Mars Kept a Secret for 3.5 Billion Years – NASA’s Curiosity Rover Finally Dug It Up

Scientists have long believed that Mars once had a thick, carbon dioxide-rich atmosphere and flowing liquid water on its surface. According to that theory, the CO₂ and water should have reacted with the planet’s rocks to form carbonate minerals. But until recently, surface analyses by rovers and orbital instruments using near-infrared spectroscopy hadn’t detected the expected levels of carbonate.