Mars Was Once a Water World | COSMOS in a minute #24

Mars was once a wet world with lakes of liquid water on its surface, and there's a great deal of evidence about it. This evidence includes ancient river valleys, craters filled with water ice, minerals that form in water, and dark streaks that appear on Mars's surface during the warm season. While the evidence is clear that Mars once had liquid water, it is unclear when or why it disappeared. Some scientists believe Mars's climate changed, making it too cold for liquid water to exist on the surface. Others believe that Mars's water was lost to space. Whatever the reason, the evidence is clear that Mars was once a much wetter place than it is today. This finding has important implications for the search for life on Mars, as liquid water is essential for life as we know it. For more videos of Cosmos in a minute, follow The Secrets of the Universe. #cosmosinaminute