Energy Use versus Time

  The  history of man's  emergence  from the  ecological  niche, 
  appropriate to medium size omnivorous mammals, to his present 
  position as the  earth's  dominant  species is  attributed to 
  his  increasing  skill in  harnessing and manipulating energy. 
  Each  stage of his  evolution has been marked by an extension 
  of his  ability to control the natural flows and  accumulated 
  energy resources. Initially, he used only food energy, as did 
  all  other  species of animals. Primitive man's use of energy 
  was of the  order of  2000 kcal/day,  mainly as  food  energy. 
  Hunting  man used some fuel wood for heating and cooking, his 
  use of energy  being about  3000 kcal/day. Early agricultural 
  man  used  animate  sources  of  energy  for  agriculture and 
  transportation, with  his  consumption  roughly  being  about 
  three  times that of hunting man. Gradually,  man  discovered 
  new  ways of using  energy  supplies to his own  advantage by 
  controlling  fire, growing  crops  and  domesticating animals. 
  Cultural  development  led to the use of other energy sources 
  and  increase  in  human  population. Thus, the  influence of 
  energy  availability is seen in the form and structure of the 
  human society itself.
  
  In a subsistence agricultural economy, majority of the people 
  spend most of their time working to obtain the food necessary 
  for their own  survival. Agriculture is essentially a process 
  by  which the  stored  energy  of  photosynthesis is directed 
  towards  man. It begins with the selection and cultivation of 
  plants. Irrigation, manure  and  fertiliser have enabled  him 
  to  maximise food production. With these, he has opened wider 
  the  gates  of  photosynthesis,  through  which  solar energy 
  becomes  his  food. The  domestication  of  animals widen the 
  control  of  natural  energy  flows. With this  domestication, 
  grasslands  have  become  energy  gatherers. Grass  otherwise 
  cannot  be  used by  man as fuel or food. With  domestication, 
  the  cattle is allowed to graze, and the  subsequent milk and 
  meat  produced  is  used  by  man. Muscle  energy is used for  
  ploughing, to lift water and  for  transportation. The use of 
  human  beings  as  slaves  was  a   feature  of   the   early 
  civilisation. They were given energy only in the form of food 
  for the work carried out. Both the slave and domestication of 
  animals  were precursors of the mechanical  engine: they were 
  means of converting the energy of food or fuel into work. 

  Village and urban  settlements were common by 2000 BC and the 
  pace  of  change  gradually increased. The growing ability to 
  harness  energy  and  therefore  reliable  food supplies gave 
  impetus to civilisation. Gradually, around 100 BC, waterwheel  
  (in the  West, China  and  India) and  windmills (in the Arab 
  countries) acquired  the  place  to  provide  energy  in  the 
  medieval  economy. This  hastened  the  pace  of  social  and 
  technical development. Tapping of fossil fuels like coal, oil, 
  etc.,  led  to  an  endless  catalogue  of  achievements  and 
  conquests of the physical world. This  led to the  industrial 
  revolution.  In  the  nineteenth  century ,  a  host  of  new 
  inventions took place in response to the growing availability 
  of energy,  for harnessing more energy sources. This resulted 
  in  advancement of science  and  technology and emergence  of 
  many  disciplines  like  civil,  structural,  mechanical  and 
  electrical  engineering. But, a declining trend  in available 
  stock  of  fossil fuels like coal, oil and natural gas in the 
  later  half of the  nineteenth  century has  necessitated the 
  search  for  viable  alternatives. In  looking at the earth's 
  energy  resources, it  is  necessary  to  go  beyond the mere 
  question  of  their  absolute  magnitude or their theoretical 
  potential, if the technology to harness them could be devised. 
  The  practical availability of energy resources is limited by 
  social,  geographical,  political,  economic  and   technical 
  constraints .  Abundant  coal  resources  in  Russia  or  oil 
  resources in middle east and constraints  associated in using 
  these  resources  by  other countries have clearly shown that 
  proving  the  existence of resources does not always  promise 
  accessibility to everyone.