Earth History Geography 106 LRS Doug Fischer Introduction – Overview of geologic history • Plate positions over time • Major biogeographic events Earth’s tectonic history • Gondwanaland – Southern continents – Formed 650mya Precambrian • Laurasia – Northern Continents – Most converged in Devonian 400mya as “old sandstone continent” • Formation of Pangaea – Late Permian ~ 275 mya Breakup of Pangaea • Started 180 mya (early Jurassic) – Prior to breakup, great mixing of biota – However, regionalization did still occur as it does on (smaller) continents today Breakup of Laurasia • Separated Europe & N. America 100 mya • Beringia rejoined them 75 mya • Intermittent connection via Greenland & Beringia through Tertiary Breakup of Gondwanaland • 180-160mya Gondwanaland started to split – Mesozoic (Triassic/Jurassic) • Mostly finished by 90 mya 152 mya 94 mya Central America and Antilles • Caribbean Plate was sandwiched between N&S America between 80 and 20 mya • Formed ring of islands • Landbridge closed ~ 3.5 mya – Great American Interchange 14 mya Biogeographic consequences of plate tectonics • Fragmentation and dispersal of ancestral biota (vicariance) • Changing barriers and coridors – biotic interchange • Speciation and extinction – changing physical and biological conditions Tour of Geologic History The geologic time scale • Phanerozoic starts with Cambrian explosion of species with hard body parts – (Some multi- cellular algae and animals lived at the end of the Precambrian) Paleozoic Paleozoic Cambrian • Animals with hard-shells appeared in great numbers for the first time • The continents were flooded by shallow seas. • The supercontinent of Gondwana had just formed and was located near the South Pole. Ordivician • ancient oceans separated the barren continents of Laurentia, Baltica, Siberia and Gondwana. • The end of the Ordovician was one of the coldest times in Earth history. Ice covered much of the southern region of Gondwana. Silurian • Laurentia collides with Baltica closing the northen branch of the Iapetus Ocean and forming the "Old Red Sandstone" continent. • Coral reefs expand and land plants begin to colonize the barren continents. • Photosynthetic sticks on mudflats Devonian • By the Devonian the early Paleozoic oceans were closing, forming a "pre-Pangea". • Freshwater fish were able to migrate from the southern hemisphere continents to North America and Europe. • Evolution of wood! Forests grew for the first time in the equatorial regions of Artic Canada. Early Carboniferous • During the Early Carboniferous the Paleozoic oceans between Euramerica and Gondwana began to close, forming the Appalachian and Variscan mountains. • An ice cap grew at the South Pole • Four-legged vertebrates evolved in the coal swamps near the Equator (tree ferns, tree- horsetails, tree club-mosses). Late Carboniferous • By the Late Carboniferous the continents that make up modern North America and Europe had collided with the southern continents of Gondwana to form the western half of Pangea. • Ice covered much of the southern hemisphere • Vast coal swamps formed along the equator (seed ferns, early conifers, and mosses). Permian • Vast deserts covered western Pangea during the Permian as reptiles spread across the face of the supercontinent. • Cycads, ginkgos appear. Glossopteris ferns spread across southern continents • 99% of all life perished during the extinction event that marked the end of the Paleozoic Era. • Massive erosion due to devegetation of continents Permo-Triassic Boundary http://palaeo.gly.bris.ac.uk/palaeof http://sens-de-la-vie.com/Images- iles/triassic/triextict.htm dok/doomsday_impact_asteroide_01.jpg • “The Great Dying” - Siberian Traps, marine CO2 venting, asteroid impact - multiple stressors likely Permian over ~100kya to 2mya • Synapsids (dinosaur ancestors) nearly wiped out • 90%+ of all known species, 80%+ of all known genera extinct • Massive reorganization of marine ecosystems - 50:50 dominance of encrusting ecosystems changed Triassic to 1:3 favoring more complex ecosystems http://www.msnbc.msn.com/id/15885653/ Mesozoic Mesozoic Triassic • The supercontinent of Pangea, mostly assembled by the Triassic, allowed land animals to migrate from the South Pole to