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Continental Drift • Lyell proposed movement of continents to account for climate change evident in fossil record • BUT did not change shape or position relative to each other Continental Drift • Tyler proposed crustal changes to account for mountains and island chains Continental Drift • Tyler proposed crustal changes to account for mountains and island chains Continental Drift • Wegener • Observations • Alignment of mountains and rock strata matched on opposite sides of Atlantic • Glacial deposits displaced towards North Pole • Coal belt of N. Amer. and Europe suggested tropics Continental Drift • Wegener’s conclusions • Continental rock, sial (silicon and Al) lighter than ocean floor (basalt), continents float on fluid mantle • Once a supercontinent, Pangaea, that broke into smaller plates • Breakup began as rift valley and widened into ocean Continental Drift • Continental blocks (plates) retained their shape except where mountain building (can still join the plates now separated) • Movement of plates different • Radioactive heating from mantle causes plate movement Late Supporting Evidence • Computer mapping fit continental shelf of continents together • Discovery of submarine volcanoes (guyouts) • Ocean floor is basalt and younger than continental rock (max. 150 mya vs. > 1 billion for continental rock) • Midoceanic ridge, continuous 65,000 km system on seafloor • Magnetic anomalies from differential deposition of magnetized rock Tracking Continental Movement – Remnant Magnetism Major Tectonic Plates Age of islands relative To distance from rift zone Drift and Life • 600 – 650 mya first multicellular life • 475 – 525 mya Cambrian explosion • 400 – 450 mya first life on land, including vertebrates and plants • ~360 mya first reptiles • 200 - 250 mya first mammals and birds Gondwanaland – 650 – 475 mya – oldest continuous land mass N. Amer. and N. Europe (PA) begin drift north NA, N. Europe & Siberia eventually collide to form Laurasia Gondwanaland drifts north Permian – time of great terrestrial and marine connectivity but were barriers – Central Pangaean Mtn. range; Pangaean Desert W. Asia and Europe collide – Ural Mtn.; other continents join to form Pangaea; East Asia isolated, Tethys Sea; One great ocean – Pathalassa Break up of Pangaea • Formation of Pangaea brought together biota formerly isolated • Diversification of Pangaea and Pathalassa probably resulted from breakup (180 mya) by creating isolation • Breakup began when Turgai Sea expanded from Arctic to split Asia and Euramerica • Separation N. America and Europe by shallow “Atlantic Sea” Break up of Pangaea • Tethys Seaway opened • Gulf of Mexico formed with separation of N. and S. America N. America and Europe reconnect (Beringea landbridge) NA epicontinental sea M and I separate; I moves toward Asia (collide ~60 mya); AU separates from Antarctica severing link to S. Amer. Many small plate collisions (65 – 2 mya) Great American Interchange – reconnected NA and NT ~4 mya (last connected ~160 mya) Hotspots – fixed, weak points in crust Epicontinental (Epeiric) Seas • Changes in continent location and sea levels • Formed barriers on terrestrial landscape • Australia divided into three parts in Cretaceous (50 mya) • North America – several epeiric seas – most recent ended ~65 mya • Europe and Asia separated by Turgai Sea until ~30 mya Paleoclimate • Relative amount of land/ocean and distributions also influence solar radiation and temperature climate, winds, and currents • Example – warm circum-equitorial currents (Tethys Seaway) replaced by cold currents Consequences of Plate Tectonics • Profound effects on both terrestrial and aquatic biota • Constant, albeit slow, change – Plates form, expand, merge, separate – Plates eliminated by subduction and consumed – Change shape • These dynamics allowed flow but also isolation through barriers Effect of lowering sea level on marine diversity (loss of seas Seafloor spread and number of species • Boxes in this chapter rich with information. • Among most useful are Tables 8.2 and 8.3