Time and Change by John Burroughs — Read

If we figure to ourselves the geologic history of the earth under the symbol of a year of three hundred and sixty-five days, each day a million years, which is probably not far out of the way, then man, the biped, the Homo sapiens, in relation to this immense past, is of to-day, or of this very morning; while the origin of the first vertebrates, the fishes, from which he has arisen, falls nearer the middle of the great year. Or, dividing this geologic year into four divisions or seasons, primary, secondary, tertiary, and quaternary, the fishes fall in the primary, the reptiles in the secondary, the mammals in the tertiary, and man in the early quaternary.

If the fluid earth hardened, and the seas were formed in the first month of this year, then probably the first beginning of life appeared in the second month, the invertebrate in the third or fourth, -- March or April, -- the vertebrates in May or June, the amphibians in July or August, the reptiles in August or September, the mammals in October or November, and man in December, -- separated from the first beginnings of life by all those millions upon millions of years.