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Precambrian life was small and aquatic.docx

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REN R360
Melanie Muise

Precambrian life was small and aquatic  Life was confined to oceans and all organisms were small.  Over the Precambrian the shallow seas slowly began to teem with life.  For most of the Precambrian, life consisted of microscopic prokaryotes (eukaryotes evolved 2/3 of the way through the era).  Unicellular eukaryotes and small multicellular animals fed on floating photosynthetic microorganisms.  Small floating organisms, plankton, were eaten by slightly large animals.  Other animals ingested sediments on the seafloor and digested the remains of organisms within them.  By late Precambrian, many kinds of multicellular soft-bodied animals had evolved. Life expanded rapidly during the Cambrian period  Cambrian period (452-488 mya) marks the beginning of the Palaeozoic era.  The O 2oncentration was approaching its current level; the continents had come together to form several large land masses.  The largest, Gondwana.  A rapid diversification of life took place  Cambrian explosion.  Most of the major groups of animals that have species living today appeared during this period.  THE ORDOVICIAN (488-444 MYA) o The continents, located primarily in the S. Hemisphere, still lacked multicellular plants. o Evolutionary radiation of marine organisms during early stages. o At the end, massive glaciers formed over Gondawa, sea levels were lowered about 50 meters, and ocean temperatures dropped. o About 75% percent of the animal species became extinct, probably because of these major environmental changes.  SILURIAN (444-416 MYA) o Northernmost continents coalesced, but the general positions did not change much. o Marine life rebounded o Animals able to swim and feed above the ocean bottom appeared for the first time. o No new major groups of marine life evolved. o The tropical se
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