Reactions to On the Origin of Species man to be envious of a naturalist like myself, immeasurably his inferior!" Darwin's had estimated that erosion of the Weald would take 300 million years, but in the second edition of "On the Origin of Species" published on 7 January 1860 he accepted that it would be safer to allow 150 million to 200 million years. Geologists knew the earth was ancient, but had felt unable to put realistic figures on the duration of past geological changes. Darwin's book provided a new impetus to quantifying geological time. His most prominent critic, John Phillips, had investigated how temperatures increased with depth
On the Origin of Species only the last chapter still to write. In September the main title still included ""An essay on the origin of species and varieties"", but Darwin now proposed dropping "varieties". With Murray's persuasion, the title was eventually agreed as "On the Origin of Species", with the title page adding "by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life". In this extended title (and elsewhere in the book) Darwin used the biological term ""races"" interchangeably with ""varieties"", meaning varieties within a species. He used the term broadly, and as well as discussions of "the several