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.
The age of the earth is one of the most contentious issues in the creation/evolution debate. Even James Ussher (1581-1656), the famous and respected Archbishop of Ireland in the seventeenth century, is today greatly ridiculed for declaring that the world was created in 4004 BC.