[music playing]NARRATOR: Earth-- a 4.5-billion-year-old planetstill evolving.As continents shift and clash, volcanoes erupt,and glaciers grow and recede.The Earth's crust is carved in countless ...

But if, on a certain day about 5.3 million years ago, you happened to go for a stroll along that mountain range, you might have discovered something odd: a trickle of water, making its way down one of ...

It isn’t easy to figure out how the Earth was built, because it happened 4½ billion years ago, and no one was there to watch. So scientists have had to look at what the Earth looks like now and at all ...