A team of geologists from Curtin University has proposed a hypothesis suggesting that the formation of Earth’s first continents was partly driven by the Solar System’s passage through the spiral arms of the Milky Way. The researchers cite the isotopic composition of ancient zircon minerals as evidence. Their study has been published in the journal Earth and Planetary Science Letters.
The Solar System orbits the center of the Milky Way approximately every 250 million years. Roughly every 150–200 million years, it crosses the galaxy’s spiral arms—regions of high gas and dust density where intense star formation occurs.
When passing through an arm, gravitational instability can disrupt the Oort Cloud—a vast spherical shell of icy bodies at the outer edge of the Solar System—sending comets hurtling toward the inner Solar System. The study’s authors propose that such impacts contributed to the formation of the first stable fragments of continental crust.
The team analyzed zircons from eleven Archean cratons across various continents. Hafnium isotopes in the zircons revealed episodes of new crust formation, while oxygen isotopes showed traces of the recycling of pre-existing material. Synchronous shifts in isotopic ratios were identified across samples from different cratons; the researchers compared these shifts with the predicted timing of spiral arm crossings and data regarding crater formation on Earth and the Moon.
The authors emphasize that, at this stage, they have identified a correlation between independent datasets rather than a proven cause-and-effect relationship. They plan to continue their research by looking for similar signals in minerals from Mars and the Moon. The logic is straightforward: if the pattern is galactic in origin, it should be evident there as well.
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