The “Blueberries” That Predicted an Ocean

The Great Basin Desert harbors enigmatic sandstone marbles that have already helped prove that Mars once had oceans. The geological mystery story starts on the Red Planet, where the robot rover Opportunity went trundling across the surface looking for signs of water and beamed back to Earth images of perplexing stone nodules, perfectly round rocks the size of blueberries scattered across the rust-red Martian surface in the equatorial plain of Meridiani Planum.

Geologists were puzzled until they discovered that University of Utah researcher Marjorie Chan predicted Opportunity would find those “blueberries” after she spent eight years studying similar stones in southern Utah.

Spacecraft orbiting Mars had previously detected surface deposits of hematite, a form of iron that on Earth forms only in water. Chan’s enigmatic stone nodules in Utah also proved rich in hematite. She concluded these concretions precipitated out of iron-rich water inside layers of saturated sandstone and grew into perfect spheres as they dissolved a little niche in the surrounding rock. On Mars, the sedimentary rock matrix for the blueberries was made of finely crushed layers of volcanic rock.