Medical brain notes 33

  ORIGIN OF LIFE - Theories   Origin of life   Our planet earth is inhabited by an enormous variety of living organ-isms. The plants and animals show remarkable biodiversity. The diversities mostly appear as adaptations for diverse habitats and living methods adopted. This vastness has always made people wonder about the origin of life and diversity. To a certain extent Charles Darwin's natural selection concept pro-vides an explanation towards an understanding of evolution of various kinds of life forms. However the theory of origin of life is still a matter of speculation. Several intelligent explanations had been provided to account for the origin of life on earth.     1.  Theory of special creation   According to the proponents of this theory all living forms with their richness in diversity were created abruptly by a super natural power. The support or acceptance of this theory is mostly due to faith rather than experi-mental or scientific evidenc...

  Geological time scale :  Palaeozoic era, Mesozoic era, Cenozoic era   Geological time scale   The oldest known rocks are about 3.8 billion (3800 million) years old. It corresponds to 38, 000, 000 centuries. According to Geologists and Geo-physicists our planet earth is 4.7 billion (4,700 million) years old.   In this ancient time scale evidenes showed that the first life originated 2.5 billion (2,500 million) years ago. Hence from the formative stage for nearly 2,200 billion years there was no life on earth . Such a period in earth's history is known as the  Azoic era  (2,200 to 5,000 billion years ago). Evidences show that during this era the earth was a hot sphere. Gradually the upper surface of the earth cooled down. It resulted in solidifica-tion and formation of rocks and rocky terrain. Further water molecules were formed resulting in accumulation of water and water reservoirs as water masses and land surface were established. These transformati...