For years, scientists studying Mars have wondered why its surface looks the way it does. Now, a new study of the Red Planet suggests that billions of years ago, an enormous region of volcanoes ejected so much lava that the weight actually caused the uppermost layers of the planet to shift.

The study published in the journal Nature focuses on a region called the Tharsis Bulge. The enormous plateau is about half the size of France and was created nearly 3.5 billion years ago. For hundreds of millions of years, the volcano-covered region spewed more than a billion billion tons of molten lava from the mantle onto Mars’ surface, creating the Tharsis Bulge, Charles Quoi reports for Space.com. But the Tharsis Bulge originally formed at a high latitude—as the lava piled on, the sheer weight caused Mars' topmost layers to shift around.

“If a similar shift happened on Earth, Paris would be in the polar circle,” study author and geomorphologist Sylvain Bouley tells the Agence France-Presse (AFP). “We’d see northern lights in France, and wine grapes would be grown in Sudan.”

Deposits of water ice that had formed at the planet’s poles and equatorial canyons carved by ancient rivers shifted as well, in a phenomenon called “true polar wander,” Quoi writes. “Scientists couldn’t figure out why the [dried up] rivers were where they are. The positioning seemed arbitrary,” Bouley tells the AFP. “But if you take into account the shift in the surface, they all line up on the same tropical band.”

This theory differs from scientists' past explanation for Mars’ surface, which was that the same eruption that created Tharsis Bulge carved the channels. But this didn't explain their seemingly-random positioning.

Bouley’s study, however, suggests that the rivers actually formed while the volcanoes that created the Tharsis Bulge were in their infancy, Marcia Bjornerud writes for The New Yorker. As they spewed magma, the volcanoes began to cool off. And without the volcanic gases to resupply Mars’ atmosphere, the planet’s rivers would have evaporated into space.

Bouley’s work suggests a new path for Mars’ geologic history, and there is still more out there for scientists to discover. If the Tharsis Bulge shifted the planet’s surface, the question of what else it altered still remains.

“Did the tilt cause the magnetic fields to shut down? Did it contribute to the disappearance of Mars’s atmosphere, or cause the rivers to stop flowing?” Bouley tells the AFP. “These are things we don’t know yet.”