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It is not surprising that humans have wondered how long Earth has existed. At one extreme, there were the Brahmans of India who believe that Earth never had a beginning and will never have an end. Others were of the opinion that Earth was old, but perhaps not eternally old. In 450 BC, for example, a Greek historian named Herodotus (484 - 425 BC) expressed the opinion that Earth was very old, basing his estimate on the results of his studies of the Nile Delta. He observed that the delta was growing layer by layer as a result of the Nile's yearly floods. He concluded that the building of the Nile Delta must have taken many thousands of years. About 500 BC, the Greek philosopher Xenophanes (570 - 475 BC ) observed fossil shells encapsulated in rocks. He properly interpreted them as being the remains of animals that once lived in an ocean that covered the land a great many years ago. But even with such insights, no one attempted to put a specific number of years on Earth's age.

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