Respuesta :
Answer is 82.6, nearly 83%.
Before oxygen came into being, the oldest growing and dividing microbe appeared on Earth nearly 3.8 billion years ago. Taking Earth's age as nearly 4.6 Billion Years, instead of 13.7 from Big Bang, unicellular life appeared nearly 3.8 ago. This percentage is 3.8/4.6 X 100 = 82.6%, of time has life existed on earth.
