<P> The oldest known sundial is from Egypt ; it dates back to around 1500 BC ( 19th Dynasty ) , and was discovered in the Valley of the Kings in 2013 . Sundials have their origin in shadow clocks , which were the first devices used for measuring the parts of a day . Ancient Egyptian obelisks , constructed about 3500 BC , are also among the earliest shadow clocks . </P>
<P> The oldest known sundial is from Egypt ; it dates back to around 1500 BC ( 19th Dynasty ) , and was discovered in the Valley of the Kings in 2013 . Sundials have their origin in shadow clocks , which were the first devices used for measuring the parts of a day . Ancient Egyptian obelisks , constructed about 3500 BC , are also among the earliest shadow clocks . </P>
when did humans start keeping track of time
when did humans start keeping track of time
about 3500 BC
about 3500 BC