Final answer:
Oceans formed at the end of the Hadean eon and the beginning of the Archean eon, around 4 billion years ago, as Earth cooled and developed an atmosphere.
Step-by-step explanation:
The oceans were formed in the early history of Earth. After Earth's formation about 4.5 to 4.6 billion years ago, it initially was molten, lacking an atmosphere and oceans. As the planet cooled, it developed a solid crust, and volcanoes released gases that contributed to the formation of an atmosphere. This atmosphere contained water vapor, among other gases, which condensed and fell as rain, contributing to the formation of the oceans. The first evidence of liquids on Earth's surface appears to be from the end of the Hadean eon, marking the beginning of the Archean eon, around 4 billion years ago. This eon provided the medium from which life, such as the photosynthetic cyanobacteria, eventually emerged.
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