Historians usually divide time into several categories, namely


  • Day – is a duration of twenty four hours (24hrs)
  • A week – is a duration of seven days (7 days)
  • Month – is a duration of four weeks (4 weeks)
  • A year – is a duration of twelve months (12 months)
  • A decade- is a duration of ten years (10 yrs)
  • A century – is a duration of of one hundred years (100 yrs)
  • A millennium – is a duration of thousand years (1000 yrs)
  • A generation – is the average differences on ages between a child and his/her parent.
  • Age – is a period based on man’s economic activities and the type of tools used g stone age, iron age, Industrial age, Science and Technology age, ect.
  • A period – is determined by one continuous event lasting for a number of


e.g     Period of slave trade in East Africa Period of long distance trade

Period of colonial rule in Africa


Some points have been chosen in order to divide time


  • Year ZERO –present the year when Jesus Christ was
  • It is known as Anno Domino


(A.D) meaning the year of the Lord


All years before Zero are called (B.C) meaning (Before Christ) HOW TO DETERMINE DATES


Dates are instrument in the science of History, this historians divided dates into four ways: –


  1. Recalling events : – here important events are recalled/remembered g drought, farming, floods, birth, eruption of diseases etc.
  2. By studying languages: – some names help people to remember dates of some E.g word “Karafuu”- started when cloves were introduced in Zanzibar.
  3. Carbon 14 – Is scientific method of determining dates. It used in the finding dates for remains of animals or plants which died beyond 5000 years


  • Carbon 14 is a gas found in carbon-dioxide which exist in the
  • It absorbed by plant or other living organisms. When died carbon 14 that has already observed starts to decay at a fixed rate from the time of death.


  1. Orders of events: Ways of showing order of events, periods and ages, among them are: –


  • Time graph
  • Time chart
  • Time line
  • Family tree

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