The second is that the rates of the physical processes in question are variable and knowledge of them was incomplete.
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.
There were various attempts to estimate the Earth's age, working back from sedimentation rates and other geophysical phenomena.
The attempts produced estimates from about 100 million years up to several billion years. The first is that the geological history was still being reconstructed.
Notable observations included: ran from about 1780-1850.
By the end of the 18'th century it was clear that the Earth had a long and varied history. The major debate was between the catastrophists, e.g., Cuvier, who held that the history of Earth was dominated by major catastrophic revolutions and the uniformitarians, e.g.
If, in the year AD 1600, you had asked an educated European how old the planet Earth was and to recount its history he would have said that it was about 6000 years old and that its ancient history was given by the biblical account in Genesis.