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Late Precambrian (Proterozoic) Life
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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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