About 4 billion years ago, oceans were able to form because cyanobacteria appeared volcanic outgassing protect the surface from meteorite bombardment the moon's gravitation cooled the earth the sun's radiation declined

Because Cyanobacteria appeared

Cyanobacteria's excrement formed a lot of oxygen in the atmosphere which make the earth temperature cold

This allow a liquid water to formed on the surface ( because if the temperature is too high, the water will evaporate) and eventually formed oceans

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Answerequatorial guinea,gabon, and western sahara;