Biblical dating standards
The catastrophists (Cuvier 1812, de Beaumont 1852, Buckland 1836) accepted that the Earth was old; they disagreed with the kind of change and the rate of change that had occurred over that long history.
There was no single estimate of the Earth's age in the mid 1800's and no good way to arrive at one.
The account in Genesis is replete with miracles that do not stand up under rational analysis.
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.The second is that the rates of the physical processes in question are variable and knowledge of them was incomplete.In the late 1800's physicists, armed with a more advanced physics than that available to Descartes, made new estimates of the age of the Earth and the Sun.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 physical models were open to question and, in retrospect, were naive. It became quite clear that many areas of the Earth had alternated between being land and being covered by seas, that there had been extensive slow sedimentation, that the mountains had not been created in situ as is but rather had a long history of slow deformation, and that long periods of erosion had shaped the Earth everywhere.