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Unformatted text preview: BIS2B Fall 2009 (Keen) Lecture 31. Brief history of Life II
20 November Biological events in life’s history Students should be able to: Discuss the role of organisms in determining the oxygen content of the earth’s atmosphere Date the appearance of eukaryotic organisms Describe the Ediacaran fauna Describe the Cambrian explosion Outline and order the major biological events taking place in the Paleozoic, Mesozoic, and Cenozoic eras. Date and describe the two major mass extinctions. • The earth is approximately how old?
a) b) c) d) 3.5 million years 3.5 billion years 4.5 billion years 7.2 billion years Changes in the Earth’s Atmosphere
Earth’s atmosphere has changed Earth Early atmosphere probably contained little or no free oxygen (O2). O2 began to increase when some bacteria evolved the ability to use H2O as a source of H+ iions in photosynthesis. O2 was a waste ons photosynthesis was product (electrons were available to reduce CO2 to form organic product compounds). compounds). Cyanobacteria formed rockllike structures called ike stromatolites which are stromatolites which abundant in the fossil record abundant Enough O2 was liberated to was allow evolution of oxidation reactions to synthesize ATP reactions Changes in the Earth’s Atmosphere
The evolution of life changed the physical nature of Earth, which The in turn changed the evolution of life... in When O2 first appeared in the atmosphere it was poisonous to the first anaerobic prokaryotes, but then some evolved the ability to metabolize the O2 metabolize Advantages: aerobic metabolism is faster and more energy is aerobic harvested; so aerobes replaced anaerobes in most environments harvested; Atmospheric O2 also made possible larger cells and more complex also organisms. organisms. About 1 billion years ago, eukaryotic cells appeared Permian extinction extinction Some approximate divergence times for life’s lineages. based on fossils Estimated divergence times using genetic data From: Evolutionary Analysis, 4th Ed, Freeman and Herron Major Events in Life’s History Major History Precambrian Era Precambrian
The Precambrian Era (4.5 bya - 542 mya) bya 542 mya For most of this era, life was microscopic, prokaryotic, and liviing in ng oceans. oceans. Eukaryotes evolved about 2/3 through the Precambrian. By the late Precambrian, soft-bodied multicellular animals had bodied evolved. Two more soft-bodied Pre-cambrian organisms These organisms are from Australia and dated at about 600 million years. Paleozoic Era
The Cambrian Period (542-488 mya) at the beginning of the Paleozoic The (542 488 mya at Era (542-241 mya) (542 241 mya O2 concentration was approaching modern levels concentration Continents formed large land masses, the largest called Gondwana Continents Rapid diversification of life took Rapid place—Cambrian explosion. place Most of the major groups of Most animals living today appeared in the Cambrian, including: arthropods, mollusks, echinoderms, mosses, vertebrates, etc. vertebrates, these were common Three different Cambrian fossil beds have preserved the soft parts of of many animals—the Burgess Shale, Sirius Passet (Greenland), and many the Passet (Greenland), Chengjiang site (southern China). Chengjiang Fossil from the Fossil Chengjiang site, Chengjiang site, Arthropod Mollusk Arthropod
Fossils from the Burgess Shale in British Columbia, Canada Canada Devonian period (416-359 mya): corals, cephalopods, Devonian (416 359 mya): and fishes radiate; jawed fishes evolve and Club mosses, horsetails, and tree ferns common in terrestrial habitats; roots accelerated soil formation; arthropod fossils on land and some amphibians present present Carboniferous period (359-297 mya) (359 297 mya Swamps of giant Swamps horsetails and treehorsetails ferns (made the fossil ferns fuels we use today) fuels Permian period
• • • • continents coalesced to form Pangaea reptiles were diverse the early mammal lineage split fishes diversified in fresh water Near the end of the Permian period (297-251mya) of the Paleozoic Near Permian 251mya) era, massive volcanic eruptions poured lava over large areas of Earth Earth Volcanic ash blocked sunlight and caused climate cooling, resultiing in ng the largest glaciers in Earth’s history the O2 concentrations dropped to concentrations about 12%—most animals about most unable to survive at elevations above 500 m above A combination of factors combination resulted in the greatest mass resulted the extinction in Earth’s history, extinction history, the Permian Extinction where 96% of species disappeared 96% Mesozoic Era At the start of the Mesozoic era (542-251 mya), the surviving organisms inhabited a relatively empty world The continents began to drift apart, so the biota became increasingly provincialized, with distinct biota’s evolving on each continent Triassic (251-200 mya): Rise of the dinosaurs, crocodilians and birds Jurassic (200-145 mya): Nasty predatory dinos on 2 legs, mammals appear, flowering plants Cretaceous(145-65 mya): A mass extinction at the end 65 mya): of the Cretaceous was caused by a meteorite of
Evidence of impacts include large craters; molecules with helium and Evidence and argon isotope ratios characteristic of meteorites, and iridium deposits argon • A llarge crater has been found beneath arge the Yucatán Peninsula in Mexico the • A massive plume of debris from the massive impact heated the atmosphere, ignited fires, and blocked the sunlight fires, All land animals larger than about 25 kg All became extinct, and many insects became • Dinosaurs went extinct and mammals Dinosaurs began to increase in numbers and types began Cenozoic Era Cenozoic
Cenozoic Era (65mya-present) is characterized by an extensive present) radiation of mammals radiation Tertiary Period (65-1.8 mya): Tertiary 1.8 mya Snakes, lizards, birds, and mammals underwent extensive radiations; ns; grasslands spread. Flowering plants came to dominate forests except in cool regions. Flowering Evolution of symbiotic associations with N-fixing bacteria. This fixing dramatically increased N available for terrestrial plants. dramatically Mammals dispersed from Mammals Asia to North America North across the Bering land across bridge (Rodents, marsupials, primates, and hoofed mammals) hoofed Cenozoic Era
Quaternary Period (1.8 mya - present): mya Divided into Pleistocene and Holocene epochs The Pleistocene epoch (1.8 mya-0.01mya) was a time of drastic The (1.8 0.01mya) cooling and climate fluctuation cooling Included four major and 20 minor “ice ages”; The last glaciers Included retreated from temperate latitudes about 15,000 years ago retreated The Pleistocene was also the The time of hominid evolution and radiation. radiation. Many large mammal species Many became extinct in Australia and the Americas when Homo sapiens arrived—possibly due to sapiens possibly hunting pressure hunting We live in Holocene epoch, beginning 10,000 years ago and including all of human civilization and We are now experiencing the 6th major extinction, major caused by humans. Animals are going extinct at 1,000 caused Animals times the “regular” rate—at the same pace observed at during the extinction of the dinosaurs! during Somewhere between 2.7 and 270 species are erased Somewhere from existence every day. from What Are the Major Events in Life’s History?
There was a slow start... There Earth was formed ~4.5 billion years ago (bya) Life first evolved about ~3.8 billion years ago _______________ ~1.5 billion years Eukaryotic organisms had evolved by about ____________ ago The number of individuals and species started to increase The dramatically in the late Precambrian dramatically Then things really took off... Three great evolutionary radiations occurred that resulted in Three three major faunas: three • The Cambrian explosion lead to the Cambrian fauna The Cambrian • 60 million years later, the radiation that resulted in the 60 arthropods, molluscs, echinoderms, vertebrates, etc. ____________________ ____________________ • After the Permian extinction, in the Triassic, the evolution After dinosaurs, mammals, ﬂowering of the ______________________ plants of
modern fauna? Paleozoic fauna? cephalopods? birds? trilobites? ...
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- Winter '09