The drift of the last glaciation was deposited during one of the most recent epochs of geologic time, the Pleistocene, which lasted from 1.8 million to 10,000 years ago.
This drift has been studied extensively in many animals and in biological activities ranging from the hatching of fruit fly eggs to wheel running by squirrels.
To quote one medical opinion, "Thousands of people drift through life suffering from the effects of too little sleep; the reason is not that they can't sleep."