When I stand among these mighty Leviathan skeletons, skulls, tusks, jaws, ribs, and vertebrae, all characterized by partial resemblances to the existing breeds of sea-monsters; but at the same time bearing on the other hand similar affinities to the annihilated antichronical Leviathans, their incalculable seniors; I am, by a flood, borne back to that wondrous period, [before] time itself can be said to have begun; for time began with man.
Moby Dick was published in 1851; for reference Origin of Species in 1859.
This was a time in the U.S. that the northern protestant traditions were grappling with how to deal with advancements in science. They would go towards a philosophy of the Bible is allegory, in contrast to southern protestant traditions which double-downed on the Bible being literal.
This passage bemused me for the way it split the difference -- a 6,000 year old earth could well be literally true, if one presumed time (and thus the ability to measure in years) only began with Adam. Dinosaurs, and mega-whales of the past, existed before man but in a timeless age.
There was also a significant "pre-Adamite" philosophy of the time regarding the races. Against the increasing power of the Abolitionists (themselves largely organized by northern tradition churches, especially the Congregationalist and their Unitarian splinter) and the context of "We hold these truths to be self-evident, that all men are created equal," that while Adam was the first *man*, other races had been created before him and thus only whites were descendants of the first man himself.
The Descent of Man would come out in 1871, but Darwin was not firing the first salvo in the debate with that book -- rather Descent was the culmination of the debate raging in social, political, religious, and scientific circles of the first two-thirds of the 19th century.
If time did not start with the creation of Adam, but man evolved, then time itself must trace itself back through the whole sequence of events that led to the birth of that first man.