May 24, 2007—With summer travel season upon us, we're taking a closer look at Yellowstone National Park—and we do mean closer.

Straddling Wyoming, Montana, and Idaho, this vacation mecca calls to mind bears, wolves, and other "megafauna." But recently a team of explorers went in search of a wild world that's decidedly mini.

Watch Yellowstone's strangely beautiful microscopic life-forms cavort in superheated water more acidic than battery acid, and see why the tiny creatures are so unique they warrant a whole new branch on the tree of life.