When did the first oceans appear?

Zircon crystals provide evidence that the first ocean formed during the Hadean eon, between 4.4 and 4 billion years ago. Originally, there was only one ocean, because there were no continents to divide it into smaller parts. It was green because of the vast amounts of iron dissolved in it, until the first photosynthetic organisms created oxygen, which bound to the iron, creating rust that sank to the sea floor, leaving the oceans blue like they are today.