it should be pointed out that it was christian geologists in search of evidence for noahs flood that first determined that the earth was old and that a flood could not have happened.
http://www.bringyou.to/apologetics/p82.htm
A History of the Collapse of "Flood Geology" and a Young Earth
From the mid-seventeenth (c. 1650 AD) to the mid-eighteenth century (c. 1750 AD), a range of British mathematicians, naturalists, and clerics from the Church of England attempted to demonstrate that belief in a global biblical deluge was perfectly compatible with extrabiblical knowledge and the latest theoretical developments in mechanistic science. They maintained that the fact that such a deluge had occurred could now be established not only on the basis of biblical authority but also on mathematical and scientific grounds. Their various theories reflected different conceptions of natural theology, the roles of science and theology, and the bearing of Scripture on the interpretation of nature. Their diluvial cosmogonies provided a mainstream scientific paradigm that stimulated hard thought, biblical exegesis, widespread geological observation, and some of the earliest geological experiments.
But if these seventeenth-century cosmogonies were on the whole plausible given the limitations of the geological science of the day, they were nevertheless seriously flawed in other ways -- perhaps most notably by the fact that their proponents based them on relatively small bodies of favorable evidence and tended to ignore damaging evidence. The cosmogonists generally avoided the insurmountable problems of animal distribution and migration, for instance, and resisted determinations that geological strata are not arranged in order of specific gravity. On the other hand, the theorists were for the most part committed to providing honest scientific accounts of physical processes associated with the flood, and they resisted making appeals to miracle in order to resolve difficulties in those accounts.
In the end, the old diluvial cosmogonies fell victim to their own success. The genuine spirit of scientific inquiry that they engendered and stimulated gradually produced a wealth of geological discoveries that undercut the premises of diluvialism. All manner of different field observations indicated that geological strata could not be the remains of layers of soft sediments deposited together at the same time. Furthermore, the plethora of exegeses of the deluge account raised doubts in many scholarly minds about whether the Bible was being properly used in trying to settle questions of geological history. By the middle of the eighteenth century, few competent proponents of diluvialism remained
