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.
By this method, the age of oceans will equal the total salt in oceans (in grams) divided by rate of salt added (grams per year). Age of Earth was calculated to be 90-100 million years. Problems: no way to account for recycled salt, salt incorporated into clay minerals, salt deposits. 1  In 1860, the thickness of total sedimentary record is divided by average sedimentation rates (in mm/yr) and calculated to be about 3 million years old.