-carbonaceous meteorites, on the other hand, are generally from the inner Solar System. Different nucleosynthetic processes, which create atomic nuclei from protons and neutrons, have resulted in minuscule differences between carbonaceous and non-carbonaceous meteorite species.

The Solar System became divided into two regions of materials during its formation, and Jupiter probably had something to do with conflicting meteorite content. When Jupiter came into being, immense amounts of gas and dust—most of it left over from the formation of the Sun—were pulled together by gravity to create the swirling orb. As it fell short of the mass it would have needed to become a star, Jupiter remained a gas giant whose gravity, but one whose was so extreme that it tore the molecular cloud that was incubating its star and surrounding planets. Jupiter’s bulk blocked material from the outer regions of the Solar System from reaching the inner regions, creating a divide that would influence the composition of objects on either side of it. While there have been questions surrounding how much, if any, protoplanetary material was able to sneak past Jupiter, Bower, and Sossi found that barely any ended up in our planet.

The lack of material from beyond Jupiter can imply only one thing. Most of Earth was made from material that originated in the inner Solar System and took the form of a planet 4.6 billion years ago. While the materials themselves are heterogeneous, Earth as a whole is relatively homogeneous, in the sense that almost all of the dust and rock that created it came from one place.

But if there was barely any carbon incorporated into the planet to begin with, what gave rise to carbon-based life-forms? It is thought that most of Earth’s water was brought by impactors from the outer Solar System in the late stages of its formation or slightly after it formed, so maybe much of the carbon came along with it.

“Our analysis shows that all elements, irrespective of their geochemical character or nucleosynthetic origin, record the same isotopic [origin],” the researchers said. “The composition of [Earth] is therefore defined as homogeneous with respect to isotopic anomalies.”