An overview of the History of Life on Earth



This is the Sargasso Sea in the western Atlantic Ocean.
It is unusual because it has a lot of seaweed
growing in it and floating on the surface.
Click on image for full size version (120K JPG)
Image courtesy of Aris Multimedia Entertainment, Inc. 1994
Of the three basic categories of life on Earth, bacteria have dominated terrestrial forms of life much longer than multi-cellular organisms. Consider the following ages:
  • the oldest fossils of bacteria/archaea are 3 billion years old.
  • the oldest multi-celled creatures are 500 million years old.
  • the earliest signs of homo sapiens are 200 thousand years old.

The forms of life which came into being may have something to do with the changing environment of the Earth over geologic time. The order of developing life seems to be:

  • bacteria to complex cells-
    • around 2.5 billion years
  • cells to colonies (or bodies), where each cell does not do the same as another cell, but cells become specialized for handling different things for the body as a whole-
    • unknown period
  • development of a complex nervous system (intelligence)-
    • this process seemed to be finished by the Triassic period on Earth, when the dinosaurs roamed freely.
  • intelligence to mammals and Homo Sapiens-
    • this process seemed to take around 250 million years on Earth.
Thus, on Earth, there was a very long time when only the most primitive forms of life existed.



An overview of the History of Life on Earth



This is the Sargasso Sea in the western Atlantic Ocean.
It is unusual because it has a lot of seaweed
growing in it and floating on the surface.
Click on image for full size version (120K JPG)
Image courtesy of Aris Multimedia Entertainment, Inc. 1994
The oldest life on Earth seems to be the bacteria. Consider the following ages:
  • the oldest fossils of bacteria/archaea are 3 billion years old.
  • the oldest multi-celled creatures, like jelly-fish, are 500 million years old.
  • the earliest signs of humans are 200 thousand years old.

The forms of life which came into being may have something to do with the changing environment of the Earth over geologic time. The order of developing life seems to be:

  • bacteria to complex cells-
    • around 2.5 billion years
  • cells to colonies (or bodies), where cells become specialized for handling different things for the body as a whole.
    • an known period of time
  • The development of a nervous system (intelligence)-
    • this process seemed to be finished by the time when the dinosaurs roamed freely.
  • intelligence to mammals and Homo Sapiens-
    • this process seemed to take 250 million years on Earth
Thus, on Earth, there was a very long time when only the most primitive forms of life existed.



An overview of the History of Life on Earth



This is the Sargasso Sea in the western Atlantic Ocean.
It is unusual because it has a lot of seaweed
growing in it and floating on the surface.
Click on image for full size version (120K JPG)
Image courtesy of Aris Multimedia Entertainment, Inc. 1994
The oldest things on Earth seemed to have been bacteria. Consider the following ages;
  • the oldest fossils of bacteria/archaea are 3 billion years old.
  • the oldest multi-celled creatures, like jelly-fish, are 500 million years old.
  • the earliest signs of humans are 200 thousand years old.
The forms of life might have come into being because of changes in the environment of the Earth over time. Life seems to have taken nearly 2.5 billion years to develop from bacteria into complex cells, a very long period of time with only very primitive life.




Last modified January 18, 1999 by the Windows Team

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