Evolution of Multicellular Life Precambrian - all periods before the Paleozoic era – 90% of Earth’s History – fossil evidence is contained in stromatolites layers of bacteria and algae Oxygen revolution – Endosymbionts Leads to multicellular animals Paleozoic Era invertebrates Cambrian period – Explosion of life! – trilobites is the most common index fossil ~500 million years ago – Aquatic based

Paleozoic Era Cambrian…Cambrian explosion Ordovician & Silurian – First vertebrates resembling suckerfish – First transition to land of both plants and animals Devonian… “Age of Fishes” – Insects and terrestrial arthropods appear – Massive increase in the diversity of bony fishes Sharks appear Carboniferous & Permian – Reptiles develop and start laying eggs – The animals and plants now inhabit the continents Mass extinction marks the end of the period – 95% of the aquatic animals dissapear

Mesozoic Era “Age of Reptiles” Triassic – Dominated by the survivors of the mass extinction – First dinosaurs appear – First mammals appear Jurassic – Dominated by dinosaurs – First birds apear Cretaceous – Still dominated by reptiles (Dinosaurs) – Plants are now diverse with seed producing flowering plants (fruit) – Turtles & crocodiles appear Mass extinction marks the end of the period

Cenozoic Era “Age of Mammals” Tertiary – Whales and Dolphins evolved – Grasses and flowering plants prompted the development of insects and grazing animals – Climate is warm and mild Quaternary – Ice ages force the movement of animals and drops the level of the oceans – Mammoths – Early ancestors of humans arrive ~4.5 mil years ago – Homo sapiens ~ 200,000 years ago in Africa Mass Extinction coming?

Cenozoic Diversity of life – Holocene… Historical time begins (.01mil yrs) – Pleistocene… Ice Ages… Humans appear (1.8mil yrs) – Pliocene… Origin of genus Homo (5.3mil yrs) – Miocene… Continued radiation of species (23mil yrs) Apelike ancestors of humans – Oligocene… Origin of primate groups (33.9mil yrs) – Eocene… Angiosperms dominate (55.8mil yrs) – Paleocene… massive radiation of mammals, birds, & insects (65.5mil yrs)