The earliest known life forms found on Earth are fossils of microorganisms in 3.46 billion year old rocks in Western Australia. Life forms, as microorganisms, may have lived much earlier. The earliest time that life forms first appeared on Earth is unknown. Such life forms may have lived as early as 4.28 billion years ago, not long after the oceans were formed 4.41 billion years ago, and not long after the formation of the Earth 4.54 billion years ago.