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Lecture 15: Evolution of the Atmosphere and Biosphere III: the Phanerozoic and The

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Lecture 15: Evolution of the Atmosphere and Biosphere III: the Phanerozoic and The Lecture 15: Evolution of the Atmosphere and Biosphere III: The Phanerozoic and the EAS 2200 Introduction to the Earth System Cambrian Explosion: 543 Ma. Almost all animal phyla now K-T present extinction 65 Ma Ediacaran and the rise Permo-Triassic of extinction 248 metazoans Ma Ithaca Formation deposited ~370Ma Darwin’s Dilemma “There is another…difculty, which is much more serious. I allude to the manner in which species belonging to several of the main divisions of the animal kingdom suddenly appear in the lowest known fossiliferous rocks. If the theory be true, it is indisputable that before the lowest Cambrian stratum was deposited, long periods elapsed…and that during these vast periods, the world swarmed with living creatures. But to the question why we do not find rich fossiliferous deposits belonging to these assumed earliest periods Darwin, Origin of Species, 1859 Rise of Metazoans As the late Proterozoic glaciations end around 630 Ma, nearly 4 billion years of Earth history have passed. Life has been around for the last 3 to 3.5 Ga, and has managed a few tricks. Complex cells (eukaryotes) have evolved, and perhaps a few colonial algae. The Sun has become nearly as bright as it is today and oxygen is reasonably abundant in atmosphere. Still, to an alien spacecraft parked in orbit, the Earth may not have looked much diferent than it did in the Archean - life is dominantly, if not exclusively, still single-celled and microscopic. But that is already beginning to change – and the pace of change will soon become breathtaking. Ediacaran Fauna As recently as about 50 years ago, no macrofossils were known from rocks older than Cambrian (i.e., Precambrian). There are now localities on every continent except Antarctica where metazoan fossils from the Ediacaran* Period (620-543 Ma) have been found. *This period is sometimes also called the Vendian Ediacara Global Stratigraphy Rodinia and the Neoproterozoic World Ediacaran Fossils - Doushantou Embryos Ediacaran Fossils - Cloudina Cloudina, earliest skeletonized fossil, from Namibia Ediacaran Fossils - Charniodiscus Charniodiscus, a Cnardian (e.g., sea pen)? from Australia Ediacaran Fossils - Microdictyon Microdictyon, an onychophoran worm from China Ediacaran Fossils - Kimberella Kimberella - from the White Sea coast of Russia. Mollusc? Ediacaran Fossils - Tribrachidium Tribrachidium, fossil of unknown afnity from the Ediacara Hills of Australia Evolutionary Significance of Ediacara Fossils In a mere 80 million years (and arguably less), the world was transformed from one (apparently) devoid of multicellular organisms to one filled with them. Some of the Ediacaran fauna can be related to modern phyla, some cannot (thus far). In most cases, the assignment of these organisms to modern phyla is still controversial. Some Ediacaran fauna seem to have survived into the Cambrian (and Phanerozoic), most did not. On the whole, the diferences between the Ediacaran and subsequent Cambrian faunas are The Phanerozoic World The beginning of the last Eon of geologic time is announced, rather unimpressively, by the appearance of this trace fossil (burrow of Trichophysus pedium). Cambrian Fauna - Small Shellies Some of the so-called small shellies from Siberia (544-530 Ma) Cambrian Fauna - Trilobites Trilobites appear a little above the Ediacaran- Cambrian boundary, at about 530 Ma. Chengjiang Fauna ~ 520 Ma Earliest fish from the Chenjiang Fauna Burgess Shale ~510 Ma Anomalocaris Tuzoia - crustacean Burgess Shale Lagerstätt (Fossil Motherlode) Charles Doolittle Walcott & the Burgess Shale Hallucigenia Onychophore? Velvent worm Burgess Shale Ecosystem The Cambrian Explosion By the end of the Cambrian at 490 Ma, all major phyla except bryozoans had appeared. The period begins with a few small skeletal fossils and ends with examples of all major body plans and abundant skeletal animals. The Cambrian is also a time of great experimentation - there are many classes and orders with only a few genera and species each, most of which later die out. Paleozoic Era Era Period Beginning, Ma Duration Ma Mesozoic Triassic 251 49 Paleozoic Permian 299 48 Carboniferous 359 60 Devonian 416 57 Silurian 444 28 Ordovician 488 44 Cambrian 543 55 Neo- Ediacaran 620 77 proterozoic Geologic Time and Biodiversity Highlights of the Ordovician Diversification - largest increase in number of families of any geologic period. Filter feeders increase in importance. First land plants - hepatophytes (e.g., liverwort) & lichens (known from spores) Ends with short, but severe glaciation and a major mass extinction Highlights of the Silurian Rapid recovery of fauna from late