Passing through the Milky Way’s arms may have helped form Earth’s solid ground
Our planet’s journey through the galaxy syncs up with the rhythm of long-ago crust formation
![illustration of the Milky Way](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2022/09/090922_kk_comet-crust_feat.jpg?fit=1002%2C580&ssl=1)
Every 200 million years, the solar system passes through a spiral arm of the Milky Way (illustrated). Those encounters may have played a role in forming Earth’s first continental crust.
MARK GARLICK/SCIENCE PHOTO LIBRARY/Getty Images