Precambrian Period.docx

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Department
Biomedical Engineering
Course Code
BMEN 515
Professor
William Huddleston

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Precambrian Period  During the Precambiran period, life consisted of microscopic prokaryotes; eukaryotes probably evolved about two-thirds of the way through the era. o Unicellular eukaryotes & small multicellular animals fed on floating photosynthetic microorganisms  Shallow Precambrian seas teemed with life, including protists and algae.  By the late Precambrian, many kinds of soft-bodied invertebrates had evolved, some of which may be members of animal lineages that have no living descendants. Cambrian Period  Cambrian period marks the beginning of the Paleozoic era  By the early Cambrian period (543–490 mya), atmospheri2 O levels had nearly reached current levels.  The continental plates came together in several masses. Gondwana was the largest land mass.  The rapid diversification of life that took place at this time is referred to as the Cambrian explosion.  The best fossils of Cambrian animals are found in China.  A mass extinction occurred at the end of the Cambrian period.  Fossils tell us only about the hard parts of organisms o 3 Cambrian fossil beds- the Burgess Shale (British Columbia), Sirius Passet(Northern Greenland) & Chengjiang (southern China) o Arthropods are the most diverse group in the Chinese fauna Paleozoic Era  Divided into the Ordovician, Silurian, Devonian, Carboniferous, and Permian periods o Each period is characterized by the diversification of specific groups of organisms o Mass extinctions marked the ends of the Ordovician, Devonian, and Permian The Ordovician (488-444 mya) o Continents mostly in the S. Hemisphere. o Intense evolutionary radiation of marine organisms. Animals lived on the sea floor or burrowed in sediments. o Ancestors of club mosses and horsetails colonized wet terrestrial environments. o Mass extinction at end: 75% of marine species lost. Sea levels dropped about 50 meters, and glaciers formed over Gondwana. The Silurian (444-416 mya) o Northern continents coalesced (united as one) , but their general position did not change. o Marine life rebounded from previous mass extinction from the Ordovician time; animals that can swim and feed above the ocean appeared for the first time, but no new major groups of marine animals evovled o The first known tracheophytes (vascular plants) appeared on land in the late Silurian. o First terrestrial arthropods (scorpions, millipedes) evolved The Devonian (416-359 mya) o rates of change accelerated in many groups of organisms during this period o the northern land mass called Laurasia, and the southern land mass called Gondwana moved slowly toward eachother o fishes diversified as jawed forms replaced jawless ones, heavy armor gave way to the less rigid outer coverings of modern fishes  all current major groups of fishes were present by the end of the period o the ancestors of gymnosperms, the first plants to produce seeds, appeared later in the Devonian o Fishlike amphibians began to occupy the land o A mass extinction of about 75% of all marine species marked the end of the Devonian The Carboniferous (359-297 mya) o Large glaciers at high latitudes and extensive swamp forests grew in tropical areas. o Fossilized remains of the forests formed the coal we now mine for energy. o Diversity of terrestrial animals increased greatly. o Snails, scorpions, centipedes, and insects were abundant, first winged insects. o Amphibians became larger, and reptiles evolved from one amphibian lineage. o Crinoids (sea lilies and feather stars) were plentiful on the seafloor The Permian (297-251 mya) o During the Permian period, the continents united to form the supercontinent Pangaea o Massive volcanic eruptions: ash blocked sunlight and cooled the climate => largest glaciers in Earth’s history. o By the end, reptiles greatly outnumbered amphibians. o The lineage leading to mammals diverged from one line of reptiles. Bony fishes radiated in the oceans. o Mass extinction at end: 96% species lost (volcanoes, meteorite & ocean turnover implicated) o At the end of the Permian, a large meteorite crashed into northwestern Australia. o Volcanic eruptions poured lava into the oceans, which dep2eted O in deep oceans. Oceanic turnover then carried the depleted water to the surface where it released t2xic CO2and H S. o O2concentrations dropped to about 12 percent—most animals would have been unable to survive at elevations above 500 m. o About 96% of all species on Earth became extinct. Mesozoic Era (251–65 mya) o At the start of the Mesozoic era (248 mya), the few surviving organisms found themselves in a relatively empty world. o Pangaea slowly separated, glaciers melted, and shallow inland seas formed. o Life proliferated and diversified. o Earth’s biota diversified and became distinct on each continent (previously more homogeneous).  Earth’s biota became increasingly provincialized: that is distinct terrestrial biotas evolved on each continent o By end of the era, the continents were close to their present positions and many organisms looked similar to those living today o Divided into The Triassic, Th
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