Ordovician extinction Warm climate, high sealevel Rapid diversification of fish First vascular plants - lycophytes Today, lycophytes are represented only by small plants like club mosses. In the Silurian, they could be 35 m tall. The associated terrestrial ecosystems included millipeds, centipeds, spiders, fungus, nematods, and perhaps earthworms. Highlights of the Devonian Ithaca Formation deposited Spermatophytes - seed producing plants appear and diversify First tetrapods (late Devonian)- terrestrial vertebrates - appear (at last some good plants for animals to eat on land!) Devonian Paleogeography Ithaca Carboniferous World Carboniferous Ecosystem Carboniferous in a Nutshell Starts out warm and moist Plants go crazy Lots of organic matter burial (in swamps, which become coal beds) Atmospheric CO2 crashes (Oxygen goes up) Climate crashes - glaciation Helped by Gondwanaland shifting to the south pole Phanerozoic Climate Modeling the Long-Term Carbon Cycle Carbon cycles between atmosphere/ ocean/ biosphere, organic sediments, and carbonate sediments Carbonate and organic sediments have very diferent carbon isotopic compositions. We can use carbon isotope ratios of ancient marine BLAG (Berner, Lasaga, and Garrels) Model of Highlights of the Permian Starts out cold - continued glaciation, but later becomes mild Final assembly of Pangea Conifers and Ginkgos begin to compete in fern- dominated forests Amniotes (ancestors of reptiles, mammals, and birds) become dominant land animals. Reptiles emerge. The Permo- Triassic Extinction 50% of families and perhaps Type section of the Permo- 90% of species (including Triassic Boundary in China the last few Trilobite genera) become extinct at this time. Extinction is more severe for marine species (~95%) than terrestrial ones (70%). Recovery was slow. Permo-Triassic was the “big one”. Permo-Triassic Extinction: What Happened? Nobody knows. But there is no shortage of ideas: Volcanic eruption (particularly the Siberian Traps flood basalt - largest flood basalt known) Asteroid Impact Formation of Pangea (lost of continental margin habitat/desertification) Climate change/glaciation There is some evidence that the extinction happened in two pulses (257Ma correlates with age of Emeishan Mesozoic: The Age of Reptiles Periods of the Mesozoic: Cretaceous 146-65 Ma Jurassic 200-146 Ma Triassic 251-200 Ma Highlights of the Triassic Pangean Supercontinent goes from pole to pole Moderate Climate Diversification of various phyla Division into a northern and southern biota First Dinosaurs - early Triassic First Mammals - late Triassic Pangea begins to split - particularly between N. America and Africa Highlights of the Jurassic Pangea contines to split Gondwana begins to break up Warm Climate Cosmopolitan biota Cycadophyta (palm-like seed- bearing plants) come to dominate terrestrial biota, but conifers and gingkos remain common Dinosaurs diversify and dominate terrestrial fauna Flying dinosaurs, including Archaeopteryx, the ancestor of birds, appear Amphibians become limited to frogs and newts and slide into the same minor role they have today Mammal present, but small and unimportant Birds, Dinosaurs, and Feathers It is now widely, although perhaps not universally, agreed that birds are descendant from dinosaurs - or to put it more dramatically, birds are dinosaurs. The skeletal similarities, as was first noted by Thomas Huxley in 1868, are striking. At least 19 genera of feathered dinosaurs have now been found. All of these are therapods. It is possible that all therapods, including T. Rex, has feathers. Feathers, which consist, like hair, of keratin, probably first evolved for insulation or display, and were only later adapted for flight. Highlights of the Cretaceous Rapid sea floor spreading, extensive plume-related volcanism High sealevel -many shallow epicontinental seas Particularly warm climate (arguably the warmest episode of the Phanerozoic) Dinosaurs continue to diversify Birds diverge from dinosaurs and largely replace flying dinosaurs Angiosperms appear and come to dominate terrestrial biota More Highlights of the Cretaceous Continued breakup of Pangea Mineralized shells become common in planktonic organisms; planktonic diatoms and foraminifera appear Mammals diversify into 3 extant types (plancentals, marsupials, monotremes) Ends with a bang The K-T Extinction Dinosaurs had reigned the Earth for nearly 200 Ma then suddenly disappeared 65 Ma ago. So did 75-80% of other species. This time, both terrestrial and marine species severely afected. What happened? Iridium (Ir) Anomalies in The Cretaceous-Tertiary Boundary marked in many regions by a boundary clay - fossils, etc. absent. High levels of Ir (iridium) found in the boundary clay in Gubbio, Italy. Ir is less rare in meteorites than the Earth (Earth’s Ir is in core). Iridium Boundary Clay and Ir anomalies
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