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  Section: Introduction to Botany » Evolution
 
 
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The First Organisms

 
     
 
Content
Evolution
  Early Changes in Thought
  Charles Darwin
  The Tenets of Darwinian Theory
  Other Theories of Evolution
  The First Organisms
  Prokaryotic Life
  Eukaryotic Life
  The Emergence of Seed Plants
  Grasses
  Human Life
  Life over Time

The first organisms to appear on earth were the blue-green algae, the cyanophytes. If life had only one beginning, then every other living thing (and all those that are extinct) derived from this single beginning. Thus, life would be monophyletic in origin. Some are highly skeptical of such a theory, however, and prefer to postulate that life arose a number of times, perhaps many times. In this case, life would be polyphyletic in origin. For the time being, the answer remains in the realm of philosophical speculation.

Early plant forms are known only through the fossil record, and, thus, much is uncertain. Not only is the fossil record incomplete, but the kinds of plants that were subject to becoming fossils grew in low elevations; in places of abundant moisture; and where they could be carried downstream and deposited at the bottoms of lakes. Plants that grew in higher, dryer places rarely became fossilized. It is with such plants, however, that evolution took place most rapidly. And it is at higher elevations that angiosperms had their origins. Unfortunately we have thus far been denied the chance to study their beginnings in detail.

Another handicap of the fossil record is that plants composed entirely of soft tissues decay; their chances of fossilization are thereby also largely denied. Fossil algae and fossil thallophytes are, thus, less widely known, although there does exist some evidence of them.

 
     
 
 
     



     
 
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