the North Pole. • Life began to rediversify after the great Permo-Triassic extinction. • Warm-water faunas spread across Tethys. Jurassic • By the Early Jurassic, south-central Asia had assembled. • A wide Tethys ocean separated the northern continents from Gondwana. • Though Pangea was intact, the first rumblings of continental break up could be heard. Late Jurassic • The supercontinent of Pangea began to break apart in the Middle Jurassic. • In the Late Jurassic the Central Atlantic Ocean was a narrow ocean separating Africa from eastern North America. • Eastern Gondwana had begun to separate form Western Gondwana. • First evidence of angiosperms Cretaceous • During the Cretaceous the South Atlantic Ocean opened. • India separated from Madagascar and raced northward on a collision course with Eurasia. • Notice that North America was connected to Europe, and that Australia was still joined to Antarctica. • Angiosperms begin to diversify rapidly, ginkgos and cycads decline K/T extinction • The bull's eye marks the location of the Chicxulub impact site. • By the Late Cretaceous the oceans had widened, and India approached the southern margin of Asia. • Massive eruptions of Deccan Traps Creatceous– Tertiary Boundary http://en.wikipedia.org/wiki/Image: http://images.forbestraveler.com/media/photos/i Impact_event.jpg nspirations/2007/08/volcano-01-g.jpg • “The Great Dying” - Deccan Traps, marine CO2 venting, asteroid impact - multiple stressors likely over ~100kya to 1mya • Dinosaurs wiped out - except for birds • 75%+ of all known species, 50%+ of all known genera extinct http://science.nationalgeographic.com/science/prehistoric-world/mass-extinction.html Cenozoic Alternating ice ages and interglacials Drying led to expansion of grasslands Cenozoic and huge herds of grazers Warm period - first extensive grasslands and kelp forests First elephants with trunks, early horses, first appearance of many grasses Hyaenodon horridus, a large carnivorous mammal Oldest known fossils of modern orders of mammals, all <20 lbs Eocene • 50 - 55 million years ago India began to collide with Asia forming the Tibetan plateau and Himalayas. • Australia, which was attached to Antarctica, began to move rapidly northward. Miocene • 20 million years ago, Antarctica was coverd by ice and the northern continents were cooling rapidly. • The world has taken on a "modern" look, but notice that Florida and parts of Asia were flooded by the sea. Pleistocene • When the Earth is in its "Ice House" climate mode, there is ice at the poles. The polar ice sheet expands and contacts because of variations in the Earth's orbit (Milankovitch cycles). • The last expansion of the polar ice sheets took place about 18,000 years ago. Holocene • We are entering a new phase of continental collision that will ultimately result in the formation of a new Pangea supercontinent in the future. • Global climate is warming because we are leaving an Ice Age and because we are adding greenhouse gases to the atmosphere. 50 my in the future? • If we continue present-day plate motions the Atlantic will widen, Africa will collide with Europe closing the Mediterranean, Australia will collide with S.E. Asia, and California will slide northward up the coast to Alaska. Mass Extinctions • Species continually go extinct • Five really BIG mass All genera extinctions in the last “Well-defined genera Trend line 540 million years “Big five” mass extinctions Other mass extinctions http://en.wikipedia.org/wiki/Extinction_event Mass Extinctions • Current extinction rate is 1000 times higher than usual • Modern mass extinction will rank with the five biggest • Modern mass extinction, expected to wipe out more than 50% The Golden Toad of Costa Rica, extinct since around 1989. Its disappearance has of Earth’s species been attributed to climate change. by 2100… Dodo and 2000+ other bird species extinct since 1500 AD (http://en.wikipedia.org/wiki/Holocene_extinction_event) Tour of Geologic history • Sponsored by the Paleomap Project – http://www.scotese.com/ • Additional information available from – UC Museum of Paleontology • http://www.ucmp.berkeley.edu • Click on “Discover the History of Life” – http://www.enchantedlearning.com/subjects/Ge ologictime.html.