Lecture 11 Biodiversity is generated by evolution via speciation Biodiversity has changed over 4 6 billion years Genetic variation Species richness Community composition Ecosystem diversity Relative time Earth is old Earth changes New species arise Species go extinct 5 mass extinctions Fossils are the preserved remains of ancient organisms Fossil record is incomplete Few individuals become fossils Rocks are not permanent Exoskeletons or bones Distribution Sedimentary rocks form later that represent different times Younger layers of rock on the surface Deposition of air or water borne sediments Radioisotopes allow us to date rocks Half life Predictable decay Earth has changed over time Plate tectonics Sea level changes Atmospheric changes Biofilms Photosynthesis Aerobic respiration Atmospheric composition has changed over time oxygen nitrogen carbon etc Carbon isotopes show evidence for carbon fixation current living things prefer to fix the 12C isotope Fossils show higher 12C isotopes compared to the surrounding rock 12C fixation has occurred for at least 3 8 by Fossils have provided a history of changing biodiversity Fossil record is incomplete Will most likely always remain incomplete 4 eras Precambrian Paleozoic Mesozoic Cenozoic Precambrian Era was dominated by small aquatic life Origin of life origin of photosynthesis first eukaryotes first photosynthetic eukaryotes first fossils of multicellular animals Extinction took place Huge changes in biodiversity took place in the Paleozoic era 6 periods Cambrian Ordovician Silurian Devonian Carboniferous Permian Ends of periods and eras often marked by extinction Marine radiations transition to land vascular plants and vertebrates Major land changes altered biodiversity in the Mesozoic era 3 periods Triassic jurassic cretaceous Extinctions and extraterrestrial events Reptile fish radiations origin of mammals flower plants arise and diversify Mammals diversified in the Cenozoic era 2 periods Tertiary and quaternary Modern continental position ice ages and climate shifts Flowering plants dominate mammalian radiations evolution of Homo