Final answer:
Scientists have determined through absolute dating that Earth is approximately 4.54 billion years old, and evidence suggests life on Earth appeared around 3.8 to 4.1 billion years ago. Eratosthenes and Aristarchus made early significant calculations about Earth's circumference and the solar system's structure.
Step-by-step explanation:
The question seems to be asking about someone's calculation regarding the age of the Earth or the start of life on Earth. If the calculation you're referring to is the estimation of the Earth's age, scientists have determined, through various methods including absolute dating, that the Earth is approximately 4.54 billion years old. This dating process establishes the exact amount of time that has passed since the Earth was formed. Historical calculations regarding the Earth's size and position, like those by Eratosthenes or Aristarchus, provide a different insight into ancient scientific achievements. Eratosthenes, for instance, calculated the Earth's circumference with remarkable accuracy using shadows and the angle of sunlight, deducing a circumference about 1/6 kilometer off the correct value of 40,000 kilometres, which was an incredible intellectual achievement of its time. Whereas Aristarchus's work suggested that the Sun was much larger than the Earth and led to the early understanding that the Earth might revolve around the Sun rather than the other way around. Concerning life's origins, it is speculated based on geological and fossil evidence that life emerged around 3.8 to 4.1 billion years ago, with discoveries of 3.95 billion-year-old rocks in Labrador supporting the idea of life originating in the earlier part of this range. This period is known as the Hadean Eon, named after the hellish conditions presumed to exist on the young Earth.