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					| Late Precambrian (Proterozoic) Life |  
					| Lecture 16 3/23/98
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					| |  | On Friday, we looked at evidence for life in the Archean (3.8 - 2.5 Ba) and the impact of life on the planet. | 
 |  | Today we will look at a major event in life history that took place in the Proterozoic (2.5 - 0.5 Ba), the evolution of eukaryotes. | 
 |  | There is very little fossil evidence of early eukaryotes. Most of this evolution is inferred from biochemical studies | 
 |  | Complex eukaryotic cells evolved after O2 began accumulating in the atmosphere. | 
 |  | Eukaryotic cells paved the way for the multicellular organisms that evolved near the end of the Precambrian | 
 |  | Differences between eukaryotes and prokaryotes | 
 |  | Respiration and Photosynthesis | 
 |  | The origin of the nucleus | 
 |  | DNA is suseptible to UV light | 
 |  | The nucleus may have been a defense mechanism to limit the impact of UV light on DNA | 
 |  | The origin of Mitochondria and Chloroplasts | 
 |  | Similarities between these organelles and bacteria | 
 |  | Both contain prokaryote style DNA | 
 |  | Both Mitochondria and Chloroplasts use biochemical pathways for protein synthesis that are similar to prokaryote pathways. | 
 |  | Mitochondria and Chloroplasts have an independent reproductive mechanism. | 
 |  | A difficult problem because of the costs involved. | 
 |  | limiting damage caused by mutations | 
 |  | increased genetic variability | 
 |  | increased rates of evolution | 
 |  | Metazoan fossils dating from 565 - 543 million years | 
 |  | First described in Australia, but have since been found all over the world | 
 |  | Soft-bodied fauna preserved as casts or molds at the base of sand beds | 
 |  | Trace fossils of worms are also common. | 
 |  | Originally, Most of the fossils were interpreted to represent types of Cnidarians (anemones and jelly fish). | 
 |  | One fossil Kimberella, has recently been interpreted as a precursor to the Mollusks. | 
 |  | Spriggina, may be an arthropod precursor | 
 |  | Others, however, are unlike any other modern animals. | 
 
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