Some of the oldest rocks ever discovered shed light on Earth's early history

Earth is approximately 4.5 billion years old, according to estimates. However, rocks dating back to the planet's earliest days are extremely rare. Hence the excitement over the discovery in northern China of some of the oldest known rocks on Earth, dating back 3.95 billion years. And one of the reasons for all the attention is that they're revealing new clues about how Earth's crust formed and evolved.