Cave diving is fraught with danger, but the reward is sights like nothing else on Earth

Exploring deep, dangerous underwater cave systems offers scientists and divers unparalleled glimpses into Earth’s history, ...
来自MSN

Caveman aliens? Martian caves could host ancient life

An ancient Martian system of canyons and valleys could be home to archaic life forms, a ground-breaking scientific paper has found. Scientists investigating the Red Planet’s mind-boggling cave system ...