The stones date back 4.16 billion years to the Hadean era and are the oldest known rocks on the planet. Earth’s early days–and rocksEarth was a ball of molten lava when it first formed about 4.5 billion years ago. Scientists originally believed that Earth’s first eon–the Hadean–ended when the first rocks formed. They found that both chronometers indicated that the rocks are 4.16 billion years old. Since the planet Earth formed roughly 4.5 billion years ago, this puts the rocks within a few hundred million years of our planet’s earliest day–somewhat close in geological time.