Scientists first make observations that raise a particular question. In order to explain the observed phenomenon, they develop a number of possible explanations, or hypotheses. This is the inductive part of science, observing and constructing plausible arguments for why an event occurred.
As indicated earlier, the Bible does not fix the age of the earth, contrary to the claims of Answers in Genesis. Historically, their claim comes from the work of James Ussher, Bishop in the Church of Ireland, from 1625 to 1656.
Many people (known as Young-Earth Creationists) believe that the only valid interpretation of the Bible indicates that the Earth is 10,000 years old or less, and they also claim to have scientific evidence that supports this view of the Earth.