He would have answered that the Earth was ancient, that there had not been a Noachian flood, and that the species of life had not been fixed over the history of Earth.In short, Genesis was an allegory and not literal history.
The great debate was won by the uniformitarians, so much so that the degree of gradualism was overstated and the importance of catastrophes was unduly minimized.The modern period has been marked by an enormous expansion of the detailed knowledge of the geological history of the Earth and the processes that have acted during that history.It was not ruled out, per se, but it was not necessary. In the new science, however, rational explanation was desirable. In 1640 Ussher produced his famous calculation that the Earth was created in 4004 BC.In 1637 Descartes produced a cosmogony that was highly influential for more than a century. It was not in their estimates of the age of the Earth - Descartes retained the biblical date.In the 1700's belief in a 6000 year old Earth crumbled.
Attempts to calculate the age of the Earth from physical considerations yielded estimates that ranged from 75,000 years (Buffon, 1774) to several billion years (de Maillet, Buffon).The rise of science produced a major change in attitude.In the pre-scientific world view the issue of the age of the Earth was a theological question.Descartes, however, attempted to discern a physical history of the Earth.His account was plausible by the immature standards of the Science of his times; however it quite definitely did not match the Biblical account of a completed creation in six days.Hutton and Lyell, who held that the history of Earth was dominated by slow relatively uniform changes in an Earth with a static over all history.